REPRESENTATIVE ASSESSMENT OF LONG-BONE SHAFT BIOMECHANICAL PROPERTIES- AN OPTIMIZED TESTING METHOD

Whole bone bending tests are commonly used in mechanical evaluation of long bones. Reliable information about the midshaft can only be obtai ned if the bending moment is uniformly distributed along the shaft, an d if the distribution of the bending stress is not adversely influence d by rigid clamping of the bone ends. A testing device was developed t o determine bending stiffness of long bones in 24 directions, perpendi cular to the bone axis. For optimal distribution of bending moment and stress, four-point bending was performed, and bone ends were simply s upported, not rigidly clamped. The method was validated by repeated te sting of a stainless steel rod, and a sheep femur. Left-right ratios w ere assessed twice in 2 groups of 5 sheep: one control group, and one group in which the left femur was stabilized with a stainless steel in terlocking nail for 2.5 yr, after a midshaft osteotomy. Test results o btained with the steel rod reproducibly were close to predicted values . Measurements with the sheep femurs were reproducible and precise for 3 of the 4 parameters of the bending test. Stiffness parameters were significantly higher in the operated sheep than in the control group. We conclude that the method described here provides accurate and repro ducible information, which is representative for the long bone shaft. (C) 1998 Elsevier Science Ltd. All rights reserved.