DE102004027659B4 - Hip endoprosthesis - Google Patents

Abstract

Hip endoprosthesis with a femoral component (1), one in a medullary cavity of a femur bone anchorable shaft (2) and a neck portion formed thereon (3) with a hip stem cone (4) for receiving a ceramic joint ball (5), wherein on an inner wall (7) of the joint ball (5) and / or on a Outer surface (13) of hip stem cone (4) a profiling (6) is formed, characterized in that between the inner wall (7) of the joint ball (5) and the outer surface (13) of the hip stem cone (4) a gap (14) is formed and the intermediate space (14) with a biocompatible plastic (15) is filled.

Description

The The invention relates to a hip joint endoprosthesis for the prosthetic restoration of the human or animal hip joint with a structure on the interacting surfaces of the Joint ball and the hip stem cone.

For example, is from the EP 0 385 572 B1 an adapter for use in assembling and securing a ceramic femoral head portion of a hip joint prosthesis and a femoral stem portion of the hip joint prosthesis. The adapter is conical and provided on an outer surface with a net-like structure of elevations and depressions, which should allow the fixation of the ceramic femoral head part on the thigh shaft part without buildup of voltage spikes.

A disadvantage of the EP 0 385 572 B1 known hip joint endoprosthesis is in particular the high cost in the manufacture of the adapter. Furthermore, although the adapter has a suitable surface for fixing, but the inner wall of the femoral head part is not designed adequately, so that no improvement in the fixation and no improvement in the load distribution is recorded.

For example, from the document DE 25 48 077 A1 a Gelenkendoprothese known, which has a thread-like or groove-like structure on a hip stem cone, while the joint ball has wave-like depressions in a conical recess.

Of the Space between the wave-like depressions and the thread-like or groove-like structure, however, remains in a compound of two components empty, which disadvantageously no satisfactory damping can be done.

From the publication DE 690 01 147 T1 shows an adapter sleeve for a hip stem cone, which serves to connect a ceramic ball joint with a metallic hip stem cone. The sleeve is placed on the hip stem cone and has a roughened surface to form a fit with the surface of a recess of the ball joint.

Also Here are the damping properties not satisfactory. In particular, here is the danger of a rapid fatigue break particularly strong, as the roughened surface only the non-positive connection the prosthesis components serves.

From the publication DE 698 15 417 T2 shows a frictional connection between a hip stem cone and a ball joint, which is achieved by irregular surface design of the corresponding surfaces of the respective components, which, however, also achieves insufficient damping effect.

Furthermore, from the CH 676 922 A5 a joint endoprosthesis with a cone-type connector between a ceramic and a metallic joint part, in which the cone-plug connection is displaced into a metallic intermediate sleeve, which is firmly pre-assembled in the ceramic joint part. Intraoperatively, only the second connector is then assembled.

A disadvantage of the CH 676 922 A5 Known articular endoprosthesis is in particular that a metallic intermediate sleeve is only inadequate to compensate for load peaks by deformations and circumferential forces in the region of the conical connector, which are caused by damage or contamination of the conical surfaces or by the wedging action of the hip stem cone.

Of the The invention is therefore based on the object, a hip joint endoprosthesis to create which is designed so that load peaks in the ceramic Joint ball can be compensated and thereby the possibility is offered to replace the joint ball, without a total operation necessary too do.

The The object is achieved by the features of claim 1 or claim 2 solved.

According to claim 1 is provided, which cooperates to form a plug connection surfaces the joint ball and / or the hip stem cone with to provide a profiling that provides a uniform load distribution and a Reduction of hoop stress over allows the scope of the joint ball.

According to claim 2 is provided, the corresponding surfaces having a surface structure to provide a frictional connection.

Further advantageous embodiments of the invention are characterized in the subclaims.

It is advantageous that the profiling is designed in the form of paragraphs, which absorb the pressure force on the joint ball and on the individual divide the areas of the paragraphs.

advantageously, the profiling of both components is identical and for example in the form of a fir tree-like, sawtooth or staircase-like Structure formed.

Farther is an advantage that a Gap between the profiles with a biocompatible Plastic such as a polymer is filled.

Farther is an advantage that the delicate collar of the ceramic joint ball by a supernatant the sleeve effective against damage can be protected during articulation of the thigh.

One embodiment The invention will be described below with reference to partially schematic representations closer in the drawing explained. In the drawing show:

1 a schematic view of an embodiment of an inventively designed hip joint endoprosthesis, and

2A C different enlarged views and sections of the inventively designed joint ball of the hip joint endoprosthesis according to 1 ,

1 shows a schematic representation of a view of a femoral component 1 for a hip joint endoprosthesis. The hip joint endoprosthesis shown in the embodiment is a total hip joint endoprosthesis, when both the femoral and the pelvic joint portion is replaced. The femoral component 1 has a shaft 2 which, in the medullary cavity of a femur, depending on the design of the femoral component 1 cemented or anchored cementless. On the shaft 2 is a neck part 3 formed at the end of a hip stem cone 4 for receiving a joint ball 5 is trained.

The measures according to the invention described in more detail below are independent of the shape of the shank 2 as well as in combination with a joint socket (not shown) or with a prosthesis head system articulating directly in the socket. The shape of the socket is arbitrary. Also the shape of the neck 3 is freely selectable.

For the sliding pairings between the joint ball 5 and the socket can be used various materials. This may be, for example, PE with a metal alloy such as CoCr or with ceramic, but this pairing has the disadvantage of heavy abrasion and associated creeping deterioration due to inclusions of the abrasion in the pan background and thus the loosening of the pan. Pairings of two metallic components are also not uncritical, since the abrasion and the subsequent heavy ion diffusion into the body lead to increased heavy metal values in the blood picture and in addition, especially in the case of nickel, can cause allergenic effects.

On the other hand, two ceramic plain bearings show very low abrasion, which is also bioinert, and enable high-precision surface treatment in the nano range. The use of joint balls 5 made of ceramic has therefore prevailed thanks to the good tribological properties in hip arthroplasty. The disadvantage here, however, the risk of sudden damage due to breakage of the joint ball 5 because the load capacity of ceramic on tensile stresses is poor.

Tensile stresses can already be caused by deformations of the hip stem cone 4 arise, which lie in the micrometer range. If the hip stem cone 4 before putting on a joint ball 5 made of ceramic is not free of particles (bones, blood, fat, soft tissue etc.) or the surface of the hip stem cone 4 not or no longer complies with the specifications, in the ball joint 5 unwanted tensile stresses occur and locally lead to voltage spikes, leading to fracture of the joint ball 5 being able to lead. It should be noted that this is not a dynamic process, for example, in strong punctual loads during exercise or the like, but a resulting from permanent static load damage pattern by the hoop stresses.

A conical connector brings high radial loads into the system. The reason for this is the wedge effect of the hip stem cone 4 which results in a circumferential expansion in the ceramic joint ball 5 leads. The resulting tensile forces and tensile stresses in the circumferential direction are already very high, now comes even a notch effect, for example by contamination or damage to the hip stem cone 4 In addition, the risk of destruction of the joint ball increases 5 strong.

Therefore, in the revision of the joint ball 5 in which the shaft 2 could remain in situ, the choice does not return to a joint ball 5 made of ceramic, as the hip stem cone 4 by removing the joint ball 5 may have been damaged and has a cone geometry different from the original geometry, resulting in the above problems analogous to contamination can lead.

Safety against damage through breakage of the joint ball 5 due to deviating geometry of the hip stem cone 4 can thus ensure only a total operation, in which not only the joint ball 5 but the entire femoral component 1 is replaced, but this has serious disadvantages. On the one hand is the shaft 2 often well integrated into the femur bone and can be removed only with great effort, which also lost bone tissue of the femur. Furthermore, the duration of surgery for a total operation is considerably longer than when replacing the joint ball 5 , In addition, the tissue section required for a total operation is larger and therefore the postoperative risk of infection is higher and the probability of the formation of scarring higher.

Object of the present invention is therefore, the joint ball 5 be designed so that the ceramic parts of the hip joint endoprosthesis are revisable, whereby a total surgery is unnecessary and a new ceramic ball joint 5 on the existing shaft 2 can be put on.

This can be made possible by the stresses in the joint ball 5 evenly over the entire available outer surface 13 of the hip stem cone 4 On the one hand, no local stress peaks with subsequent cracking can occur and, on the other hand, the circumferential stresses themselves can be reduced.

This can be achieved in two ways: first, it is possible to reduce the hoop stresses by placing them in a collar area 16 the joint ball 5 adjacent forces are distributed over the entire surface of the involved joint parts, which is made possible by a profiling of the surfaces.

Furthermore, the same effect can be achieved by the hip stem cone 4 is designed so that its depth of penetration into the joint ball 5 by a suitable surface design of the corresponding surfaces of the hip stem cone 4 and / or the joint ball 5 is limited by friction and thus the wedging action of the hip stem cone 4 and the resulting hoop stress can be reduced.

According to the invention is therefore provided according to the first possibility, as in 2A to 2C shown enlarged in different views, both in the ceramic ball joint 5 as well as on the hip stem cone 4 a profiling 6 to install, which a uniform load bearing of the compressive forces by the ball joint 5 allows and thus the risk of fracture of the joint ball 5 reduced.

The starting point for the calculation is the conical force transmission from the hip stem cone 4 in the joint ball 5 according to F H = η · F e / tanα where FE denotes the substantially axially acting joint force to be transmitted, F _H denotes the force acting essentially radially as a direct cause of the circumferential force and η the efficiency. The wedge effect is through the hip stem cone 4 given with a slope of 1:10, resulting in tanα ≈ 0.1. This means that in an ideal system with an efficiency of η = 1, the radial force F _{H is} ten times greater than the joint force F _E actually to be transmitted. Since the angle α of the hip stem cone 4 is predetermined, the reduction of the radial force F _H via a reduction of the efficiency η, ie the friction achieved and thereby the introduction of force can be reduced. This is achieved by having a macrostructured surface either in the micrometer or millimeter range, so that η <1.

How out 2 B visible, is the profiling 6 , which is located on the order of magnitude in the millimeter range, both on an inner wall 7 the joint ball 5 as well as on an outer surface 8th one on the hip stem cone 4 attached sleeve 9 educated. Alternatively, the sleeve 9 also omitted and the profiling 6 directly on an outer surface 13 of the hip stem cone 4 be educated. The following is the in 2 B illustrated embodiment with the sleeve 9 but the invention is not limited thereto.

In the former case should be between the hip stem cone 4 and the sleeve 9 a high coefficient of friction prevail, which is due to the outer surface 13 of the hip stem cone 4 for example, by a turning depth 17 or a roughness radiation can be influenced and to a frictional connection between hip stem cone 4 and sleeve 9 leads. This structuring in the micrometer range mainly causes the increase in friction to improve the frictional engagement between the hip stem cone 4 and the ball of the ball 5 respectively. in the joint ball 5 inserted sleeve 9 and thus serves to reduce the circumferential stresses by reducing the penetration depth of the hip stem cone 4 in the joint ball 5 ,

This embodiment is also based on a hip joint endoprosthesis 1 without sleeve 9 apply, in this case, the inner wall 7 the joint ball 5 and the outer surface 13 of the hip Community cone 4 Roughened and / or with a turning depth 17 Mistake.

If you look at 2C , it can be seen that the profiling 6 formed in the embodiment staircase-like. This creates heels 10 which is substantially perpendicular to the inner wall 7 the joint ball 5 or the outer surface 8th the sleeve 9 are formed or their surface normal substantially parallel to the outer surface 8th and the inner wall 7 are oriented. The paragraphs 10 on the inner wall 7 and on the outside surface 8th the sleeve 9 stand opposite each other, the paragraphs 10 on the inner wall 7 are thus in the opening direction of the joint ball 5 directed while the heels 10 the outer surface 8th the sleeve 9 are oriented opposite.

The profiling 6 can assume, for example, a fir-tree-like, sawtooth or staircase-like structure. The profiling 6 the joint ball 5 and the sleeve 9 or the hip stem cone 4 are in each case the same shape, ie a staircase-shaped profiling 6 one component is also formed on the other component, the profiling 6 the other component is identical.

This arrangement causes one on the ball joint 5 exerted compressive force in 2A is denoted by F and acts in the direction of the arrow, is divided into partial forces F ', which are each directed parallel to the original force F and the paragraphs 10 on the inner wall 7 the joint ball 5 on the heels 10 on the outside surface 8th the sleeve 9 act and be reduced in terms of amount. The extent of the reduction of the forces F 'depends on the number and the area of the paragraphs 10 from. Overall, the paragraphs should 10 be designed so that the resultant force F ', which in the region of a collar 11 the ceramic joint ball 5 acts, much smaller than the original force F, so that the stresses in this area kept small and the risk of cracking can be minimized.

Is the sleeve 9 with a profiling 6 provided, it is appropriate, the sleeve 9 in the form of a conical or cup-shaped sleeve 9 form a floor 12 having. The sleeve 9 lies completely on the outer surface 13 of the hip stem cone 4 at.

Alternatively, the profiling 6 also directly on the outer surface 13 of the hip stem cone 4 be formed, the above considerations for force application then apply analogously.

Between the profiling 6 the sleeve 9 and those on the inner wall 7 the joint ball 5 or between the profiling 6 of the hip stem cone 4 and those on the inner wall 7 the joint ball 5 is a gap 14 formed, in which for elastic transmission of the force F with a biocompatible plastic such as a polymer, for example, polyester (PE) or polyetheretherketone (PEEK) is inserted.

If the profiling 6 directly on the hip stem cone 4 is appropriate, it is appropriate to the plastic before the operation in the form of a layer on one of the two profilings 6 apply or insert in the form of a sleeve-like insert. In case of using the sleeve 9 This can also be preoperatively in the joint ball 5 inserted and then the gap 14 with the plastic 15 be filled or injected. During the operation then only the connector between the sleeve 9 and the hip stem cone 4 getting produced.

In an advantageous embodiment variant, the sleeve 9 as in the 1 and 2A to 2C shown, a collar-like projection 16 on which is axially formed so long that he the collar 11 the joint ball 5 surmounted axially. This allows the collar 11 the ceramic joint ball 5 in addition to the articulation of the thigh from damage by the biting neck 3 be protected, a burden, which also leads to cracks and subsequently to the fracture of the ceramic joint ball 5 can lead.

The invention is not limited to the illustrated embodiment and also to other forms of femoral components 1 applicable. In particular, all features of the invention can be combined with each other as desired.

Claims (13)

Hip joint endoprosthesis with a femoral component ( 1 ), which can be anchored in a medullary cavity of a femur ( 2 ) and a neck area formed thereon ( 3 ) with a hip stem cone ( 4 ) for receiving a ceramic joint ball ( 5 ), wherein on an inner wall ( 7 ) of the joint ball ( 5 ) and / or on an outer surface ( 13 ) of the hip stem cone ( 4 ) a profiling ( 6 ), characterized in that between the inner wall ( 7 ) of the joint ball ( 5 ) and the outer surface ( 13 ) of the hip stem cone ( 4 ) a gap ( 14 ) is formed and the gap ( 14 ) with a biocompatible plastic ( 15 ) is filled. Hip joint endoprosthesis with a femoral component ( 1 ), which can be anchored in a medullary cavity of a femur ( 2 ) and a neck area formed thereon ( 3 ) with a hip cone cone ( 4 ) for receiving a ceramic joint ball ( 5 ), wherein on an inner wall ( 7 ) of the joint ball ( 5 ) and on an outer surface ( 8th ) one on the hip stem cone ( 4 ) attachable sleeve ( 9 ) a profiling ( 6 ) is formed, and wherein between the inner wall ( 7 ) of the joint ball ( 5 ) and the outer surface ( 8th ) of the sleeve ( 9 ) and / or between the inner wall of the sleeve ( 9 ) and the outer surface ( 13 ) of the hip stem cone ( 4 ) a gap ( 14 ) is formed and the gap ( 14 ) with a biocompatible plastic ( 15 ) is filled. Hip joint endoprosthesis according to claim 2, characterized in that the profiling ( 6 ) in the form of paragraphs ( 10 ) is trained. Hip joint endoprosthesis according to claim 2 or 3, characterized in that surface normals of the paragraphs ( 10 ) substantially parallel to the inner wall ( 7 ) of the joint ball ( 5 ) and the outer surface ( 13 ; 8th ) of the hip stem cone ( 4 ) or the sleeve ( 9 ) are formed. Hip joint endoprosthesis according to claim 3 or 4, characterized in that the on the inner wall ( 7 ) of the joint ball ( 5 ) paragraphs ( 10 ) in the opening direction of the joint ball ( 5 ) are oriented. Hip joint endoprosthesis according to claim 5, characterized in that on the outer surface ( 13 ; 8th ) of the hip stem cone ( 4 ) and the sleeve ( 9 ) paragraphs ( 10 ) opposite to the inner wall ( 7 ) of the joint ball ( 5 ) paragraphs ( 10 ) are oriented. Hip joint endoprosthesis according to one of claims 2 to 6, characterized in that the profiling ( 6 ) is stair-shaped, sawtooth-shaped, thread-shaped or fir-tree-shaped. Hip joint endoprosthesis according to one of claims 2 to 7, characterized in that the profiling ( 6 ) of the inner wall ( 7 ) and the outer surface ( 8th ; 13 ) is identically shaped. Hip endoprosthesis according to one of the claims 1 to 8, characterized in that the biocompatible plastic is a polymer. Hip endoprosthesis according to claim 9, characterized in that the polymer is polyethylene or Polyetheretherketone is. Hip joint endoprosthesis according to one of claims 1 to 10, characterized in that the sleeve ( 6 ) is cup-shaped conically shaped. Hip joint endoprosthesis according to claim 11, characterized in that the sleeve ( 6 ) one of the inner wall ( 7 ) of the joint ball ( 5 ) facing floor ( 8th ) having. Hip joint endoprosthesis according to claim 11 or 12, characterized in that the sleeve has a projection ( 16 ), which the joint ball ( 5 ) projects in the axial direction.