AU655532B2

AU655532B2 - Modular hip prosthesis

Info

Publication number: AU655532B2
Application number: AU32944/93A
Authority: AU
Inventors: Robert Brosnahan; Michael Demane; Thomas Wade Fallin; Steve Garner; Jeff Schryver
Original assignee: Smith and Nephew Richards Inc
Current assignee: Smith and Nephew Inc
Priority date: 1989-02-08
Filing date: 1993-02-09
Publication date: 1994-12-22
Anticipated expiration: 2010-02-06
Also published as: JPH0347253A; AU4914890A; AU3294493A; JP3077762B2

Description

AUSTRALIA

PATENTS ACT 1990 DIVISIONAL APPLICATIO NAME OF APPLICANT(S): SMITH NEPHEW RICHARDS INC.

ADDRESS FOR SERVICE: 1450 Brooks Road Memphis Tennessee 38116 UNITED STATES OF AMERICA ft INVENTION TITLE: "MODULAR HIP PROSTHESIS" The following statement is a full description of this invention, including the best method of performing it known to us:

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-1c Ir II 930209,q:\oper\phh,smit1L4,2 1A The present invention relates to a modular hip prosthesis system wherein various component parts of an implant can be selected during the surgical procedure so that the implant can be custom fitted to a patient.

Increasingly, surgeons want to be able to custom fit femoral prostheses to patients. Instead of having to choose a properly sized prosthesis from a group of pre-formed implants, it would be advantageous to have a basic design which can be modified with various component parts. Thi would eliminate the need to maintain a large inventory and would provide better fitting implants.

Custom fitted implants are particularly important i :evision cases where an implant has to be removed a,.d replaced since old cement must be removed and bone resorption occurs in many cases. Unpredicatble, proximal and/or distal bone loss or deformity often occurs which must be accommodated by the replacement prosthesis.

For initial implants, basic variations in a t

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2 patient anatomy are often confronted by the surgeon.

Some patients have femoral necks that can be significantly longer or shorter than other-. Cortical shaft defects, which are not uncommon, are not discovered until during operation. Variations in intramedullary canal diameter can also occur, which if not accompanied by a properly sized implant, can result in distal toggle.

In short, it is difficult, if not impossible to predict the exact shape of a hip implant which is suitable for all patients. Since it is impractical and would be prohibitively expensive to maintain an inventory of implants for most patients, compromises must sometimes be made in supplying implants which fit o reasonably well but could be improved upon.

Several hip prostheses are known which are formed of replaceable or interchangeable component parts.

US Patent No. 3641590 discloses a selective individualized technique for acetabulum socket replacement per se or, as disclosed in US Patent No.

3228393 in conjunction with a hip replacement prosthesis for a total hip replacement, designed for all ages including the very young. A selective achorage for a cup prosthesis of a size selected from the S- 3 limited number of differently sized cups is made available. Anchorage of the acetabular socket replacement conforms to variations in dimensions, shapes and positions of the (medullary) canals of the acetabulum pelvis of the individual patient and includes at least two elongated and convergent or divergent fasteners.

A removable collar of low modulus of elasticity material is shown in US Patent No. 4012796. The collar is interpositioned between a collar of a metal prosthetic hip stem implanted in the intramedullary canal of the femur and the adjacent calcar or outer edge of the bone. A flange depends frnm the insert between the upper portion of the stem and the inner wall of the bone. The interpositioned collar is either a full elongated tapered O-shape or it is open on one side of a tapered U-shape.

US Patent No. 4404691 provides a modular hip prosthesis assembly for replacement of at least part of a joint and part of a bone shaft including a mounting component provided with a connection portion and at least two joint components of similar shape but different dimensions and which can be connected alternatively to the mounting component, each of the joint components having an engagement portion and a i II~ 4 connection part adapted for connection to the connection portion of the mounting component, the joint components each providing part of a bone shaft and part of a joint which can cooperate with an appropriate part of a natural or artificial joint.

US Patent No. 4578081 discloses a tone prosthesis comprising at least one joint component replacing a natural joint half, which is provided with a shank adapted to be connected to the bone, wherein a set of joint components is provided, and the shank is designed as a bone replacement member, with a connection portion provided adapted to be connected to the bone at one end and at the other end to the shank. One of the components is a hip prosthesis with a rounded head and hollowed hip component that connects to elongated mounting components. In another hip prosthesis embodiment, a neck with a cone shape receives a S. suitable joint head with an inner core.

A femoral component for hip prosthesis is shown in US Patent No. 4608U55 which includes a stem portion and a combined integral head and neck portion. The stem portion includes a proximal portion and a distal portion which are angularly related with respect. to one another and with the proximal portion including a recess formed therein for receipt of the tapered

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portion of the head and neck component. The head and neck component includes a substantially part spherical head portion attached to a neck portion and a tapered portion angularly attached to the neck portion via a basalar neck portion with the tapered portion being adapted to be permanently inserted into the recess portion of the proximal end of the above described stem portion. The stem portion includes a plurality of recesses on the periphery and longitudinal extend thereof for receiving fiber metal pads which are provided to allow boney ingrowth therein in order to retain the femoral comopnent permanently installed in the proximal end of the femur.

In US Patent No. 4676797 a resection prosthesis assembly unit includes a head member, an end member and an intermediate member between the head and end members, of which one member is provided with a conical pin and another member is provided with a conical bore.

The latter two members are provided with respective A w\\c first surfaces^extend tranversely to an insertion direction and which face one another and are spaced apart to define a recess when the two members are connected togther. One of the two members is further provided with a second surface extending in the is direction, and the recess being provided' to receive a wedge insertable into the recess to bear against the 6 first surfaces for forcing the two members apart while the forces exerted by the wedge are absorbed by the first surfaces and the wedge is guided by the second surface.

Additionally, end fitting distal sizers attached in a similar fashion could allow the surgeon to tailor the prosthesis tip to the canal diameter thereby reducing distal toggle.

The present invention seeks to provide a modular hip prosthesis which can be custom fitted to a particular patient by a surgeon prior to surgical insertion of the prosthesis.

In accordance with the present invention there is provided a modular hip prosthesis that can be modified to individual requirements prior to insertion comprising a prosthesis body having an upper end portion with a neck adapted to carry a rounded head ption which engages with the acetabulum or with an acetabular prosthesis and a lower stem portion adapted for placement in the intramedullary canal of the femur and means attachable to the prosthesis body for adjusting and maintaining the prosthesis body in load bearing engagement with the femur, Mteretn Yi -7the lower stem portion is provided with an internal bore and the attachable means is a tubular stem extension sleeve having a hollowed portion corresponding in shape to the stem portion including an open end portion adapted to receive the stem portion therein and wherein the extension sleeve is secured to the prosthesis body by attachment means connectable to the internal bore of the stem portion.

'-item extension and/or augmentation is provided by the present invention which allows the length of the femoral shaft to be augmented with extensions that may lock with the lower stem portion using, for example, a tapered attachment. This augmentation allows the surgeon to extend the stem length I beyond any cortical shaft defect that may be encountered intraoperatively. Additionally, a selection of tubular stem extension sleeves could allow the surgeon to tailor the prosthesis tip to the canal diameter, thereby reducing distal toggle. A selection of prosthesis bodies could be provided in a variety of inclinations of the axis of the upper end portion neck with respect to the longitudinal axis of the prosthesis body and the lower stem portion. The surgeon could intraoperatively select the most appropriate amount of version (anteversion or retroversion) to restore joint stability.

Increased attainable neck length variation may also be provided for, allowing "fitting" to patients with very short femoral necks CDH, small females) or very long femoral necks to components for proximal bone loss). Head neck assemblies could also incorporate a collar or augmented 940729,p\oper\phh,3294493 10,7 Alj 0 1 V-0 1 ,i -8extension to convert the standard stem body into a proximal one-third replacement or a revision stem. A separate set of head neck assemblies could be offered to allow the surgeon to tailor the neck snaft angle of the assembled device as well.

The tubular stem extension sleeve may be of a generally uniform cross-section. Its upper end may have an annular tapered section that registers with a correspondingly tapered section of the stem. The prosthesis body in one embodiment has a longitudinal central open ended bore that extends substantially the length of the prosthesis body. The attachment means may include an elongated fastener, preferably an elongated threaded bolt that is adapted for placement .0 within the elongated bore, extending substantially the length of the bore upon assembly. The bolt can be provided with an upper head end portion which can be manipulated by the surgeon at' the top of the prosthesis for tightening or loosening the fit between the sleeve and the prosthesis body. The stem extension sleeve may be provided with a threaded section that 20 can engage the lower end portion of the bolt to form a threaded connection. This attachment of sleeve and prosthesis body can also be made using a very short bolt which is affixed through an opening in the bottom of the extension sleeve, and into a bore in the bottom of the stem.

The aforementioned bolt can be tightened after the prosthesis and extension sleeve are in position so that the extension can twist to track the intermedullary canal during A1 940729,p:\oper\ph,32944-93210,8 ©nl j' -9insertion. After placement, the draw bolt can be used to lock the extension and prosthesis body together.

The lower stem portion and tubular stem extension sleeve advantageously form a tight friction fit which seals wear particles from body tissues that typically wear off during insertion of the stem to the sleeve. In the preferred embodiment in which the attachment means is a draw bolt, when the draw bolt is tightened, its non-threaded end presses against the prosthesis body to provide tension in the bolt and compressive force between the stem and sleeve in preferred corresponding tapered regions of the stem and sleeve. The corresponding tapered regions thus register tightly together forming a seal.

S* The neck for carrying the rounded head portion may be frustro-conical. Between the upper end portion and the lower stem portion there may be a transitional mid-section typically having a generally rectangular upper and a generally rounded lower cross-sectional area. Extension sleeves can be added to the neck for elongating the neck with respect to the prosthesis body and the head portion.

Removable transverse bearing collar means may be provided which are affixable to the prosthesis body, generally transverse to a longitudinal axis of the prosthesis body for forming a load carrying interface between the prosthesis body and the upper end of the patient's femur. In one embodiment, 94O729,p:%operphh.M324-9321,9 .i a removable bearing collar can have distal offset means such as a tab portion or extension that will compensate for proximal bone loss, i.e. at the top of the patient's femur.

In a preferred embodiment, removable pad means, comprising at least one pad is attachable to the mid-section of the prosthesis body for increasing the cross-sectional area of the prosthesis at the mid-section. One or more sockets iay be formed in the prosthesis at the mid-section for carrying the modular pads. In one embodiment, a wedge lock connection secures each pad to the prosthesis body. A locking member may be provided on the back of the or each pad to lock the pad to the prosthesis at corresponding engaging wedge surfaces thereon. The pad may carry a locking tab member which ensures complete interlocking engagement of the pad to the prosthesis body before forming the wedge lock connection. This safety feature may require that the surgeon fully engage each pad into its aforementioned socket before being able to slide the pad into the wedge-lock position. The tab on the locking 20 member of each pad may engage a recess or undercut in the socket of the prosthesis body to constrain the pad from moving in a direction away from the prosthesis body, after assembly is completed.

Pad shape can be varied to custom fit the patient's anatomy maximizing stability to transfer shear load or compression load between the prosthesis and the patient's bone as desired. The pads can be of differing materials such as 940729 ,p:\oper\phb,2944-931210 0.

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-11porous or roughened coating to promote tissue ingrowth or on growth. Also, manufacturing methods which might weaken the integrity of the prosthesis body, such as the addition of a coating of beads, can be used for the removable pads, thus not affecting the structural integrity of the prosthesis body.

For a further understanding of the present invention, reference should be had, by way of example only, to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein: t Figure 1 is a side view illustrating a plurality of hip C C prosthesis bodies which may be used with the present S' 15 invention; Figure 2 is a side view of a pair of hip prosthesis C bodies of differing sizes illustrating insertion of modular collar portions thereof; Figure 3 is a side view illustrating a plurality of sleeve extension parts which may be used with the present invention; Figure 4 is a side view of a plurality of modular pads for use with the hip prosthesis bodies of Figures 1 and 2, illustrating varying pad cross-sectional configurations; 94O729,p:\oper\phh,32944-9321,11 1 I r I; 12 Figure 5 is a perspective exploded view illustrating the preferred embodiment of the apparatus of the present invention; Figure 6 is a top view of the prosthesis body portion of the preferred embodiment of the apparatus of the present invention; r 4 0

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e rr 940729,p:koperlph,2944-a21O,12 Ir '31 Figure 7 is a side view of the prosthesis body portion of the preferred embodiment of the apparatus of the present invention; Figures 8 and 9 are top and side views illustrating the assembly portion of the preferred embodiment of the apparatus of the present invention; Figures 10 and 11 are top and side sectional views of the stem extension sleeve portions of the preferred embodiment of the apparatus of the present invention; Figure 12 is a sectional view illustrating an alternate construction of the neck extension sleeve portion of the preferred embodiment of the apparatus of the present invention; CFigure 13 is a plan view illustrating the modular collar portion of the preferred embodiment of the apparatus of the present invention; Figure 14 is a partial sectional view illustrating the preferred embodiment of the apparatus of the present invention with prosthesis body and stem extension sleeve assembled; I 930209,q:\oper\phh,smth.040,2 14- Figure 15 is a sectional elevational fragmentary view illustrating the assembly of modular pads to the prosthesis body; o e o o r r r I I Figure.16 is a sectional view taken along 16 16 of Figure 15; and Figure 17 is a sectional elevational view of another embodiment illustrating the assembly of modular pads to the prosthesis body; Figure 18 is a side exploded view of a second embodiment of 4-e-modular hip prosthesis pads -f the prcont invent-ion, Figure 19 is a side fragmentary view of the second embodiment of the modular hip prosthesis of the present invention; Figure 20 is a rear view illustrating the contruction of the modular pad of the second embodiment of the apparatus of the present invention; Figure 21 is a side view illustrating the construction of the modular pad of the second embodiment of the apparatus of the present invention; I-I Figure 22 is an end view illustrating the construction of the modular pad of the seeen embodiment of the apparatus of the present invention.

Figure.23 is a sectional view taken along lines 23-23 of Figure 19; Figure 24 is a sectional view taken along lines o 24-24 of Figure 19; and I :Figure 25 is a sectional view taken along lines 25-25 of Figure 19.

Figures 1 to 5 illustrate generally the preferred embodiment of the apparatus of the present invention designated generally by the numeral 10. In Figure there can be seen a prosthesis body 11 which includes a widened mid-section 12, a lower elongated generally cylindrically shaped stem 13 and an upper neck 14. The mid-section includes an upper generally rectangular cross-sectional portion 15 and a lower generally rounded cross-sectional portion 16 which communicates with the generally cylindrical stem 13.

The stem 13 includes three sections including an upper cylindrical section 17, a frusto-conical tapered transition section 18 and a lowermost small-diameter C'

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I 9cylindrical portion 19. The prosthesis body 11 would preferably be supplied to hospitals and surgeons in kit form with a plurality of prosthesis bodies 11, pads 26, heads 7, collars 21, 22 and extension sleeves 30 being offered in various sizes such as is shown in Figures 1 to 2, including prosthesis bodies 11A to llJ, pads 26A to 26H and sleeves 30 to 0. Each prosthesis body 11 includes a generally U-shaped annular recess 20 which extends around one edge of the transitional mid-section 12 portion of the body 11 and is receptive of generally U-shaped collars 21 or 22 (Figure Recess 20 has a shape corresponding to the inner edge portion 21C of collar 21. Collar 21 is thus generally U-shaped in plan view (Figure 13). Another embodiment of U-shaped collar 22 provides a similar, generally U-shaped body in plan view, but also includes a downwardly extending tab 23 *(Figure 2) which can be used to help transfer load between the prosthesis 10 and the femur where proximal bone tissue has eroded.

Lock pin 21B (Figure 13) extends through openings 21A, 20A in order to secure collars 21, 22 to prosthesis body 11. One of the openings 21A can be formed as a blind hole with a wall 21D and not extend all the way to the outer surface of the collar so that <T 3 !0 7 ,F *1/ 17 the pin 21B cannot be driven too far and project form the outer surface of the collar 31.

Each prosthesis body 11 includes a pair of left and right sockets 24, 25 which are receptive of one or more adjustment pads 26A to 26H. It will be noted that the cross-sectional configuration of each pad 26A to 26H can vary including pads which are thicker at the top than at the bottom for example as shown in Figure 4 with pad 26D and pad 26H which are thicker at one edge as compared with pads 26A and 26E. The pads 26A to 26H can be added by the surgeon to give a custom fit to the prosthesis body 11 in the area of the mid-section 12.

Neck 14 is a frusto-conically shaped neck adapted to receive head 27. Head 27 is provided with a socket 28 corresponding in shape to neck 14. A plurality of heads 27 can be provided in various sizes as part of the kit, for matching each respective prosthesis body 11A to lJ.

Stem 13 is rounded at its lower tip. The lowermost portion 19 of stem 13, which is of a smaller diameter, and the frustro-conical transition portion 18 of stem 13 form an attachment with a-stem extension sleeve 30 (Figures 3, 5, 10, 11 and 14). The sleeve is elongated and generally cylindrical and has an open end 31 which allows insertion of the stem 13 thereinto.

The lowermost end portion of the sleeve 30 includes a generally curved eg. hemispherical distal end portion 32.

Extension sleeve 30 is hollow providing a longitudinally extending bore 33 which extends between open end 31 and threaded aperture 34. Aperture 34 extends downwardly from bore 33, communicating with end 32. Threaded aperature 34 is receptive of the external threads 35 of a draw bolt 36. Bolt 36 includes an uppermost head portion 37 and a lower threaded portion Prosthesis body 11 thus includes a longitudinally extending central bore 40 that is receptive of elongated bolt 36.

The upper end portion of extension sleeves includes a bevelled inner annular surface 38 (Figures 3 and 11) which corresponds in shape to the furstro-conical transition portion 18 of stem 13 so that the extension sleeves 30, 30A and stem 13 can form Sa frictional tight fit upon assembly (see Figure 14).

Draw bolt 36 would be tightened after placement of prosthesis body 11 and a sleeve 30 or 30A into the intramedullary canal. Thus the extension sleeve 30 or is free to track the natural path of the intramedullary canal during insertion. After insertion i ^2-SS bolt 40 is tightened, drawing annular bevelled surface 38 of sleeve 30 or 30A 30A and transition portion 18 of stem 13 together.

Extension sleeve 30 can be a short version having a longitudinally extending bore 33 which communicates aper 4 ure with-apg oeate 34, extending to end 32. In another

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embodiment (see Figure extension sleeve 30A can be ape-rtLre j elongated extending well beyond threaded aperataur 34.

As shown in the longer sleeve in Fig. 3, the longitudinal axis of extension sleeve 30A can change angle slightly or have a curvature in order to track the intramedullary canal, with the lower end portion 39 of each extension sleeve 30A being solid and being slightly skewed with respect to the longitudinal axis of open bore 33. This allows the extension sleeve to track the natural path of the intramedullary canal which is not perfectly straight nor a pure elongated cylinder. Thus, the elongated extension sleeves 30A can i conform naturally to the femur of a patient for a custom fit.

A plurality of heads 27 of differing sizes would be provided. The distance between the prosthesis body and the head 27 could be varied using extension members or 50. Extension member 45 would be a hollowed trunion having a conical outer surface 46 and a Ntlq< Li, ~4'1' corresponding conical inner surface 47. A smaller open end portion 48 and a larger open end portion 49 define therebetween a bore which is occupied by neck 14 upon assembly of extension member 45 thereupon. Because the conical outer surface 46 at the smaller end portion 48 is the same size as the corresponding end of neck 14, a head 27 could simply be slipped upon the extension member 45 with the socket 28 engaging the extension member 45. An impact driver could load a selected extension member 45 on the head 27 with a predetermined load, with the conical surfaces fitting tightly together. In the preferred embodiment, extension members of differing lengths and of different cross-sectional dimensions would be provided to correspond to the plurality of differing neck sizes that accompany the plurality of prothesis bodies as provided in kit form (see Figure 1).

An alternative trunion construction is shown in Figure i i~i12 wherein the neck extension member 50 includes a conical outer surface 51, a conical inner surface 52 with a small end portion 53 having a threaded opening 54 that communicates with socket 56 at large diameter end portion 55 of extension member Thus, the socket 28 of a particular selected head 27 would be registered upon the end of extension member 50. In order to remove the member 50 from neck 14, the threaded opening 54 would be threadably engaged with a removal tool in the form of a shaft having one end portion which is 940729,p:oper\ph32944-93210 L q 2, threaded and the opposite end portion defining a handle, for example.

In Figures 15 to 17, pads 26 are shown as removably attached to prosthesis body 11. In Figure it should be understood that only the assembly for securing one pad 24 or 25 is shown.

In the embodiment of Figure 17, the pads 26 are held in place by a single attachment mechanism that is carried generally between the pads 26 forming a connection therebetween.

::an In the embodiment of Figure 15 there is provided San annular bushing 61 which is an extension of each pad 26 Bushing 61 includes a plurality of arcuate members 62 to 65 with spaces 66 therebetween (Figure 16) so that the bushing can expand and grip the beveled annular wall 74 of opening 60 in prosthesis body 11 which is doubled. A bolt or set screw 70 is threadably I attached to threaded bushing 61 so that the threads 72 of bolt 70 register with and threadably engage the threads 68 of bushing 61. Upon such threadable connection, the individual-aarueae members 62 65 of bushing 61 expand (see arrows 73 of Figure 15) bearing against the annular wall 74 of opening 60. An opening 67 in pad 26 communicates with a tooled opening 71 in -rn~ 22 bolt 70 so that a tool such as an alien wrench for example can be inserted through opening 67 and into reg isry rogictrtion. with the slot 71 which would be correspondingly shaped to the tool used.

In the embodiment of Figure 17, a single assembly bolt 80 is used to secure a pair of pads 26 together upon prosthesis body 11. The prosthesis body 11 includes a cylindrical transverse opening 79 which is occupied by annular bushing 81 integrally attached to pad 26. Bushing 81 includes an inner socket portion 83 which is threaded with internal threads 82. Assembly bolt 80 provides corresponding external threads 89 w which threadably engage the threads 82 of bushing 81. A socket 88 is receptive of a tool such as an allen w r wrench for example and rotates therewith to tighten pads 26 together. Pad 26 provides a bushing 85 which carries an annular retaining ring 86, which can be a split ring or the like. An opening 90 allows access through pad 26 to the tooled opening 88. Assembly bolt includes a generally circular annular head portion 91 which is held against pad 25 with ring 86 -Are-the

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threaded bolt 80 is tightened against prosthesis body 11.

Figures 18 to 25 illustrate an alternative embodiment of the apparatus of the present invention -re 23 wherein removable pads 40A, 40B attach to prosthesis ge body 11 with a wedge fit that -elt tightens the connection between each pad 40A, 40B aid the prosthesis as hip joint reaction forces push the prosthesis into the femur during use. A safety feature of each pad -id prosthesis body 11 connection is a locking membr with tabs that force the surgeon to fully engage the pad 40A, 40B into a provided opening 100 on the prosthesis body 11 before a sliding of the pad 40A, into locking engagement with the prosthesis body 11.

In Figure 19, there can be seen a fragmentary :I ,view of prosthesis body 11 having a socket therein with a peripheral edge wall 25W. Similarly, the opposite side of prosthesis body 11 would have a socket 24 proviling a peripheral side wall 25W. Each socket 24, receives a modular pad 40A, 40B respectively. In Figures 19-22, pad 40A is shown which registers during operation with the pad socket 24. The modular pad would be a mirror image of the views shown for pad of Figures 10-22.

Each modular pad 40A, 40B carries on its rear surface 39 a wedge locking member 41 having a pair of opposed inclined locking surfaces 42 which form an acute angle with respect to one another, as shown in Figure 20. During use, the surgeon places modular I 24pad 40A into its similarly shaped socket 24 registering the locking member 41 into opening 100. The locking member 41 carries a pair of tabs 42 which initially register at the enlarged end portion 100B of opening Similarly, the inclined locking surfaces 42 of locking member 41 register with similarly shaped locking surfaces 101 of opening 100. The tabs 43 must be registered with the enlarged 100B end of opening 100. Otherwise, the locking member 41 will not fit into the opening 100. This provides a safety feature because the surgeon must fully place the particular pad into its socket 24, 25 before attempting to wedge lock the pad 40A, 40B to the prosthesis body 11. Once the locking member 41 has been fully registered with tAe opening 100, the surgeon then simply slides the pad i upwardly toward the upper end 15 of the prosthesis body 11. The tabs 43 then slide under shoulders 102 and register in undercut slots 103, as shown in Figure 24.

As each pad 40A, 40B is moved into locking position by the surgeon, the surfaces 42 of the wedge locking member 41 engage the inclined surfaces 101 of the opening 100. A tight wedge-lock fit is obtained by i S: forcing the surfaces 42, 101 together using an impact driver or a mallet and a hand driver element or punch.

Each pad 40A, 40B secures tightly to the prosthesis body because the surfaces 42 wedge fit to the surfaces 101.

ICL/ i zs-- In the preferred embodiment, the outer periphery of each pad 40A, 40B has a shape corresponding to the peripheral wall 24W, 25W of each socket 24, However, the.pads 40A, 40B are sized slightly smaller than the outer configuration of each socket 24, 25 as defined by the peripheral side walls, 24W, 25W. This provides room to move each pad 40A, 40B slightly so that sliding action can be used to perfect the wedge lock connection between each pad 40A, 40B and its respective socket 24, 25. Thus, the outer edge of each pad 40A, 40B would be spaced inwardly from the peripheral wall 24W, 25W of each socket 24, 25 by a small measure.

A very tight wedge lock connection can be formed between each pad 40A, 40B and the prosthesis body 11 using an impact driver. In the preferred embodiment, each pad includes a generally flat lower surface 106. A similar flat surface 107 is provided at the bottom of each socket 24, 25. However, upon manual assembly of the pads 40A, 40B to the prosthesis body 11 by the surgeon, an impact driver can be used to tighten the pads 40A, 40B to the prosthesis body 11 using the impact driver. An impact driver is a commercially available product which carries a tooled end portion havinq, for example, a commercial screw driver tip or L~ i~ 1 wedge tip. The impact driver tool tip (not shown) is then placed in the space formed between the surfaces 106 an 107 after the surgeon places the respective pads 40B in their respective sockets 24, 25. The prosthesis is placed on a flat surface and the surgeon simply presses downwardly on the impact driver, activating the tool tip portion of the impact driver to force the surface 106 away from the surface 107. The surgeon then turns the prosthesis over and repeats the same procedure for the second pad. It has been found that using a commercially available, relatively small impact driver, such as supplied by Starrett Company, as .o much as 300 pounds of load can be generated holded each pad 40A, 40B to the prosthesis body 11.

In the event that one of the pads 40A or 40B were to become lose, because the surgeon possibly did not apply enough force to the pad in order to wedge lock it I eyvwoch~nme/b to the prosthesis body 11, the present invention provides a safety feature for continuously loading each pad 40A, 40B to the prosthesis body 11. This is insured because the pad outer surface 38 is typically beveled so that the bottom of the pad is narrower and the top of the pad is wider, as shown in Figures 21 and 22.

Thus, when the pad is installed, self tightens as the hip joint reaction force of the patient pushes the prothesis further into the femur. The femur presses on 27 0the outer surface 38 of the pad, forcing it upwardly and further forcing the wedge lock surfaces 42 of each pad 40A, 40B against the surfaces 101 of the opeining 100.

An additional safety feature of the present embodimeA -invenationis that the walls 24W, 24W of the sockets 24, contain the pads 40A, 40B if the pads are inadvertently disengaged from the locking mechanism.

eMboodctmen+ Another safety feature of the present invention are the locking tabs 42 which force the surgeon to fully engage the pads 40A, 40B into their respective slots 24, 25 before attempting to slide the wedge inclined locking surfaces 42 into engagement with the locking surfaces 101. If the surgeon does not fully engage the pads 40A, 408 into opening 101, the locking tabs prevent wedge locking of the surface 42 to the surface 101.

0 jC. quickpbecf roc hesis The 4 pro t invntion- provides thus a simple and quick modular pad construction that allows for ."installing different contours on either the anterior or posterior side of the prosthesis so that the femoral cavity can be completely filled in order to obtain a descripe4 f roTsesis better bone-prosthesis contact. The -p.ose-nt invention could be supplied with a number of trial sockets in kit x /4U) h. I- 1* I forms so that the kit could be used to size the apparatus perfectly. Then, the surgeon would have the actual prosthesis and its modular pads in pre-packaged sterilised condition. Thus, the surgeon could use the trial kit to.size the prosthesis and its modular parts and then simply open the corresponding part from a sterile package when the correct fit has been obtained.

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Claims

1. A modular hip prosthesis that can be modified to individual requirements prior to insertion comprising a prosthesis body having an upper end portion with a neck adapted to carry a rounded head portion which engages with the acetabulum or with an acetabular prosthesis and a lower stem portion adapted for placement in the intramedullary canal of the femur and means attachable to the prosthesis body for adjusting and maintaining the prosthesis body in load bearing engagement with the femur, wherein the lower stem portion is provided with an internal bore and the attachable means is a tubular stem extension sleeve having a hollowed portion corresponding in shape to the stem portion including an open 15 portion adapted to receive the stein portion therein and wherein the extension sleeve is secured to the prosthesis body by attachment means connectable to the internal bore of the stem portion.

2. A prosthesis as claimed in claim 1 wherein the lower stem J .portion terminates at a rounded tip.

3. A prosthesis as claimed in either of claims 1 and 2 i wherein the tubular stem extension sleeve is of generally uniform cross-section.

4. A prosthesis according to any one of the preceding claims wherein the tubular stem extension sleeve is substantially straight.

A prosthesis according to any one of claims 1 to 3 wherein the tubular stem extension sleeve is curved to conform to the shape of the intramedullary canal.

6. A prosthesis according to any one of the preceding claims wherein the internal bore extends substantially the length of the prosthesis body and is open at the lower end of the lower 940729,p:\oper\phh,32944-93210,29 I-I stem portion, and the attachment means includes an elongate fastener that is adapted for placement in the internal bore and extends substantially the length of the internal bore upon assembly.

7. A prothesis according to claim 6 wherein the fastener is a bolt having a threaded lower end portion and the tubular stem extension sleeve includes a threaded section that can engage the threaded lower end portion of the bolt.

8. A prothesis according to any one of claims 1 to 5 wherein the internal bore is open at the lower end of the lower stem portion.

9. A prothesis according to claim 8 wherein the internal a bore has a female threaded portion and the attachment means •includes a threaded fastener that can threadably engage the female threaded portion of the internal bore.

A prothesis as claimed in any one of the preceding claims wherein the tubular stem extension sleeve has a bore that extends longitudinally from the tubular portion and opens at *C the opposite end of the sleeve to the open end portion.

11. A prosthesis as claimed in any one of claims 1 to 9 wherein the tubular stem extension sleeve has a closed bore that extends longitudinally from the tubular portion.

12. A prosthesis according to any one of the preceding claims comprising removable pad means attachable to a transitional mid-section of the prosthesis body for increasing the cross- sectional area of the prosthesis, said pad means comprising at least one pad.

13. A prothesis as claimed in claim 12 comprising a transverse opening in the prosthesis body at the transitional 940729,p:\oper\phh,32944-93210,30 i -31- mid-section and means carried by the pad means which extends into the transverse opening for holding the pad moins to the prosthesis body.

14. A prosthesis as claimed in claims 12 or claim 13 wherein the prosthesis body includes one or more sockets and the pad means is attachable to the prosthesis body at the sockets.

A prosthesis as claimed in any one of claims 12 to 14 wherein the pad means comprises a pair of pads.

16. A prothesis as claimed in claim 15 when dependent from claim 14 wherein the prosthesis body has a pair of opposed sockets anterior and posterior, each defined by a peripheral sidewall, each socket being correspondingly shaped to a Srespective one of the pair of pads so that each pad registers C 4 within the peripheral edge of a socket.

17. A prosthesis as claimed in claim 16 when claim 14 is dependent from claim 13 wherein the sockets communicate by way of the transverse opening through the prosthesis body.

18. A prosthesis as claimed in claim 15 when dependent from claim 13 or in claim 17 wherein the holding means includes a locking bolt that fits generally between the pair of pads through the transverse opening forming a connection between the pads.

19. A prothesis as claimed in any one of claims 12 to 17 wherein the or each pad as a projection thereon extending from an inside surface and locking means is carried by the projection for forming a releasable connection with the prosthesis body.

20. A prothesis as claimed in claim 19 when dependent from claim 14 wherein the locking means comprises a locking tab and a pair of frictionally engaging load transfer surfaces carried 9OW29,p:\oper\phh32944-93210,31 4:C. -32- respectively by the tab and by the prosthesis body at the socket.

21. A prosthesis as claimed in claim 20 wherein the locking means includes wedge means for tightening the connection between the pad means and the prosthesis body as the pad is moved longitudinally with respect to the prosthesis body longitudinal axis when the load transfer surfaces are engaged.

22. A prothesis as claimed in any one of claims 12 to 21 wherein the or each pad has an interior surface shaped to register upon the prosthesis body outer surface, and an outer pad surface having a shape that differs from the pad inner surface shape.

23. A prothesis as claimed in any one of claims 12 to 22 wherein the or each pad is attachable to the anterior or posterior side of the prosthesis body.

24. A prosthesis as claimed in any one of the preceding claims wherein the neck of the upper portion is of a generally conical shape and wherein the prosthesis further comprises a neck extension sleeve having a hollowed portion corresponding in shape to the neck and open at one end to receive the neck.

A prosthesis as claimed in claim 24 wherein said S extension sleeve has an outer surface that corresponds in shape to the neck so that the rounded head portion can interchangeably fit the neck and the extension sleeve.

26. A prosthesis as claimed in claim 24 or claim 25, wherein the neck extension sleeve is of a generally uniform longitudinal cross-section.

27. A prosthesis as claimed in any one of claims 24 to 26, wherein the neck extension sleeve has a wall of uniform thickness. 940729,p:\oper\phh,32944-93.210,32 -33-

28. A prosthesis as claimed in any one of claims 24 to 27 wherein the neck has a frustro-conically shaped outer surface.

29. A prothesis as claimed in any one of claims 24 to 28 wherein the neck extension sleeve is an annular member, the hollowed portion being open at both ends.

A prosthesis according to any one of the preceding claims further comprising attachable collar means affixable to the prosthesis body generally transverse to a longitudinal axis of the prosthesis body for forming a load carrying interface with the upper end of the patient's femur.

31. A prosthesis as claimed in claim 30 further comprising securing means for holding the collar to the prosthesis body and comprising in part a pin bore at least partially extending through the collar means and pin means that can extend into the pin bore.

32. A prosthesis body as claimed in claim 31 wherein the pin bore has a closed end portion that defines a stop for movement of the pin means within the pin bore.

33. A prothesis as claimed in any one of claims 30 to 32 wherein the collar means include diutal offset means for replacing bone loss in the medial proximal area of the patient's femur.

34. A prosthesis as claimed in claim 33 wherein the distal offset means includes a tab portion that projects downwardly from a principal plane of the collar means. A prosthesis claimed in claim 33 or 34 wherein the collar means is substantially U-shaped and distal offset means extends from the medial portion of the collar means.

B940729,p:\oper\phh22944-9321033 34

36. A prosthesis substantially as hereinbef ore described with reference to the accompanying drawings. DATED this 29th day of February, 1994. SMITH NEPHEW RICHARDS INC. By its Patent Attorneys DAVIES COLLISON CAVE aSh 5t55 S S I I SI I C I S a S a S a CC 94O72,p:loperlpbb.32944-93.210,34 r ABSTRACT A modular hip prosthesis can be custom fitted to a particular patient by a surgeon prior to surgical insertion comprising a prosthesis a body having a neck portion for carrying a rounded head element, a transitional mid-section of the prosthesis body and a stem section and (ii) means attachable to the prosthesis body to adjust and maintain the prosthesis in load bearing engagement with the femur. A tubular extension sleeve to the stem may have an open end portion to receive the stem body. The stem may also include an integral bore, and an attachment in the form of an elonagated screw is provided for connection to *ilt the stem internal bore for securing the extension sleeve and the prosthesis body together, forming a compressive sealed connection therebetween. Pads can be attached to the transitional mid-section of the prosthesis body for increasing the cross-sectional shape of the prosthesis at the transitional mid-section. Removable collars can be added to the prosthesis to form a transverse load carrying interface with the upper end of the patient's femur. Frustro-conically shaped extension sleeves can be added to the prosthesis neck ior extending the neck length.