Mechanical Properties of the Shoulder Ligaments under Dynamic Loading

Thirty-three fresh human cadaver shoulders were harvested and bone-ligament-bone specimens of acromioclavicular joint, coracoclavicular joint and sternoclavicular joint were obtained. A test fixture and clamps specifically designed for this ligament study and a high-speed Instron machine were used. One quasi-static rate (nominally 0.1 %/sec) and two high rates (nominally, high rate 1 = 40,000 %/sec and high rate 2 = 15,000 %/sec) were used in this study. In the acromioclavicular joint tests, ligament failure was the most common failure mode. Bone fractures occurred most often at the clavicle rather than acromion. In the coracoclavicular joint tests, the majority of specimens failed at the ligament and bone fractures occurred at the coracoid. In the sternoclavicular joint tests, the specimen failed at the bone in most cases. In the acromioclavicular joint and coracoclavicular joint tests, high rate 2 tests and quasi-static tests had more bone fracture cases than high rate 1 tests. Cross sectional area, deflection at failure, load at failure, strain at failure, stress at failure and Young’s modulus of these three shoulder joints were found. The Young’s modulus, ultimate stress and ultimate load of the three joints were found to be significantly lower in the quasi-static rate tests compared to the high rate 2 tests but not significantly different between high rate 1 and high rate 2 tests. There are no significant relationships between cross-sectional area and age, height or weight, nor between the mechanical properties of the shoulder joint and age, height or weight.