WO2000030570A2

WO2000030570A2 - Partial endoprosthesis for knee joints and grinding tool for working a tibia

Info

Publication number: WO2000030570A2
Application number: PCT/EP1999/008904
Authority: WO
Inventors: W. Skripitz
Original assignee: Coripharm Medizinprodukte Gmbh & Co. Kg.
Priority date: 1998-11-23
Filing date: 1999-11-22
Publication date: 2000-06-02
Also published as: DE29820903U1; WO2000030570A3

Abstract

The invention relates to a partial endoprosthesis (10) for knee joints which consists of two parts of a prosthesis (12; 24). One of these parts is formed by an inlay (24) which can be inserted in a recess previously made into the initial joint surface of the tibia and which is fixated by way of bone cement. The side of said inlay facing the femur is configured as a slide surface (26) for the allocated skid-type second part of the prosthesis (12) which can be mounted in a retaining part integrated into the area of the femur opposite the slide surface. At least the inlay (24) to be fixated in the recess of the tibia is provided with a cavity (28) in its lower part facing away from the femur. Said cavity serves as a depot for the bone cement. Preferably, the skid-type part of the prosthesis (12) to be mounted in the allocated recess in the femur is provided with a cavity (18) in its lower part facing away from the tibia. Said cavity serves as a depot for the bone cement.

Description

Partial endoprosthesis for knee joints

The invention relates to a partial endoprosthesis for knee joints, consisting of two prosthesis parts, one of which is formed by an inlay which can be inserted into a recess previously made in the original joint surface of the tibia and can be fixed by means of bone cement and whose side facing the femur as Sliding surface for the assigned second prosthetic part which can be fastened in a receptacle incorporated in the area of the femur opposite the sliding surface

When replacing the functionally impaired knee joint with prostheses, total endoprosthesis systems are still used today, in which after the joint area has been surgically exposed, the tibia joint area is exposed by strong flexion of the knee and then with the help of resection guides The actual joint area is removed by means of a sawing tool, an essentially flat plateau being formed on the end of the tibia, on which a prosthetic part imitating the tibia joint area in terms of shape and function is placed and aligned by means of a pin in a hole that extends into the medullary cavity held and fixed with bone cement. Similarly, femoral on the side, several surfaces were created with the aid of resection guides and saw cut surfaces for holding the femoral component, which, after the holder surfaces had been created, was also aligned by means of pins inserted into bores in the femur and fixed with bone cement. The surgical operation when implanting such knee-total endoprostheses is time-consuming and labor-intensive and also places a great strain on the patient, especially since the knee joint must be exposed by enveloping tissues, tendons, etc., before the tibia and femur in the joint area for them Preparation of the prosthesis parts can be prepared and the prosthesis parts can then be inserted and fixed in place using the inserted bone cement.

It has now been shown that in many cases it is not necessary to replace a knee joint with a total endoprosthesis, but in itself it is sufficient if the knee joint is replaced by a partial prosthesis in the region of one of the two joint surfaces that are laterally offset (medial or lateral) is replaced. In this connection, a surgical technique for correspondingly reduced partial prostheses has already been developed, in which the operative opening of the knee joint area can be kept relatively small compared to the operation when the knee joint is replaced by a total endoprosthesis, in which case already present aids, the areas of the articular surfaces are brought to a sufficient distance and can be kept at this distance, so that the areas of the knee joint, into which recesses or are required for the prosthesis parts to be provided

Recordings have to be incorporated and are accessible for editing processes. In the previously developed surgical technique, the receptacles for the prosthesis parts, in particular for the recess of the tibiaside part of the prosthesis to be designed as a plastic inlay, are milled out by milling out the bone structure by means of a ball head designed in the manner of a milling head used in dental practices. The milling head is created by first placing the milling head along the previously recorded boundary of the recess to be produced and guiding it along and creating a slot-like circumferential recess, whereupon the material in between is gradually milled out, thus creating the recess for the inlay, which is made of suitable plastic becomes. It is of course the case that the recessed recess to be produced must be dimensioned as precisely as possible in accordance with the inlay in terms of its limitation and also its depth, so that the inlay, after being fixed in the recess with bone cement, consists of the metal-like prosthetic part of the femur contrasts that the original knee function is optimally imitated. It has been shown that this type of milled-out of the receptacle for the inlay is labor-intensive even with a mechanical antπeo of the spherical milling cutter, and is not always satisfactory with regard to the accuracy and surface quality of the created receptacle surface of the cutout, which also entails the risk of that the inlay is not implanted with the desired and precisely specified fit. It is also critical to maintain the depth of the recess in such a way that the associated metallic skid-like prosthesis part interacts with the inlay at the correct distance. This statement applies in particular to the inlay to be inserted into the recess in the TiDia and to be fixed there, while the preparation of the joint area of the femur for the skid-like prosthesis part to be provided there can largely be done by less critical saga processing and the firm fit by one of the cone opposite the skid sliding surface and a hole inserted in the femur can additionally be used for fixation by means of bone cement. Nevertheless, great care is also required here, in particular when measuring the amount of bone cement to be used, so that the prosthesis has the required firm fit and can withstand the loads to be expected. In particular, it must be ensured that the bone cement on the prosthesis side completely fills the space between the recess or receptacle and the prosthesis and, in addition, the spungiosa of the adjoining bone area penetrates and thus ensures firm anchoring in the bone and on the respective prosthesis part after hardening.

The invention is based on the object of a two-part partial endoprosthesis for knee joints, in which the desired, resilient and precisely aligned seat on or in the bone can be achieved in a simplified manner compared to the previous surgical technique. In addition, a tool which enables the production of the recess for receiving the part of the prosthesis on the Tibia side, which is designed as an inlay, is to be created with increased accuracy and reduced workload.

To solve the object is erfmdungsgemaß proposed that at a part endoprosthesis of the type mentioned at least the erfmdungsgemaß m of the recess of the tibia to be fixed inlay in its femurabgewandten underside with a serving as a bone cement depot recess ver ^¬ see is that prior to insertion is fulloar in the recess in the tibia with a predetermined amount of bone cement that meets the requirements. When inserting the inlay m the recess by pressing on the outer surface, a part of the freshly mixed bone cement m the spongiosis is pressed and thus ensures the desired firm connection after hardening.

The recess n on the underside facing away from the femur expediently has an at least largely all-round closed wall, so that bone cement is only displaced to a small extent to the recess walls surrounding the inlay.

The wall of the inlay surrounding the recess is if it is expedient to provide all or part of a texturing, roughening or a number of regularly or irregularly distributed projections which increase the adhesion of bone cement, in order to improve the adhesion of the bone cement on the prosthesis side.

At least the part of the inlay facing the skid-like prosthetic part on the femur side is preferably made of a highly durable plastic with good sliding properties, for example the high-pressure polyethylene used for total endoprostheses for the tibial component.

In the preferred embodiment of the invention, the skid-like prosthesis part to be fastened in the associated receptacle in the femur is also provided in its underside facing away from the tibia with a depression serving as a bone cement depot, which then - analogously to the inlay - m around the underside facing away from the tibia by a circumferential wall is at least mostly closed all around.

The deepening limiting wall of the ski-like prosthesis part can be provided to ensure a safe seat on or in the femur with the liability of the bone cement increasing Textuπerung, roughening oαer an on ^¬ number of regularly or irregularly distributed Vorsprungen.

The skid-like prosthesis part is preferably made in a known manner from metal, preferably a high-alloy steel, for example a cobalt-chromium-molybdenum alloy, with the skid area of this prosthesis part interacting with the joint surface of the tibial-side inlay being appropriately polished.

To ensure the exact predetermined position and for additional anchoring, it is also advantageous if From the wall of the skid-like prosthesis part that delimits the recess, at least one pin that is known per se and that can be inserted into a prepared bore in the receptacle of the femur projects.

To produce the comparatively more critical cutout to be provided in the knee joint end of the tibia for receiving the tibia-side inlay, a tool that can be inserted in a motor-driven drive machine and can be displaced by this oscillating working movement is proposed according to the invention, which tool is designed according to the invention such that it is at the end of a Form-grinding tool arranged in the tool holder of the drive machine, the working grinding surface of which is coated with abrasive particles that act on the bone substance, and the shape of which is selected in accordance with the limitation of the recess in the tibia for the inlay to be implanted, its dimensions being only m in the oscillation direction smaller by the oscillation stroke than the recess to be produced. This tool is brought into the intended working position, which rests on the working grinding surface of the form grinding tool in the region of the tibia recess to be produced. By starting the drive motor, the grinding tool is then set into oscillating motion and grinds the recess required for the inlay into the damaged joint area of the tibia, with only sufficient pressure having to be applied in the direction of the recess to be produced. The corresponding limitation of the grinding tool, taking into account the oscillation stroke, creates a recess that is optimally adapted to the inlay to be implanted. If the height of the form grinding tool is dimensioned according to the thickness of the inlay, the correct insertion depth of the recess is also automatically obtained as soon as the tool shaft comes into contact with the bone areas delimiting the recess. The tool shank is advantageously designed as an elongated flat profile, one end region of which is suitably designed to be held in the tool holder of the drive machine, in which case the form grinding tool is formed by a shaped body which appears in the other end region from a flat side of the flat profile, whose surface opposite the fastening surface on the flat profile forms the working grinding surface.

On the flat side of the tool shank opposite the flat side provided with the form grinding tool, a second form grinding tool can be provided, which e.g. is used when the first form grinding tool shows a deteriorated grinding effect after prolonged use. Alternatively, the second grinding tool can also be coated with different, for example finer, grinding particles, so that the second grinding molding tool can then be used for the final fine machining of the bottom surface of the cut-out created after processing with the first molding grinding tool. For this purpose, only the tool shank must be inserted into the tool holder of the drive machine in a position rotated by 180 °.

The working grinding surface (s) of the form grinding tool or the form grinding tools are then expediently coated with diamond grinding particles, which combine good grinding effects with a long service life of the tool.

At a distance from the form grinding tool or the form grinding tools, a stop protruding from the tool shank, for example a stop point, can be provided, the distance from the respectively assigned form grinding tool corresponding to the distance for the recess to be made in the tibial joint surface the inlay corresponds to the outer wall of the tibia. The stop pin enables simple and precise placement of the form grinding Tool in the area of the recess to be produced, in which the tool is guided up to the abutment pin against the outer bone wall. This also ensures that the hard bone wall (cortex) surrounding the recess is not attacked during the grinding process.

The length of the respective stop pin is dimensioned such that it protrudes beyond the plane of the working grinding surface of the associated form grinding tool, i.e. effective as a stop at the start of the grinding process

The invention is explained in more detail in the following description in conjunction with the drawing, which shows:

1 shows a perspective view of a two-part partial endoprosthesis according to the invention, with the two prosthesis parts at a spacing from one another,

FIG. 2 shows a bottom view of the prosthesis part assigned to the tibia, viewed in the direction of the arrow 2 FIG. 1;

3 shows a plan view of a tool for producing the recess in the tibial-side joint surface for receiving the prosthesis part designed as an inlay; and

4 is a view of the tool, seen in the direction of arrow 4.

In Fig. 1 is shown in its entirety with 10 exemplary embodiment of a two-part partial endoprosthesis according to the invention for knee joints, of which the upper skid-like prosthesis part 12 in the drawing figure is made of a cobalt-chromium-molybdenum alloy, which is polished on its convex skid surfaces 14 pointing downwards in FIG. 1 in order to achieve the lowest possible roughness. On the rear side opposite the runner surface 14, a recess 18 is formed within a circumferential low wall 16, from which projects an integrally attached pin 20 which is additionally stabilized by ribs 22 projecting from the bottom of the recess 18 on both sides in the longitudinal direction of the prosthesis part. The bottom of the depression is provided with a roughening or texturing or with a plurality of regularly or irregularly arranged protruding low projections. This roughening serves to increase the adhesion of the bone cement introduced into the depression serving as a bone cement depot in the shapeable state after it has set on the prosthesis part 12.

It can be seen that the part of the knee joint on the femur side in the area of the prosthesis part 12 to be implanted must be machined by appropriate machining in such a way that a suitable receptacle for the prosthesis part 12 is produced, a hole also being made in the femur, into which the pin 20 is inserted and thus transmits acting shear stress in the thigh. The depression 18 provided as a bone cement depot is thus filled with the freshly mixed and still plastic bone cement in a predetermined amount before the implantation and then pressed into or onto the previously produced receptacle of the thigh bone, with bone cement introduced in excess in the depression in the subsequent ones cancellous bone area penetrates and hardens there.

The second lower prosthesis part 24 is provided as an elongated, in its upper side facing the skid surface 14 with a slightly concave sliding surface 26, Inlay trained. The prosthesis part 24 is made of a high-strength plastic with good sliding properties, for example a high-pressure polyethylene. As can be seen from FIG. 2, which shows the inlay 24 from the underside, a depression 28 provided as a bone cement depot is also formed in this underside within an all-round wall 30 which defines the height of the inlay and thus also the depth of the receptacle Inlays in the tibial joint surface recess to be provided. The bottom surface of the depression 28 is in turn textured, roughened or provided with a plurality of low projections in a regular or irregular arrangement in order to increase the adhesion of the bone cement.

FIGS. 3 and 4 show a tool 34 which is intended for incorporating a recess which fits the inlay 24 exactly and the region of the knee joint of the tibia to be replaced by the inlay. The tool 34 has an elongated flat tool shaft 36, stiffened if necessary by the indicated low embossed ribs against deflection, the right end of which in the drawing figures is suitably designed for releasable mounting in the tool holder of a motor drive machine. Such motor drive machines are used in surgical operating technology, among other things, for sawing, ie for making cuts in or for severing bones. These drive machines therefore generate an oscillating, ie back and forth working movement of the driven tool. In the drawing figures, the working movement of the working stroke given to the tool 34 by the drive machine is indicated as in each case by a double arrow running in the longitudinal direction of the tool. The embodiment of the end of the tool on the drive machine side shown in the special embodiment with an essentially circular slit toward the free end Opening with an internal toothing is only to be understood here as an example and in practice depends on the drive machine used in each case or the construction of its tool holder.

At the left-hand end of the tool shaft 36, the actual form-grinding tool 38, which removes the bone material in a grinding process, is illustrated on the top of the shaft 36, the outline of which corresponds substantially to the shape of the inlay 24, although the dimension of the form-grinding tool 38 towards the working stroke is shorter by the amount of this working stroke. In this way it is ensured that the recess made in the bone with the tool 34 placed on the bone and driven in an oscillating manner corresponds exactly in its outer contour to the inlay 24 to be picked up.

The abrasive tool itself consists of a pillow-like metallic carrier that protrudes from the upper side of the tool shaft 36 and has an abrasive layer 42 of diamond particles firmly bonded to the carrier on its upper flat side facing away from the tool shaft and located in the region of the knee joint bone to be machined is provided.

FIGS. 3 and 4 each show a stop pin 44 protruding from the tool shank 36 at a distance from the actual form grinding tool 38, which protrudes beyond the actual working surface coated with the diamond particle coating and is at such a distance from the actual form grinding tool. that when the tool is placed in the working area in such a way that the stop pin 44 lies against the outside of the bone, it is ensured that the working area of the form grinding tool lies outside the area of the hard bone wall (cortex). In FIG. 4, the arrangement of a shape grinding tool 38 ′, which essentially corresponds in shape and structure to the shape grinding tool 38, on the side of the tool shaft 36 opposite the grinding tool 18 is indicated by dash-dotted lines. A stop pin 44 'also protrudes from the opposite side of the tool shank 36. This second form grinding tool 38 'either represents an immediately ready-to-use replacement tool in the event that the grinding effect of the actual Forra grinding tool 38 is inadmissibly deteriorated due to wear, or the grinding tool 38' can also be covered with diamond grinding wheels deviating grain size to produce a finer or - when using coarser diamond particles - rougher bottom surface of the recess.

In Fig. 3, in addition to the working stroke shown in the longitudinal direction of the tool by the double arrow on the tool shank, another possibility of the grinding movement of the tool is indicated by the arcuate double arrow shown on the left in front of the form grinding tool. Such a working movement oscillating on a short circular arc then naturally requires a correspondingly modified formal adaptation of the outer contour of the form grinding tool 38.

It can be seen that within the scope of the inventive idea, modifications and further developments of both the described exemplary embodiment of the partial endoprosthesis 10 and of the tool 34 can be implemented. Such modifications can relate to the exact shape and size or the arrangement of one or more anchoring pins on the skid-like prosthesis part 12 or also to the exact outline shape and thickness dimensioning as well as the concave design of the sliding surface 26 and the materials used for the prosthesis parts. With regard to the partial endoprosthesis, it is essential that at least the one assigned to the tibia 24 designed prosthesis part, but preferably also the upper, femur-associated skid-like prosthesis part in their respective bone-facing fastening side have a depression 18 or 28 serving as a bone cement depot.

Claims

Patent claims

1. Partial endoprosthesis (10) for knee joints, consisting of two prosthesis parts (12; 24), one of which is formed by an inlay (24) which can be inserted into a recess previously incorporated into the original joint surface of the tibia and by means of bone cement can be fixed and its side facing the femur is designed as a sliding surface (26) for the assigned second runners-like prosthesis part (12) which can be fastened in a receptacle incorporated in the region of the femur opposite the sliding surface, characterized in that at least the m of the recess of the tibia is closed Provide fixing inlay (24) in its underside facing away from the femur with a depression (28) serving as a bone cement depot

2. Partial endoprosthesis according to claim 1, characterized in that the recess (28) m αer femur-facing underside has an all-round closed wall (30;

3. Partial endoprosthesis according to claim 1 or 2, characterized in that the recess surrounding the wall of the inlay (24) is provided in whole or in part with a texture increasing the adhesion of bone cement, roughening or a number of regularly or irregularly distributed projections.

4. Partial endoprosthesis according to one of claims 1 to 3, characterized in that at least the part of the inlay (24) which faces the skid-like prosthesis part (12) on the femur side is made of a highly stressable plastic having good sliding properties, preferably high-pressure polyethylene. consists.

5. Partial endoprosthesis according to one of claims 1 to 4, characterized in that the runner-like prosthesis part (12) to be fastened in the associated receptacle in the femur is provided in its underside facing away from the tibia with a depression (18) serving as a bone cement depot.

6. Partial endoprosthesis according to claim 5, characterized in that the recess (18) in the underside facing away from the tibia is at least predominantly closed all around.

7. Partial endoprosthesis according to claim 5 or 6, characterized in that the wall delimiting the recess of the skid-like prosthesis part (12) is provided with a texture which increases the adhesion of bone cement, roughening or a number of regularly or irregularly distributed projections.

8. Partial endoprosthesis according to one of claims 1 to 7, characterized in that the skid-like prosthesis part

(12) is manufactured in a manner known per se from a metal, preferably a high-alloy steel, for example a cobalt-chromium-molybdenum alloy, and that the runners area (14) interacting with the joint surface (26) of the tibial-side inlay (24) of the prosthesis part (12) is polished.

9. Partial endoprosthesis according to one of claims 5 to 8, characterized in that of the recess (18) delimiting wall of the skid-like prosthesis part (12) at least one known, anchored in a prepared bore in the receptacle of the femur Protrudes (20).

10. Tool for incorporating the recess to be provided for receiving the tibial inlay (24) into the knee-joint end of the tibia by means of a tool in Oscillating working movement of a motor-driven drive machine, characterized in that the tool (34) is designed as a shaped grinding tool (38) arranged at the end of a tool shank (36) which can be inserted in the tool holder of the driving machine, the working grinding surface (42) of which is abrasive grinding particles acting on the bone substance is occupied, and its shape essentially corresponds to the limitation of the recess in the tibia for the inlay to be implanted

(24) is selected accordingly, its dimensions being only m in the oscillation direction around the oscillation stroke smaller than the recess to be produced.

11. Tool according to claim 10, characterized in that the tool shank (36) is designed as an elongated flat profile, one end region of which is suitably designed for mounting in the tool holder of the drive machine, and in that the form grinding tool (38) of one in the other end region formed from a flat side of the flat profile protruding molded body, the surface of which lies opposite the fastening surface on the flat profile (36) and forms the working grinding surface (42).

12. Tool according to claim 11, characterized in that a second form grinding tool (38 ') is provided on the flat side of the tool shank (36) opposite the flat side provided with the form grinding tool (38).

13. Tool according to one of claims 10 to 12, characterized in that the working grinding surface (s) (42) is or are covered with diamond grinding particles.

14. Tool according to one of claims 10 to 13, characterized in that at a distance from the form grinding tool

(38) or the form grinding tools (38; 38 ') each have a stop protruding from the tool shank, for example A stop pin (44; 44 ') is provided, the distance of which from the respectively assigned form grinding tool (38; 38') corresponds to the distance of the recess for the inlay (24) to be worked into the tibial joint surface from the outer bone wall of the tibia .

15. Tool according to claim 14, characterized in that the respective stop pin (44; 44 ') m of its length is dimensioned such that it over the plane of the working grinding surface (42) of the associated form grinding tool (38; 38 ') comes forward.

16. Tool according to claim 14 or 15, characterized in that the respective stop pin (44; 44 ') with respect to the form grinding tool (38; 38') can be attached to the flat profile tool shank (36) so as to be variable in distance.