[Show abstract][Hide abstract]ABSTRACT: In femoral neck fractures in the elderly, the least traumatic operative treatment is hemiarthroplasty. In our Trauma Unit, from August 1986 to December 1986 we implanted 22 concentric bipolar cups. During follow-up this cup proved to be associated with an unjustifiably high failure rate: system-caused interprosthetic dislocation in 4 patients (18%), and extraprosthetic dislocation in a further 3 (13%). In one of the latter, interprosthetic disconnection occurred during closed reduction. In all of these, i.e., in 31% out of the 22 patients, conversion to a total hip arthroplasty became necessary. Since March 1987 we have used a positive eccentric, self-centering bipolar head. Up to September 1990 322 such prostheses were implanted. Bearing in mind the reduced general physical condition of the patients, the complication rate is considered to be low (dislocations 3.4%, conversion to total hip arthroplasty 0.9%, deep wound infections 3.1%).