Acute bipolar radial head prosthesis disassembling

Objectives Radial head replacement by using a bipolar prosthesis is frequently used when unable to reconstruct fractures of the radial head. The GUEPAR © implant is a metallic bipolar prosthesis. The authors describe an uneventful complication of this implant. Four patients have sustained an acute disassembling of the GUEPAR © implant after an important grip effort. A biomechanical study was performed in order to explain this disassembling. Method The retention system of the GUEPAR implant has been tested at different temperatures: 4, 20 and 37°C. The stem and the cup were cemented in a support. Disassembling was achieved using a dynamometer. Results The study has shown that the theoretical grip strength leading to disassembling is 145.65 kg at 4°C and 51.45 kg at 37°C. Discussion The polyethylene of the floating head of the implant appears to be very influenced by the temperature. The authors state that the association of a cam effect between the floating cup and the stem with an important grip might lead to the disassembling of the GUEPAR prosthesis. This study shows that the conception of a bipolar implant is very demanding in terms of retention of the floating head on the stem.