Abstract: Apparatus for the working of a bone, especially the femur head of a human hip joint, wherein the a is to be provided with a shell-shaped endoprosthesis, is disclosed. The apparatus includes a drivable drive shaft having a free end and a pot-shaped cutting head being arranged on the free end of the drive shaft. The cutting head is open outwardly and has a guiding bore forming part of the cutting head and is centrally located thereon. The guiding bore extends in an axial direction of the drive shaft. The cutting head has an inner end face and a jacket portion on which cutting elements are arranged. Finally included is a guiding pin for cooperating with the guiding bore. The guiding pin is arranged centrally in the bone section to be treated and protrudes from the bone surface. Additional central cutting means arranged on the cutting head are disclosed.

Abstract: An endoprosthesis for a hip joint is disclosed. The endoprosthesis includes a first cap-shaped, femur head shell which is arranged on the free end of the femur head and partially overlaps the femur head. The first femur head shell has a convex outer side. A shell-shaped pan forms part of the prosthesis which has a concave inner side for supporting the first femur head shell. The pan is arranged on the free end of the acetabulum. A second cap-shaped femur head shell is included which extends outwardly beyond the edge of the first femur head shell. The second femur head shell is arranged between the first femur head shell and the femur head. The various features of the shells and pan are disclosed.