Mechanical properties of different anatomical sites of the bone-tendon origin of lateral epicondyle

A series of rabbit common extensor tendon specimens of the humeral epicondy le were subjected to tensile tests under two displacement rates (100 mm/min and 10 mm/min) and different elbow flexion positions 45 degrees, 90 degree s and 135 degrees. Biomechanical properties of ultimate tensile strength, f ailure strain, energy absorption and stiffness of the bone-tendon specimen were determined. Statistically significant differences were found in ultima te tensile strength, failure strain, energy absorption and stiffness of bon e-tendon specimens as a consequence of different elbow flexion angles and d isplacement rates. The results indicated that the bone-tendon specimens at the 45 degrees elbow flexion had the lowest ultimate tensile strength; this flexion angle also had the highest failure strain and the lowest stiffness compared to other elbow flexion positions. In comparing the data from two displacement rates, bone-tendon specimens had lower ultimate tensile streng th at all flexion angles when rested at the 10 mm/min displacement rate. Th ese results indicate that creep damage occurred during the slow displacemen t rate. The major failure mode of bone-tendon specimens during tensile test ing changed from 100% of midsubstance failure at the 90 degrees and 135 deg rees elbow flexion to 40% of bone-tendon origin failure at 45 degrees. We c onclude that failure mechanics of the bone-tendon unit of the lateral epico ndyle are substantially affected by loading direction and displacement rate .