A new modular testing system for biomechanical evaluation of tibial intramedullary fixation devices

This biomechanical study was performed to evaluate a new modular, tibial te sting system developed for analysis of tibial nails and their locking screw s. A new testing system, consisting of five modules, was designed to simulate a tibia. For this study one module was removed to simulate a 55-mm distal t ibial defect inducing maximum loading on the distal portion of the implant and locking bolts. The tibial load offsets were 23 mm proximally and 10 mm distally medial to the centreline of the tibial shaft to simulate the locat ion of the expected resultant load during the peak loading and inversion to rque on the ankle during the gait cycle. Four solid tibial nails (STN(R), S tryker-Howmedica-Osteonics, Kiel, Germany) were tested to static failure an d 15 nails were tested dynamically. Our results showed that the solid tibial nails fractured in the testing dev ice in the same manner and location as they do in clinical series. Evaluati on of the results showed the mean fatigue limit of the STN to be 1.4 kN for 500 000 cycles with a standard deviation (S.D.) of 0.33 kN. This biomechanical study establishes a standard technique for the biomechan ical testing of tibial nails, in a clinically relevant manner, avoiding the inconsistency of cadaver bone tests. As it is a standardised test set-up t his new modular testing system could serve as a standard by which small dia meter tibial nails and other devices could be evaluated and compared with o ther systems currently in use. (C) 2001 Elsevier Science Ltd. All rights re served.