WO2010072606A1 - Modular hip joint endoprosthesis - Google Patents

Abstract

The invention relates to a modular hip joint endoprosthesis having a rolling-friction-supported prosthesis head. The aim of the invention is to develop a modular hip joint endoprosthesis that has a significantly reduced frictional resistance between the implant socket sliding surface and the joint ball and that allows a nearly natural range of movement. According to the invention, the aim is achieved by inserting sliding bodies (running balls) in order to transmit the movement between the articulation surfaces of the joint ball and of the socket, wherein said sliding bodies in addition to reducing the friction also cause an effective enlargement of the joint ball diameter and thus permit a greater range of movement. The sliding-body cage is designed in such a way that collisions with the implant stem under load conditions that occur periodically do not impair the function of the joint.

Description

 Modular hip joint endoprosthesis

description

The invention relates to a modular hip joint endoprosthesis with a rolling friction bearing prosthesis head.

State of the art

The complete replacement of a worn hip joint with a hip joint prosthesis is one of the standard operations of orthopedics. The residence time of an applied conventional prosthesis is currently about 15 years at average load and is determined by physiological factors, especially by the material wear.

In the past, great efforts have been made to improve the durability of the endoprostheses. Based on the original prosthesis design according to CHARNLEY, several design variants for complete joint replacement have been established, but their basic components are similar. The prostheses consist of a socket body, a socket insert with sliding surface for the joint ball, a joint ball and a hip stem.

The pan body is made of metal or ceramic and is pressed or screwed into the roofed acetabulum. It represents the stable shell for the socket insert. The socket insert is pressed into the socket body or positively inserted and provides a spherical sliding surface for the joint ball. In the case of a few prosthesis variants, this sliding surface is integrated in the socket body and the insert is dispensed with for these variants. The joint ball slides on the Sliding surface in the various geometrically prescribed directions of compulsion and the ball is so connected to the hip stem, the movement of the compound axis of the original joint function that nut joint, can largely represent.

An overview of the different prosthesis designs is given in Effenberger H., lmhof M. (cement-free acetabular implant atlas, H. Effenberger 2002).

Due to this nature-inspired design, technical wear is unavoidable. In a healthy natural case, the wear in the femoral surface articular cartilage is very low, and an associated coefficient of friction R has a typical value of R <0.01. Possible wear products are eliminated through the metabolism, and regenerative processes also ensure the function of the joint.

The technical wear in the sliding pair of the replacement joint is harmful in two respects. On the one hand, it limits the duration of use, on the other hand, the exiting wear products burden the surrounding tissue and can lead to inflammation, tissue necrosis and further to implant loosening, which necessitate an implant replacement.

To reduce the technical wear are great

Efforts have been made. In particular, improved sliding mating materials have been developed. The following sliding mating materials are preferably used (joint head socket insert):

Ceramic-polymer,

Ceramic pottery,

Metal-ceramic,

Metal-metal

The pairing ceramic head-polymer pan insert is most commonly used because it is safe to use and satisfactory long-term experience. In this bearing the wear is determined by the polymer abrasion. The further development of the polymer material from simple polyethylene to high-density polyethylene to high-density cross-linked polyethylene made it possible to reduce wear several times. At the current stage of development of this sliding pair, a loss of 0.1 mm cup insert thickness per year is observed. The resulting abrasion remains in the surrounding tissue and can lead to complications. The tendency for larger joint balls, which allow improved mobility, requires larger articulation surfaces and thus especially in this sliding pair increased wear.

The ceramic-ceramic sliding pair with significantly lower

Wear values are becoming increasingly important due to improved ceramic properties. In particular, the mechanical properties of aluminum mixed oxide ceramics have been greatly improved in terms of impact strength, brittleness and crack propagation, so that even geometrically complicated shapes such as knee implants (tibial side) can be realized. However, in the case of the hip implant, massive destructive contact between the hip stem and the acetabular insert (impingement) can cause the ceramic particles to chip off, which then lead to a three-body wear situation in the sliding pair, which in turn has a very destructive effect on the friction values. By appropriate design measures one tries to avoid this wear case, however, must consider that the Pfannenposition in the basin (place, angular position) is not always stable.

In metal-metal sliding pairings is trying to get in a compromise, the positive properties of the previously described sliding pairings and to keep the unavoidable metal abrasion as low as possible. Under normal circumstances, this succeeds, in unfavorable cases, the surrounding tissue is penetrated by abrasion and a replacement of the prosthesis is indispensable. In addition to the material engineering efforts, a number of constructive efforts have been made to achieve improved functionality of the hip replacement joint. In particular, the increase in the range of motion was the focus of interest. Through monocentric bipolar rod ends was trying to relocate the center of rotation of the joint replacement so that a striking of the hip stem on the pan edge is possible only at much larger angles. Virtually an increase in the effective diameter of the joint ball was made at the price of introducing a second articulation surface.

The separation between bipolar condyle and movable

The tray insert and the simple joint ball are out of focus and this assignment is made arbitrarily by the implant manufacturers.

A special form of this arrangement is the bipolar bicentric

Articulated head, which is also used for semi-prostheses using the natural joint socket (Thomsen, SJ, Breusch, U. Schneider, D. Kubein-Meesenburg, H. Nägerl: Developments in hemi-hip arthroplasty and the theory of the recessed dimeric hip joint) , In this form, the ball joint can slide in a likewise movable outer ball. The geometries are to be adjusted so that the lines of action of the forces guarantee a reliable function of the duo head.

All previously described and realized implant forms are based on a sliding in a shell condyle. These implants are of practical importance and find clinical application.

From an engineering point of view, the realization of a nut joint in the form of a sliding bearing with an aspirating very long life is an unsatisfactory solution, since the Gleitreibungsverschleiß is always greater than a rolling friction wear. In the patent literature, therefore, there are also a number of proposals for the realization of a complete hip joint implant using rolling elements. The main issue In these proposals, a too one-sided technical consideration, which takes insufficient account of the physiological requirements or, in ignorance of these requirements, leads to unrealistic or potentially dangerous solutions. The slide bearing-based solutions are structurally very simple. They are reliable in the expected frame and are tolerated by the body, apart from the wear products. Their use must be operationally controlled. The corresponding rolling bearing-based proposals from the patent literature must be able to be measured against these facts and should have an improved life as the main advantage. The complicated design required for these proposals must remain operationally manageable. The fact that there is not a single rolling bearing-based implant in clinical use shows that the proposed solutions are immature and thus potentially dangerous for the patient. Some of these suggestions are discussed below.

Very technical solutions, such as e.g. FR2357235A1, contain a variety of hidden surfaces, which are suitable for the absorption of tissue residues and are therefore legitimately acceptable as an endoprosthesis. Surprisingly, some proposed solutions are completely useless, as can be seen from the corresponding figures, cf. DE 9304038 U, DE 2024583 C3, WO 94/29605. The rolling elements have no freedom of movement in the figures of the aforementioned writings.

In the patents US 5092898, JP 07059805 A, JP 07051301 A,

JP 04341258 A and FR 2060179, the Wälzkörperkäfig is connected with balls as rolling elements by an additional fixation element with the condyle and the pan, which requires an additional mechanical intraoperative step and in the impingement case, a high, loosening the pan torque.

In the patents DE 69914765 T2, DE 19527975 C1, FR 2707479 and GB 2338897 is an open rolling bearing cage with balls as rolling elements suggested a favorable solution. However, this cage is in DE 19527975 C1 and FR 2707479 losable connected to the condyle, ie the rolling elements comprise less than the hemisphere of the head.

In the patents GB 2338897 and DE 69914765 T2, this cage is captively connected to the condyle. It is not described in GB 2338897 how this captive is made because due to the geometric constraints the example described is not technically feasible. In the patent DE69914765T2 the captivity of the rolling bearing cage is realized by an additional element and three locking connections. The version of the rolling elements, the balls is given in this proposal by pressing in a positive recess using elastic deformation of the opening.

In the aforementioned patents with the proposals to open

Rolling bearing cages, a serious deficiency comes to light. In no way the necessary stability of the cage is discussed. This deficiency stems from the fact that the requirements resulting from the natural gait cycle are not reflected in the technical realization of the warehouse.

The natural gait cycle is characterized in that the projection point of the neck axis of the femur into a spherical surface lying in the acetabulum during the gait cycle writes a kidney-shaped closed curve. This means that the rolling element cage does not return to its original spatial position after passing through a cycle. Only for the theoretical special case that the projection curve would take the form of a line would the return to the starting position be given. Due to the now steady, caused by the gait cycle, uniform change in position of the roller body cage, it inevitably causes the cage and the neck of the implant stem collide. The rolling friction is in the subsequent step by a sliding friction step such interrupted, the neck of the implant stem sliding back the cage, wherein the entire force transmission through the cage over the collision point between the cage and neck of the implant stem takes place. That is, for this periodically expected, in principle inevitable situation of the bearing cage must have a mechanically sufficient stability and the structural design of securing the cage around the condyle must be guaranteed for each radial contact point.

All previously disclosed solutions can not meet these requirements. In summary, it can thus be stated that in the artificial hip joint, in addition to the necessary assurance of biocompatibility, special attention is paid to ensuring an approximately natural range of motion and the highest possible service life with the highest possible functional reliability.

Presentation of the invention

The object of the invention is a functionally reliable modular

To develop a hip joint endoprosthesis with significantly reduced frictional resistance between implant socket sliding surface and joint ball, which allows a nearly natural range of motion.

The object is achieved according to the claims.

The modular hip joint endoprosthesis according to the invention consists of a cup-shaped socket body, a cup-shaped socket insert, a ball joint and a ball cage and is characterized in that the ball race cage consists of a Laufkugelkäfig shell in half-shell shape and a Laufkugelkäfig- lower part. The upper part of the ball cage covers the joint ball almost to the equator. The bottom part of the running cage has the shape of a capped half-shell with a central opening and envelops the ball of the ball over the equator. The ball cage cage top and - Lower part are releasably or permanently connected in such a way that the tissue side of the implant creates a smooth convex surface.

The central opening of the Laufkugelkäfig base corresponds to the size of the neck of the hip stem. In the Laufkugelkäfig running balls are inserted into inwardly open pockets, with centrically open coverslips close these pockets. The number and arrangement of the balls is determined by the expected load distribution.

The reduction of wear between the sliding surface of the socket insert and the condyle is effected by the inventive transition from the usual Gleitreibungsartikulation to Rollreibungsartikulation, i. The sliding of the condyle in the sliding surface of the socket insert is inventively taught by rolling elements, in particular here running balls.

From the point of view of the surgeon, the ball connected to the ball cage hip ball as a hip ball with an effectively larger diameter. The larger ball diameter causes a greater range of motion of the hip stem. The placed ball cage secures the free rolling of the balls in all directions tangential to the articulation surface of the cup insert and thus the free rotational movement of the joint ball or the hip stem in the physiologically necessary area.

Tissue irritation through the use of Laufkugelkäfigs and the

Running balls are not to be expected, since all surfaces which could come into sliding contact with tissue are convex or have uncritical radii of curvature.

For the surgeon, there is no conversion of the conventional surgical technique. Brief description of the illustrations

The invention will be explained in more detail with reference to drawings. Show this

FIG. 1 Basic structure of the hip joint endoprosthesis according to the invention,

FIG. 2 Section of the endoprosthesis in the assembled state, FIG. 3 Positive connection of the running cage cage parts, FIG. 4 Elbowed hip stem in the hip joint endoprosthesis according to the invention.

Embodiment of the invention

In Figure 1 is an exploded view of the modular hip joint endoprosthesis according to the invention with the rolling friction bearing prosthesis head without hip stem to see. This consists of a cup-shaped pan base body 1, which is stably introduced into the roofed tank pan and a likewise cup-shaped socket insert 2 with a hemispherical inner sliding surface 2a. The socket insert 2 is seated positively and against rotation in the socket body 1. The edge of the hemispherical inner sliding surface 2a is rounded such that spherical rolling elements (running balls 11) can easily enter the sliding surface 2a.

The running balls 11 are guided in an at least two-part shell-shaped ball race cage 3, which is arranged in the inner sliding surface 2a. Number and arrangement of the running balls 11 is determined by the expected load distribution.

The ball cage 3 must be connected to the ball joint 8 freely movable but captive. This is achieved by a two-part ball cage 3, the running ball cage upper part 4 has half-shell shape and the ball joint 8 covers approximately to the equator. The Laufkugelkäfig base 5 has the shape of a capped half-shell, ie that the bottom of the Laufkugelkäfig base 5 has a central opening in the size of the neck of the hip stem 10. The Laufkugelkäfig base 5 complements the Laufkugelkäfig- upper part 4 to a capped ball, which surrounds the ball joint 8 to over the equator. Both Laufkugelkäfig parts 4 and 5 are preferably joined together by a positive engagement in overcoming a material tension on the joint ball surface. Since the opening of the Laufkugelkäfig base 5 is smaller than the diameter of the ball joint, the assembled cage can be separated again only by overcoming the material tension of the positive connection and is under physiologically relevant forces captive.

In another exemplary embodiment, the two parts of the ball cage 3 are joined by joining, e.g. Welding undetachably connected.

The design of the Laufkugelkäfigs 3 is at maximum mechanical

Stability oriented, i. its thickness is maximized to the effect that the running balls 11 can still run free. The running balls 11 are inserted into inwardly open pockets of the cage and enclosed with centrically open coverslips that close these pockets in the pocket with free movement. The coverslips are sealed by joining, e.g. Welding, secured.

In the sectional view of Figure 2, the articulation of the running balls 11 on the sliding surface 2a of the socket insert 2 and the joint ball surface 8 can be seen. The running balls 11 ensure the polyaxiality of the movement of the joint ball 8 and thus of the hip stem 9 in arbitrary spatial directions.

In Figure 3 is shown, for example, how a simple reliable form-locking connection between the upper and lower part of the ball race cage 3 takes place. By this type of connection is ensured to the tissue side of the implant that a possibly rubbing tissue contact takes place only with smooth convex surfaces. In the sliding surface 2 a of the socket insert 2 is indirectly articulating the ball joint 8, which is connected to the hip stem 9. The deflected hip stem 9 in FIG. 4 shows that there are no restrictions with regard to the achievable range of motion due to the introduction of the running ball cage 3. The effective increase in diameter of the joint ball 8 through the ball cage contributes to increasing the range of motion.

LIST OF REFERENCE NUMBERS

1 pan basic body

2 pan insert

2a sliding surface

3 ball cage

4 ball cage upper part

5 ball cage lower part

6 Positive locking ball cage upper part

7 Positive connection of running ball cage lower part

8 joint ball

9 hip stems

10 neck of the hip stalk

11 running ball

Claims

claims 1. Modular Hüftgelenkendoprothese consisting of a cup-shaped Pfannengrundkörper, a cup-shaped socket insert, a ball joint and a ball cage characterized in that the ball race cage (3) from a Laufkugelkäfig upper part (4) in a half-shell shape, which covers the joint ball (8) approximately to the equator , and a running ball cage lower part (5), which has the shape of a clipped half-shell with a central opening and the joint ball (8) envelops over the equator consists. 2. Modular hip joint endoprosthesis according to claim 1, characterized in that Running ball cage upper part (4) and lower running cage cage (5) are so releasably connected by positive engagement, that the tissue side of the implant creates a smooth convex surface. 3. Modular hip joint endoprosthesis according to claim 1, characterized in that Running ball cage upper part (4) and lower running cage cage (5) by joining, in particular welding, are so inextricably linked, that the tissue side of the implant creates a smooth convex surface. 4. Modular hip joint endoprosthesis according to one of claims 1 to 3, characterized in that the central opening of the Laufkugelkäfig base (5) the neck of the hip stem (10) allows the physiological range of motion. 5. Modular Hüftgelenkendoprothese according to one of claims 1 to 4, characterized in that in the ball cage (3) running balls (11) are inserted into inwardly open pockets, wherein centrically open coverslips close these pockets. 6. Modular hip joint endoprosthesis according to one of claims 1 to 4, characterized in that Number and arrangement of the running balls (11) is determined by the expected load distribution.