Implant system

The invention relates to an implant system having at least one shaft of a prosthesis, in particular a hip joint prosthesis, which can be anchored without cement, and a set of instruments for the preparation of the bone in which the shaft is to be anchored.

A shaft of a hip joint prosthesis which can be anchored without cement is known from EP 0 135 755 A1. This prosthesis shaft is straight, has a trapezoidal cross-section and has groove-like recesses in the proximal region. The rib structure formed hereby is intended to improve the absorption of torsional forces in the proximal shaft region.

It is a problem on the insertion of straight shafts that the trochanter major of the femur can hereby be impaired. When curved shafts are used, in contrast, the trochanter can admittedly be maintained. However, the insertion of a curved shaft is again a problem if the shafts should have rib structures such as were mentioned above.

The reason for this is that the shaft can reach a pre-determined end position in the bone when hammered on a plurality of different movement paths. This is not a problem as long as the shaft has no rib structures. However, if the shaft is provided with rib structures, there is a risk that the ribs cut their own track into the bone which allows the shaft to move onto an incorrect path on which the shaft cannot be driven into the end position, at least no longer in the desired manner.

Due to these problems occurring on the insertion, curved shafts provided with ribs have not become as widespread as would have been expected due to the existing advantages per se of such shafts.

It is the object of the invention to provide an implant system with which curved prosthesis shafts can also be reliably anchored in the bone in a simple and reliable manner.

This object is satisfied by the features of claim 1 and in particular in that the shaft has an arcuate base body and the set of instruments includes a first instrument which is shaped in accordance with the arcuate shape of the shaft and with which a recess serving for the reception of the base body can be established in the bone, and wherein the shaft is provided with ribs in the proximal region and the set of instruments includes a guide body for a second instrument which is shaped in accordance with the arcuate shape of the shaft and with which second instrument structures can be established in the bone serving for the fixing of a path for the shaft ribs when the guide body is located in the recess.

In accordance with the invention, in addition to the instrument, in particular a rasp, serving for the establishment of the recess for the base body, a further instrument is provided with which the bone can be directly prepared for the guidance of the shaft ribs. The invention is characterized in that the recess previously established by means of the first instrument is used for the working to be carried out by the second instrument in that a guide body is used which is likewise shaped in accordance with the base body of the shaft, is inserted into the recess and then serves as a guidance for the second instrument. A path is subsequently fixed for the shaft ribs, and thus for the shaft overall, by means of the second instrument guided in a defined manner, said shaft subsequently being hammered to the bone working taking place by means of the second instrument.

Since a guide body corresponding to the shaft with respect to the arcuate form serves as a reference for the working movement of the second instrument, it can be ensured in accordance with the invention that a track is established for the shaft ribs and thus a path is pre-determined which is adapted to the arcuate shape of the base body of the shaft. It is hereby ensured that the curved shaft provided with the ribs moves in the desired manner into the end position previously pre-determined by means of the first instrument.

The ribs or the tangents at the ribs extend in accordance with the shaft curvature at an angle to the shaft axis different from zero. This rib angle in particular lies in the range from 0° to 45°, with, however, larger angles also being possible, and is selected in dependence on the arcuate shape of the shaft.

The guide body can be provided in the form of a separate part. Alternatively, the first instrument can simultaneously be made as the guide body for the second instrument. In this case, an additional guide body can be dispensed with.

Further preferred embodiments of the invention are also recited in the dependent claims, in the description and in the drawing.

Provision is thus preferably made for the cross-section of the shaft to be rectangular or trapezoidal with pronounced longitudinal edges which establish the contact to the cortex. Provision is preferably furthermore made for the arcuate shape of the base body to be selected in particular with respect to curvature and length in relation to two oppositely disposed edges, i.e. a lateral edge and a medial edge, such that an end position of the base body results which is clearly defined by a plurality of contact positions, in particular three contact positions, at the cortex of the bone. It is hereby ensured that the respective base body centers itself on insertion in accordance with its rectangular or trapezoidal cross-section and that hollow spaces are no longer present between the base body and the bone bed formed by the cortex in the end position since a clamping also takes place between the base body and the bone bed formed by the two lateral edges and between the two medial edges. The curvature of the base body and the length of the base body and/or of the shaft are in particular matched to one another in a pre-determined manner.

It is particularly advantageous if, in accordance with a further embodiment of the invention, the extent of the shaft ribs is adapted to the arcuate shape of the base body of the shaft such that an end position of the base body clearly defined by a plurality of contact positions, in particular three contact positions, at the cortex of the bone can be reached between oppositely disposed lateral and medial edges. Provision is made for the contact positions not to be punctual, but to be formed in the form of zones stretched in the longitudinal direction.

The ribs of the shaft can extend in both a straight and in a curved manner. In this process, it is not compulsory for all ribs to be straight or for all ribs to be curved. Both straight and curved ribs can be provided within a rib structure including a plurality of ribs. It is basically also possible to provide only one single rib on each side of the shaft. It is furthermore possible that one or more ribs are only provided on one side.

The extent of the ribs can in particular be made dependent on their respective length. In this process, ribs not exceeding a specific length can be made straight, whereas ribs exceeding a specific length can extend in a curved manner.

Provision is furthermore preferably made for the shaft ribs to extend toward distal starting from an at least approximately common plane. This common plane is preferably disposed in the region of a resection plane of the bone with an inserted shaft.

If both straight and curved shaft ribs are present, provision is preferably made in accordance with a further embodiment of the invention for the straight shaft ribs, on the one hand, and tangents at the curved shaft ribs, on the other hand, to extend to the shaft axis at the same angle different from zero.

Provision can in particular be made with a relatively long shaft for its base body to be provided with a flattened area at its lateral side in the region of its distal end. This preferably also applies to the first instrument and to the guide body. The observation of an optimum path on the hammering in of the shaft or on the insertion of the first instrument and of the guide body is hereby facilitated. The distal tip can in each case be displaced asymmetrically toward medial.

It is furthermore proposed that the first instrument is provided with a respective chamfer at the anterior and posterior sides.

Provision can furthermore be made for the distal end of the first instrument to project in the distal direction beyond a base body of the first instrument corresponding to the base body of the shaft. The first instrument is hereby provided with a distal extension in comparison with the shaft.

The second instrument, with which the structures serving for the fixing of a path for the shaft ribs are established in the bone, is preferably movable toward distal along a guide path pre-determined by the guide body. This guide path and the shaft ribs are adapted to one another with respect to their extent so that the shaft ribs run in their own, pre-determined track on the hammering in of the shaft. The guide path is preferably curved in accordance with shaft ribs extending in a curved manner.

The guide provided at the guide body for the second instrument is furthermore preferably made as a compulsory guide in full or regionally.