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 epicondyle were subjected to tensile tests under two displacement rates (100 mm/min and 10 mm/min) and different elbow flexion positions 45°, 90° and 135°. Biomechanical properties of ultimate tensile strength, failure strain, energy absorption and stiffness of the bone-tendon specimen were determined. Statistically significant differences were found in ultimate tensile strength, failure strain, energy absorption and stiffness of bone-tendon specimens as a consequence of different elbow flexion angles and displacement rates. The results indicated that the bone-tendon specimens at the 45° 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 strength at all flexion angles when tested at the 10 mm/min displacement rate. These results indicate that creep damage occurred during the slow displacement rate. The major failure mode of bone-tendon specimens during tensile testing changed from 100% of midsubstance failure at the 90° and 135° elbow flexion to 40% of bone-tendon origin failure at 45°. We conclude that failure mechanics of the bone-tendon unit of the lateral epicondyle are substantially affected by loading direction and displacement rate.