Special instruments and prosthetic cups for the removal and replacement of a total hip prosthesis.

In the course of replacing more than 500 total hip prostheses over a period of five years the authors have developed a new set of instruments for the removal of the defective prosthesis and cement and for improved anchorage of the new prosthetic cup. The set comprises: 1. A set of special chisels and an axially guided drill for removal of the old cement from the femur. These instruments greatly simplify the latter procedure. 2. A new type of prosthetic cup with a weight-bearing collar. This cup is used for cases in which the amount or structure of the acetabular bone is such that it will not support a conventional cup. 3. A new type of drill with a flexible drive and easily exchangeable drill bits for cutting anchorage holes in otherwise inaccessible parts of the acetabular bone.