Joint endoprosthesis

The invention relates to a joint prosthesis implant, in particular for knee prostheses, which can be attached with a first implant part to a first bone end and with a second implant part to a second bone end of two joint-forming bone ends, wherein the first implant part and the second implant part each articulation surfaces for formation having a pivot joint, which allows pivoting about an approximately transversely to the longitudinal extent of the first and second bone ends having first and second bone directed pivot axis, and further comprising a sliding part, which additionally allows a rotational movement and a displacement movement of the bone ends to each other, wherein the rotational movement about an axis of rotation approximately transversely to the pivot axis and approximately in the longitudinal direction of the first bone and the displacement movement takes place in a plane approximately parallel to the pivot axis and approximately transversely to the axis of rotation.

The first generation of useful knee joints was equipped with a hinge joint. Forced steering for desperate axis conditions and extreme belt instabilities, these axle linkers are still in limited use today. Although the positive guidance eliminates the instability, but leads to significant disadvantages, such as increased material stress and, above all, loosening of the implants from their anchorage in the bone.

A next large generation of knee joints consists of so-called surface prostheses, which only create new artificial sliding surfaces when the wear of cartilage and menisci has to be compensated, but the natural ligament and soft tissue apparatus maintains joint stability.

The widespread use of surface prostheses initially led to a significant improvement in femurotibial joint articulation. This type of prosthesis grants a high degree of range of movement of the femoral and tibial sliding surfaces to the extensively obtained ligaments. These are so-called flat forms, ie sliding surfaces designed as flat as possible. At the same time, however, this development led to severe setbacks in the development of artificial knee prostheses. With all these prosthetic designs in the movement, the metal femoral blade has only a punctiform or linear support on the polyethylene sliding surface of the tibia, an implant material that is still indispensable today. The selective overloading of the polyethylene sliding surface often leads to premature destruction of superficial sliding parts as well as of batches lying below the loaded surface. It comes to more or less significantly increased abrasion, which can lead to bone irritation, bone destruction and bone dissolution (osteolysis). In the aggregate, this attrition phenomenon can be referred to as polyethylene disease, which can lead to premature dysfunction of the artificial joints and bone.

The histological, tribological and clinical findings led to the development of a new generation of artificial knee joint surfaces. The goal of the development lies in the creation of new surface structures of the sliding partners and improvement of the anchoring conditions, in order to stop the early loosening of the implants, which arise by increased abrasion and by incorrect loading of the implants.

The natural conditions of movement of the knee joint are complex and can not be fully understood by artificial constructions. The dominant flexion and extension movement, which is complex with rotational movements, whose rotation center is constantly moving, and so on. zw. Because of dislocation of a sliding partner in anterior-posterior direction (AP) by the so-called rolling sliding movement. This complex biomechanical movement is constantly influenced by additional factors, such as lateral and AP strains of the ligamentous apparatus, as well as the joint capsule, the muscular traction, the patellar flexion, and especially the changes in the axis of the femur-tibial bone geometry.

The endeavor of the current generation of knee joints goes from the flat forms to the more conformable forms, since the low conformity leads to excessive contact stress of the polyethylene, which in turn causes increased abrasion. The increased conformity on the other hand carries the risk to limit the movement. After all, the rotational movements and sliding movements in the AP direction should not deviate too much from the natural conditions. Today's endeavor is to achieve a high level of conformity without restricting the rotational and sliding movements.

There are already functioning knee joints (US-A 4 340 978 and US-A 4 309 778), on the one hand the rotational movement, so-called rotating-platform zuiassen and on the other hand manicuring Menisci, so-called meniscal-bearing on a kind of rail guide in AP direction drive and imitate the AP dislocation. Known from the two above-cited US Patent knee joints are so far complicated in construction, as between the first and the second implant part on the first implant part two spaced apart and guided on the first implant part in rails and the joint surfaces forming the pivot joint forming sliders used which sliders allow both a rotational movement and a pivoting movement, especially since the rail guides arcuate

AT 405 014 Β are arranged. However, this has the disadvantage that the Schienenfürhrungen to the joint are completely free and open and that the rotational movements are carried out only after the rail guides, but this has the consequence that a sliding movement is no longer possible. According to another embodiment form according to the US patents, however, the rail guides on a very large game, so that not only rotational movements, but also in a very limited extent displacement movements are possible, whereby the rotational movements are completely uncontrolled and not oriented on a rotation axis. A combination of both movements, namely the rotational movement and the sliding movement, could not be solved satisfactorily so far, since the rotating platform does not migrate and the rail-guided Meniscal movement can not or hardly rotate. In particular, it has not been possible to carry out displacement movements independently of the rotational movement, ie in each rotational position.

The invention aims to avoid these disadvantages and difficulties and has as its object to provide a joint prosthesis implant of the type described above, in which, however, a combination of both the rotational movement and the displacement movement is feasible, such that the rotational movement also controls larger Amounts can take place and at the same time a sliding movement can also be carried out in a controlled scope, u.zw. regardless of the rotational movement. As a result, the anchoring parts of the joint prosthesis implant to be spared and a long shelf life of the anchorage to be achieved. Furthermore, all compressive, tensile, lateral and shear forces should be extensively transferable and neutralizable; Peak loads should be prevented.

This object is achieved in that the first implant part has a retractable housing in the first bone end, which is anchored in this first bone end, that in the housing a first slider is rotatably mounted about the axis of rotation, that in the first slider a second slider in a direction is mounted displaceably about transverse to the axis of rotation,

- That the second sliding body protrudes from the housing,

- That the second sliding body on the protruding from the housing part carries a joint surface against which abuts the second implant part with the joint surface arranged on it and

- That the second sliding body with a sliding surface on a Gegengleitfläche, which is provided on the housing, rests.

In this case, the first sliding body is advantageously completely enclosed laterally by the housing and can be inserted into the housing or removed from the housing by an opening of the housing facing away from the first bone.

To stabilize the joint prosthesis implant advantageously the first slider is secured in the direction of the longitudinal extent of the first bone in the housing in the direction of the axis of rotation against removal from the housing, u.zw. expediently by means of a bayonet-type device, which is advantageously characterized in that for axial securing two transversely .With the housing extending and are provided approximately parallel to each other pins extending in a direction approximately parallel to the pivot axis and the direction of a first slider arranged foot part are under-handles, wherein the foot part in one direction only has a maximum width, which corresponds to the distance) of the two pins and in a direction to about 90 · standing direction has the pins engaging behind projections.

A preferred embodiment is characterized in that the first sliding body is provided with an undercut groove open to the opening of the housing, which is formed by mutually parallel side walls, which groove extends in the direction of displaceability of the second sliding body with respect to the first sliding body. and wherein the second sliding body is provided with a tongue corresponding to the groove and thus engages in the groove, wherein expediently, the groove extends transversely through the entire first sliding body and the spring of the second sliding body has a smaller displacement about the displacement in the direction of the displaceability of the second sliding body relative to the first sliding body than the groove.

The first slider is advantageously made of metal for strength reasons.

A preferred embodiment is characterized in that the housing has a cylindrical portion of the interior extending inwardly from the opening of the interior and a conical portion adjoining the bottom of the housing, in particular a frusto-conical portion, wherein the housing is advantageously provided at its in the Bone extending end having a support anchor for insertion into the medullary cavity, to which preferably an extension anchor can be attached.

For reasons of strength, the housing is also made of metal.

In order to ensure a good sliding of the second slider on the housing, the housing is advantageously on the side facing away from the first bone with a radially projecting from the housing to the outside

AT 405 014 Β

Provided slide plate, wherein suitably the second slider is provided with a sliding plate which is approximately the same size as the housing and rests with this sliding plate on the sliding plate of the housing.

To adapt to the bone contour and for the purpose of obstacle-free guidance of a band, such as a cruciate ligament, when using the joint prosthesis implant as a knee joint expedient both the sliding plate of the housing and the sliding plate of the second joint body designed kidney-shaped, with the longitudinal extent of the sliding plate of the housing extends approximately in the direction of the pivot axis.

The second sliding body is preferably made of plastic, in particular of polyethylene.

The preferred use of the joint prosthesis implant is as a knee joint. Here, the housing is anchored in Tibiakopf.

For optimum anchoring of the first implant part in the bone, this has on its outer sides bone-structured surfaces, in particular the first implant part on the side of the sliding plate on which this rests on the bone end, a plurality of cylindrical depressions, in particular holes with diameters from 0.3 to 1 mm, preferably 0.5 to 1 mm, and with depths between 0.3 and 1 mm, preferably 0.5 and 1 mm, so that a porosity between 50 and 80%, preferably 60 and 70%, is effected. Preferably, in addition to the cylindrical recesses cylindrical projections with diameters between 0.3 and 1 mm, preferably 0.5 and 1 mm, and heights between 0.3 and 1 mm, preferably 0.5 and 1 mm, the ratio of Number of cylindrical protrusions to the number of cylindrical recesses is 3: 7 and a porosity between 50 and 80%, preferably 60 and 70%, is present ..

On the nonplanar surfaces of the first implant part with which it is in contact with the bone, crater-shaped depressions with depths of up to 0.5 mm are provided.

The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the drawing, in which FIGS. 1 and 2 are each side views of the joint prosthesis implant, u.zw. Fig. 2 according to the arrow II of Fig. 1, and Figs. 3 and 4 sections through the first implant part, u.zw. Fig. 3 along the line III-III of Fig. 2 and Fig. 4 along the line IV-IV of Fig. 1 show. FIG. 5 shows a side view of the first slider, FIG. 6 7 is a plan view of the same in the direction of the arrow VII of FIG. 9 shows a side view of the second slider, FIG. 10 shows a view in the direction of the arrow X in FIG. 9. In FIGS. 11 and 12 and 13 and 14, surface structures are respectively in plan view and in section along the lines XII-XII and XIVXIV FIG. 11 and FIG. 13 illustrates.

The joint prosthesis implant according to the invention, which is shown in the drawing, is designed as a knee prosthesis. However, it could be used with modifications for other joints. It has a first implant part 1, which can be anchored in the tibial plateau, either cementless or by cementing. It forms with a second implant part 2, which can be fastened to the femur, a pivot joint, which allows a pivoting possibility about a pivot axis 3, which corresponds to the pivoting of the lower leg relative to the thigh.

The first implant part 1 is essentially formed by three parts, namely a housing 4, a first and a second sliding body 5 and 6. The housing, which has approximately a uniform wall thickness, has a cylindrical part 7 and a subsequent frusto-conical part 8, which merges into a support anchor 9. The housing is 4 either integrally or screwed with its cylindrical and frusto-conical parts 7, 8 wholly deployable in the tibial plateau, wherein the support anchor 9 projects into the medullary cavity. An extension anchor of appropriate length may optionally be attached to the support anchor 9 should this be necessary due to the bone structure.

At the upper end of the housing 4, ie at the end which is averted from the tibial plateau, the housing 4 has a sliding plate 10 projecting radially outwards from the housing 4 with an approximately kidney-shaped surface extension. The longitudinal extent of this kidney-shaped sliding plate is aligned approximately parallel to the pivot axis 3. The tibia-free side of the slide plate 10 is polished, the underside of the slide plate resting on the tibial plateau has a textured surface as shown in Figs. 11 and 12, and the like. the structuring is achieved by a plurality of cylindrical bores 10 'with diameters of 0.3 to 1 mm, preferably 0.5 to 1 mm, and with depths between 0.3 and 1 mm, preferably 0.5 and 1 mm. Furthermore, there are still cylindrical elevations 10 available, u.zw. with diameters between 0.3 and 1 mm, preferably 0.5 and 1 mm, and heights between 0.3 and 1 mm, preferably 0.5 and 1 mm, wherein the ratio of the number of cylindrical protrusions 10 to the number of cylindrical bores 10 'is 3: 7. Overall, this results in a porosity of between 50 and 80, preferably 60 and 70%. As porosity is the percentage of the air volume over a surface area, with holes or Surveys, against the massive volume

AT 405 014 Β understand this surface area.

On the non-planar surfaces, with which the housing 4 is in contact with the bone, crater-shaped recesses with depths of up to 0.5 mm are provided, as shown in FIGS. 13 and 14.

The housing 4 is formed of metal; in particular, the following metals can be used here; Pure titanium, a titanium cast or titanium forged alloy or a cobalt-chromium alloy.

In the housing 4, a first slide member 11 is inserted, which has a cylindrical and a frusto-conical portion 12 and 13 and with these parts in the cylindrical and frusto-conical inner recess 14 of the housing 4 with a small clearance fits, so that the first slide member 11 relative to the Housing 4 is rotatable, u.zw. about an axis of rotation 15, which is directed approximately parallel to the longitudinal axis of the tibia.

This first slide fits completely into the inner recess 14 of the housing 4 and is secured against falling out of the housing 4 by a kind of bayonet lock. This bayonet-like device is characterized by two transversely through the inner recess 14 of the housing, u.zw. by the frustoconical recess of the housing extending pins 16 which are inserted into corresponding holes 17 of the housing 4 and are fixed in these bores 14, for example by a press fit, realized. The longitudinal axes of the pins are symmetrical to the axis of rotation 15 and at a lateral distance from this. The first slider 11 has at its lower end to a foot portion 18 which has a maximum width 19 in one direction, which corresponds to the distance 20 of the two pins 16 from each other. In a direction rotated by about 90 *, the foot portion 18, the pins 16 engaging behind projections 21. In this way, the first slide member 11 is inserted into the housing 4 only in a very specific rotational position of the first slider 11 to the housing 4, u.zw. then, the foot part 18 with its extensions 21 is approximately aligned parallel to the pins 16. After rotation through a certain minimum angle, the projections 21 engage behind the pins 16 and the first slide 11 can no longer by a movement along the axis of rotation 15 from the Housing 4 are removed. The first sliding body is also formed like the housing made of metal.

The first slider 11 serves to receive a second slider 22, which is displaceable relative to the first slider 11, and thus also relative to the housing 4, u.zw. in a plane which is approximately parallel to the pivot axis 3 and perpendicular to the axis of rotation 15. The second slider 22 also has a slide plate 23 which corresponds in its peripheral configuration of the housing 4 arranged slide plate 10, that is also designed kidney-shaped. When inserted into the housing 4 second sliding member 22, the sliding plate 23 of the second sliding member 22 rests on the sliding plate 10 of the housing 4. However, in order not to protrude at shifts the sliding plate 23 of the second slider 22 on the slide plate 10 of the housing 4, the sliding plate 23 of the second slider 22 is dimensioned slightly smaller in its areal extent than the sliding plate 10 of the housing 4th

The second slider 22 is not only slidably mounted relative to the first slider 11, but against this also against axial removal, u.zw. secured in the direction of the axis of rotation 15. These two functions are fulfilled by an undercut groove 24 provided in the first sliding body 11, to which the second sliding body has a correspondingly formed and integrally formed with the sliding plate 23 spring 25, with which it is inserted into the groove 24. The displacement of the second slider 22 relative to the housing 4 is defined by the longitudinal extent 26 of the spring 25. The longitudinal extension 26 of the spring 25 is dimensioned to be shorter by the desired displacement path 27 than the inner diameter 28 of the inner space 14 of the housing 4 (compare FIGS. 3 and 8). The second slider 22 can thus always be moved only by the stop of the spring 25 on one side of the housing 4 until the stop of the spring 25 on the other side of the housing 4.

The second sliding body 22, which is made of plastic, preferably made of polyethylene, has on the upper side of the sliding plate 23, ie the side facing away from the housing 4 side sockets 29 for the second implant part 2, which is connected to the femur, on.

The function of the joint prosthesis implant is explained in more detail below:

The joint prosthesis implant according to the invention takes into account the natural multicentric movements, u.zw. in greatly improved form than the previous joint prosthesis implants. The movement of the invention, which is made possible by the joint prosthesis implant, is that in the anterior-posterior Dislokationsbewegung, which is modeled on the natural sliding movement, simultaneously at all their movement points each create a new center of rotation and therefore at the same time on all these Gleitpunkten the rotation can take place medially and laterally. This so-called multiplex movement, which is effective with its dislocation distance in the movement sector of flexion and extension of its main burden of walking, has rotational freedom, which depends on the needs of the soft tissue apparatus, the bone axis geometry and other individual requirements

AT 405 014 Β nisse, in short, in the sum of the complex requirements that are required for each individual knee joint. From this Muitiplex movement principle results in the equipment possibility of TibiaGleitflächen with a high conformity of the joint partners of femoral implant part 2 and tibial implant part 1, as it was previously not possible. The high conformity of the polyethylene sliding surface of the slider 22 allows a maximum distribution of pressure and sliding forces between the femur implant part 2 and the slider 22 arise. In particular, the stress load of the polyethylene sliding surface of the slider 22, which is due to the rolling sliding movement of the AP dislocation, is significantly reduced. The multi-rotational movements on all points of the dislocation path of the tibial sliding surface of the slider 22 further capture the lateral stress and push movements that would otherwise be fully at the expense of the tibial anchorage.

The new multiplex movement-sliding principle leads to three major improvements of the artificial knee joint:

1. Higher conformity of the articulation surface of the femur and tibia.

Second Reduction of stress on the polyethylene tibial sliding surface.

Third The multiform movement protects the anchoring parts.

The function of simultaneity of the movement of medial and lateral rotation as well as the anterior-posterior dislocation movement is essential to the invention. This function is transmitted to the second slider 22. All compressive, tensile, lateral and shear forces are large, ie at maximum support of the femoral component, ie of the second implant part 2, transmitted to the second slider 22 of the tibia and neutralized by the inventive Multiplex-Bewegungspririzip. This distribution of force prevents selective or small-area focusing stress load on the polyethylene and at the same time prevents Spitzenbeiastungen on the anchoring of the implants 1, 2 of the tibia and femur.

The finely polished table-like slide bearing of the second slider 22, which conforms to the second femoral implant part 2, allows the necessary rolling and sliding movement in flexion and extension of the joint at maximum surface contact, but is held laterally by the conformity. The second sliding body 22 itself moves over a large area on the sliding plate 10 of the housing 4th The forces are thus transferred over a large area from the bottom of the second slider 22 on the large sliding plate 10 of the housing 4 and do not go to the detriment of the lower lying games that exercise only a guiding and holding function. The new Muitiplex movement principle according to the invention strives for a minimum of material loading, especially of the tibial implant part 1. A goal achieved by this invention is the reduction of polyethylene disease, another aim also achieved is to protect the anchorage to prevent premature loosening of the implants which limits their life span.