Mechanical failure in intramedullary interlocking nails.

PURPOSE: To study clinical and mechanical factors that predispose to failure of interlocking nails. METHODS: Between October 1996 and December 2002, 286 femoral fractures, 211 tibial fractures, and 47 humeral fractures were repaired using variously designed interlocking nails. Fracture pattern, level and site, nail size and type, weight bearing after nailing, and union status were reviewed after a mean follow-up of 22 months. RESULTS: Nail failure occurred in 27 fracture repairs (17 femoral, 9 tibial, and one humeral; 13 from our institution and 14 referred from elsewhere). In 55% of failed repairs, the fracture was distal. A high rate of tibial nail failure was noted. CONCLUSION: Distal fractures and stress concentration at the distal screws predispose to interlocking nail failure and can be prevented by protected weight bearing combined with the use of longer and larger nails. Routine supplementary cancellous bone grafting is unnecessary during renailing surgery when adequate reaming and a larger nail are used.