WO2014079753A1

WO2014079753A1 - Endoprosthetic head for a hip joint

Info

Publication number: WO2014079753A1
Application number: PCT/EP2013/073744
Authority: WO
Inventors: Christian Fabry; Hans-Georg Neumann; Ernst-Dieter Klinkenberg
Original assignee: Dot Gmbh
Priority date: 2012-11-23
Filing date: 2013-11-13
Publication date: 2014-05-30
Also published as: DE102012111365A1

Abstract

The invention relates to an endoprosthetic head for a hip joint with a hip head cup (16) which has a partly spherical inner bearing surface (28), a bearing sphere (20) which is provided to be connected to a hip stem, a plurality of spherical roller bodies (18) which are arranged between the inner bearing surface of the hip head cup and the bearing sphere, and a reception space (30) for further roller bodies. The minimum cross-sectional dimension of the reception space is noticeably larger than the diameter of the roller bodies, particularly larger than 1.5 times the diameter of the roller bodies.

Description

Hüftgelenkendoprothesenkopf

The invention relates to a Hüftgelenkendoprothesenkopf with a bearing element having a part-spherical inner bearing surface, a bearing ball which is intended to be connected to a hip stem, a plurality of spherical rolling elements, which are arranged between the inner bearing surface and the bearing ball and a receiving space for further rolling elements.

In the natural, healthy hip joint, the femoral head articulates in a pan-like structure of the pelvic bone (acetabulum). The joint surfaces of the articulation partners are covered with a hyaline cartilage layer, which ensures a pain-free and low-friction movement. Natural joint cartilage wear is the most common indication for hip replacement in addition to fractures, necrosis, and inflammation (see "The Swedish Hip Arthroplasty Register," Annual Report 2010. Dept of Orthopedics, Lund University Hospital, 2010, and Closhisy JC, Calvert G., et al. Tull F., McDonald D., Maloney WJ: "Reasons for revision hip surgery - a retrospective review", Clin. Orthop. Relat. Res. 2004; 188-92).

However, the hip replacement also wears out, so that replacement operations (revisions) of the endoprostheses become more and more important. Aseptic implant loosening is the main cause of a short residence time and the following necessary revision surgery, which, apart from fixation problems in the first postoperative months, is mainly due to tissue reactions as a result of material wear (particle disease) (see Harris WH: "Wear and Periprosthetic Osteolysis: The Problem, "Clin Orthop., 2001; 393: 66-70, and Kadoya Y., Kobayashi A., Ohashi H.," Weare and Osteolysis in Total Joint Replacements ", Acta Orthop., Scand.Suppl 1998; 278: 1 -16).

Based on the original prosthetic design according to Charnley (Charnley J.: "Surgery of the hip joint", Br. Med. J. 1960; i: 821-6) from the 60s, several design variants for the complete Hip replacement, which to this day preferably consists of the following prosthesis elements:

1 . a pan body,

2. a socket insert with an inner sliding surface for a hip ball, 3. a sliding ball (hip ball, ball bearing),

4. a shaft (hip stem).

The pan body is usually made of metal or ceramic and forms the positive connection of the endoprosthesis to the milled bone bearing of the pelvis. Furthermore, it serves as a receptacle for the usually made of polyethylene or ceramic socket insert, which represents the counter bearing for the sliding ball with its inner spherical sliding surface. The sliding ball is positively connected to the implant shaft, which is anchored in the prepared medullary cavity of the dissected femur. Due to the ligament and muscle apparatus, the hip ball is held in the basin-side slide bearing and grants an approximately physiological joint function.

An overview of the various types of endoprostheses is given in detail in Effenberger H., Imhof M .: "Implant Atlas" ISBN 3-9501520-0-8 Great efforts have been made to reduce the technical wear, in particular by means of modified sliding mating materials Ceramic polymer, ceramic-ceramic and metal-metal (femoral head - socket insert) material combinations have been favored In addition to material engineering efforts, a number of constructive implant design variants have been tested which should reduce wear and also reduce the risk of dislocation of the joint due to increased range of motion. In the 1970s, using the Bousquet principle, an endoprosthesis system with increased luxation security was presented, a PE shell being placed over a hip ball and articulated directly in the acetabulum or in a monolithic pan. In the majority of the movements, the articulation takes place in the inner sliding pairing between the hip ball and the PE shell. A special form of this design is the bicentric condyle. In contrast to the Bousquet design, the PE head shell and the hip ball do not share a common center of rotation. Instead, the center of rotation of the hip ball is shifted towards the hip-side pole of the PE shell. The distance between the centers of rotation causes a force on the PE shell, which thereby aligns itself in the direction of the force. In this arrangement of the shell and head, the PE shell can not tilt uncontrollably and wear unevenly in the following unfavorable position.

A further and substantial reduction of the problematic abrasion is possible only by a change of the bearing principle of sliding friction to rolling friction, for which one finds suggestions in the patent literature.

Solution proposals such as EP 0 481 855 and US 2006/0271200 show weaknesses in the design. Disclosed is a hip joint endoprosthesis with a rolling friction pairing. To return the rolling elements, a return is provided, which is separated only by a thin wall from the camp. On the one hand, the achievable range of movement for typical everyday movements is insufficient, so that dangerous impingement situations are to be expected for the implant. On the other hand, the specified Wälzkörperführung is problem-free only at low and axially directed forces. Investigations on contact forces in the hip joint showed, however, that the direction of the resulting joint force varies greatly depending on the activity (see Bergmann G .: HIP98, "Loading of the hip joints", Compact Disc, Free University Berlin 2001 and Fabry C, Herrmann S., Kaehler M., Klinkenberg E.- D., Woernle C, Bader R .: "Generation of physiological parameter sets for hip joint motions and loads during daily life activities for application in wear Simulators of the artificial hip joint", Med. Eng. Phys. 2012, in press). In addition, it should be noted that in most cases the socket body is positioned at 45 ° inclination with respect to the main force direction. Accordingly, the indicated thin-walled delimitation of the ball return space for acting forces, such as during stumbling, is greatly undersized. Any deformation of this boundary leads to a catastrophic failure of the whole implant. The fact that no rolling friction endoprostheses are used to date shows that the previous designs are biomechanically unqualified and not suitable for the patient.

The object of the invention is to provide a Hüftgelenkendoprothesenkopf, which granted an approximately physiological range of motion and guaranteed by low material abrasion a long service life with the highest possible reliability.

The solution to this problem is achieved in a Hüftgelenkendoprothesenkopf of the type mentioned fact that the minimum cross-sectional dimension of the receiving space is significantly larger than the diameter of the rolling elements, in particular greater than 1, 5 times the diameter of the rolling elements. By the invention it is avoided that the formation of a receiving space for the rolling elements takes place at the expense of functional reliability. Furthermore, a perfect Wälzkörperführung is ensured even with strong and not axially directed forces by the inventive design of the receiving space.

For example, the receiving space connects directly to the inner bearing surface of the femoral head shell, via which the load transfer between the femoral head shell and the bearing ball takes place, whereby unnecessary friction losses are avoided by longer distances of the rolling elements.

Preferably, the ratio of the cross-sectional dimensions of the receiving space to the diameter of the rolling elements in the range of 2: 1 to 3: 1. This ratio leads to a particularly high reliability, since jamming of the rolling elements and thus blocking the Wälzkörperumlaufs is avoided.

According to one embodiment, the receiving space adjacent to the inner bearing surface of the femoral head shell in the region of the inner equator of the bearing ball, whereby a maximum range of movement of the bearing element is achieved with low-friction storage. For example, the receiving space extends substantially on the side facing the opening of the femoral head shell side of the inner equator of the bearing element. By this arrangement it is achieved that the entire loaded area of Hüftgelenkendoprothesenkopfes for the rolling friction mating of inner bearing surface, rolling elements and bearing ball can be used and the inner bearing surface is not weakened by the "behind" (ie in an area through which the loading direction) arranged receiving space in their capacity.

According to a further embodiment of the invention, the receiving space is defined by the space between the bearing ball, the femoral head shell and a locking ring. As a result, a simple production of the receiving space is guaranteed. Preferably, the closure ring has a bearing surface designed in such a way for the neck of a hip stem that, in the case of contact, there is linear contact with the neck. In this way, damage to the hip stem and the locking ring is counteracted because the neck of the hip stem and the locking ring have the greatest possible flatness. In one embodiment of the invention, the bearing ball undergoes a battered contact by a bead on the edge of the receiving area of the hip stem such that their range of motion is limited, so that the rolling elements can not leave the space between the inner bearing surface and the bearing ball and the receiving space. This prevents the escape of rolling elements from the hip joint endoprosthesis head, which would impair its function.

According to a further embodiment, the closure ring is provided with transport openings for synovial fluid, so that the rolling elements can be lubricated in the contact area and in the receiving area by the synovial fluid.

In a further embodiment of the invention, the femoral head shell is designed as a bearing shell, which has a spherical outer bearing surface, which in turn is slidably mounted in a Hüftgelenkendoprothesenschale. This design of a second bearing increases the range of motion of the Hüftgelenkendoprothesenkopfes additionally.

Preferably, the centers of curvature of the ball bearing and the Hüftkopfschalenaußen are different, in particular that the Center of curvature of the bearing ball in the normal position closer to the surface of the part-spherical inner bearing surface is located as the center of curvature of the Hüftkopfschalenaußenfläche, and therefore when force is transmitted via the ball bearing an aligning moment for the Hüftkopfschale such that after resulting alignment, the centers of curvature of the ball bearing and the Hüftkopfschalenaußenseite the force line are located. In this way, the tilting of the femoral head shell is prevented in an extreme Varusposition.

Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings, to which reference is made. In the drawings show:

FIG. 1 shows an exploded view of a hip joint endoprosthesis with the hip joint endoprosthesis head according to the invention,

2 shows a cross section through the hip joint endoprosthesis head according to FIG. 1, and FIGS. 3a) and 3b) show cross sections of the hip joint endoprosthesis head according to FIG. 1.

1 shows a hip joint endoprosthesis 10 in an exploded view consisting of a hip socket 12 with an insert 14, the hip joint endoprosthesis head 16, 18, 20, 32 according to the invention and a hip stem 24. The hip joint endoprosthesis 10 consists of a cup-shaped acetabulum 12 which is equipped with a milled out bone bearing of the pelvis (not shown) is positively connected by pressing or screwing. In the cup-shaped acetabulum 12, a likewise cup-shaped insert 14 is received, in turn, a femoral head shell 16 engages positively as a bearing element. In this case, the insert 14 and the Hüftkopfschale 16 in sliding contact and thus form a sliding bearing.

By means of rolling elements 18, a bearing ball 20 is movably received in the femoral head shell 16 and is largely enclosed by this. The bearing ball 20 is held by a locking ring 22 which is attached to the femoral head shell 16 in the femoral head shell 16. On the bearing ball 20, one end of the hip stem 24 is fixedly mounted, with his the other side is anchored in a femur (not shown) of the patient. Thus, the femur is rotatably connected via the hip stem 24 and the bearing ball 20 in the femoral head shell 16 and thus - via the insert 14 and the acetabular cup 12 - movably connected to the pelvis. In Figure 2, the hip joint endoprosthesis 10 with the inventive

Hüftgelenkendoprothesenkopf 16, 18, 20, 32 shown as a cross section. It can be seen that the femoral head shell 16 has a cup-shaped outer contour, which is designed as a spherical bearing shell outer surface 26. The bearing shell outer surface 26 has a radius of curvature Ri. On its radially inner side, the femoral head shell 16 has a part-spherical inner bearing surface 28 with a radius of curvature R ₂ , see also FIG. 3a. The centers of curvature of the bearing shell outer surface 26 (Z _G ) and the inner bearing surface 28 (Z _R ) are not in the same point. Thus, the thickness of the femoral head shell 16 increases from its pole. The inner bearing surface 28 of the femoral head shell 16 extends from the pole of the femoral head shell 16 into the region of the equator of the radially inner contour of the femoral head shell 16. The inner bearing surface 28 immediately adjoins the receiving space 30. The receiving space 30 is formed from a recess in the femoral head shell 3 with an approximately semicircular cross-section and a region which extends radially between this recess and the bearing ball 20. The receiving space 30 extends parallel to the equator of the femoral head shell 16 along the entire inner circumference of the femoral head shell 16 and can thus be considered approximately as a torus about the ball bearing 20. In the femoral head shell 16, the bearing ball 20 is used with the radius of curvature R ₃ , so that their center of curvature coincides with the center of curvature Z _{R of} the inner bearing surface 28. In this arrangement, a bearing gap 32 is formed between the bearing ball 20 and the inner bearing surface 28. The bearing gap 32 is filled with a plurality of spherical rolling elements 18, wherein the radial width of the bearing gap 32 corresponds approximately to the diameter of the rolling elements 18. Also, the receiving space 30 is filled with rolling elements 18. The femoral head shell 16 and the bearing ball 20 thus form by means of the rolling elements 18 a rolling friction pairing. The degree of filling with Rolling elements is highly selected so that a free movement in the rolling friction pairing can take place.

The femoral head shell 16 is closed on its side remote from the acetabulum 12 by a locking ring 22. The closure ring 22 also simultaneously closes the bearing gap 32 so that the rolling elements 18 can not leave the bearing gap 32 and the receiving space 30. In addition, transport openings 34 for synovial fluid, which extend in the axial direction through the closure ring 22, are provided in the closure ring 22. The surface of the closure ring 22 facing away from the acetabulum 12 is made beveled towards its center in such a way that it provides a linear fit for the neck of the hip stem 24, in order to provide the largest possible contact surface in the case of contact.

The hip joint endoprosthesis head uses a rolling friction and a sliding friction pairing to realize the approximate range of movement of the natural hip joint, a nut joint. The femoral head shell 16 and the bearing ball 20 with the rolling elements 18 arranged between them form the rolling friction pairing, their center of rotation being the center of curvature Z _{R of} the ball bearing 20. The sliding friction mating is provided by the insert 1 and the femoral head shell 16 sliding therein. The center of rotation of this pairing is the center of curvature Z _{G of} the bearing shell outer surface 26.

Movements of the hip stem 24 are made possible by the rigidly connected to the hip stem 24 ball bearing 20 can rotate in the Hüftkopfschale 16 friction. For this purpose, the bearing ball 20 rolls on the rolling elements 18, which thereby move through the bearing gap 32. The rolling elements 18, which have arrived at the end of the bearing gap 32, are moved out of the bearing gap 32 through the bearing ball 20 into the receiving space 30. Since the volume of the receiving space 30 and the bearing gap 32 is almost completely filled with rolling elements 18, at the same time on the opposite side of the bearing ball 20 rolling elements 18 are forced out of the receiving space 30 in the bearing gap 32. In this way, a complete circulation of the rolling elements 18 is realized. This ensures that the bearing gap 32 is filled with movable rolling elements 18 at all times, so that a low-friction movement of the Bearing ball 20 in the femoral head shell 16 is made possible. The lubrication of the sliding friction pairing is effected by synovial fluid, which can pass through the transport openings 34 formed in the closure ring 22 into the bearing gap 32 and the receiving space 30. The movement of the bearing ball 20 and the hip stem 24 is interrupted only by the linear contact between the hip stem 24 and the locking ring 22 shown in FIG. Thus, this contact limits the range of motion of the rolling friction pairing.

Activities with significantly larger ranges of motion, which can not be satisfied by the rolling friction pairing, additionally require the freedom of movement of the sliding friction pairing. The operation of the sliding friction pairing is shown in Figures 3a) and 3b).

If the hip stem 24 is moved beyond the point where it comes into linear contact with the locking ring 22, the femoral head cup 16 is slid over the locking ring 22 from the hip stem 24 slidably in the acetabulum cup. As a result, the range of motion of the rolling friction pairing is supplemented by that of the sliding friction pairing.

In order to reduce the frequency of such a contact situation and to prevent tilting of the femoral head shell 16 in an extreme Varusposition, the staggered arrangement of the centers of rotation of the rolling friction pairing Z _R and the sliding friction pairing Z _{G is} utilized. Under load of the Hüftgelenkendoprothesenkopfes along the force line F, the distance of the Rotationszent Z _R , Z _G causes a torque M on the Hüftkopfschale 16. The torque M is directed from the pole of the femoral head shell 16 to the force line F and causes a rotation of the femoral head shell 16 in just this direction until the centers of rotation Z _R and Z _G have aligned along the line F of force. The hip joint endoprosthesis head has now, as seen in FIG. 3b), been transferred back to its starting position. Thus, his full range of motion for the rolling friction is available again.

Claims

claims

1 . A hip joint endoprosthesis head having a femoral head shell having a part spherical inner bearing surface, a bearing ball intended to be connected to a hip stem, a plurality of spherical rolling elements disposed between the inner bearing surface of the

Hüftkopfschale and the bearing ball are arranged, and a receiving space for further rolling elements, characterized in that the minimum cross-sectional dimension of the receiving space is appreciably larger than the diameter of the rolling elements, in particular greater than 1, 5 times the diameter of the rolling elements.

2. Hüftgelenkendoprothesenkopf according to claim 1, characterized in that the receiving space connects directly to the inner bearing surface of the femoral head shell, via which the load transfer by means of rolling elements between the femoral head shell and the ball bearing takes place.

3. Hüftgelenkendoprothesenkopf according to any one of the preceding claims, characterized in that the ratio of the cross-sectional dimensions of the receiving space to the diameter of the rolling elements in the range of 2: 1 to 3: 1.

4. Hüftgelenkendoprothesenkopf according to one of the preceding

Claims, characterized in that the receiving space adjacent to the inner bearing surface in the region of the inner equator of the femoral head shell.

5. Hüftgelenkendoprothesenkopf according to one of the preceding claims, characterized in that the receiving space is in

Substantially extends on the opening of the femoral head shell facing side of the inner equator of the femoral head shell.

6. Hüftgelenkendoprothesenkopf according to one of the preceding claims, characterized in that the receiving space between the bearing ball, the femoral head shell and a locking ring is defined.

7. Hüftgelenkendoprothesenkopf according to claim 6, characterized in that the closure ring has a support surface formed in such a manner for the neck of a hip stem, that in the contact case, a linear contact with the neck is given.

8. Hüftgelenkendoprothesenkopf according to claim 7, characterized in that the bearing ball by a bead at the edge of the receiving area of the hip stem experiences a abutting contact such that their range of motion is limited, so that rolling elements do not leave the space between the inner bearing surface and the bearing ball and the receiving space can.

9. Hüftgelenkendoprothesenkopf according to one of claims 6 to 8, characterized in that the closure ring is provided with transport openings for synovial fluid.

10. Hüftgelenkendoprothesenkopf according to any one of the preceding claims, characterized in that the bearing element is designed as a bearing shell having a spherical bearing shell outer surface, which in turn is slidably mounted in a Hüftgelenkendoprothesenschale.

1 1. Hüftgelenkendoprothesenkopf according to claim 10, characterized in that the centers of curvature of the bearing ball and the bearing shell outer surface of the femoral head shell are different, in particular that the center of curvature of the bearing ball in the normal position is closer to the part-spherical inner bearing surface than the center of curvature of the bearing shell outer surface, and therefore when force on the Bearing ball an aligning moment for the bearing element results in such that are after resulting alignment, the centers of curvature of the bearing ball and bearing shell outer surface, on the line of force.

12. Hüftgelenkendoprothesenkopf according to one of claims 6 to 8, characterized in that the closure ring is provided with transport openings for synovial fluid.

13. Hüftgelenkendoprothesenkopf according to claim 10, characterized in that the center of rotation of the formed between Huftgelenkendoprothesenschale and Hüftkopfschale pivot joint, based on the center of the ball bearing, on the side of the hip stem.