DE4223373C2 - Endoprosthesis socket for knee joints and process for its manufacture - Google Patents

Description

The invention relates to an endoprosthesis stem for cementless Implantation for knee joints, consisting of one in one Tibial or femoral medullary canal or in a bone canal cored leaf-shaped tapering towards the distal end Shaft with a rotation-preventing profile.

DE 28 39 093 A1 describes an endoprosthesis for Hip, knee or angle joints are described in which the shaft is designed as a tapered plug, which has threads on the circumference, which are defined by four longitudinal grooves are exempted.

WO 83/02555 also describes a knee joint endoprosthesis wrote that in the femoral as well as tibial anchoring part a first section carrying an external thread, one thereon attached pin and in the lower part with an end piece Has longitudinal grooves.

DE 21 54 338 A1 relates to a joint prosthesis, the one has a star-shaped cross section in the shaft area. Indeed this prosthesis is intended for cementation.

DE 26 31 531 C2 also deals with a knee joint endopro thesis, which is anchored in the bone by means of a binding agent should, in particular, special methyl methacrylate adhesive fabrics suggested.

DE 37 43 329 C1 relates to an endo prosthetic hollow shaft for cementless implantation in the form of a truss made of pro filen is built and the bending stiffness of the hollow shaft at every point of the bending stiffness of the bone  by dimensioning the profile shapes, profile thicknesses and Arrangement of the profiles approximately corresponds.

The endoprostheses known for the prior art for However, knee joints have several disadvantages. So has to a relatively healthy bone sub through large-volume pre-drilling be sacrificed to create a cavity for the shaft To create anchoring part. In addition, the be knew the surface structures of prosthetic sockets regularly not effective to loosen the shaft in the bone effectively prevent.

It is therefore an object of the present invention to begin with improve the endoprosthesis so that forces and Moments primarily via the implant / cortex contact surface and implant / cancellous bone in the femur or tibia while maintaining and the greatest possible protection of the existing bone substance will wear that from the occurring torsional moments directed forces can be safely absorbed and that a Loosening of the prosthesis is prevented. Here, the endo prosthesis largely to the individual patient femur or -tibia can be customized.

This task is performed by an endoprosthesis stem Claim 1 solved. Other than that just a shallow depth pointing ribs or grooves allow the wings to be fixed Seat of the endo inserted into the tibia or femoral cavity prosthesis. The wings prevent rotation of the shaft to the bone, with additional endoprosthesis shaft material can be saved since the Pro The largest diameter of these theses is no larger than that previously Known endoprostheses according to the prior art are direct. Each of the wings is leaf-shaped, with what optimal material savings for the endoprosthesis shaft and thus a reduction in the bone to be removed volume results. To better anchor the shaft in the  To reach the tibia or femur are in the wing or in the flue holes, through which cancellous bone can grow.

There is a further reduction in the risk of loosening by making each of the wings from a sheet with a bending rigidity adapted to the bone. As a material for the endoprosthesis shaft, cobalt-chromium-molybdenum, Co balt-nickel-chromium-molybdenum or titanium alloys or unle alloyed titanium or tantalum or niobium. These substances are largely corrosion-resistant and biocompatible. Before the shaft is differentiated over its axial length have flexural rigidity.

Preferably, the shaft or the wings can over the Surface have different thicknesses, especially for distal end less than the proximal end there.

Furthermore, the expected different force Introduction to different locations and the tibia or Fe Mur shape corresponding to the wings of a different width have, preferably the respective adjacent wing have the same angular positions to each other. With four wings they are at right angles to one another in a cross shape.

In the simplest case, the endoprosthesis socket can be such that the wings consist of several strips of sheet metal fen exist, which together in the middle along the longitudinal axis are welded. Preferably, the shaft has on its pro ximal end a conical recess as a support for bearings and sliding surfaces of the joint part.

The invention further relates to a method for producing egg Nes endoprosthesis shaft, which is characterized in that The holes in sheet metal strips for a predefinable bending stiffness before or after cutting to a certain size and  punched, drilled or otherwise in a specific arrangement are brought over and / or the sheet thickness of the sheet strips the area in different places to different degrees is reduced by machining, the Metal strips are preformed so that they are along a Longitudinal central axis can be connected by welding. With this Manufacturing process is possible from standardized sheet metal share special shapes for each patient Adaptation to the geometry and inner contour of the femur or tibia easy way to create when x-rays out at least two levels can be consulted. In contrast to the stems used so far, the wings in  The medullary cavity is inserted in the correct position, the veran kerungsteile be fixed in that they optimal contact to the existing cancellous bone 'and wall of the bone cavity take, wax there and so a secure power transmission can make. Due to the shape of the anchoring parts with a variety of breakthroughs and that into these breakthroughs bone material that has grown in after implantation is collected compared to conventional rigid, relatively smooth anchoring part len a largely secure secondary fixation with optima rotation stability and with a better approximation the natural stress distribution in the bone reaches this was previously possible. By selecting the number of sheet metal strips as well as through their mechanical preparation, further bending changes in stiffness are made.

An embodiment of the invention is in the drawings shown. Show it

Fig. 1 and b are longitudinal sections respectively of the Endoprothesenschaftes according to the invention,

Fig. 2 shows a cross section along the line II-II and

Fig. 3 shows a cross section along the line III-III in Fig. 1a.

The endoprosthesis shaft 10 shown in FIGS. 1 a, 3 b is a conical receptacle 11 at its proximal end. The shaft typically consists of four cross-shaped wings 13 arranged at right angles to one another, the outer contour of which can be individually adapted to the shape of the medullary cavity based on pre-operative X-ray recordings made perpendicular to one another. The outer contour of the anchoring shaft is then supported over its entire length on the cor tikalis. Each of the wings has holes 13 of different sizes and arrangements, which on the one hand the bending stiffness of the endoprosthesis anchoring part can be adapted to the bending stiffness of the bone (femur, tibia) and on the other hand allows bone to grow through. The wings are connected to one another along the longitudinal axis in the area of the weld 14 . The calculation of the geometry and distribution of the holes for the predeterminable bending strength can be determined, for example, by the method of the finite elements.

Basically, the wing shape shown is also for others suitable as a knee joint endoprosthesis, as long as the rigidity the endoprosthesis that essentially shapes the shaft profile is sufficiently large.

Claims (11)

1. Endoprosthesis shaft for cementless implantation for knee joints, consisting of a leaf-shaped shaft ( 10 ) to be anchored in a tibia or femur medullary canal or in a bone canal with a rotation- preventing profile, characterized in that the shaft ( 10 ) has more than two leaf-shaped wings ( 12 ) with a plurality of openings (holes ( 13 )). 2. Endoprosthesis shaft according to claim 1, characterized in that each of the wings ( 10 ) consists of a sheet metal with a bending stiffness adapted to the bone. 3. Endoprosthesis shaft according to one of claims 1 or 2, characterized in that the shaft ( 10 ) consists of CoCrMo, CoNiCrMo or a titanium alloy or unalloyed titanium or tantalum or niobium. 4. Endoprosthesis shaft according to one of claims 1 to 3, characterized in that the bending stiffness of the shaft ( 10 ) is different over the axial length. 5. Endoprosthesis shaft according to one of claims 1 to 4, characterized in that the shaft ( 10 ) or the wing gel ( 12 ) on the surface have different strengths. 6. Endoprosthesis shaft according to one of claims 1 to 5, characterized in that at least one wing ( 12 ) in a cross section has a different width from the width of the other wing ( 12 ). 7. Endoprosthesis shaft according to one of claims 1 to 6, characterized in that each adjacent wing ( 12 ) have the same angular positions to each other. 8. Endoprosthesis shaft according to one of claims 1 to 7, characterized in that four wings ( 12 ) are provided. 9. Endoprosthesis shaft according to one of claims 1 to 8, characterized in that the wings ( 12 ) consist of several sheet metal strips which are welded together in the middle along the longitudinal axis (14). 10. Endoprosthesis shaft according to one of claims 1 to 9, characterized in that the shaft ( 10 ) has at its proximal end a conical recess ( 11 ) as a carrier for bearings and sliding surfaces. 11. Process for the manufacture of an endoprosthesis shaft one of claims 1 to 10, characterized in that holes in one for a predeterminable bending stiffness Sheet strips before or after cutting in a be agreed size punched in a certain arrangement, drilled or otherwise introduced and / or the sheet Strengthen the sheet metal strips across the surface at different Places to different degrees by machining Bear processing is reduced that the metal strips are preformed and to form a multi-winged shaft with are welded to each other.