DE2814752A1 - ENDOPROSTHETIC JOINT - Google Patents

Description

28U752

PATENT ADVOCATE DR. RICHARD KNEiSSL VVider.maysrcir. 45

D-8000 MUNICH Tel. 089/295125

Folder 24 440

ICI case no. Z / PH. 29455

IMPERIAL CHEMICAL INDUSTRIES LIMITED London, United Kingdom

Endoprosthetic joint

809842/081

28U752

description

The invention relates to an enaoprosthetic joint, in particular on an endoprosthetic ginglynus (hinge joint) and especially a metacarpophalangeal joint (Han & kiöchel joint).

Ginglyai, with which the present invention is concerned, are hinge joints, which in humans are particularly known as interphalangeal (finger and toe joints) and elbow joints occur, as well as the metacarpophalangeal joints. It is pointed out that the invention can be described in particular with reference on a metacarpophalangeal joint is described, but that the invention can also be applied to other ginglymi can.

The gradual degeneration of the joints is a particularly serious problem in pathological rheumatoid arthritic diseases and osteo-arthritic conditions. The effect of rheumatoid arthritis is often especially in the metacarpo and interphalangeal joints of the hand, which results in a serious deterioration in the ability to manipulate.

It is now common to surgically replace artificial joints (endoprosthetic joints) instead of defective ones use natural joints. However, there are currently only a small number of endoprosthetic metacarpophalangeal joints (hereinafter referred to as MCP joints), which also have disadvantages. The main parts of this Disadvantage is based on the difficulty of imparting the articulation ability of the natural joint to the MCP joint, which is primarily capable of flexion-extension (flexion-extension), but also limited abduction-adduction (lateral to and fro movement), but this abduction-adduction is maximal when the joint

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is elongated, and is minimal when the joint is flexed.

Several of the MCP joints currently in use have components that which are fully connected and held together by the natural joint capsule and associated ligaments v / earth. Such KCP joints suffer from the disadvantage that the natural joint capsule and the natural ligaments, especially in arthritic joints, are often opposite to their normal state are badly deformed. Since the natural joint capsule and the natural ligaments are also required for their function such joints cannot be moved until healing from surgical implantation in the body is complete is. Because of their indirect mechanical connection, such joints generally cannot do without even moderate forces transfer the risk of dislocation.

Other currently used MCP joints have a direct mechanical connection, for example in the form of a hinge tift with ^s. However, even such joints are not without disadvantage, since they do not give way due to their direct mechanical connection, even under excessive load. As a result, the bone ends in the vicinity of the joint often break, or the seat of the endoprosthesis in the bone end is loosened. Such joints can also only perform a pivoting movement about one axis, which is why they do not have the abduction-adductor ability. of the natural joint.

Another currently used variant of a conventional one

elastic Ginglyaus is of one-piece construction made of / plastic, such as e.g. a silicone elastomer. Mechanically, these joints are relatively weak, so that they only do a disservice. They allow practically unlimited flexion in the lateral direction and in the longitudinal direction and often break at the Inner line of repeated flexion. In addition, because of their elasticity, they are relatively poor in the bone ends to fix.

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Koch another type of MCP joint currently in use is of the general ball socket type, with a protruding ball on one component into a socket on the other component is snapped. Such joints are normally capable of smooth pivoting movement about more than one axis without excessive wear takes place on the bearing surfaces, even under high loads, but they result in normal use easy to dislocate. It is true that they have bearing surfaces of sufficient smoothness and with sufficient structural properties Tolerance in order to keep the wear and tear of the joint low during use, but such joints have so far been of relative importance complex construction in order to limit the abduction-adduction abilities of the natural joint in its extended state simulate why such joints are relatively difficult to manufacture.

The invention was now based on the object of an endoprosthetic To create ginglymus that largely has the articulation properties of a normal natural joint without being light Dislocates during normal use and which can be made relatively easily.

The subject of the invention is therefore an endoprosthetic ginglymus, consisting of cooperating first and second components, polygons to which to be connected by this joint Bones can be attached, the characteristic being that the first component is a bearing part with a fork-shaped Has head, being bridged to the fork prongs. the same a bearing is attached, which has a first bearing surface with a convex shape in the circumferential direction, which is arranged symmetrically about an axis passing through the fork prongs; that the second component comprises a hook part with a hook having a second bearing surface on its radially inner surface possesses, which is approximately complementary to the first bearing surface, so that it can cooperate with this so that a

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Pivotal movement between the first and second components about the bearing is possible; and that the fork prongs and the hook part are provided with structures which cooperate in such a way that they convert the pivoting movement of the joint into a pivoting movement about the mentioned, limit the axis passing through the forks.

The first bearing surface can have a shape that is convex in the circumferential direction and a shape that is convex in the axial direction, such as a spheroidal shape, which is currently preferred, in which case the second La ^ ercbsrflache by a curved, longitudinally concave Bearing shell surface is formed, which is recessed on the radial inner surface of the hook. Alternatively can the first bearing surface have a shape which is convex in the circumferential direction and a concave shape in the axial direction, such as the shape of a in the axial direction concave bobbin, in which case the second bearing surface through the radially inner surface of the hook is formed which has a longitudinally concave and transverse convex shape with a convex radius of curvature, which is smaller than the concave radius of curvature of the bobbin.

It should be noted that the overall dimensions of the hook necessarily by the overall dimensions of the fork-shaped Head are limited in order to enable such a pivoting movement of the first ur.d second components around the bearing to a large extent corresponds to the capacity for flexion-extension and the limited capacity of abduction-adduction of the natural ginglymus.

In a preferred embodiment, the hook is sufficiently elastic, for example by being made of a physiologically inert consists of elastic plastic, for example of high molecular weight polyethylene, and extends the second bearing surface to such an angular extent, for example at an angle between 180 and 200 °, that the hook over the first Bearing surface can snap so that it is held there, but still a pivoting movement between the first and two-

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th components as discussed above. This variation is; tasüiiders beneficial as they connect the joint components during the surgical implantation of the endoprosthetis before the joint facilitates and generally a pivoting movement the gel at an earlier point in time after the implantation, than is the case with a joint that is based on the cooperation the natural joint capsule and the associated ligaments to hold the joint together.

It should be noted that the term "spheroidal" surfaces bordered, which are exactly spherical, and also surfaces, which by rotation of an ellipse around the major or minor axis are formed.

The special structures on the fork prongs and aa hook part, which cooperate so that they the pivoting movement of the joint in a pivoting movement about the aforementioned, passing through the fork prongs Limit axis, and which are presently preferred, consist of a transitional cam-like Extension, which is arranged eccentrically at the end of each fork prong, υιηά a flanged shoulder on the hook part, the extends laterally outward from hooks, these parts being of a size and being arranged to be at a pivoting movement of the joint on the through the fork prongs hinüurer: .geher.ee axis capable of mutual interaction are.

The first and second components of the joint can be attached to each other The connecting bones can be attached by means of measures known per se in the art, which ensure stable localization of the Gelerk enable. For example, you can use a stem, for example a long stem, which tapers in the direction of the bone and which on his AuBenssits in the longitudinal direction 1-Iuten has to a Plague posture in the intramedullary canal of the bone in question, the

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to be connected with d3n Galonk, to facilitate and twist to keep it to a minimum «Alternatively, you can use a stem be provided, for example over part of its length has a screw thread or spaced circumferential grooves, to facilitate fixation in the intramedullary canal. As a further alternative they can be provided with a stem, which has a semi-porous surface in which the natural Cook cells can grow into it after the joint is implanted, so that the retention in the bone is facilitated. In general-Eia-in & ii long stems are preferred, but other types of stems may also be suitable. Furthermore, the above-mentioned Alternatives can be combined with one another.

For a better understanding of the invention there are now two embodiments of an MCP joint according to the invention with reference to the accompanying drawings. In the Drawings show:

Figure 1 is a bottom view of a first embodiment of the MCP joint ;

FIG. 2 is a longitudinal sectional view taken along line 2-2 of FIG. 1; 3 is a partial bottom plan view of the metacarpal component of the MCP gelank of the first embodiment;

Figure 4 is a cross-sectional view taken on line 4-4 of Figure 3; Fig. 5 is a partial side view of the proximal phalangeal com-

poriente of the KCP joint of the first embodiment ^ form; Figure 6 is a cross-sectional view taken along line 6-6 of Figure 5; 7 and 5 show partial views of the KCP joint of the first embodiment in the extended and flexed state; and 9 is a bottom view of an alternative embodiment of the MCP joint.

The illustrated metacarpal component of the first embodiment has a bearing part 11 of integral construction (e.g. made of physiologically inert plastic) with a fork-shaped head that looks roughly like a U, the base 12 of which has a stop for a bone and from which a stalk 13 forms

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extends. The stalk, 'which has a smaller cross-section than that Has head and becomes a narrow rounded end 14 tapered, is equipped with two diametrically arranged longitudinal grooves 15, around the insertion and fixation within the intra-edular canal of the ketacarpal bone connected by the joint should be to facilitate. The groove 15 can have a curved cross section, such as that shown in FIG is.

The fork-shaped head has two essentially parallel, plate-shaped © and mirror-image fork prongs 16 (which represent the side arms de, 3 U), to which a bearing in a bridging manner 17 is attached to an approximately spherical bearing surface. The bearing is cylindrical with two diametrically arranged Axle journals 18, each of which has a blockable free end 19 which fits into a corresponding hole near the center fits the face of a fork prong and is shaped to prevent rotation of the bearing in use. The axle journals may alternatively have a tapered cylindrical shape so that their free ends are wider than the ends on the Bearing surface to allow better attachment of the bearing to the forks.

Each of the plate-shaped forks has a partially curved outer end which is approximately centered at the point where a journal of the bearing is attached, and over part of the curvature a substantially constant radius of curvature and has an increasing radius of curvature over the remainder, so that each fork prong is an eccentrically arranged cam-like Has extension 20.

The illustrated proxial phalangeal component of the first embodiment is also expediently of integral construction (for example made of physiologically inert plastic) and has a hook part 21 with an elastic hook 22 on one

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Ετ.άε ur.d a handle 23 with a smaller cross-section than the hook, for uptake in the intramedullary canal of the proximal fhalan ~ eul> cinponente, which is to be connected by the joint is designed in a manner similar to that described above for the metacarpal component has been described. The hook 22 and the handle 23 are connected to one another by a flanged shoulder 24, which extends outwardly from the base of the hook around two symmetrically arranged curved ribs 25 on either side of the Hook 22 to form which is in the same direction as the hook 22 are curved. Dar has hook 22 on its radial inner Surface a recess so that a curved, longitudinally concave bearing shell surface 26 is formed, the curved surface is approximately complementary to the spherical bearing surface of the bearing 17 in the Ketacarpalkoniponente. The bearing shell surface 26 extends angularly by slightly more than 180 °, the hook 22 being of such elasticity that it can snap over the bearing 17 and is held there so that the ketacarpal component and the proximal phalangeal component are capable of a mutual pivoting movement.

The curved ribs 25 have approximately the same center of curvature as the bearing shell surface 26 and a radius of curvature, which is slightly smaller than the maximum elevation of the cam-like extension 20 on each fork prong 16 above the attachment point an axis 18 of the bearing 17 so that when the two components are connected to one another to form the KCB joint are, the cam-like extension 20 of the ketacarpal component and the ribs 25 on the proximal phalangeal component to one another when the joint is bent by 90 °, as can be seen in FIG. The flexion movement of the joint is reduced to a Limited pivoting movement about a first single axis which passes through the journal 18 of the bearing.

"Similarly, if the assembled MCP joint is in is in the stretched state, as can be seen in Figures 1 and 7, then are the ribs 25 and the cam-like

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Projections 20 not: to one another, which is why a dev / isse pivoting movement even. around a second axis is possible, which is at an angle runs from 90 ° to the first axis. The angular extent of the pivoting movement ues the zvsite axis is due to the contact of the ribs 25 of the hook part 21 at the curved outer ends of the fork tines 16 and / or limited by the contact of the outer open end 27 dos Haksns on the inner surface of each fork prong 16, depending on the individual dimensions and distances between the hooks 22, then ribs 25 and the fork prongs 16. In of the embodiment shown is the maximum angular Scliv / enkcevendung limited to an arc of approximately 10 to 15 °, since then the ribs 25 of the hook part 21 on the curved outer 3 end of each fork prong 16 rest.

Sor: it enables the ribs 25 to be dimensioned accordingly and the curved outer end of each fork prong 16 the proximal phalangeal component 21 or on the ketacarpalkoxponente 11 also approximately the possibility of back and forth movement of the natural MCP joint, as discussed above .

~ 2bl represents a second Ausführungsforci erfindungsgeaäßen MCP-Ge-Ienlc3 vary the IIstacarpalkoEponente 31 and the per-3: ir: 3 2e Phalangeaikomponente 32 from those of the first Ausführunrrsforn only with respect to the bearing and of the hook. In the second embodiment shown in FIG. 9, the bearing has the form: an axially concave bobbin 33, which is attached to the fork prongs of the fork-shaped head of the metacarpal component 31 by axle journals 34, the design of which is that of the corresponds to the first embodiment, and that the hook 35 has a concave shape in the longitudinal direction and a convex shape in the transverse direction, where the convex radius of curvature is smaller than the concave radius of curvature of the bobbin 33. As in the first embodiment, the hook 35 has such a shape V-lean-like extension and elasticity that it has over the bearing

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can snap, so that a pivoting movement is possible. Sins lateral movement corresponding to the back and forth movement possible> eix d'is natural joint is through sliding and rolling of the hook 35 on the bobbin 33 due to the difference in the toothing possible. This back and forth motion is accurate in in the same way as in the first execution form has been described, namely by planting the cam-like Extensions 2 o of the fork tines 16 on the ribs 25 on the corresponding. Components 31 and 32.

It is clear that a KCP joint according to the invention can easily be modified, for example by reducing the size of the peculiar extensions and accordingly also reducing the distance between the ribs 25 and the center of the curvature of the bearing part of the hook 22 or 35 in the case of the corresponding components, so that the nc peculiar projections 20 and the ribs 25 within a größsren Seuga stretching region of the hinge abut one another, whereby the input ν? Λ Herbewegungsvermögen is reduced. Such a modified joint according to the invention can be used instead of a ginglymus which has practically no back and forth movement, as is the case, for example, with the proximal interphalangeal finger joint.

It should be noted that excessive stretching (hyperextension) of an inventive MCP joint by placing the back dös sheet 22 or 35 at the base 12 of the forked head dsr corresponding components is limited. Similarly, a flexion through an angle greater than 90 ° is increasing Interaction zx-iischsn the ribs 25 on the hook part and the nc peculiar projections 20 limited to the fork prongs 16 when dsr flexion is exceeded by 90 °. First will the increasing interaction due to the elasticity of the hook 22 or 35 caught, but excessive bending is sufficient the interaction of pulling the hook 22 or 35 over the bearing 17 or 33.

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This property of a local change in the excessive bending is of particular advantage, \ v ^T hen a erfindungsgenäßes KCP joint instead of arthritic natural joint is used. The bones of such joints are often so weakened by arthritis that excessive pressure on the body from a sitting position, such as when falling or using the ends with clenched fingers, would result in a fracture of the bones if it would be transmitted through the MCP joint. In addition, the hook 22 or 35 can easily be snapped back via the bearing 17 or 33, Iz. generally without surgery.

The ketacarpal component with the bearing and the proximal phalangeal component of the illustrated embodiments are expediently of integral construction and, for example, of a physiological one inert elastic plastic, such as high molecular weight polyethylene, which is why they are conveniently replaced by conventional Forming techniques, as they are known for such materials, can be produced. That is why the need becomes complicated Machining that is often necessary in the manufacture of KCP joints is avoided.

Because of the design of an MCP joint according to the invention it is also possible to incorporate a bearing from one material, d & L · differs from the rest of the KCP joint, such as 3. a metal bearing, for example by placing the bearing in the mold sets in before the rest of the metacarpal component is molded around it will. This is particularly advantageous because the exact size, shape and surface properties of the bearing surfaces in endoprosthesis Hinges is critical, especially when the hinge must endure significant loads and therefore surface wear must be kept low. Particularly suitable materials from which the bearing for a joint according to the invention can be produced, are in addition to high molecular weight polyethylene and all commonly used physiologically inert

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Storage materials, for example, a chromium / cobalt alloy stainless steel or titanium.

In addition, the bearing part of the hook on which, for example in the first embodiment, the bearing rail surface 2o is formed separately from a suitable physiological one inert storage material, as defined above, are formed and first introduced into a mold as a Einaxz, whereupon the remainder of the proximal phalar geal component is molded around it. In this case and also when the bearing is used as a molding the remainder of the proximal phalangeal component is incorporated, For example, the material used for molding may be a physiologically inert plastic that is unsuitable for storage purposes, such as e.g. a polyester or polypropylene.

The insertion of an MCP joint according to the invention can be performed using known surgical techniques are carried out, as for example by M. Devas. and V. Shah in "Journal of Bone and Joint Surgery ", 1975, £ 7.» 72 to 77. It's just a relatively small incision is necessary because the surgeon first has to separate the components and the corresponding bone ends are introduced and set in it, whereupon the hook is snapped over the bearing. The components of the MCP joint can only be found in the medullary canal of every bone by mechanical means or with the help of a suitable adhesive or cement.

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Claims (10)

28U752 claims 1. Endoprosthetic Ginglymus, consisting of working together first and second components which are attached to the bone to be joined together by this joint can, characterized in that the first component is a bearing part (11) with a fork-shaped Has head, with the fork prongs (16) bridging the same a bearing (17) is attached, the first Bearing surface with a convex shape in the circumferential direction, the one symmetrically around one passing through the fork prongs Axis is arranged; that the second component has a hook part (21) with a hook on its radially inner Surface has a second bearing surface which is approximately complementary to the first bearing surface, so that they with this can work together to allow a pivoting movement between the first and second components around the bearing is possible; and that the fork prongs (16) and the hook part (21) are provided with structures (20, 25) which cooperate so that they the pivoting movement of the joint into a pivoting movement about the aforementioned axis passing through the fork prongs (16) restrict. 2. Sndoprosthetic Ginglymus according to claim 1, characterized in that the first Lagsroberfläche one In five orientations convex and in the axial direction convex Has shape and that the second bearing surface is in the form of a curved, longitudinally concave bearing shell surface which is recessed in the radially inner surface of the hook. 3 * Endoprosthetic Ginglyraus according to claim 2, characterized in that the first bearing surface is a has spheroidal shape. 809842 / ü811 ORIGINAL INSPECTED 28U752 4. Endoprosthetic Ginglymus according to claim 1, characterized in that the first bearing surface is a has convex in the uni-circumferential direction and concave in the axial direction and that the second bearing surface through the radially inner surface of the hook is formed, which has a longitudinally concava and a transverse convex shape with a convex radius of curvature that is smaller as the concave radius of curvature of the first bearing surface. 5. Endoprosthetic Ginglyaus according to claim 4, characterized in that the first bearing surface Fora has a concave bobbin in the axial direction. 6. ErxLoprosthetic Ginglymus according to one of the preceding claims, characterized in that the hook of the second component is sufficiently resilient and that the second bearing surface extends angularly so far that the hook can snap over the first bearing surface, Un to be held on this and still «a pivoting movement to allow between the first and second components. 7. Endeprosthetic ginglymus according to one of the preceding claims, characterized in that the structures on the fork prongs (16) and on the hook part (21), which cooperate so that they the pivoting movement of the joint restrict in a pivoting movement about the aforementioned, through the fork prongs (16) penetrating axis, from a transition having cam-like projection / which is eccentric at the end of each fork prong (16), and a flanged shoulder (24) extending from the hook part (21) extends outside, exist. 8. Endoprosthetic ginglymus according to one of the preceding claims, characterized in that the 8098Ä2 / 0811 first and second components are designed so that they can be attached to the bones to be joined together, in that they have a stem (13, 23) which tapers in the direction of the bone and which on its Has rivets (17) running longitudinally on the outer surface. 9. End prosthesis Ginglynus according to one of the preceding claims , characterized in that the first and second components of integral construction are made of a physiologically inert elastic plastic. 10. Endoprosthetic ginglymus according to one of claims 1 to 8, characterized in that the camp is made Ketall and that the bearing part and the second component are each of integral construction and consist of a physiologically inert plastic.