The fatigue strength of small diameter tibial nails

This study was performed to evaluate the fatigue strength of commonly used small diameter tibial nails. Five types of small diameter tibial nails (7 m m aap Biorigid Nail (R); 8 mm aap Biorigid Nail (R) ,8 mm Ace UTN (R), 8 mm RT Tibial Nail (R), 8 mm Synthes UTN (R)) with a sample size of 30 implant s (six samples of each nail:type) were tested with a new modular testing sy stem. One module of the testing system was removed, simulating a 55-mm dist al tibial defect, to induce maximum loading on the distal portion of the im plant and locking bolts. The average yield strengths were obtained from static, single cycle tests a nd revealed an average static ultimate load of 1072 N (aap7), 1820 N (aap8) , 1812 N (Ace), 1942 N (R&T), and 1543 N (Syn). The fatigue limits were eva luated by cyclic, sinusoidal loading and revealed a fatigue strength of 750 N (aap7), 1092 N (aap8), 906 N (Ace), 971 N (R&T), and 771 N (Syn) to endu re 500000 cycles. Our results showed that the solid tibial nails fractured in the testing device in the same manner and location as they do in-the cli nical series. This study showed that all the small diameter tibial nails tested are obvio usly able to transmit loads of more than average body weight. The fatigue s trength of the implants is relatively high, which means that patients witho ut bone defects could be mobilised with full weight bearing as tolerated by pain. However, according to the results of this study, early mobilisation with full weight bearing in a normal gait cycle can not be suggested in pat ients with segmental tibial fractures or fractures with defect zones. (C) 2 001 Elsevier Science Ltd. All rights reserved.