CA1125453A - Joint prosthesis - Google Patents
Joint prosthesisInfo
- Publication number
- CA1125453A CA1125453A CA379,598A CA379598A CA1125453A CA 1125453 A CA1125453 A CA 1125453A CA 379598 A CA379598 A CA 379598A CA 1125453 A CA1125453 A CA 1125453A
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- prosthesis
- joint
- pin
- component
- components
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Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a prosthesis for replacing a skeletal joint in a human body comprising a first joint component adapted for connection with a first element, a second joint component adapted for connection with a second element, at least one of said first and second elements being a portion of a human body, a pivot component disposed between said first and secont joint components, means for resiliently connecting said pivot component to said first and second joint components, said resilient means including a first body of elastomeric material disposed between and attached to said first joint component and said pivot component, a second body of elastomeric material disposed between and attached to said joint second component and said pivot component, said first and second bodies of elastomeric material being spaced apart and suspending said pivot component between said first and second joint components to permit motion of said first and second joint components relative to each other about said pivot component in simulating the operation of a skeletal joint in a human body.
The present invention provides a prosthesis for replacing a skeletal joint in a human body comprising a first joint component adapted for connection with a first element, a second joint component adapted for connection with a second element, at least one of said first and second elements being a portion of a human body, a pivot component disposed between said first and secont joint components, means for resiliently connecting said pivot component to said first and second joint components, said resilient means including a first body of elastomeric material disposed between and attached to said first joint component and said pivot component, a second body of elastomeric material disposed between and attached to said joint second component and said pivot component, said first and second bodies of elastomeric material being spaced apart and suspending said pivot component between said first and second joint components to permit motion of said first and second joint components relative to each other about said pivot component in simulating the operation of a skeletal joint in a human body.
Description
" iiZ5~S3 The present inYentiOn relates to joint prostheses that are similar in structure and operation to joint prostheses described, illustrated, and claimed in two commonly owned, con-currently filed applications of James B. Koeneman, entitled "Knee Joint Prosthesis" and "Joint Prosthesis ~ith Contoured Pin", and in a commonly owned, concurrently filed joint applica-tion of Leonard J. Schwemmer and Howard T. 1^7ilson, entitled "Ankle Joint Prosthesis".
This application is a div;sional application of copending applicant No. 316,296 filed November 15, 1978.
Resilient màterials, such as elastomers, have long ~ been used in external prosthetic devices for the human body - to cushion impact or shock loads. Recause t:: ~:
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ll'Z5453 impa` loads are nece_sarily and regularly encountered in wall~ing, two common prosthetic devices that have often incorporated resilient materials are artificial feet arld ar~kle joint prostheses for use ~ith artificial îeet. In early designs, an ankle joint prosthesis was typically a metallic pivot that included a plain (e. g sleeve) bearing or a rolling element (e g., ball) bearing, Resilient or elastomeric m~Lteria~ was disposed both about the pivot to help limit its motion and in various portions of an associated artificial foot to cushion or absorb impact loads, Typical combinations of a cushioned artificial foot and an ankle joint prosthesis that in-corporates a metal-on-metal pivot are described and ill~1strated in Ehle U. S
PatentNo. 487,697, RowleyU. S PatentNo. 1,090,881, andKaiserU S Patent No. 2, 183,076.
Later in the development of ar~{le joint prostheses for external use, resilient or elastomeric matelial came to be utilized for properties otker than its ability to absorb or cushion impact loads. In Desoutter U. S Patent No.
1,911,~40, for example, a tubular rubber bushing is secured between a pin and a metal steeve that circumscribes the pin to form a pivot for an ankle joint prosthesis, The outer sleeve is connected to an artificial foot, while the pin is connected to an artificial lower leg. Articulation is permitted by torsional de-flection of the bushing. Because of the resilience of the bushing material, th;~
ar~le joint prosthesis automatically returns to a preselected position after it is deflected. The prosthesis also does not require lubrication because the bushing separates the adjacent metal surIaces of the pin and the sleeve. Similar ankle joint prostheses that employ a tubular bushing or body of elastomer between an outer rigid sleeve and an inner pin or sleeve are described and illustrated in BurgeretalU S PatentNo. 2,~05,475andPrahlU. S PatentNo. 3,480,97.
A pivot or pivotable assembly that incorporates a relatively thin, tubular body of elastomer secured between a pin and a larger diameter sleeve is only capable OI ei~tensive pivotal or rotational movement about a single aY.is In a typical ankle joint prosthesis, such as the Desoutter and Prahl prostheses, such an elastomeric pivot is oriented generally perpendicular to the longitudinal axis of the wearer's leg and transverse to the longitudinal axis of the wearer's artificial foot. In the orientation that has been described, the elastomeric pivot perrnits extensive flexin in the dorsal and plantar directions. An elastomeric pivot so oriented, however, can only provide a limited degree of inversion and eversion of a foot about its longitudinal axis or a parallel axis and only a limited degree of internal and external rotation of the foot about the longitudinal axis of 'he leg. The motions other than flexion are all accommodated primarily through compression of the elastomeric bushir~g, which is relatively tnin and cannot afford any significant degree of deflection. To overcome some of the motion limitations ir~erent in the ankle joint prostheses of the Desoutter and Prahl patents, the ankle joint prosthesis of the previously mentioned Burser et al patent incorporates two elastomeric pivots disposed at right angles to each other. The Burger et al ankle joint prosthesis thus car~ resiliently permit both extensive dorsal and plantar flexion and extensive inversion and eversion Cther external ankle joint prostheses attempt to provide the three types of movement af~orded by a natural anlcle joint throu~h the use of relatively rnassive blocks of elastomer, rather than the tubular bushings discussed above. The blocks of elastomer may be specially shaped or contoured in order to provide appropriate stlfinesses or motion capabilities in the three critical rctational directions. Examples of ex-ternal ankle joint prostheses that incorporate large blocks of elastomer are described and illustrated in Bennington et al U S Patent No. 2,692,392 and Asbelle et al U. S. Patent No. 3, 982, 280 5~53 ... ~ .
Although resilient materials, and particularly elastomeric materials, have for many years been suggested for use in external joint pr~sthesest the use of resilient or elastomeric materials in internal joint prostheses has only recently been proposed, The apparent delay in the appearance of proposals for the use of resilient or elastomeric materials internally of the human body is probably at-tributable in part to the lack of a physiologically inert elastomeric material that could safely ~e used in the body. Nonetheless, with the development of suitable elastomeric materials, such as Dow Corning Corporation's Silastic~9 silicone elastomer, a number of surgically implantable, elastorneric joint prostheses have been proposed, particularly for finger joints The finger joint prostheses, in particular, tend to be entirely formed of elastomer or nearly so Unfortunately, such designs req~lire the elastomer to be bent or flexed~xtensively at some point to provide a pivot, The result is alternating tension and compression loading of the elastomer, which is detrimental to its long-term fatigue life. The use of notches in the elastomer to locate the pivot point further adds to the stresses in-the elastomer. Examples of finger joint prostheses that are entirely formed of elastomer or nearly so are described and illustrated in Swanson U. S. Patent No.
3~462~7O5~ Niebauer et al U S. Patent No. 3,593,3a~2, Lynch U. S Patent No, 3,681,786, andSwansonU S. PatentNo. 3,875,594. Ctherthanthefinger;olnt prostheses mentioned above, relatively few implantable prostheses that employ resilient or elastomeric material have been identified. Nonetheless~ the use of elastom~ric material in an implantable hip joint prosthesis is suggested in Buechel et al U, S. Patent No. 3, 916, 451, particularly Figure 1, and in Bokros et al U. S. Patent No, 3, 707, 006, particularly Figure 5.
The ankle join. prostheses described in the previously mentioned patents to ~esoutter, Bur~er et al, and Prahl appear to represent the best presently known designs for use of the desirable properties of elastorneric material in a il254S3 prosthesis thataccomodates piyotal or rotational motion. None-theless, the elastomeric pivots that are incorporated in the ankle joint prostheses o~ these three patents do not make optimal use of elastomeric material within the space provided. In parti-cular, the relatively thin, tubular bodies of elastomer in the ankle joint prostheses of Desoutter, Burger et al, and Prahl are subjected to relatively high, torsionally-induced strains, which, over periods of extended use, will lead to failure of the elastomeric bodies. While the strains experienced by the elastomeric bodies of the patented ankle joint prostheses may ~; not be detrimental in terms of a few hundred or even a few thousand articulations of the prostheses, the strains are critical when one considers several million articulations or deflections of the prostheses. Such numbers of articulations may easily be experienced during a vear or two of normal use.
In an ankle joint prosthesis that is used externally of the human body, replacement of the elastomeric elements of the prosthesis may merely represent additional expense and some inconvenience to the user. If such a joint prosthesis were ~ implanted in the body of the user, on the other hand, failure of~the elastomeric elements within one or two years would seriously limit the desirabilitv of using such a prosthesis.
In copending application No. 316,296 there is dis-closed and claimed a ioint prosthesis comprising (a) a first relatively inextensible component; (b) a second relatively : : :
inextensible component that is spaced from the first component along a first axis; (c) means defining a relatively inextensible pivot member disposed between and spaced from each o~ the first and second components, the pivot member having a center and a central axis which passes through said center and which is oriented generally perpendicular to said first 2XiS, the first and second components being disposed entirely on opposite sides ~ 5 :^ ~
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il~5~S3 of and separated by a plane oriented generally perpendicular to said first axis and aenerally parallel to said central axis of the pivot member; and (d) means for resiliently securing the pivot member to each of the first and second components, the securing means includinq (i) a first portion that secures the pivot member to the first component, and (ii~ a second portion that secures the pivot member to the second component, each of the first and second portions of the securing means having at least one exposed surface that extends outwardly from adjacent the pivot member, said at least one exposed surface of the first portion of the securing means being spaced from said at least one exposed surface of the second porti.on of the securing means throughout at least a majority of their respective lengths measured generallv radially of said central axis of the pivot member, the first and second components being coupled to each other only through the pivot member and the first and second portions of the securing means, the relative extensibility of the first and second components and the pivot member being determined in comparison to the securing means, the securing means resiliently permitting and accommodating relative rotation between the pivot member and the first component and between the pivot member and the second component so that the first and second components can move toward and away from each other in directions ~enerally parallel to said first axis through rotation about a second axis that is disposed at least adjacent to and at least approximately parallel to the central axis of the pivot member.
The present invention is thus directed to a joint prosthesis which is suitable for either internal or external use and which is constructed resiliently to permit and accommodate pivotal or rotational movement, with a view to providing maximum useful life. A joint prosthesis according to the invention - 5a -~ :` -COmpriseS a pair of primary components that are formed of relatively ~nextensible material and are spaced apart from one another. Disposed between and spaced from each of the two components is a pivot member that is also formed of relatively inextensible , . .
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material. The piVot member is resiliently secured to each of the primary components so as to permit andaccomodates relative rotation between the pivot member and the components. As a result, the two primary components of the prosthesis can rotate toward and awav from each other ahout an axis that is disposed at least adjacent to and at least approximately parallel to a central axis of the pivot member. The use of a pivot member and a pivot axis that are separate from the primary components of a joint prosthesis permits the prosthesis to have, for example, a relatively small size for a given angular motion to be accomm-odated and aiven maximum strain in the material that resiliently secures the pivot member to the primary components. Alternatively, the prosthesis of the present invention will pe~mit, for a given angular motion to be accommodated and given size of the pros-thesis , a lower maximum strain in and a larger service life for the resilient material that secures to~ether the pivot member and the primary components of the prosthesis. The foreqoing advantages are experienced particularly with reference to a prosthesis such as the prostheses of Desoutter U.S. Patent No. 1,911,440 and Prahl U.S. Patent No. 3,480,972, in which the pivot member or pin is rigidly secured to one of the primary components of the prosthesis.
The pivot member is secured to the primary components of the prosthesis by a member that is at least partially formed of elastomer. Attachment of the pivot member to the primary components only through a member of body that is regilient in ~- whole or part will insure that the prosthesis is free of any relatively inextensible, and hence motion restraining, connection between the primary components. The resilient securing member will typically include a first portion that secures the pivot ~; member to one of the primary components of the prosthesis and a second portion that secures the pivot member to the other primary .
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~ - 6 a -5~S3 portioi of the resilient securing member are preIerably arcuately shaped when viewed in section taken generally normal to the central longitudinal axis of the pivot ~ember, Each of the first and second portions of the securing member will also preferably include a pair of exposed surfaces that e~tend generally lengthv.Tise of the pivot member and outwardly from adjacent the pivot member, The e~uosed surfaces of one portion of the resilient securing member are spaced apart from the exposed surfaces of the other portion of the securing member throughout at least a majority of their respective lengths measured generally radially of the pivot member, Such a spacing between the two portions of the resilient securing member facilitates relative pivotal motion or rotation between the pivot member and either of the primary components of the prosthesis without interference from the other primary component of the prosthesis or its associated portion of the securing member, Also to facilitate relative pivotal motion or rotation, each of the primary components of the prosthesis will preferably include a surface that is concavely arcuate in shape when viewed in section taken generally normal to the central longitudinal axis of the pivot member.
Each of the arcuate surfaces of the primary components is presented to and spaced from a convexly arcuate surface of the pivot member. At least one of the two primary com~onents of the prosthesis should include structure for attaching the component to a limb associated with the human body.
When the present invention is embodied in an external ankle joint prosthesis, for example, the securing member that includes two portions which ~ .
resiliently secure the primary components of the prosthesis to the pivot member also includes a portion secured to at least one OI the primary componen s at a point behind an arcuate surface of the component which is presented to the pivot member. This third portion of the securing member extends from the primary component to which it is attached toward the other primary component of the ( 13~Z5~.~S3 pros sis resiliently to limit relative rotation between the two primary com-ponents~ particularly retative rotation between the rcar portions of the primary components The resilient securing member ~ay al.o include a fourth p~)rtion that is secured to at teast one of the two primary components of the prosthesis at a point in front of the arcuate surface of the component which is presen~ed to the pivot member ~he fourth portion of the securing member extends Irom the component to which it is secured toward the other primary ~omponent of the prosthesis With such an orientation, the fourth portion of the securing rnember resiliently limits relative rotation between the front of one primary component and the front of the other primary component. Each of the third and fourth portions of the securing member should be at least partially formed of elastomer. The opposed surfaces of the two primary components of the ankle joint prosthesis should each include an arcuately shaped portion presented to the pivot member of the prosthesis, a portion disposed in front of the arcuate portion, and a portion disposed to the rear of the arcuate portion. The front portions of the opposed surfaces OI the two primary components should be disposed to diverge frorn one another in a direction away from the pivot member. The rear portions of the two opposed surfaces should be similarly disposed.
Brief DescriPtion of the Drawings For a better understanding of the invention, reference may be made to the Iollowing description of several exemplary embodiments~ taken in conjunction with the ~lgures of the accompanying drawings, in which:
Figure 1 is a side view of an ankle joirlt prosthesis according to the invention mounted between an artificial leg and an artificial foot;
1~2S~53 Flyure 2 is a plan view, partly in section, of the joint prosthesis of Figure 1, taken along line 2-2 of F~gure 1;
Figure 3 is a side view, on an enlarged scale, of the anlcle joint prosthesis of Figure 1;
Figure 4 is a side view of a second ankle joint prosthesis according to the inven~ioni Figure 5 is a plan view of the joint prosthesis of Figure 4;
Figure 6 is a side view, in section, of another embodiment of an ankle joint prosthesis according to the invention;
Figure 7 is a side view of yet another embodiment of an ankle joint prosthesis according to the invention;
Figure 8 is a sectional view of the an~le joint of Figure 7, taken along line 8-8 of Figure 7; and Figure 9 is a perspective view of an endoprosthetic finger joint according to the invention.
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Description of Embodiments Figure 1 OI the drawings illustrates, in side view, an ankle joint prosthesis 10, according to the present invention, mounted between an artificial lower l~g 12 and an artificial foot 14. The artificial leg 12 rnay be formed of any one of a number of materials that have the strength necessary to support the weight of the human bodyJ such as metal, wood, nylon, or reinforced plastic. The leg 12 is . ,~, ~hollow and includes a generally tubular body portion 16 and an end wall 18 that is disposed adjacent the prosthesis 1û. The end wall 18 is formed with an opening ''! 20 which extends axially of the leg 12 and which receives and fixedly mounts a nut 22. Screwed into the nut 22 is the threaded stud 24 of a rnetal mounting adapter :
26. The adapter 26 includes both the threaded stud 24 and a circular base plate - - 9 - ~
S~3 28 Erom one side of which the stud ~Xojects in a direction per-pendicular to the plane of the base plate. As best shown in Figure 2, the base plate 28 has four circumferentially spaced apart holes formed in it. Each of the holes in the base plate 28 receives a screw 29 that is screwed into an upper surface of the ankle ]oint prosthesis 10 to secure the mounting adapter 26 to the prosthesis. A second metal mounting adapter 30, which is, but need not be, identical to the adapter 26, is secured to a lower surface of the prosthesis 10 opposite the surface to which the adapter 26 is secured. Four screws (not shown) are received in holes formed in the base plate 32 of the adapter 30 and are screwed into the prosthesis 10. A threaded stud 34, which is immovahly connected to the base plate 32, extends perpendicularly away from the plane of the base plate and into an opening 36 formed vertically through the artifical foot 14 just forward of the heel of the foot. The opening 36 in the foot 14 receives and fixedly mounts a nut 38 into which the threaded stud 34 is screwed.
The artificial foot 14, like the artificial leg 12, is formed of a material,, such as metal, wood nylon, or reinforced plastic, that ,; 20 is stronqenough to support the weight of the human body. In addition, the material of which the foot 14 is formed should also-afford some resilience or give. Resilience of the foot will attenuate, to some extent, the shock loads imposed on the foot and transmitted from the foot through the ankle joint prosthesis 10 and the artificial leg 12 to the user's body when the foot ~- strikes a!hard surface, as in walking. Additional resilience ; ,m,ay be provided by incorporating within the artificial foot i4 one or more bodies of elasto~er or other resilient material.
A typ~cal artificial foot that incorporates several discrete bodies of elastomer disposed to provide additional resilence is described and illustrated in Kaiser U.S. Patent No. 2,183,076.
The ankle joint prosthesis 10 incorporàtes two identical ll~S4S3 and vertically spaced apart primary components 40 and 42.
Each of the primary components 40 and 42 is formed of a rela-tively inextensible material, such as metal, plastic, or reinforced plastic. The material of which the primary components 40 and 42 are formed must be suitable for bonding to elastomer, for reasons that will become a~parent, and is to be judged as to ~ts relative inextensibility through comparison to the elastomer utilized in the prosthesis 10. The components 40 and 42 incorporate contoured surfaces 44 and 46, respectively, which are presented toward, but spaced apart from each other.
Opposite their respective contoured surfaces 44 and 46, the componentS 40 and 42 have ~enerally planar surfaces 48 and 50, respectively~ ~he planar surface 48 of the component 40 is presented to and juxtaposed with the surface of the adapter base plate 28 opposite the stud 24. The screws 29 that are received in the holes in the base plate 28 are screwed into threaded, blind bores (not shown) formed in the surface 48 and the com-~onent 40 In a similar manner, the planar surface 50 of the com-ponent 42 is presented to and juxtaposed with the surface of ~` 2-0 the adapter base plate 32 opposite the stud 34. The screws . . ~
:~:;.; ~ (not shown~ that are received in the holes (not shown) in the base plate 32 are screwed into threaded, blind bores (not shown) ormed in the planar surface 50 and the component 42. Although ,.:.......................... .
; the primary components 40 and 42 of the prosthesis 10 are attached to separate mounting adapters 26 and 30, respectively, the studs :
.~ 24 and 34 of the adapters could each be formed in one piece `~` with an adjacent primary component.
~:` The contoured surface 44 of the primary component 40 of the prosthesis 10 includes a central portion 52 that is 3Q concavely arcuate in shape, when viewed from the side, as in - Figure 1. To the rear of its central portion 52, the surface ~ 44 includes a planar rear portion 54 that slopes toward the 11;~5453 surface 48 from front to rear of the prosthesis 10. In front of its central portion 52, the surface 44 includes a planar front portion 56 that slopes toward the surface 48 from rear to front of the prosthesis 10. The contoured surface 46 of the com-ponent 42 similarly includes a concavely arcuate central portion 58, a planar rear portion 60, and a planar front portion 62.
The front and rear portions 62 and 60 of the surface 58 slope toward the surface 50. Disposed between the spaced apart arcuate portions 52 and 58 of the contoured surfaces 44 and 46 is a cylindrical pivot member or pin 64. The pin 64 is formed of a relatively inextensible material such as metal, reinforced plastic, or nylon, and is oriented such that its central longi-tudinal axis 66 is generally perpendicular to the lon~itudinal axis of the leg 12 and transversely disposed relative to the longitudinal axis of the foot 14. Because of its shape and orientation, the pin 64 presents a convexly arcuate surface to each of the arcuate surface portions 52 and 58 of the primary - components 40 and 42, respectively, of the prosthesis 10.
The pin 64 is resiliently secured to the components 40 and 42 of -~
the prosthesis 10 hy a body or mass of resilient material 68, such as elastomer. The elastomer in the mass 68 may be natural rubber or a synthetic elastomer. Although all of the resilient material in the prosthesis 10 is part of a single interconnected : ,.
mass 68, each of the various portions or sections of the mass 68 which are described hereinafter may be formed as a discrete member if such a procedure appears desirable for manufacturing or other purposes.
The convexly arcuate, outer circumferential surface of the pin 64 is resiliently secured to the arcuate surface - 30 portion 52 or the component 40 by an arcuately shaped portion 70 of the resilient or elastomeric mass 68. When viewed in section taken normal to the lon~itudinal axis 66 of the pin 64, 11~59~S3 the elastomeric ~Qrtion or section 70 resemb]es a truncated wed~e taken from an annulus. The elastomeric section 70 is bonded, by vulcanization or adhesives, for example, to both a portion of the :: 10 '`: :
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- 12a -convexly arcuate outer surfa~e of the ~in 64 and to the concavely arcuate centralportion 52 of the surface 44. To secure the pin 64 to the other primary component 42, a similar arcuately shaped portion or section 72 of the mass of elastomer 68 is disposed between and bonded to a portion of the convexly arcuate outer surface of the pin 64 and to the concavely arcuate surface portion 58 of the component 42. The elastomeric sections 70 and 72 include pairs of exposed surfaces 74 and 76,respectively, that ~ extend len~thwise of the pin 64 and outwardly, in a generally .~. 10 radial direction, form the outer circumferential surface of the pin. Throu~hout most of their lengths, as measured radially of the pin 64, the exposed surfaces 74 of the elastomeric section 70 are spaced apart from the exposed surfaces 76 of the elastomeric section 72. The surfaces 74 do intersect the surfaces 76 adjacent the pin 64, but diverge from the surfaces 76 with an increasing radial distance from the pin. In a similar manner,the f:rontplanar portion 56 of the contoured sur-face 44 o.f the component 40 diverges from the front planar portion 62 of the contoured surface 46 of the component 42. The rear portions 54 and 60 of the surfaces 44 and 46 also diverge V~th increasing radial distance from the pin 64. As a result of the diver~ence between the surfaces 74 and 76 ~nd between . ~ the surface portions 56 and 62 and 54 and 60, there can be relative pivotal or rotational movement between the pin 64 and the primary component 40, for examplel without inter-ference between the elastomeric section 70 that will be deflected to accommodate such relative rotation and the elastomeric sect~dn 72 without interference between the two primary compo -nents 40 and 42 of the prosthesis 10.
The elastomeric portions 70 and 72 of the mass of elas-tomer 68 in the prosthesis 10 will resiliently permit and, to a limited extent, resiliently resist relative rotation between ~25~53 the pin 64, on the one hand, and the primary components 40 and 42, on the other hand. 'i~otational or ~ivotal motion that corres-ponds to dorsal or plantar flexion of a natural ankle joint will occur about an axis that is disposed at least adjacent to and at least approximately parallel to the longitudinal axis ; 66 of the pin 64. Although the elastomeric sections 70 and 72 will offer some resilient resistance to dorsal and plantar flexion, the elastomer will be loaded in torsional shear and will not offer sufficient resistance to flexion to cushion and limit this motion. Thus, secured to the rear portions 54 ` and 60 of the contoured surfaces 44 and 46 of the components /;
40 and 42 are rear elastomeric bumper portions 78 and 80, respectively~ of the elastomeric mass 68. Each of the rear bumpers 78 and 80 extends away from the surface portion 54 or 60 to which the bumper is secured and toward the other rear bumper. Nonetheless, the rear bumpers 78 and 80 are separate from each other and are spaced sli~htly apart when the pros-thesis lO is in its normal undeflected position. Consequently, nG tenslon load will be applied to either of the bumpers 78 and 80~ when, for example,~relative rotation between the primary components 40 and 42 of the prosthesis 10 causes the rear por-tions 54 and 60 of the surfaces 44and 46 to move away from each other. The ankle joint prosthesis 10 also includes front bumpers 82 and 84 that are portions of the mass of elastomer ~;
~8 incorporated in the prosthesis. The frontbumpers 82 and 84 are securedto front portions 56 and 62, respectively, of the ~ .
contoured surfaces 44 and 46 of the primary components 40 and 42. Each of the bumpers 82 and 84 extends away from the front portions 56 or 62 to which it is secured and toward the other front bumper, Like the rear bumpers 78 and 80, the bumpers 82 and 84 are not joined together so that no tension loads can be ~mposed on the bumpers 82 and 84, when, for example, relative 1~5~S3 , .
rotationbetween the co~ponents 40 and 42 ~f the prosthesis 10 causes the surface ~ortions 56 and 62 to move away from each other.
As should be apparent, the bumpers 78, 80, 82 and 84 will resist flexion of the prosthesis 10 through compression loadina of the elastomer in the bumpers.
The operation of the ankle joint prosthesis 10 will be described with the user or wearer extending the artificial leg 12 and foot 14 to take a step. As the heel of the artificial ~oot 14 strikes the ground, the rear of the primary component ; 10 40 of the prosthesis 10 rotates toward the rear of the primary component 42 about the axis 66 of the pin 64. The elastomeric portions 70 and 72 that secure the components 40 and 42 to the pin 64 deflect in torsional shear to permit the relative rotation that occurs between the primary components and the pin.
At the same time, the rear bumbers 78 and 80 come together and are compressed to limit the rotational movement and to help absorb the impact load imposed on the fool 14. As the weight of the user or wearer of the prosthesis 10 comes forward on the prosthesis and the foot 14, the rear of the component 40 be-ains to rotate away from the rear of the component 42. The rotation relieves the torsional deflection of the elastomeric port~ons 70 and 72 and the compression loads on the bumpexs 78 and 80. As the weight of the user and the leg 12 continue to move forward, the elastomeric portions 70 and 72 are again deflected in torsional shear and the front bumpers 82 and 84 come together and are compressed so as to limit relative move-~ent of the front of the component 40 toward the front of the component 42, ~7hen the user lifts the artificial foot 14 from the groun~ as he prepares to take another step, the loads on the bumpers 82 and 84 and the elastomeric portions 70 and 72 are relieved.
The primarv motion that the prosthesis 10 is designed - 15 ~
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to accommodate is dorsal and plantar flexion of the foot 14 with respect to the artificial le~ 12. Flexion occurs about an axis disposed generally perpendicular to the lonyitudinal axis of the le~ 12 and transverse to the lonqitudinal axis of the foot 14 or, in other words, about an axis that is at least adjacent to and at least approximately parallel to, if not coincident with,the longitudinal axis 66 of the pin 64.
Coincidence between the axis of rotation and the axis 66 will dependr in part, on whether the pin 64 shifts during rotation between the pin 64 and a pri~ary component 40 .
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t - 15a -or 42, orporation of resilient material into the prosthesis 10 also permits the prosthesis to accommodate limited degrees of internal and e~ternal rotation, as well as inversion and eversion, of the artificial foot 14 To perrnit inversion and eversion of the foot 14, which is rotation about an axis generally parallel to the lonçritudinal axis of the foot, the primary components 40 and 42 of the prosthesis 10 must rotate toward each other adjacent one or the other ol the two sides of the prosthesis. The relative rotation between the components 40 and 42 is accorn-modated by compression of the two elastomeric portions 70 and 72 adjacent one side of the prosthesis 10 or one end of the pin 64. Adjacent the other side of the prosthesis 10 and the other end of the pin 64, the elastomeric portions 70 and 72 may be placed in tension as the primary components 40 and 42 rotate away from each other. Alternatively, the weight of the user or wearer of the prosthesis 10 ~y impose a sufIicient compressive preload on the elastomeric portions 70 and 72 so that the relative rotation of the components 40 and 42 away from each other .merely relieves the preload without impcsing tension loads.
External and internal rotation of the foot 14, which occurs about an axis that is generally parallel to, if not coincident with, the longitudinal axis of the leg 12, is accom~nodated primarily through shearing deflection of the elastomeric portions 70 and 72. Because of the spaces betw~en the exposed surfaces 74 and 76 of the elastomeric portions 70 and '72, respectivelyJ and because of the spacing between the primary components 40 and 42, there is essentially no compression of elastomer required to accom~odate rotation of the foot 14. Consequently, external and internal rotation is accomplished more easily or with less force than inversicn or eversion If the prosthesis 10 is unable to provide a su~icient de~ree of rotation, a supplemental ro~ator may be used with the prosthesis. Such a `" ~lZ5~S3 .
rotat ~ ~ould be disposed between the upper prim~ry component 90 of the prosthesis 10 and the artificial lower leg 12, for e~ample. ~ypical supplemental rotators are described and illustrated in Moore U S. Patent No 3, 356, 775, HauptU. S PatentNo 4,007,497, andCwens etal U. S. PatentNo. 4,038,705.
Although the ankle joint prosthesis 10 of ~gures 1 and 2 rnay be perceived as having a structure that is similar to the structure of the ankle joint prosthesis shoYm in Prahl U. S Patent No. 3, 480, 972, for example, there is a difference in structurP that is significant in terms of the useful service life of the two prostheses. In the Prahl an~le joint prosthesis, and in similar prostheses, a tubular bushing of elastomer is disposed between and bonded to a rigid outer sleeve and an inner pin. The sleeve is attached to an artificial lower leg, for example, while the pin is attached to an artificial foot, for example. Flexion between the foot and the leg is accommodated by torsion21 defLection of the elasto-meric bushing. The degree of the resulting strain in the elastomer of the bushing will depend upon the radial thickness of the bushing and the amount of rotational or torsional motion that must be accommodated For a given amount of torsional motion, a relatively thin elastomeric bushing will experience relatively high strains and will pro~de a relatively short service life because of early fatigue failure of the elas omer. A thicker bushing will reduce the strains experienced by the elastomer and provide improved service life, but will also probably in-crease the overall size of the prosthesis. In addition, the effective spring rate of an element of elastomer at any distance from a point about which pivotal motion occurs is proportional to the spring rate of the elastamer in translational shear multiplied by the square of the distance from tne pivot point. Since the elastomer that 3s closest to the pivot point is effectively much softer in rotational shear than elastomer that is farther from the pivot point, the major portion of the torsiQnal il~25453 strail deflection in an elastomeric bushing, for example, wilt occur in the elastomar that is closest to the pivot point. Consequently, doubling the radial thickne~s of an elastomeric bushing ~ ill not halve the rnai~imum strains e~
perienced by the elastomer as it deflects to permit pivotal motion, but will have a much smaller effect on reducing the strains.
The prosthesis 10 affords a more efficient and effective method of con-trolling strains in its constituent mass of elastomer 68 because the rotational motion that is necessitated by flexion between the leg 12 and the foot 14 is accom-modated by two distinct portions 70 and 72 of the elastomeric mass which are disposed at equal distances from the axis of pivotal motion. Approximately half of the rotational motion between the primary components 40 and 42 of the prosthesis 10 which is required by flexion between the foot 14 and the leg 12 is accommodated by deflection of the elastomer 70 between the pin 6a and the com-poIlent 40, The other half of the motion is accommodated by deflection of the elasto~ier 72 between the pin 64 and the primary component 42 of the prosthesis 10. Thus~ for the same diametral dimensions, the prosthesis 10 will ef~ectively provide twice as much motion accommodation for a given maximum strain or half as much strain for a given degree of flexion as will a prosthesis constructed such as the one shown in the Prahl patent.
Figures 4 and 5 of the application drawings illustrate another embodiment 10' of the ankle joint prosthesis 10 shown in Figures 1, 2 and 3. In Figures 4 and 5, elements of the prosthesis 10' that correspond to elements of the prosthesis 10 are designated with corresponding, but primed reference numerals. The prosthesis 10', like the prosthesis 10, includes a pair of spaced apart, primary components 40' and 421 that are fabricated of a relatively nonexter.sible material. Each of the primary components 40' and 42' includes a contoured surface 44' or 46' and an 1~5453 OppO5 ` planar suriace 48' or 50' Disposed between concavely arcuate portions 52' and 58' of the contoured surfaces 44' and 461 is a cylindrical pin 54' that is formed of a relatively inextPnsihle material. Elastomeric elements 70' and 72' secure the pin 64' to the components 40' and 42', respectively.
Cne difference bet~een the prosthesis 10' and the prosthesis 10 is that a single, one-piece rear bumper 86 is disposed between the components 40' and 42' of the prosthesis 10', unlike the separate rear bumpers 78 and 80 of the prosthesis 10. The one-piece rear bumper 86 facilitates molding of the elastomeric portions of the pro$thesis 10' by eliminating the need to maintain a narrow space between two separate rear bumpers. In addition, the one-piece construction eliminates the possibility that dirt and grit will be introduced betuJeen two separate bumpers and thereafter absde and wear the elastomer in the bumpers. The bumper 86 may, however, be subjected to tension load.s during operation of the prosthesis 10' to accommodate flexion. As previously discussed, tension loads are detriment31 to the fatigue life of an elastomeric member, particulærly when the tension loads alternate with compression loads, as would be the case with the bumper 86. Nonetheless, the bumper 86 will also be subjected to a compressive preload that results from the weight of the user of the prosthesis. The compres-sive preload will ~' least minimize, and perhaps totally eliminate, what would otherwise be tension loads on the bumper 86 as the prosthesis 10' flexes to bring the front portions of the pri~ary components 40' and 42' of the p~osthesis toward each other. The possibility of tension loads on the one-piece rear bumper 86 will also be reduced because the front portions 56' and 62' of the contoured surfaces 44~ and 46', respectively, of the prosthesis components 40' and 42' are relatively close together, as comp~red to the corresponding surfaces 5G and 62 in the prosthesis 10. Thus, the plantar llexion of which the prosthesis 10' is capable is ~l'ZS453 signif. ntty tess than the fLe~ion of which the prosthesis 10 is capable Another difference between the prosthesis 10' and the prosthesis 10 is that the primary components 40' and 42' of the prosthesis 10' have roughly octagonal shapes in plan view, as shown in Figure 5, as opposed to the rectan-gular shapes of the components 40 and 42 of the prosthesis 10. As should be apparent from ~gure 2, the octangonal shapes of the components 40' and 42' -eliminate the corners of the components 40 and 42 which project beyond the side surfaces or outline of the upper portion of the foot 14. The prosthesis 10' also includes relatively prominent grooves 88 formed in the surface of the rear bumper 86 adjacent the interfaces between the bumper and the primary com-ponents 40' and 42'. The grooves 88 tend to relieve the high stresses that rr.ught otherwise occur at the interfaces The pin 64' includes a blind bore 90 in each end to facilitate locating the pin in its proper orientation and position in a mold for forming the elastomeric portions of the prosthesis 10'. Projections in the mold are provided to engage the blind bores 90 and hold the pin 64' in place during transfer and curing of the elastomer.
Yet another embodiment 10" of the present invention is illustrated in section in Figure 6 As with the ankle joint prosthesis 10' of Figures 4 and 5, double primed reference numerals are used in :~igure 6 to designate elements of ~e prosthesis 10" that correspond to similarly referenced elements of the prosthesis 10. Cne difference between the ankle joint prosthesis 10" and the prosthesis 10 of Figures 1 and 2 is the incorporation into the prosthesis 10" of a one-piece- rear bumper 92, similar to the one-piece rear bumper 86 of the prosthesis 10'. The rear burnper 92 is not formed wholly of elastomer, however, but includes a shim 94 formed of a relatively nonextensible material, such as metal or reinforced plastic. The shim 94 will theoretically reduce the ability of - ~0 -. ll~S~3 the elastorner in the bumper 92 to bulge under cornpressive loads. Consequently, as compared to a similar bumper without a shim, the bumper 92 should be able to support a substantially greater load for a given outward bulge or vertical deflection. The use of one or more shims 94 is a method of increasing the com-pression stiffness or spring rate of the rear bumper 92 without utilizing a type or grade of elastomer in the rear bumper that is different from the elastcmer used elsewhere in the prosthesis A problem with using the shim 94, however, is that there is a definite tendency for the shim to displace outwardly from the elastomer by moving to the left as viewed in Figure 6, thereby defeating the intended purpose of the shim A possible solution to the problem is taper the shim 94 such that the thickest portion of the shim is closest to the pin 64.
The ankle joint prosthesis 1Q" of Figure 6 incorporates a rotator 96 to supplement the capability of the basic prosthesis structure to accommodate in-ternal and external rotation. The supplemental rotator 96 includes a cylindrical bo~y of elastomeric material 98 in which are embedded three annular shims 100 that are fabricated of relatively nonextensible material As with other components of the prostheses 10~ 10' and 10", the elastomeric material 98 may be natural or synthetic rubber, while the inextensible material m~y be metal, reinforced plastic, or any other material which will bond to the elastomer 98 and which is relatively inextensible as compared to the elastomer. The rotator 96 is received in a recess 102 formed in the planar upper surface 48 " of the primary component 40" of the prosthesis 10". Placing the rotator 96 in the recess 102 decreases the extent to which the rotator 96 increases the total height of the prosthesis 10".
The elastomer 98 in the rotator 96 is bonded, at one end, to the surface 48" of the component 40" at the bottom of the recess 102 and, at the other end, to a supplemental plate 104. The plate 104 is spaced from the upper sur~ce 48" of _ 21 -~lZ~3 the ~ri ry prosthesis component 40" and is provided with t~Jo threaded bores 106. The bores 106 will accept screws (not shown) for securing the prosthesis 10"
to ~n element such as a mounting adapter or an artificial lower leg. In operation, the rotator 96 wilt permit internal and external rotation of a foot through torsional shearing of the elastomer 98. The shims 100 will reduce the tendency of the rotator 96 to defLect under the weight of a user's body.
To guard against tension loads in the elastomer of both the rotator 96 and the rear bumper 92, a member 108 that is flexible, but relatively inex-tensible, such as a wire cable, extends between the lower primary component 42" of the prosthesis 10" and the supplemental plate 104 at the upper end of the pros.hesis. The cable 108 is received in a bore 110 which is formed vertically thro.lgh the center of the prosthesis 10" and which has a diameter sufficiently greater than the outer diameter of the cable to permit the prosthesis to function without interference from the cable. Buttons 112 at each end of the cable 108 hold the cable in place in the primary component 42" and the supplemental plate 104 of the prosthesis 10". The amount of compressive preload that is to be applied to the elastomeric elements of the prosthesis 10" will determine the amount of tension to be imposed on the cable 108. It would be possible to provide for ad-j~tment of tension in the cable 108 during use of the prosthesis 10" by proviling a thraaded engagement between the buttons 112 and the cable, as suggested by AsbelleetalU. S. PatentNo~ 3,982,280.
A fourth e~odiment of an ankle joint prosthesis 10"' of the present in-vention is shown- in Figures 7 and 8 As with the prostheses 10' and 10" of F~gures 4 and 5 and Figure 6, respectivelyJ elements of the prosthesis 10"' of Figures 7 and 8 corresponding to elements of the prosthesis 10 of Figures 1 and
This application is a div;sional application of copending applicant No. 316,296 filed November 15, 1978.
Resilient màterials, such as elastomers, have long ~ been used in external prosthetic devices for the human body - to cushion impact or shock loads. Recause t:: ~:
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ll'Z5453 impa` loads are nece_sarily and regularly encountered in wall~ing, two common prosthetic devices that have often incorporated resilient materials are artificial feet arld ar~kle joint prostheses for use ~ith artificial îeet. In early designs, an ankle joint prosthesis was typically a metallic pivot that included a plain (e. g sleeve) bearing or a rolling element (e g., ball) bearing, Resilient or elastomeric m~Lteria~ was disposed both about the pivot to help limit its motion and in various portions of an associated artificial foot to cushion or absorb impact loads, Typical combinations of a cushioned artificial foot and an ankle joint prosthesis that in-corporates a metal-on-metal pivot are described and ill~1strated in Ehle U. S
PatentNo. 487,697, RowleyU. S PatentNo. 1,090,881, andKaiserU S Patent No. 2, 183,076.
Later in the development of ar~{le joint prostheses for external use, resilient or elastomeric matelial came to be utilized for properties otker than its ability to absorb or cushion impact loads. In Desoutter U. S Patent No.
1,911,~40, for example, a tubular rubber bushing is secured between a pin and a metal steeve that circumscribes the pin to form a pivot for an ankle joint prosthesis, The outer sleeve is connected to an artificial foot, while the pin is connected to an artificial lower leg. Articulation is permitted by torsional de-flection of the bushing. Because of the resilience of the bushing material, th;~
ar~le joint prosthesis automatically returns to a preselected position after it is deflected. The prosthesis also does not require lubrication because the bushing separates the adjacent metal surIaces of the pin and the sleeve. Similar ankle joint prostheses that employ a tubular bushing or body of elastomer between an outer rigid sleeve and an inner pin or sleeve are described and illustrated in BurgeretalU S PatentNo. 2,~05,475andPrahlU. S PatentNo. 3,480,97.
A pivot or pivotable assembly that incorporates a relatively thin, tubular body of elastomer secured between a pin and a larger diameter sleeve is only capable OI ei~tensive pivotal or rotational movement about a single aY.is In a typical ankle joint prosthesis, such as the Desoutter and Prahl prostheses, such an elastomeric pivot is oriented generally perpendicular to the longitudinal axis of the wearer's leg and transverse to the longitudinal axis of the wearer's artificial foot. In the orientation that has been described, the elastomeric pivot perrnits extensive flexin in the dorsal and plantar directions. An elastomeric pivot so oriented, however, can only provide a limited degree of inversion and eversion of a foot about its longitudinal axis or a parallel axis and only a limited degree of internal and external rotation of the foot about the longitudinal axis of 'he leg. The motions other than flexion are all accommodated primarily through compression of the elastomeric bushir~g, which is relatively tnin and cannot afford any significant degree of deflection. To overcome some of the motion limitations ir~erent in the ankle joint prostheses of the Desoutter and Prahl patents, the ankle joint prosthesis of the previously mentioned Burser et al patent incorporates two elastomeric pivots disposed at right angles to each other. The Burger et al ankle joint prosthesis thus car~ resiliently permit both extensive dorsal and plantar flexion and extensive inversion and eversion Cther external ankle joint prostheses attempt to provide the three types of movement af~orded by a natural anlcle joint throu~h the use of relatively rnassive blocks of elastomer, rather than the tubular bushings discussed above. The blocks of elastomer may be specially shaped or contoured in order to provide appropriate stlfinesses or motion capabilities in the three critical rctational directions. Examples of ex-ternal ankle joint prostheses that incorporate large blocks of elastomer are described and illustrated in Bennington et al U S Patent No. 2,692,392 and Asbelle et al U. S. Patent No. 3, 982, 280 5~53 ... ~ .
Although resilient materials, and particularly elastomeric materials, have for many years been suggested for use in external joint pr~sthesest the use of resilient or elastomeric materials in internal joint prostheses has only recently been proposed, The apparent delay in the appearance of proposals for the use of resilient or elastomeric materials internally of the human body is probably at-tributable in part to the lack of a physiologically inert elastomeric material that could safely ~e used in the body. Nonetheless, with the development of suitable elastomeric materials, such as Dow Corning Corporation's Silastic~9 silicone elastomer, a number of surgically implantable, elastorneric joint prostheses have been proposed, particularly for finger joints The finger joint prostheses, in particular, tend to be entirely formed of elastomer or nearly so Unfortunately, such designs req~lire the elastomer to be bent or flexed~xtensively at some point to provide a pivot, The result is alternating tension and compression loading of the elastomer, which is detrimental to its long-term fatigue life. The use of notches in the elastomer to locate the pivot point further adds to the stresses in-the elastomer. Examples of finger joint prostheses that are entirely formed of elastomer or nearly so are described and illustrated in Swanson U. S. Patent No.
3~462~7O5~ Niebauer et al U S. Patent No. 3,593,3a~2, Lynch U. S Patent No, 3,681,786, andSwansonU S. PatentNo. 3,875,594. Ctherthanthefinger;olnt prostheses mentioned above, relatively few implantable prostheses that employ resilient or elastomeric material have been identified. Nonetheless~ the use of elastom~ric material in an implantable hip joint prosthesis is suggested in Buechel et al U, S. Patent No. 3, 916, 451, particularly Figure 1, and in Bokros et al U. S. Patent No, 3, 707, 006, particularly Figure 5.
The ankle join. prostheses described in the previously mentioned patents to ~esoutter, Bur~er et al, and Prahl appear to represent the best presently known designs for use of the desirable properties of elastorneric material in a il254S3 prosthesis thataccomodates piyotal or rotational motion. None-theless, the elastomeric pivots that are incorporated in the ankle joint prostheses o~ these three patents do not make optimal use of elastomeric material within the space provided. In parti-cular, the relatively thin, tubular bodies of elastomer in the ankle joint prostheses of Desoutter, Burger et al, and Prahl are subjected to relatively high, torsionally-induced strains, which, over periods of extended use, will lead to failure of the elastomeric bodies. While the strains experienced by the elastomeric bodies of the patented ankle joint prostheses may ~; not be detrimental in terms of a few hundred or even a few thousand articulations of the prostheses, the strains are critical when one considers several million articulations or deflections of the prostheses. Such numbers of articulations may easily be experienced during a vear or two of normal use.
In an ankle joint prosthesis that is used externally of the human body, replacement of the elastomeric elements of the prosthesis may merely represent additional expense and some inconvenience to the user. If such a joint prosthesis were ~ implanted in the body of the user, on the other hand, failure of~the elastomeric elements within one or two years would seriously limit the desirabilitv of using such a prosthesis.
In copending application No. 316,296 there is dis-closed and claimed a ioint prosthesis comprising (a) a first relatively inextensible component; (b) a second relatively : : :
inextensible component that is spaced from the first component along a first axis; (c) means defining a relatively inextensible pivot member disposed between and spaced from each o~ the first and second components, the pivot member having a center and a central axis which passes through said center and which is oriented generally perpendicular to said first 2XiS, the first and second components being disposed entirely on opposite sides ~ 5 :^ ~
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il~5~S3 of and separated by a plane oriented generally perpendicular to said first axis and aenerally parallel to said central axis of the pivot member; and (d) means for resiliently securing the pivot member to each of the first and second components, the securing means includinq (i) a first portion that secures the pivot member to the first component, and (ii~ a second portion that secures the pivot member to the second component, each of the first and second portions of the securing means having at least one exposed surface that extends outwardly from adjacent the pivot member, said at least one exposed surface of the first portion of the securing means being spaced from said at least one exposed surface of the second porti.on of the securing means throughout at least a majority of their respective lengths measured generallv radially of said central axis of the pivot member, the first and second components being coupled to each other only through the pivot member and the first and second portions of the securing means, the relative extensibility of the first and second components and the pivot member being determined in comparison to the securing means, the securing means resiliently permitting and accommodating relative rotation between the pivot member and the first component and between the pivot member and the second component so that the first and second components can move toward and away from each other in directions ~enerally parallel to said first axis through rotation about a second axis that is disposed at least adjacent to and at least approximately parallel to the central axis of the pivot member.
The present invention is thus directed to a joint prosthesis which is suitable for either internal or external use and which is constructed resiliently to permit and accommodate pivotal or rotational movement, with a view to providing maximum useful life. A joint prosthesis according to the invention - 5a -~ :` -COmpriseS a pair of primary components that are formed of relatively ~nextensible material and are spaced apart from one another. Disposed between and spaced from each of the two components is a pivot member that is also formed of relatively inextensible , . .
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material. The piVot member is resiliently secured to each of the primary components so as to permit andaccomodates relative rotation between the pivot member and the components. As a result, the two primary components of the prosthesis can rotate toward and awav from each other ahout an axis that is disposed at least adjacent to and at least approximately parallel to a central axis of the pivot member. The use of a pivot member and a pivot axis that are separate from the primary components of a joint prosthesis permits the prosthesis to have, for example, a relatively small size for a given angular motion to be accomm-odated and aiven maximum strain in the material that resiliently secures the pivot member to the primary components. Alternatively, the prosthesis of the present invention will pe~mit, for a given angular motion to be accommodated and given size of the pros-thesis , a lower maximum strain in and a larger service life for the resilient material that secures to~ether the pivot member and the primary components of the prosthesis. The foreqoing advantages are experienced particularly with reference to a prosthesis such as the prostheses of Desoutter U.S. Patent No. 1,911,440 and Prahl U.S. Patent No. 3,480,972, in which the pivot member or pin is rigidly secured to one of the primary components of the prosthesis.
The pivot member is secured to the primary components of the prosthesis by a member that is at least partially formed of elastomer. Attachment of the pivot member to the primary components only through a member of body that is regilient in ~- whole or part will insure that the prosthesis is free of any relatively inextensible, and hence motion restraining, connection between the primary components. The resilient securing member will typically include a first portion that secures the pivot ~; member to one of the primary components of the prosthesis and a second portion that secures the pivot member to the other primary .
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~ - 6 a -5~S3 portioi of the resilient securing member are preIerably arcuately shaped when viewed in section taken generally normal to the central longitudinal axis of the pivot ~ember, Each of the first and second portions of the securing member will also preferably include a pair of exposed surfaces that e~tend generally lengthv.Tise of the pivot member and outwardly from adjacent the pivot member, The e~uosed surfaces of one portion of the resilient securing member are spaced apart from the exposed surfaces of the other portion of the securing member throughout at least a majority of their respective lengths measured generally radially of the pivot member, Such a spacing between the two portions of the resilient securing member facilitates relative pivotal motion or rotation between the pivot member and either of the primary components of the prosthesis without interference from the other primary component of the prosthesis or its associated portion of the securing member, Also to facilitate relative pivotal motion or rotation, each of the primary components of the prosthesis will preferably include a surface that is concavely arcuate in shape when viewed in section taken generally normal to the central longitudinal axis of the pivot member.
Each of the arcuate surfaces of the primary components is presented to and spaced from a convexly arcuate surface of the pivot member. At least one of the two primary com~onents of the prosthesis should include structure for attaching the component to a limb associated with the human body.
When the present invention is embodied in an external ankle joint prosthesis, for example, the securing member that includes two portions which ~ .
resiliently secure the primary components of the prosthesis to the pivot member also includes a portion secured to at least one OI the primary componen s at a point behind an arcuate surface of the component which is presented to the pivot member. This third portion of the securing member extends from the primary component to which it is attached toward the other primary component of the ( 13~Z5~.~S3 pros sis resiliently to limit relative rotation between the two primary com-ponents~ particularly retative rotation between the rcar portions of the primary components The resilient securing member ~ay al.o include a fourth p~)rtion that is secured to at teast one of the two primary components of the prosthesis at a point in front of the arcuate surface of the component which is presen~ed to the pivot member ~he fourth portion of the securing member extends Irom the component to which it is secured toward the other primary ~omponent of the prosthesis With such an orientation, the fourth portion of the securing rnember resiliently limits relative rotation between the front of one primary component and the front of the other primary component. Each of the third and fourth portions of the securing member should be at least partially formed of elastomer. The opposed surfaces of the two primary components of the ankle joint prosthesis should each include an arcuately shaped portion presented to the pivot member of the prosthesis, a portion disposed in front of the arcuate portion, and a portion disposed to the rear of the arcuate portion. The front portions of the opposed surfaces OI the two primary components should be disposed to diverge frorn one another in a direction away from the pivot member. The rear portions of the two opposed surfaces should be similarly disposed.
Brief DescriPtion of the Drawings For a better understanding of the invention, reference may be made to the Iollowing description of several exemplary embodiments~ taken in conjunction with the ~lgures of the accompanying drawings, in which:
Figure 1 is a side view of an ankle joirlt prosthesis according to the invention mounted between an artificial leg and an artificial foot;
1~2S~53 Flyure 2 is a plan view, partly in section, of the joint prosthesis of Figure 1, taken along line 2-2 of F~gure 1;
Figure 3 is a side view, on an enlarged scale, of the anlcle joint prosthesis of Figure 1;
Figure 4 is a side view of a second ankle joint prosthesis according to the inven~ioni Figure 5 is a plan view of the joint prosthesis of Figure 4;
Figure 6 is a side view, in section, of another embodiment of an ankle joint prosthesis according to the invention;
Figure 7 is a side view of yet another embodiment of an ankle joint prosthesis according to the invention;
Figure 8 is a sectional view of the an~le joint of Figure 7, taken along line 8-8 of Figure 7; and Figure 9 is a perspective view of an endoprosthetic finger joint according to the invention.
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Description of Embodiments Figure 1 OI the drawings illustrates, in side view, an ankle joint prosthesis 10, according to the present invention, mounted between an artificial lower l~g 12 and an artificial foot 14. The artificial leg 12 rnay be formed of any one of a number of materials that have the strength necessary to support the weight of the human bodyJ such as metal, wood, nylon, or reinforced plastic. The leg 12 is . ,~, ~hollow and includes a generally tubular body portion 16 and an end wall 18 that is disposed adjacent the prosthesis 1û. The end wall 18 is formed with an opening ''! 20 which extends axially of the leg 12 and which receives and fixedly mounts a nut 22. Screwed into the nut 22 is the threaded stud 24 of a rnetal mounting adapter :
26. The adapter 26 includes both the threaded stud 24 and a circular base plate - - 9 - ~
S~3 28 Erom one side of which the stud ~Xojects in a direction per-pendicular to the plane of the base plate. As best shown in Figure 2, the base plate 28 has four circumferentially spaced apart holes formed in it. Each of the holes in the base plate 28 receives a screw 29 that is screwed into an upper surface of the ankle ]oint prosthesis 10 to secure the mounting adapter 26 to the prosthesis. A second metal mounting adapter 30, which is, but need not be, identical to the adapter 26, is secured to a lower surface of the prosthesis 10 opposite the surface to which the adapter 26 is secured. Four screws (not shown) are received in holes formed in the base plate 32 of the adapter 30 and are screwed into the prosthesis 10. A threaded stud 34, which is immovahly connected to the base plate 32, extends perpendicularly away from the plane of the base plate and into an opening 36 formed vertically through the artifical foot 14 just forward of the heel of the foot. The opening 36 in the foot 14 receives and fixedly mounts a nut 38 into which the threaded stud 34 is screwed.
The artificial foot 14, like the artificial leg 12, is formed of a material,, such as metal, wood nylon, or reinforced plastic, that ,; 20 is stronqenough to support the weight of the human body. In addition, the material of which the foot 14 is formed should also-afford some resilience or give. Resilience of the foot will attenuate, to some extent, the shock loads imposed on the foot and transmitted from the foot through the ankle joint prosthesis 10 and the artificial leg 12 to the user's body when the foot ~- strikes a!hard surface, as in walking. Additional resilience ; ,m,ay be provided by incorporating within the artificial foot i4 one or more bodies of elasto~er or other resilient material.
A typ~cal artificial foot that incorporates several discrete bodies of elastomer disposed to provide additional resilence is described and illustrated in Kaiser U.S. Patent No. 2,183,076.
The ankle joint prosthesis 10 incorporàtes two identical ll~S4S3 and vertically spaced apart primary components 40 and 42.
Each of the primary components 40 and 42 is formed of a rela-tively inextensible material, such as metal, plastic, or reinforced plastic. The material of which the primary components 40 and 42 are formed must be suitable for bonding to elastomer, for reasons that will become a~parent, and is to be judged as to ~ts relative inextensibility through comparison to the elastomer utilized in the prosthesis 10. The components 40 and 42 incorporate contoured surfaces 44 and 46, respectively, which are presented toward, but spaced apart from each other.
Opposite their respective contoured surfaces 44 and 46, the componentS 40 and 42 have ~enerally planar surfaces 48 and 50, respectively~ ~he planar surface 48 of the component 40 is presented to and juxtaposed with the surface of the adapter base plate 28 opposite the stud 24. The screws 29 that are received in the holes in the base plate 28 are screwed into threaded, blind bores (not shown) formed in the surface 48 and the com-~onent 40 In a similar manner, the planar surface 50 of the com-ponent 42 is presented to and juxtaposed with the surface of ~` 2-0 the adapter base plate 32 opposite the stud 34. The screws . . ~
:~:;.; ~ (not shown~ that are received in the holes (not shown) in the base plate 32 are screwed into threaded, blind bores (not shown) ormed in the planar surface 50 and the component 42. Although ,.:.......................... .
; the primary components 40 and 42 of the prosthesis 10 are attached to separate mounting adapters 26 and 30, respectively, the studs :
.~ 24 and 34 of the adapters could each be formed in one piece `~` with an adjacent primary component.
~:` The contoured surface 44 of the primary component 40 of the prosthesis 10 includes a central portion 52 that is 3Q concavely arcuate in shape, when viewed from the side, as in - Figure 1. To the rear of its central portion 52, the surface ~ 44 includes a planar rear portion 54 that slopes toward the 11;~5453 surface 48 from front to rear of the prosthesis 10. In front of its central portion 52, the surface 44 includes a planar front portion 56 that slopes toward the surface 48 from rear to front of the prosthesis 10. The contoured surface 46 of the com-ponent 42 similarly includes a concavely arcuate central portion 58, a planar rear portion 60, and a planar front portion 62.
The front and rear portions 62 and 60 of the surface 58 slope toward the surface 50. Disposed between the spaced apart arcuate portions 52 and 58 of the contoured surfaces 44 and 46 is a cylindrical pivot member or pin 64. The pin 64 is formed of a relatively inextensible material such as metal, reinforced plastic, or nylon, and is oriented such that its central longi-tudinal axis 66 is generally perpendicular to the lon~itudinal axis of the leg 12 and transversely disposed relative to the longitudinal axis of the foot 14. Because of its shape and orientation, the pin 64 presents a convexly arcuate surface to each of the arcuate surface portions 52 and 58 of the primary - components 40 and 42, respectively, of the prosthesis 10.
The pin 64 is resiliently secured to the components 40 and 42 of -~
the prosthesis 10 hy a body or mass of resilient material 68, such as elastomer. The elastomer in the mass 68 may be natural rubber or a synthetic elastomer. Although all of the resilient material in the prosthesis 10 is part of a single interconnected : ,.
mass 68, each of the various portions or sections of the mass 68 which are described hereinafter may be formed as a discrete member if such a procedure appears desirable for manufacturing or other purposes.
The convexly arcuate, outer circumferential surface of the pin 64 is resiliently secured to the arcuate surface - 30 portion 52 or the component 40 by an arcuately shaped portion 70 of the resilient or elastomeric mass 68. When viewed in section taken normal to the lon~itudinal axis 66 of the pin 64, 11~59~S3 the elastomeric ~Qrtion or section 70 resemb]es a truncated wed~e taken from an annulus. The elastomeric section 70 is bonded, by vulcanization or adhesives, for example, to both a portion of the :: 10 '`: :
., ~1 ~
~ .
~ 20~ ~
':' .
- 12a -convexly arcuate outer surfa~e of the ~in 64 and to the concavely arcuate centralportion 52 of the surface 44. To secure the pin 64 to the other primary component 42, a similar arcuately shaped portion or section 72 of the mass of elastomer 68 is disposed between and bonded to a portion of the convexly arcuate outer surface of the pin 64 and to the concavely arcuate surface portion 58 of the component 42. The elastomeric sections 70 and 72 include pairs of exposed surfaces 74 and 76,respectively, that ~ extend len~thwise of the pin 64 and outwardly, in a generally .~. 10 radial direction, form the outer circumferential surface of the pin. Throu~hout most of their lengths, as measured radially of the pin 64, the exposed surfaces 74 of the elastomeric section 70 are spaced apart from the exposed surfaces 76 of the elastomeric section 72. The surfaces 74 do intersect the surfaces 76 adjacent the pin 64, but diverge from the surfaces 76 with an increasing radial distance from the pin. In a similar manner,the f:rontplanar portion 56 of the contoured sur-face 44 o.f the component 40 diverges from the front planar portion 62 of the contoured surface 46 of the component 42. The rear portions 54 and 60 of the surfaces 44 and 46 also diverge V~th increasing radial distance from the pin 64. As a result of the diver~ence between the surfaces 74 and 76 ~nd between . ~ the surface portions 56 and 62 and 54 and 60, there can be relative pivotal or rotational movement between the pin 64 and the primary component 40, for examplel without inter-ference between the elastomeric section 70 that will be deflected to accommodate such relative rotation and the elastomeric sect~dn 72 without interference between the two primary compo -nents 40 and 42 of the prosthesis 10.
The elastomeric portions 70 and 72 of the mass of elas-tomer 68 in the prosthesis 10 will resiliently permit and, to a limited extent, resiliently resist relative rotation between ~25~53 the pin 64, on the one hand, and the primary components 40 and 42, on the other hand. 'i~otational or ~ivotal motion that corres-ponds to dorsal or plantar flexion of a natural ankle joint will occur about an axis that is disposed at least adjacent to and at least approximately parallel to the longitudinal axis ; 66 of the pin 64. Although the elastomeric sections 70 and 72 will offer some resilient resistance to dorsal and plantar flexion, the elastomer will be loaded in torsional shear and will not offer sufficient resistance to flexion to cushion and limit this motion. Thus, secured to the rear portions 54 ` and 60 of the contoured surfaces 44 and 46 of the components /;
40 and 42 are rear elastomeric bumper portions 78 and 80, respectively~ of the elastomeric mass 68. Each of the rear bumpers 78 and 80 extends away from the surface portion 54 or 60 to which the bumper is secured and toward the other rear bumper. Nonetheless, the rear bumpers 78 and 80 are separate from each other and are spaced sli~htly apart when the pros-thesis lO is in its normal undeflected position. Consequently, nG tenslon load will be applied to either of the bumpers 78 and 80~ when, for example,~relative rotation between the primary components 40 and 42 of the prosthesis 10 causes the rear por-tions 54 and 60 of the surfaces 44and 46 to move away from each other. The ankle joint prosthesis 10 also includes front bumpers 82 and 84 that are portions of the mass of elastomer ~;
~8 incorporated in the prosthesis. The frontbumpers 82 and 84 are securedto front portions 56 and 62, respectively, of the ~ .
contoured surfaces 44 and 46 of the primary components 40 and 42. Each of the bumpers 82 and 84 extends away from the front portions 56 or 62 to which it is secured and toward the other front bumper, Like the rear bumpers 78 and 80, the bumpers 82 and 84 are not joined together so that no tension loads can be ~mposed on the bumpers 82 and 84, when, for example, relative 1~5~S3 , .
rotationbetween the co~ponents 40 and 42 ~f the prosthesis 10 causes the surface ~ortions 56 and 62 to move away from each other.
As should be apparent, the bumpers 78, 80, 82 and 84 will resist flexion of the prosthesis 10 through compression loadina of the elastomer in the bumpers.
The operation of the ankle joint prosthesis 10 will be described with the user or wearer extending the artificial leg 12 and foot 14 to take a step. As the heel of the artificial ~oot 14 strikes the ground, the rear of the primary component ; 10 40 of the prosthesis 10 rotates toward the rear of the primary component 42 about the axis 66 of the pin 64. The elastomeric portions 70 and 72 that secure the components 40 and 42 to the pin 64 deflect in torsional shear to permit the relative rotation that occurs between the primary components and the pin.
At the same time, the rear bumbers 78 and 80 come together and are compressed to limit the rotational movement and to help absorb the impact load imposed on the fool 14. As the weight of the user or wearer of the prosthesis 10 comes forward on the prosthesis and the foot 14, the rear of the component 40 be-ains to rotate away from the rear of the component 42. The rotation relieves the torsional deflection of the elastomeric port~ons 70 and 72 and the compression loads on the bumpexs 78 and 80. As the weight of the user and the leg 12 continue to move forward, the elastomeric portions 70 and 72 are again deflected in torsional shear and the front bumpers 82 and 84 come together and are compressed so as to limit relative move-~ent of the front of the component 40 toward the front of the component 42, ~7hen the user lifts the artificial foot 14 from the groun~ as he prepares to take another step, the loads on the bumpers 82 and 84 and the elastomeric portions 70 and 72 are relieved.
The primarv motion that the prosthesis 10 is designed - 15 ~
~Z5~3 .
to accommodate is dorsal and plantar flexion of the foot 14 with respect to the artificial le~ 12. Flexion occurs about an axis disposed generally perpendicular to the lonyitudinal axis of the le~ 12 and transverse to the lonqitudinal axis of the foot 14 or, in other words, about an axis that is at least adjacent to and at least approximately parallel to, if not coincident with,the longitudinal axis 66 of the pin 64.
Coincidence between the axis of rotation and the axis 66 will dependr in part, on whether the pin 64 shifts during rotation between the pin 64 and a pri~ary component 40 .
~ .
t - 15a -or 42, orporation of resilient material into the prosthesis 10 also permits the prosthesis to accommodate limited degrees of internal and e~ternal rotation, as well as inversion and eversion, of the artificial foot 14 To perrnit inversion and eversion of the foot 14, which is rotation about an axis generally parallel to the lonçritudinal axis of the foot, the primary components 40 and 42 of the prosthesis 10 must rotate toward each other adjacent one or the other ol the two sides of the prosthesis. The relative rotation between the components 40 and 42 is accorn-modated by compression of the two elastomeric portions 70 and 72 adjacent one side of the prosthesis 10 or one end of the pin 64. Adjacent the other side of the prosthesis 10 and the other end of the pin 64, the elastomeric portions 70 and 72 may be placed in tension as the primary components 40 and 42 rotate away from each other. Alternatively, the weight of the user or wearer of the prosthesis 10 ~y impose a sufIicient compressive preload on the elastomeric portions 70 and 72 so that the relative rotation of the components 40 and 42 away from each other .merely relieves the preload without impcsing tension loads.
External and internal rotation of the foot 14, which occurs about an axis that is generally parallel to, if not coincident with, the longitudinal axis of the leg 12, is accom~nodated primarily through shearing deflection of the elastomeric portions 70 and 72. Because of the spaces betw~en the exposed surfaces 74 and 76 of the elastomeric portions 70 and '72, respectivelyJ and because of the spacing between the primary components 40 and 42, there is essentially no compression of elastomer required to accom~odate rotation of the foot 14. Consequently, external and internal rotation is accomplished more easily or with less force than inversicn or eversion If the prosthesis 10 is unable to provide a su~icient de~ree of rotation, a supplemental ro~ator may be used with the prosthesis. Such a `" ~lZ5~S3 .
rotat ~ ~ould be disposed between the upper prim~ry component 90 of the prosthesis 10 and the artificial lower leg 12, for e~ample. ~ypical supplemental rotators are described and illustrated in Moore U S. Patent No 3, 356, 775, HauptU. S PatentNo 4,007,497, andCwens etal U. S. PatentNo. 4,038,705.
Although the ankle joint prosthesis 10 of ~gures 1 and 2 rnay be perceived as having a structure that is similar to the structure of the ankle joint prosthesis shoYm in Prahl U. S Patent No. 3, 480, 972, for example, there is a difference in structurP that is significant in terms of the useful service life of the two prostheses. In the Prahl an~le joint prosthesis, and in similar prostheses, a tubular bushing of elastomer is disposed between and bonded to a rigid outer sleeve and an inner pin. The sleeve is attached to an artificial lower leg, for example, while the pin is attached to an artificial foot, for example. Flexion between the foot and the leg is accommodated by torsion21 defLection of the elasto-meric bushing. The degree of the resulting strain in the elastomer of the bushing will depend upon the radial thickness of the bushing and the amount of rotational or torsional motion that must be accommodated For a given amount of torsional motion, a relatively thin elastomeric bushing will experience relatively high strains and will pro~de a relatively short service life because of early fatigue failure of the elas omer. A thicker bushing will reduce the strains experienced by the elastomer and provide improved service life, but will also probably in-crease the overall size of the prosthesis. In addition, the effective spring rate of an element of elastomer at any distance from a point about which pivotal motion occurs is proportional to the spring rate of the elastamer in translational shear multiplied by the square of the distance from tne pivot point. Since the elastomer that 3s closest to the pivot point is effectively much softer in rotational shear than elastomer that is farther from the pivot point, the major portion of the torsiQnal il~25453 strail deflection in an elastomeric bushing, for example, wilt occur in the elastomar that is closest to the pivot point. Consequently, doubling the radial thickne~s of an elastomeric bushing ~ ill not halve the rnai~imum strains e~
perienced by the elastomer as it deflects to permit pivotal motion, but will have a much smaller effect on reducing the strains.
The prosthesis 10 affords a more efficient and effective method of con-trolling strains in its constituent mass of elastomer 68 because the rotational motion that is necessitated by flexion between the leg 12 and the foot 14 is accom-modated by two distinct portions 70 and 72 of the elastomeric mass which are disposed at equal distances from the axis of pivotal motion. Approximately half of the rotational motion between the primary components 40 and 42 of the prosthesis 10 which is required by flexion between the foot 14 and the leg 12 is accommodated by deflection of the elastomer 70 between the pin 6a and the com-poIlent 40, The other half of the motion is accommodated by deflection of the elasto~ier 72 between the pin 64 and the primary component 42 of the prosthesis 10. Thus~ for the same diametral dimensions, the prosthesis 10 will ef~ectively provide twice as much motion accommodation for a given maximum strain or half as much strain for a given degree of flexion as will a prosthesis constructed such as the one shown in the Prahl patent.
Figures 4 and 5 of the application drawings illustrate another embodiment 10' of the ankle joint prosthesis 10 shown in Figures 1, 2 and 3. In Figures 4 and 5, elements of the prosthesis 10' that correspond to elements of the prosthesis 10 are designated with corresponding, but primed reference numerals. The prosthesis 10', like the prosthesis 10, includes a pair of spaced apart, primary components 40' and 421 that are fabricated of a relatively nonexter.sible material. Each of the primary components 40' and 42' includes a contoured surface 44' or 46' and an 1~5453 OppO5 ` planar suriace 48' or 50' Disposed between concavely arcuate portions 52' and 58' of the contoured surfaces 44' and 461 is a cylindrical pin 54' that is formed of a relatively inextPnsihle material. Elastomeric elements 70' and 72' secure the pin 64' to the components 40' and 42', respectively.
Cne difference bet~een the prosthesis 10' and the prosthesis 10 is that a single, one-piece rear bumper 86 is disposed between the components 40' and 42' of the prosthesis 10', unlike the separate rear bumpers 78 and 80 of the prosthesis 10. The one-piece rear bumper 86 facilitates molding of the elastomeric portions of the pro$thesis 10' by eliminating the need to maintain a narrow space between two separate rear bumpers. In addition, the one-piece construction eliminates the possibility that dirt and grit will be introduced betuJeen two separate bumpers and thereafter absde and wear the elastomer in the bumpers. The bumper 86 may, however, be subjected to tension load.s during operation of the prosthesis 10' to accommodate flexion. As previously discussed, tension loads are detriment31 to the fatigue life of an elastomeric member, particulærly when the tension loads alternate with compression loads, as would be the case with the bumper 86. Nonetheless, the bumper 86 will also be subjected to a compressive preload that results from the weight of the user of the prosthesis. The compres-sive preload will ~' least minimize, and perhaps totally eliminate, what would otherwise be tension loads on the bumper 86 as the prosthesis 10' flexes to bring the front portions of the pri~ary components 40' and 42' of the p~osthesis toward each other. The possibility of tension loads on the one-piece rear bumper 86 will also be reduced because the front portions 56' and 62' of the contoured surfaces 44~ and 46', respectively, of the prosthesis components 40' and 42' are relatively close together, as comp~red to the corresponding surfaces 5G and 62 in the prosthesis 10. Thus, the plantar llexion of which the prosthesis 10' is capable is ~l'ZS453 signif. ntty tess than the fLe~ion of which the prosthesis 10 is capable Another difference between the prosthesis 10' and the prosthesis 10 is that the primary components 40' and 42' of the prosthesis 10' have roughly octagonal shapes in plan view, as shown in Figure 5, as opposed to the rectan-gular shapes of the components 40 and 42 of the prosthesis 10. As should be apparent from ~gure 2, the octangonal shapes of the components 40' and 42' -eliminate the corners of the components 40 and 42 which project beyond the side surfaces or outline of the upper portion of the foot 14. The prosthesis 10' also includes relatively prominent grooves 88 formed in the surface of the rear bumper 86 adjacent the interfaces between the bumper and the primary com-ponents 40' and 42'. The grooves 88 tend to relieve the high stresses that rr.ught otherwise occur at the interfaces The pin 64' includes a blind bore 90 in each end to facilitate locating the pin in its proper orientation and position in a mold for forming the elastomeric portions of the prosthesis 10'. Projections in the mold are provided to engage the blind bores 90 and hold the pin 64' in place during transfer and curing of the elastomer.
Yet another embodiment 10" of the present invention is illustrated in section in Figure 6 As with the ankle joint prosthesis 10' of Figures 4 and 5, double primed reference numerals are used in :~igure 6 to designate elements of ~e prosthesis 10" that correspond to similarly referenced elements of the prosthesis 10. Cne difference between the ankle joint prosthesis 10" and the prosthesis 10 of Figures 1 and 2 is the incorporation into the prosthesis 10" of a one-piece- rear bumper 92, similar to the one-piece rear bumper 86 of the prosthesis 10'. The rear burnper 92 is not formed wholly of elastomer, however, but includes a shim 94 formed of a relatively nonextensible material, such as metal or reinforced plastic. The shim 94 will theoretically reduce the ability of - ~0 -. ll~S~3 the elastorner in the bumper 92 to bulge under cornpressive loads. Consequently, as compared to a similar bumper without a shim, the bumper 92 should be able to support a substantially greater load for a given outward bulge or vertical deflection. The use of one or more shims 94 is a method of increasing the com-pression stiffness or spring rate of the rear bumper 92 without utilizing a type or grade of elastomer in the rear bumper that is different from the elastcmer used elsewhere in the prosthesis A problem with using the shim 94, however, is that there is a definite tendency for the shim to displace outwardly from the elastomer by moving to the left as viewed in Figure 6, thereby defeating the intended purpose of the shim A possible solution to the problem is taper the shim 94 such that the thickest portion of the shim is closest to the pin 64.
The ankle joint prosthesis 1Q" of Figure 6 incorporates a rotator 96 to supplement the capability of the basic prosthesis structure to accommodate in-ternal and external rotation. The supplemental rotator 96 includes a cylindrical bo~y of elastomeric material 98 in which are embedded three annular shims 100 that are fabricated of relatively nonextensible material As with other components of the prostheses 10~ 10' and 10", the elastomeric material 98 may be natural or synthetic rubber, while the inextensible material m~y be metal, reinforced plastic, or any other material which will bond to the elastomer 98 and which is relatively inextensible as compared to the elastomer. The rotator 96 is received in a recess 102 formed in the planar upper surface 48 " of the primary component 40" of the prosthesis 10". Placing the rotator 96 in the recess 102 decreases the extent to which the rotator 96 increases the total height of the prosthesis 10".
The elastomer 98 in the rotator 96 is bonded, at one end, to the surface 48" of the component 40" at the bottom of the recess 102 and, at the other end, to a supplemental plate 104. The plate 104 is spaced from the upper sur~ce 48" of _ 21 -~lZ~3 the ~ri ry prosthesis component 40" and is provided with t~Jo threaded bores 106. The bores 106 will accept screws (not shown) for securing the prosthesis 10"
to ~n element such as a mounting adapter or an artificial lower leg. In operation, the rotator 96 wilt permit internal and external rotation of a foot through torsional shearing of the elastomer 98. The shims 100 will reduce the tendency of the rotator 96 to defLect under the weight of a user's body.
To guard against tension loads in the elastomer of both the rotator 96 and the rear bumper 92, a member 108 that is flexible, but relatively inex-tensible, such as a wire cable, extends between the lower primary component 42" of the prosthesis 10" and the supplemental plate 104 at the upper end of the pros.hesis. The cable 108 is received in a bore 110 which is formed vertically thro.lgh the center of the prosthesis 10" and which has a diameter sufficiently greater than the outer diameter of the cable to permit the prosthesis to function without interference from the cable. Buttons 112 at each end of the cable 108 hold the cable in place in the primary component 42" and the supplemental plate 104 of the prosthesis 10". The amount of compressive preload that is to be applied to the elastomeric elements of the prosthesis 10" will determine the amount of tension to be imposed on the cable 108. It would be possible to provide for ad-j~tment of tension in the cable 108 during use of the prosthesis 10" by proviling a thraaded engagement between the buttons 112 and the cable, as suggested by AsbelleetalU. S. PatentNo~ 3,982,280.
A fourth e~odiment of an ankle joint prosthesis 10"' of the present in-vention is shown- in Figures 7 and 8 As with the prostheses 10' and 10" of F~gures 4 and 5 and Figure 6, respectivelyJ elements of the prosthesis 10"' of Figures 7 and 8 corresponding to elements of the prosthesis 10 of Figures 1 and
2 are designated with the same reference numerals as the elements of the ~25~S3 Prosthesis 10, but with a triple-prime superscript. Generally speakinq, the ankle joint prosthesis 10ll' closely resemhles the ankle ~oint prosthesis 10' of Fi~ures 4 and 5. There are two si~nificant differences, one of which is the addition of curved shims 114 of nonextensible material to the portions 70" ' and 72"' of the elastomeric mass 68''' which secure the pin 64 " ' to the primary components 40 " ' and 42 " ' of the prosthesis 10ll' . The shims 114 will increase the compression load carrying capahility of the prosthesis 10" ' without signi-10 ficantly interfering with its ability to accorr~nodate rotationalmotion of the components 40" ' and 42 " ' of the prosthesis about the longitudinal axis of the pin 64 " ', for example.
~nother sianificant difference between the prosthesis 10 " ' and the prosthesis 10' is that the pin 64 " ' is arcuate in shape not only in planes normal to its lon~itudinal central axis 66'~ but also in planes that are parallel to and extend ., ~, . :~
~hrough the longitudinal axis of the pin, as best shown in Fi~ure 8. The arcuate port~ions 52 " ' and 58 " ' of the primary ~ ~ components 40" ' and 42 " ' ,respectively, are also curved in ,'j'''.51.':~ ~ 20~ two perpendicular planes, as are the shims 114. The result Of the double curvature of the outer surface of the pin 64 " ' and the corresponding surfaces of other elements in the pros-:, ~
thesis 10 " ~ will be an increased ability of the prosthesis 10 " ' ~- to accommodate inversion and eversion, as compared to the pros-theses 10, 10l and 10~'. -Although all the foregoing embodiments of the invention .
have been ankle joint prostheses intended for use externallyof the human body, the basic pivot structure that: is incorporated in each of the foregoing embodiments of the invention may also 3Q be utilized in a joint prosthesis intended for use internally o~ the body. Fi~ure 9 of the drawings illustrates a finger-joint prosthesis 116, for example, that incorporates two opposed :::, i~5~53 and spaced apart primary components 118 and 120. The primary components 118 and 120 are formed of a relatively inextensible and physiolo~icallv inert material, such as titanium, stainless steel, ~ 10 , .
~ 20 : ` ;
:
';
, ' .
~ 30 . .
- 23a -i~S4~3 cobal~ hromium alloys, nylon, silicone resirls, or high density polyethylene.
The components 118 and 120 include head portions 122 and 124, respectively, and shank or stem por~ons i26 and 128, respectively. The h~ad portiorLs 122 and 124 are each fi~ed to one end of their respective stem portions 126 and 128, which are relatively long and tapered to facilitate insertion into the intramedullary canals of the ~nger bones. The stem portions 126 and 128 of the components 118 and 12û, respectively, will typically be cemented in place in their respective finger bones and m3.y have specially contoured outer surf~ces to improve the attachment to the bones Alternatively, or additionally, the stem portions 126 and 128 may be coated with or formed from a porous material into which boney tissue may grow to secure the primary components 118 and 120 of the prosthesis 116 to their respective finger bones.
The head portions i22 and 124 of the prirnary components 118 and 120 of the prosthesis 116 include surfaces 130 and 132, respectively, that are arcuate in at le~st one plane, The concavely arcuate surfaces 130 and 132 of the head portions 122 and 124 are presented generally toward each other and are spaced apart from each other. Interposed between and spaced from each of the arcuate surfaces 130 and 132 is a cylindrical pin 134. The pin 134 is secured to the surface 130 by a body of resilient material 136 1nd to the surface 132 by a similar body of resilient material 138. Each of the bodies of resilient material 136 and 138 is preferably formed of an elastomer that is physiologically inert.
When viewed in section taken normal to the central longitudinal axis 140 of the pin 134, each of the bodies of resilient material 136 and 138 resembles a truncated wedge. The curved base of each wedge-lll;e body of resilient material 136 or 138 is bonded to a correspcnding arcuate surface 130 or 132 of a cornponent 118 or 120, while the curved, truncated apex of the resilient body 136 or 138 is bonded to the ~lZ5~53 conve; arcuate outer surface of the pin 134. The bodies OI resilient material 136 and 138 are bonded to the outer circumference of the pin 134 at approY.imately opposite locations and have pairs of exposed surfaces 142 and 144, respectively, that eY.tend length~Tise of the pin 134 and outwardly fromadjacent the circumference of the pin. The exposed surfaces 142 of the body of resilient material 136 are spaced apart from the exposed surfaces 144 of the body of resilient material 138 along all of their respective lengths measured in a generally radial direction outward from the pin 134, In operatio~, the finger joint prosthesis 116 functions in much the same manner as the an~le joint prosthesis 10 of Figures 1 and 2. For example, flexi~
between adjacent bones in the finger into which the prosthesis 116 is implanted causes relative rotation between the pin 134 and one or both of the primary com-ponents 118 and 120 about an axis that is at least adjacent to and at least approx-imately parallel to the longitudinal axis 140 of the pin. The motion is resiliently permitted and accommodated through torsional deflection of the bodies of resilient material 136 and 138. The motion limiting effects provided by the front and rear bumpers 78, 80, 82, and 84 in the external an~le joint prosthesis 10 shown in Figures 1 and 2, for example, are provided for the prosthesis 116 by the mlLscles, tenc~ns, and ligaments of the finger into which the prosthesis is implanted. The muscles and tendons wlll nor~ally not be destroyed or rend~red inoperative by the implantation procedure. Pivotal motions between the finger bones into which the prosthesis 116 is implanted which correspond to inversion and eversion and internal and external rotation of a foot will be accommodated prirnar~ily by compression and shearing, respectively, of the resilient bodies 136 and 138.
Although the bodies of resilient material 136 and 138 are illustrated as l~S~53 being -- 'qolly formed of elastomer, it would be possible to incorporate into the resilient bodies shims of nonextensible material, as was done in the ankle joint prosth~sis 10"' of Figures 7 and 8. It is unlikely? however, that the compressive loads on the bodies of resilient material 136 and 138 in the finger joint prosthesis 116 ~ill be of such a magnitude to require the addition of shims. Similarly, the pin 134, the bodies of resilient material 136 and 138, and the arcuate surfaces 130 and 132 of the prosthesis 116 might be curved both in planes that are normal to the longitudinal axis 140 of the pin and in planes that are parallel to the longi-tudinal axis and pass through the axis, as with the pin 64"' of Figure 8. In a finger joint prosthesis for a proximal interphalangeal joint, the additional motion accommodation associated with such a double curvature is probably not required.
Cn the other hand,, in prostheses for other joints of the body, such as metacarpal-phala~ngeaL joints or shoulder joints, double curvature of the various components of the prostheses may be desirable to provide additional motion accommodation.
The additional motion accommodation may also be a~orded by shortening the length of the pin 134, for ex~mple, or by increasing the thicknesses of the bodies of resilient material 136 and 138, as measured generally radialLy of the pin 134. Conversely, lengthening the pin 134 or decreasing the thicknesses of the resilient bodies 136 and 138 will decrease the motion accommodation that is afforded about axes other than the axls 140 or an adjacent, parallel axis Such .
structural adjustments to alter the motion accommodation characteristics of ~e prosthesis 116 may also be used in the prostheses 10, 10', 10" and 10"' and in similar prostheses for replacement of other body joints. In this regard, although thc illustrated embodiments of the invention are an ankle joint for ex-ter~l use and a finger joint for internal use, the prosthesis of the invention is suitable as an external or internal replacement for both an ankle joint and a finger ll~S453 joint and for other joints in the hodv, includin~ shoulder joints, hip joints, elbow joints, and knee joints. In some joint pros-theses, pivot members or pins that are curved in more than one plane may be a distinct advantage, if not a necessity.
As should be apparent from the various Figures of the drawin~s, the spacin~ between the two elastomeric sections that secure the pin to the primary components of each prosthesis may vary considerablv. In the prosthesis 116 of Figure 9, or examPle, the exposed surfaces 142 and 144 of the resilient bodies 136 and 138 are widelv spaced apart, even at their closest points. In the prosthesis 10" of Fiqure 6, on the other hand, the exposed surfaces 74" and 76" of the elastomeric sections 70" and 72", respectively, are relatively close together, parti-cuIarly in the front of the prosthesis. It would be possible and acceptable, moreover, for the elastomeric sections 70" and 72", for example, to be completely interconnected and form a continuous annulus. The disadvantaqe of using a continuous annulus is that relative pivotal motion between the primary ~: .
components of a prosthesis would recJuire both torsional shearing 20 and compression of the elastomer as soon as the motion began.
Because any body of elastomer naturally has a compression modulus that is three or more times its shear modulus, the recluire-ment for immediate compression loading would mean that pivotal motion would be more difficult to accommodate or, in other words, wQuld reauire more actuating force.
It will be understood that the embodiments decribed above are merelY exemplar~ and that persons skilled in the art may make many variations and modifications without departinc ~rom the sp~rit and scope of the invention. All such modi-30 fications and variations are intended to be within the scopeof the invention as defined in the appended claims.
~nother sianificant difference between the prosthesis 10 " ' and the prosthesis 10' is that the pin 64 " ' is arcuate in shape not only in planes normal to its lon~itudinal central axis 66'~ but also in planes that are parallel to and extend ., ~, . :~
~hrough the longitudinal axis of the pin, as best shown in Fi~ure 8. The arcuate port~ions 52 " ' and 58 " ' of the primary ~ ~ components 40" ' and 42 " ' ,respectively, are also curved in ,'j'''.51.':~ ~ 20~ two perpendicular planes, as are the shims 114. The result Of the double curvature of the outer surface of the pin 64 " ' and the corresponding surfaces of other elements in the pros-:, ~
thesis 10 " ~ will be an increased ability of the prosthesis 10 " ' ~- to accommodate inversion and eversion, as compared to the pros-theses 10, 10l and 10~'. -Although all the foregoing embodiments of the invention .
have been ankle joint prostheses intended for use externallyof the human body, the basic pivot structure that: is incorporated in each of the foregoing embodiments of the invention may also 3Q be utilized in a joint prosthesis intended for use internally o~ the body. Fi~ure 9 of the drawings illustrates a finger-joint prosthesis 116, for example, that incorporates two opposed :::, i~5~53 and spaced apart primary components 118 and 120. The primary components 118 and 120 are formed of a relatively inextensible and physiolo~icallv inert material, such as titanium, stainless steel, ~ 10 , .
~ 20 : ` ;
:
';
, ' .
~ 30 . .
- 23a -i~S4~3 cobal~ hromium alloys, nylon, silicone resirls, or high density polyethylene.
The components 118 and 120 include head portions 122 and 124, respectively, and shank or stem por~ons i26 and 128, respectively. The h~ad portiorLs 122 and 124 are each fi~ed to one end of their respective stem portions 126 and 128, which are relatively long and tapered to facilitate insertion into the intramedullary canals of the ~nger bones. The stem portions 126 and 128 of the components 118 and 12û, respectively, will typically be cemented in place in their respective finger bones and m3.y have specially contoured outer surf~ces to improve the attachment to the bones Alternatively, or additionally, the stem portions 126 and 128 may be coated with or formed from a porous material into which boney tissue may grow to secure the primary components 118 and 120 of the prosthesis 116 to their respective finger bones.
The head portions i22 and 124 of the prirnary components 118 and 120 of the prosthesis 116 include surfaces 130 and 132, respectively, that are arcuate in at le~st one plane, The concavely arcuate surfaces 130 and 132 of the head portions 122 and 124 are presented generally toward each other and are spaced apart from each other. Interposed between and spaced from each of the arcuate surfaces 130 and 132 is a cylindrical pin 134. The pin 134 is secured to the surface 130 by a body of resilient material 136 1nd to the surface 132 by a similar body of resilient material 138. Each of the bodies of resilient material 136 and 138 is preferably formed of an elastomer that is physiologically inert.
When viewed in section taken normal to the central longitudinal axis 140 of the pin 134, each of the bodies of resilient material 136 and 138 resembles a truncated wedge. The curved base of each wedge-lll;e body of resilient material 136 or 138 is bonded to a correspcnding arcuate surface 130 or 132 of a cornponent 118 or 120, while the curved, truncated apex of the resilient body 136 or 138 is bonded to the ~lZ5~53 conve; arcuate outer surface of the pin 134. The bodies OI resilient material 136 and 138 are bonded to the outer circumference of the pin 134 at approY.imately opposite locations and have pairs of exposed surfaces 142 and 144, respectively, that eY.tend length~Tise of the pin 134 and outwardly fromadjacent the circumference of the pin. The exposed surfaces 142 of the body of resilient material 136 are spaced apart from the exposed surfaces 144 of the body of resilient material 138 along all of their respective lengths measured in a generally radial direction outward from the pin 134, In operatio~, the finger joint prosthesis 116 functions in much the same manner as the an~le joint prosthesis 10 of Figures 1 and 2. For example, flexi~
between adjacent bones in the finger into which the prosthesis 116 is implanted causes relative rotation between the pin 134 and one or both of the primary com-ponents 118 and 120 about an axis that is at least adjacent to and at least approx-imately parallel to the longitudinal axis 140 of the pin. The motion is resiliently permitted and accommodated through torsional deflection of the bodies of resilient material 136 and 138. The motion limiting effects provided by the front and rear bumpers 78, 80, 82, and 84 in the external an~le joint prosthesis 10 shown in Figures 1 and 2, for example, are provided for the prosthesis 116 by the mlLscles, tenc~ns, and ligaments of the finger into which the prosthesis is implanted. The muscles and tendons wlll nor~ally not be destroyed or rend~red inoperative by the implantation procedure. Pivotal motions between the finger bones into which the prosthesis 116 is implanted which correspond to inversion and eversion and internal and external rotation of a foot will be accommodated prirnar~ily by compression and shearing, respectively, of the resilient bodies 136 and 138.
Although the bodies of resilient material 136 and 138 are illustrated as l~S~53 being -- 'qolly formed of elastomer, it would be possible to incorporate into the resilient bodies shims of nonextensible material, as was done in the ankle joint prosth~sis 10"' of Figures 7 and 8. It is unlikely? however, that the compressive loads on the bodies of resilient material 136 and 138 in the finger joint prosthesis 116 ~ill be of such a magnitude to require the addition of shims. Similarly, the pin 134, the bodies of resilient material 136 and 138, and the arcuate surfaces 130 and 132 of the prosthesis 116 might be curved both in planes that are normal to the longitudinal axis 140 of the pin and in planes that are parallel to the longi-tudinal axis and pass through the axis, as with the pin 64"' of Figure 8. In a finger joint prosthesis for a proximal interphalangeal joint, the additional motion accommodation associated with such a double curvature is probably not required.
Cn the other hand,, in prostheses for other joints of the body, such as metacarpal-phala~ngeaL joints or shoulder joints, double curvature of the various components of the prostheses may be desirable to provide additional motion accommodation.
The additional motion accommodation may also be a~orded by shortening the length of the pin 134, for ex~mple, or by increasing the thicknesses of the bodies of resilient material 136 and 138, as measured generally radialLy of the pin 134. Conversely, lengthening the pin 134 or decreasing the thicknesses of the resilient bodies 136 and 138 will decrease the motion accommodation that is afforded about axes other than the axls 140 or an adjacent, parallel axis Such .
structural adjustments to alter the motion accommodation characteristics of ~e prosthesis 116 may also be used in the prostheses 10, 10', 10" and 10"' and in similar prostheses for replacement of other body joints. In this regard, although thc illustrated embodiments of the invention are an ankle joint for ex-ter~l use and a finger joint for internal use, the prosthesis of the invention is suitable as an external or internal replacement for both an ankle joint and a finger ll~S453 joint and for other joints in the hodv, includin~ shoulder joints, hip joints, elbow joints, and knee joints. In some joint pros-theses, pivot members or pins that are curved in more than one plane may be a distinct advantage, if not a necessity.
As should be apparent from the various Figures of the drawin~s, the spacin~ between the two elastomeric sections that secure the pin to the primary components of each prosthesis may vary considerablv. In the prosthesis 116 of Figure 9, or examPle, the exposed surfaces 142 and 144 of the resilient bodies 136 and 138 are widelv spaced apart, even at their closest points. In the prosthesis 10" of Fiqure 6, on the other hand, the exposed surfaces 74" and 76" of the elastomeric sections 70" and 72", respectively, are relatively close together, parti-cuIarly in the front of the prosthesis. It would be possible and acceptable, moreover, for the elastomeric sections 70" and 72", for example, to be completely interconnected and form a continuous annulus. The disadvantaqe of using a continuous annulus is that relative pivotal motion between the primary ~: .
components of a prosthesis would recJuire both torsional shearing 20 and compression of the elastomer as soon as the motion began.
Because any body of elastomer naturally has a compression modulus that is three or more times its shear modulus, the recluire-ment for immediate compression loading would mean that pivotal motion would be more difficult to accommodate or, in other words, wQuld reauire more actuating force.
It will be understood that the embodiments decribed above are merelY exemplar~ and that persons skilled in the art may make many variations and modifications without departinc ~rom the sp~rit and scope of the invention. All such modi-30 fications and variations are intended to be within the scopeof the invention as defined in the appended claims.
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A prosthesis for replacing a skeletal joint in a human body comprising a first joint component adapted for connection with a first element, a second joint component adapted for connection with a second element, at least one of said first and second elements being a portion of a human body, a pivot component disposed between said first and second joint components, means for resiliently connecting said pivot component to said first and second joint components, said resilient means including a first body of elastomeric material disposed between and attached to said first joint component and said pivot component, a second body of elastomeric material disposed between and attached to said second joint component and said pivot component, said first and second bodies of elastomeric material being spaced apart and suspending said pivot component between said first and second joint components to permit motion of said first and second joint components relative to each other about said pivot component in simulating the operation of a skeletal joint in a human body.
2. A prosthesis as defined in claim 1 wherein said first body of elastomeric material includes a first side surface and said second body of elastomeric material includes a second side surface, said first and second bodies of elastomeric mate-rial being deflectable to allow said first and second joint components to move toward each other and relative to said pivot component, said first and second side surfaces on said bodies of elastomeric material being disposed on opposite sides of a plane which extends through said pivot component, said first and second side surfaces being further disposed to move toward each other and toward said plane over a range of movement of said first and second joint components toward each other.
3, A prosthesis as defined in claim 2 wherein said pivot component comprises a pin having at least one arcuate outer surface circumscribing a longitudinal central axis, said first and second bodies of elastomeric material being deflectable about axes which are parallel to the central axis of said pin to allow said first and second joint components to rotate toward and away from each other about the outer surface of said pin, said first and second side surfaces of said first and second bodies of elastomeric material extending generally away from the outer surface of said pin, said first and second side surfaces being disposed on opposite sides of a plane which intersects said pin and is oriented parallel to the central axis of said pin, said first and second side surfaces being further disposed to move toward each other and toward said plane as said first and second joint components move toward each other about said pin.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA379,598A CA1125453A (en) | 1977-11-16 | 1981-06-11 | Joint prosthesis |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/852,183 US4229839A (en) | 1977-11-16 | 1977-11-16 | Joint prosthesis |
| US852,183 | 1977-11-16 | ||
| CA316,296A CA1112805A (en) | 1977-11-16 | 1978-11-15 | Joint prosthesis |
| CA379,598A CA1125453A (en) | 1977-11-16 | 1981-06-11 | Joint prosthesis |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1125453A true CA1125453A (en) | 1982-06-15 |
Family
ID=27165982
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA379,598A Expired CA1125453A (en) | 1977-11-16 | 1981-06-11 | Joint prosthesis |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1125453A (en) |
-
1981
- 1981-06-11 CA CA379,598A patent/CA1125453A/en not_active Expired
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| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |