DE19904126A1 - Hip endoprosthesis in which at least the articulation surface of the femoral head is replaced - Google Patents

Abstract

According to the invention, the femoral head is essentially replaced by an artificial head provided in the form of a sturdy ball (7) which is entirely comprised of the same biocompatible material. In addition, the dimensions of the ball (7) are matched to the dimensions of the articular surface (8) of the natural femoral head, and the ball (7) is anchored in the femoral neck bone (17) by means of a pin (22). An artificial socket (1) is implanted in the hip bone (15) if the acetabulum lacks a natural articular surface for the artificial femoral head, otherwise known as the ball (7).

Description

The invention relates to a hip endoprosthesis according to the preamble of first claim.

Depending on the degree of wear of a hip joint and the life expectancy of the Patients will have a corresponding replacement of the bone of the joint partner made by prostheses, thereby restoring the joint function. If the acetabular cup is still intact, the full or only partial replacement of the femoral head is sufficient. When worn, both Affects joint partners is a total replacement of both joint partners, both by the Implantation of an artificial femoral head as well as by implanting one Acetabular cup, required. A total replacement in particular leads to a deep intervention in the bone substance with corresponding bone loss. For this reason, the bone substance and its have always been tried Maintain viability as much as possible.

From US-PS 3,521,302 it is known to place a pan in the pelvic bones insert, which is held by means of a pin cemented into the pelvic bone becomes. The articulation surface of the femoral head is defined by the femoral head adapted cap, which is also replaced by a in the remaining Bone substance of the femoral head cemented pin is fixed. In the Machining the femoral head to adapt a cap is usually the Supply vessels of the femoral neck largely destroyed. This is the No longer supplying the stump of bone under the cap guaranteed. Especially with caps with a large coverage of the Bone tissue there is a risk that the bone tissue will regress and the cap loosens.  

A prosthesis for the femoral head is known from DE-PS 11 64 019. she has the Shape of a hollow sphere, consists of a biocompatible metal and is with her The inner surface of the welded pins is anchored in the femur neck. At the Due to their position, the pins must be put on exactly and in the correct assignment to the holes. The head prosthesis is replaced by hardenable plastic filled into the hollow sphere to the bone surface customized. The plastic is also said to have an insulating effect possibly corrosive influences between the pin attachments, d. H. between the welds inside the sphere. To attach the A prosthesis requires a device with which it is possible to close the holes Anchor the pins in the right places in the femur drill. The holes penetrate the entire bone, which is the case with the three in the Pens usually provided for a corresponding weakening of the Bone substance leads. The filling of the hollow sphere with plastic mass must be done carefully done so that no voids are created. In addition, the amount of Be dimensioned such that the position of the cap, for example by lifting, not changing.

The object of the present invention is to present a hip endoprosthesis at whose use of bone loss is kept to a necessary minimum in order to especially in young patients with a long life expectancy To maintain bone stock, which is used in the event of a due reoperation can be.

The task is solved with the help of the characteristic features of the first Claim, advantageous embodiments of the invention are in the Claimed claims.

With the hip endoprosthesis according to the invention it is possible, depending on the stage of wear and tear to replace the joint partners accordingly. Is the acetabulum in The condition of the femur becomes a condition that still allows its function as a joint partner  essentially replaced in the part that encompasses the articulation surface. This is done the replacement according to the invention by a solid ball made entirely of the same, biocompatible material. This ball is in its dimensions adjusted to the dimensions of the articulation surface of the natural femoral head. Compared to hollow balls or caps, a solid ball has the advantage that it is cannot deform under loads. In addition, unlike caps, a large coverage of the bone tissue with those listed above Disadvantages avoided. It is attached with just one pin in the Femoral neck bones so that the bone substance only in one place must be drilled.

The ball is advantageously attached to the pin by means of a Cone connector. The attachment of balls by means of cone plug connections in the hip endoprosthesis is easy to use and has proven itself for years. The conical connector allows the pin to be implanted into the bone first and then put the ball on. The ball needs, in contrast to one Cap not to be lined up. The pin consists of a cone-shaped Pin for attaching the ball and a subsequent one Anchoring part that is implanted in the bone.

In a further advantageous embodiment of the invention, the ball has a Recess on. With this recess, the ball is on the recess adapted approach of the femoral head placed on the femur neck. The Recess is designed so that when the joint is stressed, in particular perpendicular to the pin, the protruding bone tissue the ball against the side Moving supports. The shear forces on the pen are reduced and local, one-sided force of the pin on the bone avoided.

An easy to manufacture and effective form of the recess is one conical recess of the ball. The approach of the femoral head is corresponding milled on the femur neck. The cone angle can be based on the size of the  Ball, especially its diameter, and the available Bone substance to be coordinated on which the ball is to be supported. It lies in a range of 80 to 170 degrees. A range from 100 to 130 is preferred Degree. The hole into which runs through the tip of the cone-shaped bone the pin is implanted with which the ball is attached to the bone.

By choosing the size of the ball and the shape of the pin, the prosthesis can be optimally matched to the geometry of the joint to be restored. The center of the ball can lie on the center line of a straight pin. The Line of symmetry of the ball with respect to its recess can also be with the Center line of the anchoring part of the pin inserted into the bone Include angles up to 20 degrees. This difference then also exists between the center line of the pin and the center line of the anchoring part of the pin.

To facilitate insertion and to apply a certain clamping force the pin inserted into the bone runs towards its end, that of the ball is turned away, conical.

When anchoring the ball in the femur, it is advantageous if the length and the diameter of the pin anchored in the bone so on the Dimension of the bone are matched that the anchoring essentially in hard bone tissue occurs. The diameter and length of the pin must therefore on the age and build of the patient and on what is available Bone tissue to be matched. Therefore, the dimensions of the pins in adolescents who are not yet fully grown and small patients differ in diameter and length from the dimensions of the for Adults with an adult bone structure and a strong build provided.

In a further advantageous embodiment of the invention, the ball is made of one biocompatible material. All biocompatible materials can be used in the  Prosthetics applicable metals and ceramic materials are called. Since the Fastening pin for the ball does not have to be firmly connected to this ball, can the choice of the material of the ball for the respective application, especially to the material of a pan.

The use of ceramics has proven to be advantageous, especially when if a ball head has an implanted socket as a joint partner. Endoprostheses, where ceramics are articulated by ceramic have the lowest abrasion rate. Ceramic balls are anchored in the bone with metal pins, since ceramic and metal do not interact with one another causing corrosion.

In an advantageous embodiment of the invention, the ball can be on its non-articulated Surface roughened. In addition or alone, it can be an osteoconductive layer wear, for example, from hydroxyapatite, which ingrown the bone in the Ball and thus a particularly good anchoring of the ball on the bone enables.

The hip endoprosthesis according to the invention makes it possible that the ball directly Can articulate acetabulum if this is still in a suitable Condition. However, the acetabulum is also worn or Disease affected, according to the invention, only the main load area of the Acetabulum replaced by an implanted cup, which then articulates the ball. So that as little bone as possible is lost during implantation and is damaged, the pan is limited to a functional angle between 90 and 170 degrees.

With regard to a long life of the prosthesis, it is under consideration the age of the patient and the stage of wear advantageous if the Material of the surface of the pan articulated by the ball in each case on the Ball material is matched that the material pairing is tribologically optimal.  

Tribologically possible are, for example, pairings between balls made of cobalt Chrome and pan inserts made of polyethylene or between ceramic balls and Pan inserts made of polyethylene. A pairing of is tribologically optimal Ceramic pans with ceramic heads, like those already found in hip arthroplasty is known.

The fact that when using the cup of the hip endoprosthesis according to the invention in the pelvic bone only the one absolutely necessary for an application Bone is removed, it is beneficial if it is in the bone used surface of the pan has elements to increase the tilting stability. For this purpose, webs can be provided, for example, which are in the vertical or almost vertical direction from the plane of the pan inserted into the bones raise. They are cut into the correspondingly milled recess of the hip bone used.

As with the ball, the pan can also be placed on the bone Surface roughened. In addition to roughening or alone, it can also wear an osteoconductive layer to prevent ingrowth in the hip bones facilitate and accelerate.

The invention is explained in more detail using exemplary embodiments.

Show it:

Fig. 1 is cut a pan of the hip prosthesis according to the invention made of ceramic,

A ball as a prosthesis of the femur head cut Fig. 2,

Figure 3 is an anchored by a pin in the femur ball., Cut, which articulates an implanted in the hip socket, and

Fig. 4 shows a prosthesis with a composition of ball and pin as a cone connector, the center line of the pin and the axis of symmetry of the ball enclosing an angle of 10 degrees and the implanted ball articulates the acetabulum directly.

In Fig. 1, 1 denotes an acetabular cup. In the present exemplary embodiment, it consists of ceramic, for example of high-purity aluminum oxide. However, it can also consist of another biocompatible material such as metal, for example cobalt-chrome, or plastic, for example polyethylene. The choice of material depends on the material of the other joint partner, the prosthesis of the femoral head. It is made in such a way that there is a tribologically optimal material pairing, for example ceramic pan with ceramic head or polyethylene pan with ceramic or metal. The socket 1 has a recess, the functional surface 2 , in the form of a spherical cap for receiving the prosthesis of the femoral head, a ball. In the present exemplary embodiment, there are two elements on the surface 3 of the pan 1 inserted into the bones, two webs 4 in the form of circular arcs, which are inserted into correspondingly milled recesses in the hip bone in order to increase the tilting stability of the pan 1 .

The surface 3 , as shown here in the left half of the figure, can be roughened, as designated by the reference number 5 , in order to allow the bone tissue to grow in and thus to better anchor it in the bone. In addition to the rough surface or even without roughening, the surface 3 can be coated with an osteoconductive layer, not shown here, for example hydroxylapatide, which also promotes the ingrowth of the bone tissue.

The functional angle 6 , which includes the functional surface 2 , lies at 100 degrees at the lower end of the claimed angular range.

The prosthesis of the femoral head shown in FIG. 2 is a solid ball 7 , which in the present exemplary embodiment consists of ceramic, for example of high-purity aluminum oxide. Other biocompatible materials are also possible, whereby their selection depends on whether the prosthesis of the femoral head articulates the acetabulum directly or a cup. In the latter case, as already mentioned above, attention should be paid to a tribologically optimal material pairing. The shape of the femoral head prosthesis 7 corresponds to that of the known ball head prostheses. The dimensions of the articulation surface 8 are adjusted to the dimensions of the natural femoral head. It is attached to the thigh bone with a pin. The ball 7 is fastened on this pin by means of a conical plug connection, as is already known from hip arthroplasty. A slightly conical bore 9 is provided for plugging onto the pin.

The ball 7 has a recess 10 which is conical in the present case. It connects to the bore 9 and is arranged symmetrically to this. The imaginary tip 12 of the recess 10 thus lies on the line of symmetry 11 of the ball 7 . The cone angle 12 can be matched to the size of the ball, in particular its diameter, and the available bone substance on which the ball is to be supported. It is in the range of 80 to 170 degrees. A range of 100 to 130 degrees is preferred.

In order to achieve an optimal connection between the ball 7 and the bone tissue, the surface of the recess 10 , comparable to the surface of the socket 1 , which is anchored in the bone tissue, can be roughened 14 and additionally or instead of the roughening, an osteoconductive layer, not shown here wear.

FIG. 3 shows a ball anchored in the femur by means of a pin, which articulates with a socket 1 implanted in the hip bone 15 . As the following exemplary embodiment shows, compared to a total resection of the femoral neck, only the femoral head is removed except for its conically milled attachment. It is anchored using a pin that is embedded in the hard tissue of the femur. The hole and pin can also penetrate the femur completely. If a new operation is necessary due to bone regression or progressive pathological changes in the bone, there is sufficient bone material available, at least for conventional prosthetics with a shaft inserted into the femur.

As can be seen from FIG. 3, the femoral head on the thigh bone 16 has been severed at the level of its shoulder on the thigh neck 17 . A slightly conical bore 21 is made in the femur neck 17 through the tip 19 of the conical milled bone contour 18 , centered on its center line 20 . A pin 22 is implanted in it, the conically tapered anchoring part 23 is inserted in the bore 21 . The end of the pin 22 protruding from the bone is a conical pin 24 on which the ball 7 with its bore 9 is placed.

When the femoral head prosthesis is implanted, the anchoring part 23 of the pin 22 is first driven into the bore 21 . Because of its taper, there is a tight fit in the bone. Then the ball 7 with its conical bore 9 is placed on the pin 24 and a slight fit with the pin 24 is achieved by light impacts on the ball. The surface of the recess 10 is supported on the conically milled stump 18 of the femoral neck 17 . In particular in the case of loads in which the force acting on the ball 7 is essentially perpendicular to the center line 20 of the pin 22 , the force is better introduced into the bone than if the ball and the bone meet in a plane perpendicular to the center line of the pin.

FIG. 4 shows a prosthesis of a femoral head in which the femoral head prosthesis, the ball, articulates the acetabulum 26 directly. The center line 120 of the pin 122 and the line of symmetry 11 of the ball 7 enclose an angle of 10 degrees. In the present exemplary embodiment, the ball 7 corresponds to the ball shown in FIGS. 2 and 3. The shape of the pin 122 implanted in the femur 17 differs from that of the pin 22 of FIG. 3. The center line 120 of the conical anchoring part 123 forms an angle 25 of 10 degrees with the line of symmetry 11 of the ball 7 . The center line of the pin 124 , which carries the ball 7 , coincides with the line of symmetry 11 of the ball.

The material of the pen consists of a high-strength, biocompatible metal, such as a titanium alloy or an alloy of cobalt, chromium and molybdenum. As with the stems known in hip arthroplasty, which are inserted into the femur itself, the anchoring part 123 of the pin can also be roughened and / or provided with an osteoconductive layer in order to enable better ingrowth in the bones.

Claims (20)

1. Hip endoprosthesis, in which at least the articulation surface of the femoral head is replaced by a spherical prosthesis, the prosthesis being supported outside its articulation surface on the femur neck, characterized in that the femoral head is essentially made up of an artificial head in the form of a solid one , biocompatible material existing ball ( 7 ) is replaced, that the dimensions of the ball ( 7 ) are matched to the dimensions of the articulation surface of the natural femoral head and that the ball ( 7 ) is anchored in the femur neck ( 17 ) by means of a pin ( 22 ; 122 ) . 2. Hip endoprosthesis according to claim 1, characterized in that the pin ( 22 ; 122 ) consists of a pin ( 24 ; 124 ) for attaching the ball ( 7 ) and an anchoring part ( 23 ; 123 ) for anchoring in the femur ( 17 ) and that the ball ( 7 ) is attached to the pin ( 22 ; 122 ) by means of a conical plug connection ( 9 , 24 ). 3. Hip endoprosthesis according to claim 1 or 2, characterized in that the ball ( 7 ) has a recess ( 10 ) and that the ball ( 7 ) with its recess ( 10 ) on the bone ( 18 ) of the femoral neck ( 17 ) adapted to the recess ) is attached. 4. Hip endoprosthesis according to one of claims 1 to 3, characterized in that the recess ( 10 ) in the ball ( 7 ) is conical. 5. hip endoprosthesis according to one of claims 1 to 4, characterized in that the recess ( 10 ) in the ball ( 7 ) includes a cone angle ( 13 ) of 80 to 170 degrees, preferably from 100 to 130 degrees. 6. Hip endoprosthesis according to one of claims 1 to 5, that the line of symmetry ( 11 ) of the ball ( 7 ) and the center line ( 20 ) of the pin ( 22 ) coincide. 7. Hip endoprosthesis according to one of claims 1 to 5, characterized in that the line of symmetry ( 11 ) of the ball ( 7 ) and the center line ( 120 ) of the anchoring part ( 123 ) of the pin ( 122 ) enclose an angle of up to 20 degrees. 8. Hip endoprosthesis according to one of claims 1 to 7, characterized in that the anchoring part ( 23 ; 123 ) of the pin ( 22 ; 122 ) tapers conically. 9. Hip endoprosthesis according to one of claims 1 to 8, characterized in that the dimensions of the pin ( 22 ; 122 ) are matched to the dimensions of the bone ( 17 ) and that the anchoring takes place essentially in the hard bone tissue. 10. Hip endoprosthesis according to one of claims 1 to 9, that the ball ( 7 ) is made of a biocompatible material. 11. Hip endoprosthesis according to claim 10, characterized in that the material of the ball ( 7 ) is ceramic. 12. Hip endoprosthesis according to one of claims 1 to 11, characterized in that the ball ( 7 ) is roughened ( 14 ) on its non-articulated surface ( 10 ). 13. Hip endoprosthesis according to one of claims 1 to 12, characterized in that the ball ( 7 ) on its non-articulated surface ( 10 ) carries an osteoconductive layer. 14. Hip endoprosthesis according to one of claims 1 to 13, characterized in that the ball ( 7 ) articulates the acetabulum ( 26 ) directly. 15. Hip endoprosthesis according to one of claims 1 to 13, characterized in that the main load area of the acetabulum is replaced by an implanted cup ( 1 ) which articulates the ball ( 7 ). 16. Hip endoprosthesis according to claim 15, characterized in that the cup ( 1 ) has a functional angle ( 6 ) of 90 to 170 degrees. 17. Hip endoprosthesis according to claim 15 or 16, characterized in that the material of the ball ( 7 ) articulated functional surface ( 2 ) of the socket ( 1 ) is matched to the material of the ball ( 7 ) in such a way that the material pairing is tribologically optimal is. 18. Hip endoprosthesis according to one of claims 15 to 17, characterized in that the surface ( 3 ) of the socket ( 1 ) used in the hip bone ( 15 ) has elements ( 4 ) for increasing the tilting stability. 19. Hip endoprosthesis according to one of claims 15 to 18, characterized in that the surface ( 3 ) of the socket ( 1 ) used in the hip bone ( 15 ) is roughened ( 5 ). 20. Hip endoprosthesis according to one of claims 15 to 19, characterized in that the surface ( 3 ) of the socket ( 1 ) used in the hip bone ( 15 ) carries an osteoconductive layer.