Method for implantation of a femoral implant
The invention relates to a cap-shaped implant for implanting on a prepared stump of a femoral head. The implant is in the form of a ball section, having a flat base surface and a polar axis which is arranged in a perpendicular in relation to the base surface. According to the invention, a cavity is arranged in ball section which protrudes from the base surface, said cavity is rotationally symmetrical and comprises a hollow spatial axis which is arranged below an angle (a) which is different form zero in relation to the polar axis.
1. A method for implantation of an implant made in a cap shape onto a femoral head of a femur, comprising:
choosing an implant made in a cap shape which comprises:
a spherical outer surface defining a polar axis extending through a spherical center (M),
a planar base, said polar axis perpendicular to a plane containing said planar base;
a hollow space which is rotationally symmetrical about a hollow space axis the hollow space axis forming an angle α different than zero to the polar axis;
resecting the femoral head so as to obtain a prepared stump representing a mating shape to the hollow space of the implant and being rotationally symmetrical with respect to an implantation axis (A); and
working the femoral head so that the implantation axis (A) is inclined at least in a frontal plane with respect to the femoral neck axis (N) of the femur.
2. A method in accordance with claim 1 , further comprising:
inserting a first drill wire into the femoral head along the femoral neck axis (N),
placing an alignment instrument onto the first drill wire, said alignment instrument comprising an indication means for defining the inclination of the implantation axis (A) with respect to the femoral neck axis (N) and thus defining the implantation axis (A);
inserting a second drill wire into the femoral head along the implantation axis (A) inclined with respect to the femoral neck axis (N); and
removing the alignment instrument and the first drill wire before the resecting of the femoral head.
3. A method in accordance with claim 2 , further comprising using the second drill wire as a guide tool in the working of the femoral head.
4. A method in accordance with claim 2 , further comprising removing the second drill wire before placing the implant made in cap shape onto the prepared stump.
5. A method in accordance with claim 2 , further comprising implanting the implant such that the hollow space axis and the implantation axis (A) coincide on the placing of the implant made in cap shape onto the prepared stump.
6. A method in accordance with claim 5 , further comprising securing the implant against tilting of the hollow space axis with respect to the implantation axis (A).
7. A method in accordance with claim 2 , further comprising working the femoral head so that the implantation axis (A) is inclined with respect to the femoral neck axis (N) both in the frontal plane and in a sagittal plane.
8. A method in accordance with claim 1 , wherein the step of working the femoral head such that the inclination of the implantation axis (A) with respect to the femoral neck axis (N) corresponds to the angle between the polar axis and the hollow space axis of the implant.
9. A method in accordance with claim 1 , further comprising placing the implant on the prepared stump of the femoral head such that the polar axis of the implant and the femoral neck axis (N) coincide.
10. A method in accordance with claim 1 , wherein the angle α lies in the range of 15° to 50°.