DE29918589U1 - Endoprosthesis for a shoulder joint - Google Patents

Description

Endoprosthesis for a shoulder joint

[0001] The invention relates to an endoprosthesis for a shoulder joint with a shaft part which has an axial shaft stem for implantation in the humerus and a shaft head, with an articulation surface in the region of the shaft head, and an aligning piece which can be articulated on the articulation surface and extends along an aligning axis, which can be pivoted in all directions and can be fixed in a selectable pivot position relative to the shaft part, as well as a head cap which can be connected to the shaft part via the aligning piece.

[0002] EP 0 712 612 discloses a shoulder joint prosthesis whose shaft part has a depression with a hemispherical base in its metaphyseal end, into which depression a ball is inserted. This ball has a central, continuous bore and a slot connected to the bore over its entire length, which splits the ball ring in a C-shape. A stem connected to the calotte is inserted in the bore. Grub screws are provided in the shaft part in order to immobilize the ball in the depression in a selectable angular position and to deform the ball ring, thereby clamping the stem in it.

[0003] The disadvantage of this prosthesis is that the calotte is

direction must be placed precisely before it can be fixed in this position.

To do this, it must be held in this position by a surgeon while the grub screws are firmly tightened. In addition, the optimal position of the cap can only be approximated, as the distance between the cap axis and the shaft axis is constant. Aligning the cap center in an anterior/posterior direction always inevitably involves a cranial or caudal shift. In addition, the grub screws must be tightened before the prosthesis is inserted, as they are no longer accessible afterwards. This requires multiple test manipulations on the operated arm and corrections to the bone cut surface during the operation, and makes it impossible to correct the alignment after implantation.

[0004] FR 2 773 469 discloses a shoulder joint prosthesis with a shaft part, a pivotable intermediate piece or aligning piece attached thereto, which intermediate piece carries a spherical cap. In this prosthesis, the metaphyseal

A hemispherical groove with a threaded hole at the base is provided at the end of the shaft part. The groove and threaded hole are aligned with a neck axis, the angle of which to the shaft axis is preselected. In the groove there is a pivoting intermediate piece with a hemispherical surface concentric with the hemispherical surface of the groove at its humeral end. At the other end, the intermediate piece has a conical surface that is eccentric with respect to the center of the two spherical surfaces and on which the head cap sits with a corresponding conical recess. The axis of this recess is arranged eccentrically with respect to the center of the cap. The intermediate piece has an axial hole with a hemispherical base. A screw with a ball head is inserted into the hole with the shaft first, with the threaded section of the shaft being pushed through a conical hole in the hemispherical base of the intermediate piece and screwed into the threaded hole in the shaft part. When the screw is tightened, the centers of the spherical surfaces of the pit in the shaft part, the inner and outer hemisphere surface on the intermediate piece and the spherical surface of the screw head are at a common central point. This means that the intermediate piece can be pivoted in all directions relative to the shaft part and can be rotated at the same time. By pivoting the intermediate piece, its longitudinal axis is placed parallel to the desired neck axis direction, and by rotating the intermediate piece about its longitudinal axis and rotating the cap in accordance with this rotation, the deviation of the neck axis to be achieved from the approximate neck axis can be compensated. Once the optimal position of the intermediate piece has been determined, it can be fixed by tightening the screw on the shaft part.

[0005] With this prosthesis, the direction of the joint neck can also be adjusted continuously according to the conditions of the original joint. By adjusting the inclination and rotation with respect to the shaft axis using a manipulation head, the neck axis can be adjusted parallel to the optimal neck axis. This approximation can then be adjusted continuously across the axis direction using the cooperating eccentrically arranged conical surfaces on the intermediate piece and the calotte. The length of the joint neck is regulated by a set of calottes of different thicknesses. This allows a calotte to be fixed at any location in any desired position, so that the location of the calotte can be optimally adapted to the original conditions of the joint or the intended

Correction can be aligned and the original center of rotation of the shoulder joint can be restored.

[0006] Since the success of a shoulder prosthesis depends largely on the

Since the restoration of the muscular balance of the shoulder muscles depends on the original center of rotation of the shoulder joint being able to be restored by this individual positioning of the head cap. The smallest possible distance can also be achieved between the bone cut surface and the artificial head cap, so that the muscles are provided with continuous support during every movement. Another advantage is that the inclination and rotation of the intermediate part in relation to the shaft part can be aligned with the bone cut surface or the desired alignment of the head cap and fixed in this position even after the shaft part has been implanted, since the screw fixing the intermediate part remains accessible from the head cap side.

[0007] The disadvantage of this prosthesis, however, is that the spherical surfaces must be manufactured exactly concentrically, which is complex and expensive.

Ball joints also offer a very small contact surface. This contact surface is also reduced in the area of the main pulling direction of the screw due to the conical hole in the ball wall of the intermediate piece. Ball joints generally have the disadvantage that they do not allow a press fit in the sense of a conical clamping. The fixation of this ball joint therefore remains uncertain even after the operation has been completed.

[0008] In addition, the intermediate piece must be correctly positioned in every respect before it can be fixed. In particular, rotation around the alignment axis, namely its own longitudinal axis, in order to rotate the eccentric cone into the desired position is only possible if the angular position of the intermediate piece is also unstable. The intermediate piece can be accidentally adjusted when removing the manipulation head, inserting the screw, tightening the screw and adjusting and fitting the head cap.

[0009] Finding the correct rotational position of the intermediate piece, in which the two eccentric conical surfaces on the intermediate piece and the head cap interact in such a way that the head cap comes to rest in the desired position, is very difficult. In practice, the eccentricity of the conical surface on the intermediate piece is therefore directed with the help of a manipulation head in such a way that the conical axis

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as close as possible to the axis estimated to be optimal and then the calotte is placed on top. However, the alignment of the calotte center in the anterior/posterior direction is always inevitably associated with a cranial or caudal shift.

[0010] It is therefore the object of the invention to propose an endoprosthesis for a shoulder joint in which the advantages of the cited prior art are retained and the disadvantages mentioned are avoided. In particular, the largest possible friction surface should be achieved between the individual parts that can be moved and rotated relative to one another. Furthermore, it should be possible to set the direction and position of the joint axis independently of one another. The adjustment of the direction and position of the spherical axis should be simplified compared to the prior art. The sensitivity of the settings of the axis direction with regard to inclination and rotation to unintentional changes in the inclination or rotation position by adjusting the other setting should be minimized as far as possible. The direction of the axis should also be as uninfluenceable as possible by changing the position of the spherical axis in relation to the position of the longitudinal axis of the intermediate piece or straightening piece.

[0011] This object is achieved in that a rotating piece is arranged between the shaft part and the straightening piece, which can be rotated about a first axis relative to the shaft part, and in that the straightening piece is mounted so as to be rotatable about a second axis with respect to the rotating piece, which second axis runs transversely to the first axis and transversely to the straightening axis, wherein contact surfaces between the shaft part and the rotating piece, or between the rotating piece and the straightening piece, each only allow a relative movement between the shaft part and the rotating piece, or between the rotating piece and the straightening piece, about the respective common first or second axis as the center of rotation.

[0012] By separating the swivel movement of the straightening piece into two swivel movements around two crossing axes, the entire range of motion offered by a ball joint is retained, but compared to a ball joint, the risk of unintentionally changing a swivel position with respect to one axis by swiveling around the other axis is significantly reduced. The articulation and friction surfaces between the shaft part, the swivel piece and

The surfaces of the guide pieces are not spherical, but surfaces of axial · ··_ ···· .·· ·· : : .:

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Rotational bodies, e.g. cylinders, toruses, cones, to name just the simplest, whose surfaces are easier to manufacture precisely. The contact surfaces can therefore be designed to be larger than spherical surfaces. A press fit is also possible by providing conical sections in the articulation surface. In addition to the alignment of the first axis parallel to the neck axis, it is also possible to choose the first axis approximately perpendicular to the neck axis or the alignment axis and the second axis approximately perpendicular to these two. The rotation position can then be adjusted around one of the axes and the inclination position around the other.

[0013] At least one eccentric ring or one slotted ring is advantageously provided between the straightening piece and the head cap. This ring allows the position of the cap or the distance between the straightening axis and the center of the cap to be changed and fixed. This allows the direction and amount of the distance between the straightening axis and the cap axis or the center of the head cap to be selected. In this way, a shift in the second axis resulting from a pivoting about the first axis can also be compensated. Therefore, the first and second axes do not have to intersect at one point.

[0014] In a simplified embodiment, the dome can be directly attached to the

The recess with which it is placed on the straightening piece can be incorporated into the calotte centrally or eccentrically. The calotte does not have to have a spherical surface, but can have a design that differs from this idealized articulation surface.

[0015] Conveniently, the straightening piece has an outer cylindrical or conical surface, the centre of rotation of which is the longitudinal axis of the straightening piece, i.e.

is the alignment axis. The head cap, the eccentric ring or the slotted ring can be placed on this surface. The conical surface is preferred, on which these parts can be fixed to the alignment piece by pressing them on. For the slotted ring, which requires a locking device, e.g. grub screws, anyway, the surface can be cylindrical. Cylindrical surfaces in conjunction with locking devices, both for the slotted ring and for an eccentric ring, allow the distance between this ring and the shaft head to be selected, and consequently the distance between the center of the head cap of the cap arranged on it on the one hand and the shaft axis on the other.

[0016] Preferably, the alignment of the first axis corresponds to the alignment of a preselected neck axis. As a result, the rotating piece is mounted in the shaft part so that it can rotate about the neck axis and can be attached to the shaft part in a rotationally fixed manner using very simple means. By adjusting the straightening piece about the second axis relative to the rotating piece, hardly any forces are to be expected that can pivot the rotating piece about the first axis, at least in a narrower area around the middle position, since these two axes or pivoting directions are essentially perpendicular to each other. Since the first axis runs approximately parallel to the straightening axis, a fundamentally different manipulation is required for rotation about this first axis than for pivoting about the second axis, which is perpendicular to the straightening axis.

[0017] The rotating piece advantageously has a concave rotational body surface directed towards the straightening piece with the second axis as the rotation center. The rotating piece is expediently rotatable about the neck axis. Alternatively, however, the rotating piece has a convex rotational body surface directed towards the straightening piece with the second axis as the rotation center. In particular, a cylinder, torus or cone surface, but also more complicated rotational body surfaces, e.g. with steep conical side surfaces or multi-directionally curved surfaces, are conceivable, as are actual hinge joints with inserted axle bolts.

[0018] Even if the two axes do not have to intersect, the first axis intersects the second axis in one embodiment at a central point. This makes it possible to fix the two pivoting movements together with a common locking device. This locking device, which is preferably a screw that can be screwed into a threaded hole in the shaft part, and the straightening piece must have spherical contact surfaces, the centers of which coincide with the intersection point of the two axes, the central point, when screwed together.

[0019] Advantageously, there is a recess in the shaft part with a side wall, which side wall corresponds to a surface of rotation around the first axis or the neck axis. A rotating piece with an outline corresponding to the side wall is mounted therein so as to be rotatable about the first axis, which rotating piece has a linkage surface for the straightening piece in the form of a surface of rotation around the second axis. The side wall can be cylindrical, conical or with a thread.

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In any case, the rotary piece can be rotated by at least 360° before fixing. When fixing, in the case of a conical side wall, a conical clamping occurs on the side wall; in the case of a cylindrical side wall, the pressing takes place over the bottom surface of the recess or the rotary piece. In the case of a thread, the pressing also takes place over large areas, namely the thread flanks.

[0020] The straightening piece has a counter-shape corresponding to the straightening piece-side articulation surface of the rotating piece and an axial conical surface for attaching a conical surface of the head cap or an eccentric ring.

In this case, a threaded hole is advantageously provided in the shaft part and the straightening piece has an inner hole in which the head of a screw can be accommodated, as well as a hole for the screw shaft. The straightening piece with the screw can be screwed into the threaded hole through a hole in the rotating piece. The hole in the straightening piece for the screw shaft is designed as a slot which allows the screw shaft to move by ± 30° and whose width is adapted to the diameter of a threadless part of the screw shaft which interacts with the hole in order to prevent the straightening piece from moving sideways relative to the rotating piece.

[0021] In another embodiment, the two independent rotational movements about the first and second axes can also be individually fixed. This makes it easier to determine or fix the individual pivoting movements. This means that, for example, the rotation of the alignment axis with respect to the shaft axis can first be determined and fixed, in order to then determine and fix the inclination in a second step.

[0022] Where conditions permit, the head cap can have an inner conical surface that is eccentrically arranged with respect to the head cap instead of a centrally arranged one, which can be plugged onto the outer conical surface of the straightening piece or the eccentric ring. This allows the distance and direction between the center of the cap and the longitudinal axis of the straightening piece to be adjusted. The eccentricity of both the inner conical surface in the cap and the outer conical surface on the eccentric ring is not visible, but is covered by the cap. This makes it difficult to set the direction and distance precisely. Therefore, two eccentric rings that can be plugged together via conical surfaces are advantageously arranged between the head cap and the straightening piece, these allow the

Visual control of the position of the cone outlines in relation to each other and to the outline of the bone cutting surface, so that the eccentric rings can be centered in the center of the outline in order to subsequently place a cap with a centric cone surface on the second eccentric ring.

[0023] However, it is advantageous to use a manipulation head instead of a second eccentric ring. This has an inner conical surface that is eccentrically arranged with respect to the calotte axis, which can be plugged onto the outer conical surface of the eccentric ring and whose eccentricity corresponds to the eccentricity of the inner conical surface of the calotte. In addition, it is designed in such a ring-shaped manner that the eccentric ring is visible and adjustable through the eccentric ring opening of the manipulation head. This allows a visual comparison between the edge of the manipulation head and the edge of the bone cutting plane when adjusting the eccentric ring. Because the eccentricities of the calotte and manipulation head match, the optimal rotational position of the eccentric ring 5 can be easily determined by this comparison, the eccentric ring can be hammered or pressed onto the alignment piece and the calotte can be placed in its place in the same orientation as the manipulation head. Finding the optimal rotational position of the cap with the straightening piece and eccentric ring optimally aligned is then easy.

[0024] As an alternative to an eccentric ring between the straightening piece and the cap, it is also possible to provide an eccentric piece between the rotating piece and the shaft part. The eccentric piece can be fixed to the shaft part using an eyebolt, for example. The rotating piece and straightening piece would then have to be attached to the eccentric piece.

[0025] As an alternative to the double eccentric ring, an elongated hole ring can be provided which has an elongated hole with which it can be placed on the straightening piece. The ring has a locking device with which it can be fixed to the straightening piece in a selectable sliding and rotating position. The use of an elongated hole ring between the straightening piece and the head cap is independent of the pivoting device on the shaft part. An elongated hole ring can therefore also be used in a prosthesis according to the known state of the art.

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[0026] In a design of the straightening piece that is advantageous for production, its extension lies within a roller or cylinder piece with the radius of the convex articulation surface. This makes it possible to manufacture the straightening piece from a roller piece with this radius by machining the connecting part to the joint head with the inner bore out of the roller piece using cutting means.

[0027] In an alternative embodiment to the above, with a screw screwed into the shaft part, a bore concentric with the articulation surface between the rotating piece and the straightening piece is provided in the rotary piece and a cylindrical body is arranged in the bore. This body or head part is connected to a screw shaft, the wall between the bore and the articulation surface having a slot running transversely to the second axis through which the screw shaft extends. The straightening piece has a link disk and a pressure disk, the link disk having a bore for the screw shaft and an articulation surface corresponding to the articulation surface of the rotating piece, and on the opposite side a pressure surface that interacts with the pressure disk. The pressure disk is connected to the screw shaft. The connection between the pressure disk and the screw shaft ensures that by rotating the pressure body or the screw shaft, a relative rotation between the screw shaft and the cylindrical body and/or the pressure body results, thereby changing the distance between the cylindrical body and the pressure body. For this purpose, an internal thread is provided either in the cylindrical body or in the pressure body, or in both, which interacts with an external thread on the screw shaft. This allows the straightening piece and the rotating piece to be fixed to one another. Therefore, the rotating piece can in turn be fixed to the shaft part using a ring that can be screwed onto or into the shaft part, independently of the fixing of the straightening piece to the rotating piece.

[0028] In such an endoprosthesis for a shoulder joint, at least two of the following parts are advantageously assembled and at least temporarily attached to one another before the implantation of the prosthesis: shaft part, rotating piece including any head piece, straightening piece including any articulation and pressure disc, and screw, as well as any eccentric disc or slotted disc. These parts are secured against falling apart, for example, with coupling rings or tongues. This has the advantage that the surgeon does not have to deal with small parts that are difficult to handle.

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in the fingers. A practical combination from the range of possibilities is to provide the shaft part with the rotating piece secured to it and the straightening piece separately, possibly composed of a linkage and pressure disk, with an inserted screw or screw shaft. The rotating piece can also be combined with the straightening piece or all parts can be temporarily assembled.

[0029] The interacting concave and convex contact surfaces between the rotary piece and the straightening piece, between the straightening piece and the screw, or between the straightening piece and the articulation disk can correspond to one another in terms of geometry and size. However, they can also correspond only in such a way that a line contact takes place between the contact surfaces. For this purpose, for example, the articulation surface on the rotary piece is designed as a groove with two flat surfaces at an angle to one another. The hole in the straightening piece into which the screw is inserted does not have a hemispherical cavity, but rather a conical hole, or one or more circular edges along approximately the same geometric spherical surface. The articulation disk, in turn, is equipped with two flat surfaces at an angle to one another, corresponding to the rotary piece. The contact surfaces can also have edges or mandrels that can be pressed into the counter surface when the screw is tightened. The advantage of line contact over surface contact is that the contact surfaces are pressed together while the material is deformed, making the connection very stable when the screw is tightened. The design of the concave contact surfaces in such a way that they only touch the convex contact surface in a line also has the advantage that the concave contact surfaces are very easy and inexpensive to manufacture.

[0030] The invention is explained in more detail below using examples shown schematically in the figures. It shows:

Figure 1: an exploded view with partially cut parts of a first embodiment,

Figure 2: a top view of a slotted ring,
Figure 3: a top view of an eccentric ring,
Figure 4: a bottom view and a side view of the straightening piece according to the one shown in Fig.

example shown,

Figure 5: a side view and a top view of the rotating piece according to the one in Fig. 1

example shown,
Figure 6: a schematic section through a second embodiment in assembled state,
Figure 7: a schematic section through a third embodiment, with indication of the humerus, with flat contact surfaces on the articulation disc.

[0031] The first embodiment according to Figures 1 to 5 has a shaft part 11 with a shaft stem 13 along a shaft axis 15 and a shaft head 17. A device 19 for inserting the shaft stem 13 into the bone is provided on the shaft head 17. This also serves to remove it from the bone. Furthermore, a rib 21 with holes 23 is provided on the shaft head 17. Soft tissue can be attached to this rib 21 or to the holes 23. Furthermore, a concave, frustoconical articulation surface 25 is provided on the shaft head 17, the axis 27 of which is parallel to the neck axis, here at an angle of 135° to the shaft axis 15 and is referred to below as the first axis. Axially to this first axis 27, a hole 31 with an internal thread is provided in the base 29 of the articulation surface 25.

[0032] A rotary piece 33 can be inserted into the concave recess of the articulation surface 25 on the shaft part 11 (see also Figure 5). The rotary piece 33 is a conical disk or a truncated cone with an inclination of the conical surface 34 which corresponds to the inclination of the conical surface of the articulation surface 25. On the side of the truncated cone base surface, the rotary piece 33 has a cylindrical recess 35 with a second axis 37 transverse to the first axis 27. A bore 39 is provided in the rotary piece 33 axially to the first axis 27.

[0033] The guide piece 41 fits into the recess 35 (see also Figure 4).

This has a cylindrical articulation surface 43 which is curved to match the cylindrical surface 35 of the recess. The axes of the corresponding surfaces coincide in the assembled state, which is why the axis of the articulation surface 43 on the straightening piece 41 is designated with the reference number 37'.

Furthermore, a connecting part 44 with a truncated cone or conical surface 45 is provided on the straightening piece 41. The axis 46 of the connecting part 44 and the conical surface 45 is perpendicular to the axis 37' of the articulation surface 43. The joint head of the prosthesis can be placed on this connecting part 44 from the side facing away from the articulation surface 43. The straightening piece 41 has an axial bore

47 with a hemispherical bore bottom 49 from the joint head side and a conical elongated hole 51 through the articulation surface 43. The longitudinal direction of the elongated hole 51 is perpendicular to the axial direction of the articulation surface 43, the conical formation of the elongated hole 51 only exists at its ends.

[0034] Shaft part 11, rotary piece 33 and straightening piece 41 can be joined together with the corresponding fittings, articulation surface 25 on the shaft part and truncated cone with conical shell 34 on the rotary piece 33 on the one hand, and cylindrical recess surface 35 on the rotary piece and articulation surface 43 on the straightening piece 41 on the other hand, and can be screwed together with a screw 53. The screw 53 has a shaft 55 with a threaded section 57 and a smooth shaft part 59, as well as a spherical screw head 61. The spherical radius of the screw head corresponds to the spherical radius of the spherical bore base 49 of the straightening piece 41. The straightening piece 41 is machined from a roller piece 52. The radius of the roller piece is the radius of the articulation surface 43.

[0035] If the shaft part 11 and the straightening piece 41 are now to be assembled, the rotating piece 33 is first inserted with the cylindrical recess facing outwards into the truncated cone-shaped articulation surface 25 in the shaft part 11 and then the straightening piece 41 with its cylindrical articulation surface 43 is inserted into the cylindrical surface 35 of the recess. The screw 53 is then inserted with the shaft 55 first into the bore 47 and the screw shaft 55 is pushed through the elongated hole 51 in the straightening piece and the bore 39 in the rotating piece 33 and screwed into the thread in the bore 31 in the shaft part 11. If the screw is firmly tightened, the axes 37 and 37' coincide and the center of the spherical screw head 61 lies at the intersection point of the axes 37, 37' with the first axis 27.

[0036] If the screw 53 is not tightened, then on the one hand the rotary piece 33 can be rotated about the first axis 27 in the shaft part, whereby the direction of the second axis 37 can be selected, and on the other hand the straightening piece 41 can be pivoted about the second axis 37 in the rotary piece 33. By superimposing these two rotation and pivoting movements, the straightening axis 46 can be adjusted in all directions at a selectable angle to the preselected neck axis, which in this embodiment corresponds to the first axis 27. The angle between the first axis 27 and the straightening axis 46 can be selected between 0 and about 30 degrees. The angle with respect to the

Rotation of the rotating piece around the first axis 27 can be selected between 0 and 360 degrees.

[0037] To ensure that the surgeon has the parts that are as handy as possible, small parts are preferably assembled and connected to one another before they are implanted. For example, the rotating piece 33 can be inserted into the shaft part 11 and fixed or secured there. The screw 53 can be inserted into the aligning piece 41 and secured there. The screw 53, the aligning piece 41 and the rotating piece 33 can also be assembled and temporarily connected to one another in preparation. Other ways of reducing the number of parts to be assembled during the operation and of combining the small parts are to assemble the aligning piece 41 and the rotating piece 33 beforehand, or to assemble the aligning piece 41, rotating piece 33 and shaft part 11 with or without the screw 53. The screw 53 can be loosely tightened or in a provisional position of the aligning piece 41. In the other embodiments, analogous combinations of the parts are useful.

[0038] The joint prosthesis head can be placed on the guide piece 41, which is directed in the optimal direction of the joint neck and fixed in this position with the screw 51. In the embodiment according to Figure 1, the joint prosthesis head consists of an eccentric ring 63 and a head cap 65 with a radius that approximately corresponds to the original articulation surface of the shoulder joint to be replaced. The eccentric ring 63 has two truncated cone surfaces that are aligned in the same direction and have parallel axes 46' and 67 that are spaced apart from one another (see also Figure 3). This eccentric ring 63 has an inner conical surface 69 arranged centrally around the axis 46", which is matched to the conical surface 45 on the straightening piece 41, and an outer conical surface 71 with the eccentric axis 67 as the center of rotation. The outer conical surface 71 of the eccentric ring 63 is matched to the conical surface 73 in the head cap 65.

[0039] The head cap 65 is advantageously a spherical section similar to the osteotomized joint ball section. The articulation surface 75 of the cap 65 lies in an idealized cap on a radius around its spherical center 77. The cap 65 has a flat underside 79 opposite the spherical surface 75. The plane of the underside 79 geometrically intersects the theoretical spherical surface in a circle. A spherical _axis 81 is determined by the center of this circle and the spherical _center J7j .

Eccentrically to the calotte axis 81, a conical recess is provided in the underside 79, the conical wall 73 of which is formed axially around the eccentric axis 67' and the depth of which is matched to the mass of the outer conical surface 71 of the eccentric ring 63. The spherical surface 75 of the calotte 65 is intended to cooperate with the natural articular surface of the glenoid or with an implanted glenoid part.

[0040] The joint head is placed on the straightening piece 41 by pressing the inner conical surface 69 of the eccentric ring 63 onto the conical surface 45 of the connecting part and pressing the cap with the recess 83 onto the outer conical surface 71 of the eccentric ring. The axes 46 and 46' coincide, as do the eccentric axes 67 and 67'. By rotating the eccentric ring about the straightening axis 46 and the cap about the eccentric axis 67, the direction and distance between the axes 46, 46' and 67/67' can be added to the direction and distance between the axes 67, 67' and 81 as vectors. Provided that the axis distances are the same , the spherical axis 81 can be arranged at a selectable distance from the longitudinal axis 46 of the straightening piece 41 between 0 and the sum of these axis distances. The spherical axis can also be brought into any rotational position between 0 and 360 degrees around the straightening axis 46 without rotating the straightening piece 41. As a result, the spherical axis 81 can be aligned exactly through the original joint ball center point after the direction of the straightening axis 46 has been fixed.

[0041] If the osteotomy is carried out in such a way that the bone cut is guided along the edge of the joint ball, the underside 79 of the calotte can be aligned parallel to the bone cutting plane by directing the guide piece 41 perpendicular to the bone cutting plane. The position of the calotte axis 81 can then be determined using the outline of the bone cut. The position of the sphere center must then be adjusted in a known manner using a set of head calottes 65 with different calotte heights based on muscle tension.

[0042] In Figure 2, an elongated hole ring 87 is shown. The elongated hole ring 87 can be used as an alternative to the eccentric ring 63. When using an elongated hole ring 87, it is not necessary to arrange the conical recess 83 in the dome bottom 79 eccentrically. Rather, it is advantageously arranged centrally. The elongated hole ring ₈₇ has an elongated hole ring 87, one of the

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conical depression 83 in the underside 79 of the cap 65 corresponding outer conical surface 71. If the conical depression 83 is expediently arranged centrally in the cap underside 79, the conical surface can also be shaped differently from a strict truncated cone surface, e.g. as a truncated pyramid. The slot ring has a slot 89 parallel to the eccentric axis 67", the longitudinal extent of which extends transversely to the eccentric axis 67". The slot 87 has two semi-cylindrical or two semi-truncated conical walls with two flat connecting surfaces. The center of one semi-curved wall lies on the eccentric axis 67", the center of the other at a selected distance from it.

[0043] The elongated hole can be conical if the straightening piece 41 to be inserted into the elongated hole has a cone 45. The straightening piece 41 can also have a cylindrical connecting part 44. However, this requires locking means in the eccentric ring 63 or in the elongated hole ring 87. Locking means, in particular two grub screws 91, are arranged in the elongated hole ring 87. One is directed perpendicular to the longitudinal direction of the elongated hole to the center of one semi-arch wall, the other to that of the other. This allows a connecting part 44 of the straightening piece 41 inserted into the elongated hole 89 to be fixed in a selectable rotational position and displacement position in the elongated hole.

[0044] Figures 3 to 5 are described above in connection with the embodiment according to Figure 1. Two further embodiments are shown in Figures 6 and 7. The corresponding parts are designated with the same reference numerals, even if the parts sometimes have significantly different shapes.

[0045] The schematic section according to Figure 6 shows a second embodiment in which, as in the first example, the first axis 27 corresponds to the middle neck axis and the first axis 27 and the second axis 37 intersect at a point which, after the implantation of the shaft in the humeral bone 86, lies as far as possible in the bone cutting plane 103 of the severed joint ball. In this embodiment, however, the rotating piece 33 has a convex cylindrical surface 35. The rotating piece 33 can also be fixed to the shaft part 11 independently of the fixation of the tilting movement of the straightening piece 41 with respect to the rotating piece 33. The following construction is provided for this purpose:

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[0046] In the shaft part 11, in particular in the shaft head 17, a cylindrical recess 25 is provided, the cylinder axis 27, which is the first axis, is aligned approximately with the natural neck axis. This recess 25 is provided with a thread. In this recess 25, the rotating piece 33 is arranged so as to be rotatable about the first axis 27. The rotating piece 33 has a base 87 with a circular edge 89, which edge 89 protrudes laterally beyond a semi-cylindrical bulge. This bulge is the articulation surface 35' for the straightening piece 41. This edge 89 works together with an eyebolt 91 screwed into the thread in the recess 25 in such a way that by tightening the eyebolt 91, the edge 89 is pressed against the bottom 29 of the recess 25. The rotating piece 33 is thereby fixed in the recess 25. The axis 37 of the semi-cylindrical bulge 35, i.e. the second axis, runs perpendicularly through the first axis. A bore 93 is provided in the rotating piece 33, concentric with the bulge surface 35. A cylindrical body 95, which fills the diameter of the bore, is inserted into the bore 93. This body or head part 95 can be rotated about the axis 37 in the bore. A screw shaft 55 is connected to the head part 95. The screw shaft is perpendicular to the second axis 37. In Figure 6, the screw shaft 55 is even aligned with the central neck axis. The screw shaft 55 pierces the wall between the bore 93 and the articulation surface 35'. For this purpose, a conical elongated hole 51' is provided in this wall on the rotating piece 33. The longitudinal direction of the elongated hole 51' is perpendicular to the axial direction of the articulation surface 35", the conical design of the elongated hole 51' only exists at its ends. The elongated hole allows the head part 95 to be rotated together with the screw shaft 55 about the second axis 37.

[0047] A link disk 97 and a pressure disk 99, which takes on the role of the connecting part 44, are placed on the screw shaft 55. The link disk 97 and the pressure disk 99 together form the straightening piece 41, which can be pivoted about both the first and the second axis. The link disk 97 has a circular outline with the axis 46 and has a concave cylinder surface 43' on one side corresponding to the link surface 35' on the rotating piece, and on the opposite surface a pressure surface onto which the pressure disk 99 can press flatly. Axially, a bore is formed in the link disk 97, through which the screw shaft 55 fits. The pressure disk 99 has a

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circular outline with the axis 46. A threaded hole is formed axially, with which the pressure disk 99 can be screwed onto the screw shaft 55. The pressure disk 99 can alternatively also be firmly connected to the screw shaft 55, which, however, requires a threaded connection between the screw shaft and the head part 95.

[0048] However, this threaded connection between the head part 95 and the screw shaft 55 is also advantageous in other ways because it allows the head part 95 to be first fixed in the rotating piece 33 before the straightening piece 41 is arranged on the screw shaft 55. By tightening the screw shaft in the head part 95, this can be easily clamped to the rotating piece. However, if a point 101 is formed on the shaft part or head part side of the screw shaft 55, this drills into the rotating piece 33 when the screw is tightened, so that the straightening piece is reliably prevented from rotating about the second axis 37.

[0049] Alternatively, the rotary piece 33 can be designed such that the bore 93 is open towards the shaft part 11 and only encompasses the head part 95 on the side of the aligning piece 41, but leaves it free towards the bottom 29 of the recess 25 in the shaft part 11. The head part 95 then sits, for example, in a slot formed parallel to the second axis 37 with the width and height of the head piece 95 and a semi-cylindrical slot base. This allows the screw shaft tip to be pressed into the base 29. The base can have a concave spherical surface in this area with the center at the intersection point of the first and second axes, so that the tip 101 penetrates into the surface of the base 29 perpendicular to the latter. This also prevents the rotary piece from accidentally twisting about the first axis.

[0050] By screwing the connecting part 99 onto the screw shaft 55 or by screwing the screw shaft attached to the connecting part into the head part 95, the head part 95 and the articulation disk 97 are pulled together. This allows the straightening piece 41 to be fixed to the rotating piece 33 in any pivoting position.

[0051] The pressure disk 99 has an outer conical surface 45 on which an eccentric ring 63 is placed. The head cap 65 is seated on the eccentric ring 63. Due to the eccentricity of the eccentric axes 46', 67 and the axes 67' and 81 of the conical recess 83 on the cap 65 and the head cap 65, the

The spherical cap axis 81 can be arranged in a selectable direction and at a selectable distance with respect to the straightening axis 46 (eccentric axes 67, 67" are not shown). The straightening axis 46 can be pivoted in a selectable direction and by a selectable angle with respect to the first axis 27 (or the shaft axis 15). Alternatively, the eccentric ring can be omitted and the head cap can be placed directly on the conical surface of the straightening piece.

[0052] Thanks to this adjustability of the axes, in a first step the straightening axis 46 can be set perpendicular to the bone cutting surface 103 and the straightening piece and the rotating piece can be fixed in this position. In a second step, the position of the calotte axis 81 with respect to the straightening axis 46 can then be adjusted to the bone cutting outline and the calotte 65 can be hammered onto the straightening piece 41.

[0053] The third embodiment according to Figure 7 finally makes it clear that the first and second axes do not necessarily have to intersect at a common pivot point in or near the bone cutting plane 103. The axes 27 and 37 can run at right angles or oblique angles to each other and can be arranged at a distance from each other. In the third embodiment, the first axis 27 is not aligned according to the natural neck axis, but parallel to the shaft axis 15. As a result, the recess 25 in the shaft part 11, in which the rotating piece 33 is mounted and can be fixed, is aligned orthogonally to the shaft axis 15. The rotating piece 33 has a shaft-side pivot part 105 and a pivot part 107 on the straightening piece side. The straightening piece-side articulation part 107 is designed analogously to the cylindrical bulge 35' of the second embodiment and is provided with a convex articulation surface 35', but could also have a concave articulation surface 35, analogously to the first embodiment. Here too, a cylindrical head part 95 is arranged in a cylindrical bore concentric with the cylindrical articulation surface 35'. The screw shaft 55 is screwed into the head part 95 through an elongated hole 51' in the wall with the articulation surface 35'. The screw shaft 55 therefore has a freedom of pivoting corresponding to the length of the elongated hole 51'. As in the second embodiment, a articulation disk 97 and a pressure disk 99 are arranged on the screw shaft. The pressure disk 99 together with the articulation disk 97 form the straightening piece 41.

[0054] Alternatively, the straightening piece can be formed by the pressure disk 99 alone. In this case, the articulation disk 97 is expediently designed with a smaller diameter than the pressure disk 99. Two eccentric rings 63, 64 are seated on the straightening piece 41. The position of the spherical cap axis 81 can be adjusted using the two eccentric rings. The spherical cap 65 therefore has a recess 73 in its underside 79 which interacts with the second eccentric ring 64 and which is located centrally on the spherical cap axis 81. By rotating the eccentric rings 63, 64, the outer conical surface 71' of the outer eccentric ring 64 can be arranged relative to the outline of the bone cut in such a way that the spherical cap 65 sits optimally in relation to the position of the original articulation surface axis after being placed on the eccentric ring 64.

[0055] The rotation position is fixed by tightening the screw 111. The screw 111 is axial to the first axis 27 and forms the pivot axis for the rotating piece 33 relative to the shaft part 11. For this purpose, the rotating piece has an axial bore 113 in its shaft-side articulation part 105 through which the screw 111 extends into a threaded bore 115 in the shaft part 11. The fixation takes place through the pressure exerted by the screw head of the screw 111 on the shaft-side articulation part 105, or through the pressing together of the contact surfaces between the rotating piece 33 and the shaft part 11.

[0056] The articulation disk 97 is designed with a flat articulation surface 43". This enables the articulation disk and rotary piece to be pressed together with material deformation, whereby a very good hold can be achieved.

[0057] Thanks to the adjustability of the position of the calotte axis 81 with respect to the alignment axis 46, the calotte 65 is displaceable with respect to the humeral bone 86 or the outline of its cutting surface 103, as shown by the dotted line 109. This allows an approximate, imprecise implantation of the shaft part 11 in the bone 86 with respect to the desired position of the calotte 65, on the one hand, but also a displacement of the alignment axis 46 when adjusting the angle of the alignment axis 46 with respect to the shaft axis 15 or the rotational position of the alignment axis 46 with respect to the humeral bone 86.

[0058] By adjusting the rotational position of the straightening piece 41, the position of the passage point of the straightening axis 46 through the surface of the bone cut 103 is also shifted in the third embodiment. A rotation according to

anterior causes a shift of the passage point anteriorly. On the other hand, pivoting the alignment axis 46 cranially, i.e. anti-clockwise in Figure 7, causes a shift of the passage point of the alignment axis through the bone cutting plane 103 caudally, i.e. downwards to the right in Figure 7.

[0059] Thanks to the fact that a rotating piece 33 that can be rotated about a first axis 27 with respect to the shaft part 11 is articulated on the shaft part, and a straightening piece 41 is arranged on this rotating piece 33 so that it can pivot about a second axis 37, which second axis 37 is perpendicular to the first axis 27, it is possible to align the straightening piece with respect to the bone cutting plane 103 in all directions. Any resulting shifts in the point where the straightening axis 46 passes through the bone cutting plane 103 can be corrected at the same time as the adjustment of the cap axis 81 to the desired, individual position with respect to the bone cut or the original cap position is carried out. This allows all the necessary parameters to be set so that the head cap 65 can finally be placed in the optimal position corresponding to the original position.

[0060] The muscle tension is adjusted as usual by selecting a cap from a set of caps with different cap heights. However, it is also possible to set the final cap height by inserting a spacer disc 117 between the articulation disc 97 and the pressure disc 99. By using such spacers or pressure discs of different heights, which are cheaper to manufacture than head caps, it is no longer necessary to manufacture and provide a whole set of head caps with different cap heights. Furthermore, the central arrangement of the recess 73 in the underside 79 of the cap 65 also makes it possible to screw the cap 65 onto the outer eccentric ring 64 or the slotted ring 87 using a thread. This allows a continuous adjustment of the dome height, but requires a locking device, e.g. in the form of a lock nut which is first screwed onto the thread and which can be tightened against the underside 79 of the dome 65.

[0061] In summary, an endoprosthesis for a shoulder joint has a rotary piece 33 pivoted to a shaft part 11 about a first axis 27 and an axial straightening piece 41 pivoted to the rotary piece 33 about a second axis. The two pivot axes 27, 37 are transverse to each other and the second axis

37 is perpendicular to the axis 46 of the straightening piece 41. The head cap 65 is either arranged directly on the straightening piece 41, or an eccentric ring 63 or an elongated hole ring 87 is provided between the head cap 65 and the straightening piece 41, which carries the head cap 65. Two or more eccentric rings 63, 64 are also possible. The head cap 65 can each have a centric or eccentric conical surface 73. The direction of the first axis 27 can be selected relatively freely, i.e., for example, parallel to the shaft axis 15, approximately parallel to the central alignment of the straightening axis 46, approximately parallel to the plane of the bone cut, and in particular approximately perpendicular to the straightening axis 46 and the second axis 37.

Claims (25)

1. Endoprosthesis for a shoulder joint,
with a shaft part ( 11 ) which has an axial shaft stem ( 13 ) for implantation in the humerus ( 86 ) and a shaft head ( 17 ),
with an articulation surface ( 25 , 29 , 35 , 35 ') in the region of the shaft head ( 17 ), and an alignment piece ( 41 ) which is articulated to the articulation surface ( 25 , 29 , 35 , 35 ') and extends along an alignment axis ( 46 ), which can be pivoted in all directions with respect to the shaft part ( 11 ) and can be fixed in a selectable pivot position relative to the shaft part ( 11 ),
and a head cap ( 65 ) connectable to the shaft part ( 11 ) via the straightening piece ( 41 ), characterized in that
that a rotary piece ( 33 ) is arranged on the shaft part ( 11 ), which is rotatable relative to the shaft part ( 11 ) about a first axis ( 27 ),
that the straightening piece ( 41 ) is mounted so as to be rotatable about a second axis ( 37 ) with respect to the rotating piece ( 33 ),
that the second axis ( 37 ) runs transversely to the first axis ( 27 ) and transversely to the straightening axis ( 46 ),
and that articulation or contact surfaces ( 25 , 29 , 35 , 35 ', 43 , 43 ', 43 ") between the shaft part ( 11 ) and the rotary piece ( 33 ), or between the rotary piece ( 33 ) and the straightening piece ( 41 ), respectively, only permit a relative movement between the shaft part ( 11 ) and the rotary piece ( 33 ), or between the rotary piece ( 33 ) and the straightening piece ( 41 ), respectively, about the respective common first ( 27 ) or second ( 37 ) axis as the center of rotation. 2. Endoprosthesis according to claim 1, characterized by at least one eccentric ring ( 63 , 64 ) or elongated hole ring ( 87 ) independent of the straightening piece (41) between the straightening piece ( 41 ) and the head cap ( 65 ). 3. Endoprosthesis according to claim 1 or 2, characterized in that the straightening piece ( 41 ) has an outer conical or cylindrical surface ( 45 ), the center of rotation of which is the straightening axis ( 46 ), onto which conical or cylindrical surface ( 45 ) the head cap ( 65 ), the eccentric ring ( 63 , 64 ) or the elongated hole ring ( 87 ) can be plugged. 4. Endoprosthesis according to one of claims 1 to 3, characterized in that the rotary piece ( 33) which can be rotated about the first axis (27 ) with respect to the shaft part ( 11 ) has a concave axial rotation body surface ( 35 ) directed towards the directing piece ( 41 ) with the second axis ( 37 ) as the center of rotation. 5. Endoprosthesis according to one of claims 1 to 3, characterized in that the rotary piece ( 33 ) which can be rotated about the first axis with respect to the shaft part has a convex rotation body surface ( 35 ') directed towards the directing piece ( 41 ) with the second axis ( 37 ) as the center of rotation. 6. Endoprosthesis according to one of claims 1 to 5, characterized in that the first axis ( 27 ) intersects the second axis ( 37 ) at a central point. 7. Endoprosthesis according to one of claims 1 to 5, characterized in that the two axes ( 27 , 37 ) are spaced apart from one another. 8. Endoprosthesis according to one of claims 1 to 7, characterized in that the first axis ( 27 ) is transverse to the neck axis. 9. Endoprosthesis according to one of claims 1 to 7, characterized in that the first axis ( 27 ) is parallel to the neck axis. 10. Endoprosthesis according to one of claims 1 to 9, characterized in that the rotational movements about the first ( 27 ) and the second axis ( 37 ) can be individually fixed. 11. Endoprosthesis according to one of claims 1 to 9, characterized in that the rotational movements about the first ( 27 ) and the second axis ( 37 ) can be fixed together. 12. Endoprosthesis according to claim 2, possibly in conjunction with one of claims 3 to 11, in which a single eccentric ring ( 63 ) is used, characterized in that the head cap ( 65 ) has an inner conical surface ( 73 ) which is arranged eccentrically with respect to the cap axis ( 81 ) and which can be plugged onto the outer conical surface ( 71 ) of the eccentric ring ( 63 ). 13. Endoprosthesis according to claim 12, characterized by a manipulation head which has an inner conical surface ( 73 ) arranged eccentrically with respect to the cap axis ( 81 ), which can be plugged onto the outer conical surface ( 71 ) of the eccentric ring ( 63 ) and whose eccentricity corresponds to the eccentricity of the inner conical surface ( 73 ) of the cap, and which is designed in such a ring-shaped manner that the eccentric ring ( 63 ) is visible and adjustable through the ring opening of the manipulation head. 14. Endoprosthesis according to claim 2, possibly in conjunction with one of claims 3 to 11, characterized by an elongated hole ring ( 87 ) which has an elongated hole ( 89 ) with which it can be placed on a connecting part ( 44 ) of the straightening piece ( 41 ), and with a locking device ( 91 ) with which the elongated hole ring ( 87 ) can be fixed to the straightening piece ( 41 ) in any desired displacement and rotational position with respect to the latter. 15. Endoprosthesis according to claim 14, characterized in that the recess ( 73 ) in the head cap ( 65 ) which cooperates with the elongated hole ring ( 87 ) is arranged concentrically with the cap axis ( 81 ). 16. Endoprosthesis according to one of claims 1 to 13, characterized in that in the shaft part ( 11 ) there is a recess ( 25 ) with a side wall ( 25 ) which corresponds to a surface of rotation about the first axis ( 27 ), in which a rotary piece ( 33 ) with an outline corresponding to the side wall ( 25 ) is mounted so as to be rotatable about the first axis ( 27 ), which rotary piece ( 33 ) has an articulation surface ( 35 , 35 ') for the aligning piece ( 41 ) in the form of a surface of rotation about the second axis ( 37 ), the aligning piece ( 41 ) has a counter-shape ( 43 , 43 ') corresponding to this articulation surface and an axial conical surface ( 45 ) for attaching an inner conical surface ( 69 ) of the head cap ( 65 ) or an eccentric ring ( 63 ). 17. Endoprosthesis according to claim 16, characterized in that a threaded bore ( 31 ) is provided in the shaft part ( 11 ) and the aligning piece ( 41 ) has an inner bore ( 47 ) in which the head ( 61 ) of a screw ( 53 ) finds space, that the rotating piece ( 33 ) and the aligning piece ( 41 ) have a bore ( 39 , 51 ), and that the aligning piece ( 31 ) can be screwed into the threaded bore ( 31 ) with the screw ( 53 ) through the bores ( 39 , 51 ). 18. Endoprosthesis according to claim 17, characterized in that the bore ( 51 ) in the guide piece ( 41 ) for the screw shaft ( 55 ) is designed as a slot which allows a range of movement of the screw shaft ( 55 ) of ± 30° and whose width is adapted to the diameter of the screw shaft ( 55 ), in particular of a threadless part ( 59 ) thereof which cooperates with the bore ( 51 ). 19. Endoprosthesis according to one of claims 1 to 18, characterized in that the radius of the articulation surface ( 43 ) of the straightening piece ( 41 ) is selected to be so large that the entire straightening piece ( 41 ) including the connecting part ( 44 ) lies within a cylinder piece with this radius. 20. Endoprosthesis according to claim 5, possibly in conjunction with one of claims 6 to 19, characterized in that a bore ( 93 ) concentric with the articulation surface ( 35 ') about the second axis ( 37 ) is provided in the rotary piece (33), and that a cylindrical body ( 95 ) is arranged in the bore ( 93 ), which body ( 95 ) is connected to a screw shaft ( 55 ), the wall between the bore ( 93 ) and the articulation surface ( 35 ') has a slot ( 51 ') running transversely to the second axis ( 37 ), through which the screw shaft ( 55 ) extends, and that the aligning piece ( 41 ) has an articulation disk ( 97 ) and a pressure disk ( 99 ), wherein the articulation disk ( 97 ) has a bore for the screw shaft ( 55 ) and one of the Articulation surface ( 35 ') of the rotary piece ( 33 ) corresponding articulation surface ( 43 '), and on the side opposite this a pressure surface interacting with the pressure disk ( 99 ), and that the pressure disk ( 99 ) is connected to the screw shaft ( 55 ), wherein the distance between the cylindrical body ( 95 ) and the pressure disk ( 99 ) can be changed by a relative rotation between the screw shaft ( 55 ) and the cylindrical body ( 95 ) and/or the pressure disk ( 99 ). 21. Endoprosthesis according to one of claims 16 to 20, characterized in that the rotating piece ( 33 ) can be fixed to the shaft part ( 11 ) by means of a ring ( 91 ) that can be screwed onto or into the shaft part ( 11 ). 22. Endoprosthesis for a shoulder joint
with a shaft part ( 11 ) with an axial shaft stem ( 13 ) for implantation in the humerus ( 86 ) and a shaft head ( 17 ),
a linkage surface ( 25 , 29 , 35 , 35 ') in the region of the shaft head,
an axial guide piece ( 41 ) which can be pivoted to the articulation surface ( 25 , 29 , 35 , 35 ') and which can be pivoted in all directions with respect to the shaft part ( 11 ) and can be fixed in a selectable pivot position relative to the shaft part ( 11 ),
and a head cap ( 65 ) connectable to the straightening piece ( 41 ), characterized in that an elongated hole ring ( 87 ) is arranged between the head cap ( 65 ) and the straightening piece ( 41 ), which has an elongated hole ( 89 ) with which it can be placed on the straightening piece ( 41 ), and a locking device ( 91 ) with which the elongated hole ring ( 87 ) can be fixed to the straightening piece ( 41 ) in any desired displacement and rotational position with respect to the latter. 23. Endoprosthesis for a shoulder joint according to one of the preceding claims, characterized in that at least two of the following parts are assembled and at least provisionally fastened to one another before the implantation of the prosthesis: shaft part ( 11 ), rotating piece ( 33 ) including any head piece ( 95 ), straightening piece ( 41 ) including any articulation disk ( 97 ) and pressure disk ( 99 ), and screw ( 53 ), as well as any eccentric disk ( 63 ) or slotted disk ( 87 ). 24. Endoprosthesis according to one of the preceding claims, characterized in that one of the two contact surfaces ( 35 ', 43 ", 49 , 61 ) between the rotary piece ( 33 ) and the straightening piece ( 41 ), the rotary piece ( 33 ) and the articulation disk ( 97 ), or between the straightening piece ( 41 ) and the screw ( 53 ) anchored in the shaft part ( 11 ) is designed such that there is a linear contact between the contact surfaces ( 107 , 43 "). 25 Endoprosthesis according to one of claims 1 to 24, characterized in that both contact surfaces ( 35 , 35 ', 43 , 43 ', 49 , 61 ) between the rotating piece ( 33 ) and the aligning piece ( 41 ), the rotating piece ( 33 ) and the articulation disk ( 97 ), or between the aligning piece ( 41 ) and the screw ( 53 ) anchored in the shaft part ( 11 ) correspond to one another in geometry and size.