CA2102430A1

CA2102430A1 - Joint prosthesis

Info

Publication number: CA2102430A1
Application number: CA002102430A
Authority: CA
Inventors: Randolf Scholz; Reinhard Ehall
Original assignee: Individual
Current assignee: LOGIMED MEDIZINISCHE SPEZIALPRODUKTE GmbH
Priority date: 1992-03-09
Filing date: 1993-03-09
Publication date: 1993-09-10
Also published as: ATA45792A; HUT66221A; AT398371B; CZ233793A3; JPH06507567A; SK122693A3; WO1993017638A1; HU9303147D0; EP0583457A1

Abstract

ABSTRACT OF THE DISCLOSURE
In a joint prosthesis (3) with two projections (4,5) which are pivotable with respect to each other about an axis (6) and are connected to bones, wherein one of the projections (5) has a fork-like head and the other projection (4) has a head portion providing a bearing eye inserted into the fork-like head, and wherein the joint axis extends through aligned bores of the fork-like head and the bearing eye, the joint axis (6) is provided by a bolt which tapers toward one end and/or has a smaller outer diameter, such that the latter end is formed as a circular locating member which cooperates together with corresponding circular location members on one of the aligned openings of the fork-like head.
(Fig. 1)

Description

210~3~

JOINT PROSTHESIS
The invention relates to a joint prosthesis having two projections pivotally mounted relative to one another about an axis and intended for connection to bones, in which one of the projections includes a fork-like head and the other projection has a head portion which defines a bearing eye and is insertable within said fork-like head, wherein the joint axis extends through aligned bores in the fork-like head and in the bearing eye.
Prostheses of the kind mentioned above can be found, for example, in US-PS 4 193 139. A further joint endoprosthesis, which can be found, for example, in DE-A
2351,912, is, in accordance with its construction, primarily intended for the elbow joint. Generally, the greater part of the prostheses known up till now are more or less particularly adapted for special uses or for the replacement of a particularly selected joint.
Joint prostheses which, like the joint prosthesis according to the present invention, are primarily intended to replace a finger joint, are found particularly in the above-mentioned US-PS 4 193 139 and also in EP-B 1 214 773. These two known joints are limited with respect to the fact that they are intended for use a8 finger joints having a single-axis hinging of the bone portions intended to be pivotally connected together, wherein the apparent intention is to use the prosthesis primarily in the second joint inward from the end of the finger. However, the known construction of this kind of joint prosthesis requires that a relatively large length of the bone on its front surface, where the ~oint is intended to be inserted, be removed in order to create enough room to install the joint. This operation results in the removal of a region of the bone to which originally the ~oint ligaments were connected, with the consequence that a new location for the connection of ligament~ to the bone must be sought. Experience has shown that an attempt to attach bone ligaments to a `` ~102~30 location different from the original natural location i5 attended by considerable problems.
Mechanical joints proposed as prostheses, in addition to possessing substantial mechanical strength, must also be simple to assemble, in order that the operation time for insertion can be kept correspondingly short.
An aim of this invention is to provide a hinge joint, i.e. a joint prosthesis particularly for use as a metacarpal bone joint, which because of its construction i5 such that, during insertion, only small portions of the adjacent front surfaces of the bones intended to be pivotally connected together must be removed, and in p~rticular that the removal of the frontal bone surface is sufficiently limited as to leave undamaged the connection locations for ligaments. A further aim is to provide A joint prosthesis of the kind described above, which is characterised by a particularly simple construction and assembly, without expensive instruments.
To realize these aims, the ~oint prosthesis in accordance with the invention i8 such that the joint axis is provided by a bolt which tapers toward one end and/or steps down to a smaller outer diameter, wherein the said end i8 configured as a circular locating member which cooperates with corresponding circular locating members on one of the aligned bores of the fork-like head.
Because the joint axis is defined by a bolt, it is possible to keep the joint itself relatively small and to ensure a secure anchoring of the projections in the respective bones before undertaking the simple assembly of the joint within a relatively small space.
Specifically, all that is necessary to assemble the joint is simply to push the bolt into the corresponding bores, for which a relatively small space is required, this having the further result that the bones intended to be connected together by this kind of artificial joint need be trimmed or cut away over only a short length. In ' ' . : .

addition to this guiding capability, particularly advantageous in terms of a simple assembly, the end of the bolt can have a tapering configuration in order to facilitate centering and entry of the bolt, 80 that the final assembled condition is achieved by the guiding of the free end of the bolt into the corresponding locating members of the fork-like head. Assembly can be further facilitated to a great degree by providing the axis-defining bolt, at its end remote from the locating member, with a blind bore for receiving an implement, wherein a particularly simple insertion of an implement for the manipulation of the relatively small-scale axis-defining bolt is possible if the construction is such that the blind bore has an internal thread. Generally, with this construction, relatively small-scale axis-defining bolts for corresponding small-scale joints can be securely assembled in the least possible space, due to the capability of using a correspondingly light and manipulable implement.
Advantageously, the construction of the ~oint prosthesis according to the invention is such that the loc~ting members are constructed a~ circular grooves andlor circular ribs. In order to make possible the elastic registration of such circular grooves with circular ribs, it is advantageous to utilize physiologicAlly harmless synthetic material, wherein the ~s~e~bly or manufacture of the ~oint i8 considerably simplified in that the ~ligned bores of the fork-like head have substantially the same inner diameter, and in that the locating members are provided in a bearing insert which is securely installed in one of the two bores of the fork-like head. Providing the aligned bores with essentially the same inner diameters permits the selection of correspondingly simple assembly instruments for the projections and the fork-like head, whereby to ensure the necessary small tolerances through the corresponding, precision-built insert portions, ~ln~30 particularly the bearing insert. Further, it is po~Aible to select corresponding high-strength material, particularly metallic material, for the pro~ections and the construction of the head. By using bearing inserts with correspondingly small tolerances, and in particular bearing inserts of physiologically harmless material, the durability of the joint is significantly improved and frictional wearing of metal parts against each other is avoided. Such an undesirable frictional wear between metallic parts of the joint, using up the self-lubricating characteristics of various physiologically harmless synthetic materials, also arises if the configuration is such that the bearing insert has a ring flange with an outer diameter greater than the inner diameter of the bores, the said outer diameter, when the ~oint i8 assembled, being positioned on the inside of the fork of the fork-like head, by which it is possible to achieve lateral stabilization of the joint with a correspondingly smaller tolerance, seen looking in the direction of the joint axis. This effect can be still further improved by providing in the bearing eye of the head portion of the sQcond projection a bearing insert which includes a ring flange having an outer diameter greater than the inner diameter of the receiving bore for the be~ring insert, whereby it can be ensured that, to either side of the head portion carrying the bearing eye, wearing of metallic portions of the inner walls of the fork receiving this head portion can be avoided.
With reference to the use of the inventive joint prosthesis as a ~oint in the metacarpal or finger region, all that is needed i8 a hinge articulation of which the construction, which broadly imitates the actual natural movement characteristics of such hand joints, is advantageously so arranged that the head portion carrying the bearing eye has at least one abutment shoulder which cooperates with the fork-like head of the other projection. In this manner, at least one of the limit -` 21~30 positions, for example the stretched position of the joint, can be clearly limited by mechanical inter~erence, without making it necessary to provide another spacQ-occupying component.
In order to achieve a secure anchoring of the projections, even with a small-scale joint of thi~ kind, the configuration is aavantageously such that the projections be essentially symmetrical about the elongational axis which crosses the bearing axis, wherein advantageously the projections have preferably sharp-edged ribs extending in the direction of the long axis and distributed over the periphery. Such ribs, particularly with sharp edges, facilitate the anchoring of the projections in the end region of the bones, and offer a number of advantages during the installation of the projections in the bones. Whereas with known maximally asymmQtrical projections, stringent requirements as to the precision of the corresponding bone recess must be met to allow quick and secure installation, the largely centrally symmetrical pro~ections herein have substantially lower requirements a8 to the maximum permissable tolerances of such recesses, without prejudicing the sQcurity of the installation. In order to secure a sufficient anchoring effect immediately following insertion, the configuration is advantageously 80 arranged that the sharp-edged ribs decreasQ in height in the direction toward the free end of the projection, while for the subsequently necessary binding to the bone material, the configuration is advantageously 80 arranged that the projections carry a coating of biologically degradable ceramic material. The insertion of the projections into the easily prepared recesses in the adjacent ends of the bones intended for pivotal connection is substantially simplified and attainable with a smaller degree of force, by providing a conical taper at the free ends of the projections.

-`~ 21 0~

The invention will now be described in greater detail with reference to an example embodiment illustrated schematically in the drawings. The latter illustrate: in Fig. 1 a schematic section, ~or example through a metacarpal joint, with an installed ~oint prosthesis in accordance with the invention; in Fig. 2 a plan view of the one joint portion or projection supporting the fork-like head, for the inventive joint prosthesis of Fig. l; in Fig. 3 a side elevation of the projection or joint portion seen in the direction of arrow III in Fig. 2; in Fig. 4 an elevation view in the direction of arrow IV of Figs. 2 and 3; in Fig. 5 a side elevation of the second joint portion or projection carrying the bearing eye, of the inventive joint prosthQsis according to Fig. 1, analogous to the illustration in Fig. 3; in Fig. 6 a plan view of the second projection seen in the direction of arrow VI of Fig. 5; in Fig. 7 an elevation of the joint-axis-defining bolt of the joint prosthesis according to the invention;
in Fig. 8 a sectional view through a bearing insert adapted to be inserted in one part of the fork-like head, the latter carrying a locating member for cooperation with the bolt illustrated in Fig. 7; and in Fig. 9 a section through a further bearing insert, which is insertable in the bearing eye of the head portion of the second projection of the ~oint prosthesis in accordance with this invention.
Fig. 1 shows generally at 3 a joint prosthesis installed as a replacement for the natural joint between two bones 1 and 2, wherein the joint prosthesis 3 includes two projections 4 and 5 which are intended to be inserted in bored or hollow regions of the bones, and which are more fully described below in detail. The two projections or joint portions 4 and 5 are pivotally connected together about a pivot axis which is identified schematically in Fig. 1 by the number 6. The pivot axis is provided by a bolt insertable in aligned bore~ of the ~10~

projections 4 and 5, the bolt being illustrated in Pig.
7. The actual joint regions of the ~oint prosthesis, i.e the portions which project out of the bone~ 1 and 2, are short enough, when using a bolt as the ~oint axis, that the natural growth locations for the ligaments in the end regions of the bones do not need to be removed, the said growth locations for the ligaments being schematically identified by the numeral 7.
Figs. 2 and 3 illustrate more fully the projection or joint portion 5 which supports a fork-like head.
Directly adjacent the projection 5, which tapers conically to its free end 8, two fork-portions are provided which define two aligned bores 10 which have essentially the same diameter. Again, the pivot axis is identified by the numeral 6. As can be clearly seen in Fig. 4, the pro;ection 5 defines, extending in the direction of its long axis 11 and distributed around the periphery, sharp-edged ribs 12. Fig. 4 also clearly shows the conically tapering configuration of the pro~ection.
In assembled condition, the fork portions 9 enclose the bearing eye 13 of the second projection or joint portion 4, which is illustrated in detail in Figs. 5 and 6. The projection 4 or bearing eye 13 defines an opening 14 aligned with the bores 10 of the second projection 5, the opening 14 in the assembled condition also receiving the bolt illustrated in Fig. 7. The projection illustrated in Fig. 5 and 6 additionally includes a conically tapering cross-section in the direction of its free end 15, and is likewise provided with sharp-edged ribs 12. Generally, the two projections or joint portions 4 and 5 are such that the portions extending into the bones are both essentially symmetrical and identically constructed, so that the joint can be installed in both positions.
The sharp-edged ribs 12 distributed about the circumference are arranged such that, when installed in -` 21 02~13~

the bones, only a single rib is located on the inside, i.e. on the bending side of the ~oint, wherea~ the two remaining ribs 12 shown in the drawing are directed toward the outside, as is schematically indicated ln Fig.
1. Beginning at the respective free ends 8 and 15, the ribs have a gradually increasing height, thereby to facilitate the insertion of the respective pro~ections into the interior of the bones. Generally, the ribs serve to anchor the pro~ections in the bones, and to avoid any rotation of the joint portions in the bones.
Further, because of the presence of the ribs 12, the geometric configuration of the recesses in the bones does not need to meet excessively stringent requirements, since the ribs, due to their graduated heights, can compensate for irregular recesses in the bones.
In one of the fork portions 9 within the corrQsponding bore 10, there is provided a bearing insert 16 illustrated in Fig. 8, including a ring flange 17, which is placed to the inside of the corresponding fork portion. In a similar manner, the bearing insert 18 illustratQd in Fig. 9 is inserted into the bearing eye 13 of the second pro~ection, the item 18 also having a ring flange 19 which lies to the inside of the bearing eye, thus being located between the bearing eye 13 and the ad~acently lying fork portion 9. Naturally, the bearing insert 16 is installed in the sQcond fork portion 9 provided.
For the assQmbly of the joint prosthesis, the bolt 20 shown in Fig. 7 is insQrted either through the openinge 10 and 14 of the pro~ections 5 and 4, or through the openings provided in the bearing inserts 16 and 18, the bolt 20 defining the joint axis. The bolt 20 is configured such that it tapers at one end to a smaller diameter, wherein at the free end 21 of the bolt 20, a ring-shaped locating member 22, in the form of a circular rib, is provided. When the bolt 20 is inserted from that side of the assembled joint prosthesis which is adjacent "` ~102~.3~

the fork portion 9 containing the bearing insert 16, th~
bolt initially passes through the ~ir~t opening of the first fork portion 9, thereafter pa~sing through the opening 23 of the bearing insert 18 in the bsaring eye, and finally reaching the bearing in~ert 16 in the ~econd fork portion. As can be seen in Fig. 8, the bearing insert 16 has a circular projection 24 determined by the diameter of the circular rib 22 of the bolt 20, 80 that, when the joint locating bolt is fully inserted, the circular rib is guided by the circular projection 24 of the bearing insert 16, and the joint is closed in a simple manner, i.e., the two projections or ~oint portions 4, 5 are pivotally linked with each other.
For the insertion of a handling implement, the joint bolt 20 is provided with a blind bore 25 which has an internal thread over a schematically indicated region 26, 80 that there can be provided, for example, a threaded member or the like for the simple simple manipulation of the bolt or the application of the required force, whereby the implement, after assembly, can be removed in a simple manner.
In the use of the present ~oint prosthesis for the bones of the fingers or the metacarpus, only a single-axis hinged connection is necessary, a limit position for the ~oint prosthesis 3 being illustrated in Fig. 1, wherein a bend angle of roughly 90 is obtainable. In order to prevent excessive stretching or bending in the opposite direction, the bearing eye 13 illustrated in Fig. 5 and 6 has an abutment shoulder 27, which in the stretched condition makes contact with the inner surface 28 of the pro~ection 5 between the forked portions 9, thus preventing excessive bending beyond the stretched position. Because of this contact, the angle attainable beyond the stretched position is limited to about 10.
As materials for the joint prosthesis special titanium-aluminum alloy8 are utilized, which are noted for their low specific weight, high elasticity, high 21Q~.3~

strength and excellent corrosion resistance. The bearing inserts 16 and 18 illustrated in Fig. 8 and 9 are provided not only to lock the ~oint portions together, but also to prevent the rubbing of metallic parts again~t each other. To this end, the bearing inserts are constructed of a biologically compatible material, having good sliding characteristics with the least possible wear, along with optimal damping characteristics. For a rapid installation of the prosthesis, in particular for the projections 4 and 5 in the bones, a suitable biologically degradable coating of material is applied to the projections 4 and 5, for example through plasma spraying, making it possible to shorten the discomfort time, and permitting an earlier use of the joint.
BecausQ of the complete accommodation of the bones to the implanted projections 4 and 5, attained as just mentioned, the artificial joint achieves an early and satisfactory load-carrying capability.
In order to accommodate different bone sizes, the ao projQctionB 4 and 5 can be provided with different external diameters. The conical taper of the projections 4 and 5 is selectQd such that, during the anchoring of the ribs 12, a self-locking connection is attained which opposQs the removal of the projQctions from the bones, wherQin, corresponding to the material used and the bonQs, a bending angle of 5 to 7 is selected. In the evQnt that, contrary to the illustrated embodiment, a smaller number Or ribs is found to be sufficient, the rib on the bending side can be removed, based on the kinematics of the joint.

Claims

1. A joint prosthesis (3) with two projections (4,5) pivotal with respect to each other about an axis (6) and connected to bones, wherein one of the projections (5) has a fork-like head (9) and the other projection (4) has a head portion defining a bearing eye (13) and located in the fork-like head, and in which the joint axis (6) extends through aligned bores (10,14) of the fork-like head (9) and the bearing eye (13), characterised in that the joint axis is defined by a bolt (20) which tapers toward one end and/or has a smaller outer diameter, wherein the said end is constructed as a circular locating member (22), which cooperates with corresponding circular locating members (24) on one of the aligned bores (10) of the fork-like head (9).

2. A joint prosthesis according to Claim 1, characterised in that the bolt (20) has, at its end remote from the locating members, a blind bore (25) for engagement with an implement.

3. A joint prosthesis according to Claim 2, characterised in that the blind bore (25) has an internal thread (26).

4. A joint prosthesis according to Claim 1, 2 or 3, characterised in that the locating members are formed as circular grooves and/or circular ribs (22).

5. A joint prosthesis according one 1 of Claims 1 through 4, characterised in that the aligned bores (10) of the fork-like head (9) have essentially the same diameter, and in that the locating members (24) are provided on a bearing insert (16) which is installed in one of the two bores of the fork-like head (9) so as to be secured against coming apart.

6. A joint prosthesis according to Claim 5, characterised in that the bearing insert (16) has a circular flange (17) of which the outer diameter is greater than the inner diameter of the bores (10), the flange lying against the inside of the fork portion of the fork-like head (9) in the assembled condition.

7. A joint prosthesis according to one of Claims 1 through 6, characterised in that there is provided in the bearing eye (13) of the head portion of the second projection (4) a bearing insert (18) which has a circular flange having an outer diameter greater than the inner diameter of the bore (14) for the bearing insert (18).

8. A joint prosthesis according to one of Claims 1 through 7, characterised in that the head portion providing the bearing eye (13) has at least one abutment shoulder (27), which works together with the fork-like head (9) of the other projection (5).

9. A joint prosthesis according to one of Claims 1 through 8, characterised in that the projections (4,5) are, with respect to their longitudinal axis (11) intersecting the bearing axis, substantially centrically symmetrically formed.

10. A joint prosthesis according to Claim 9, characterised in that the projections (4,5) have preferably sharp-edged ribs (18) on the outside thereof, distributed over the periphery and extending in the direction of their long axis (11).

11. A joint prosthesis according to Claim 10, characterised in that the sharp-edged ribs (12) have a decreasing height in the direction toward the free end of the projections (4,5).

12. A joint prosthesis according to Claims 1 through 11, characterised in that the projections (4,5) have a coating of biologically degradable ceramic material.

13. A joint prosthesis according to one of Claims 1 through 12, characterised in that projections (4,5) have a substantially conical taper toward their free end (8,15).