Tibial Member of a Knee Joint Endoprothesis

1. Field of the Invention

The invention relates to the tibial member of a knee joint endoprosthesis as a substitute for a resectioned tibia head, consisting of a shank which is to be anchored within the tibia and of a bridge element upwardly supporting the tibial endoprosthesis knee joint member, which is provided with a clamping element attachable by screw means, for the fastening of natural or artificial tendons.

2. Description of the Prior Art

In case of a resection of a tibia head, an endoprosthesis which has a shank anchored in the tibia is utilised as a substitute. The resection also severs the natural downwardly directed tendon of the patella, and the patella or the residual part of the natural tendon must thereupon be connected to one or two artificial tendons which should then be fastened to the bridging element of the tibia head endoprosthesis. This fastening operation was performed until now by means of clamps or collars, or windable securing wires or by retaining the natural or artificial tendon against a second plate by means of a clamping plate attachable by screw means, e.g. as apparent from DE-OS 24 00 834. To this end, the tendon was exposed to one or more acute deflections, so that it could be damaged at least after a particular period by being clamped tightly and could finally be severed. In this arrangement, the clamping plates were screwed to the patient's bones.

In the case of the implantation of the tibial member of a knee joint endoprosthesis, the object of the invention consists in being able to connect natural or artificial tendons to the tibial member of an endoprosthesis replacing the tibia head which is to be resectioned, in such manner that the tendons do not have to extend over sharp edges or holes, whereby they could incur damage and be finally caused to tear.

In the case of the initially referred to tibial member of a knee joint endoprosthesis, this problem is resolved in that the bridge element is provided with an outer and concave tray comprising rounded-off edges, for reception of a tendon extremity which may be pressed into the concave tray or pan by means of a convex clamping element. The procedure advantageously applied to this end is such that the convex pan is provided at the lower extremity of a shackle or flap firmly joined to the bridge element, and that this shackle merges into an outwardly projecting arcuate surface above the surface of the concave tray or pan.

Thanks to this solution according to the invention, the tendons which are to be clamped fast are firmly joined to the bridge element of the implant in a simple, reliable and durable manner without damaging actions. Thanks to this clamping method, it is also possible that one or both artificial tendons may first be passed through between the clamping element and the bridge element or the shackle joined to the bridge element, and to grasp the extremities for tensioning until the patella has reached its required position, and is correctly adjusted, whereupon the clamping element may be screwed on tightly and thereby unequivally grips fast the tendon or tendons.

The invention is described in the following with reference to the drawings. In these:

FIG. 1 shows a sideview of the tibial member of a knee joint endoprosthesis,

FIG. 2 shows a front view of the tibial member according to FIG. 1.

In a known manner, the replacement for a resectioned tibia head of a knee joint endoprosthesis comprises a metal bridge element 1 which is intended to have a shank 2 anchored in the tibia and is provided at the top with the joint member 3 whereof the friction surfaces situated at either side of a web 4 bear the ridges of the corresponding known femur joint member which is not illustrated.

In the region of its upper collar 5, the bridge element 1 is provided at the front side with a downwardly directed shackle or flap 6 which forms a clamping element together with a plate 9 which may be screwed on. The shackle or flap 6 is secured to the bridge element 1, at the upper and lower extremities threof, and is provided at the lower extremity with a concave and preferably partly cylindrical contact surface pan 7 matched by the convex rear side of the plate 9 which may be connected to the shackle 6 by means of a screw 8. The surface of the contact area 7 is advantageously finely roughened and the oppositely situated rear side of the plate 9 is contoured, e.g. with a saw-tooth shaped outline as indicated in FIG. 1.

For implanting the tibial prosthesis member, the patella marked 10 in FIG. 2, or the natural retaining tendon of the patella which is shown dash-dotted, is connected to a strap or tendon 11 of an appropriate plastics material, which is passed through downwards between the clamping plate 9 and the shackle 6 and is lodged behind the screw 8 in a crossed manner. The surgeon thus has the means by grasping and pulling on the extremities of the tendon 11 to set up the precise required position of the patella 10 and then of tightening the screw 8, whereby the tendon 11 is clamped fast between the plate 9 and the shackle 6. The clamping fast of the tendon 11 is concomitantly assisted by the contouring of the rear side of the plate and the roughened finish of the concave contact surface of the shackle. The downwardly directed free extremities of the tendon 11 are advantageously secured by being sewn for example, to a rib 12 provided with perforations below the shackle 6.

As apparent from FIG. 1, the tendons 11 led through between the pan 7 and the clamping element 9 do not run over sharp edges, and the shackle 6 is moreover provided in continuation of the concave pan 7 with an upwardly adjacent and outwardly projecting arc 13 which merges smoothly into the pan surface 7. This arc also has the advantage that the tendon cannot exert any excessive pressure on the joint members of the prosthesis during bending movements of the leg.

Whilst the invention and many of its attendant advantages will be understood from the foregoing description, it will be apparent that various changes may be made in the form, construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form described merely being a preferred embodiment thereof.