Mechanical Properties of the Shoulder Ligamentsunder Quasi-static and Dynamic Loading

Introduction: The tensile properties of the shoulder ligaments under dynamic loading have not been investigated. A recent finite element model showed the ligaments in the shoulder were subjected to dynamic tensile loading during 8.65 m/s lateral shoulder impact [1]. The mechanical properties of shoulder joints under dynamic loading are needed to better understand shoulder injury mechanisms, to improve shoulder finite element models and to further develop the shoulder of car crash dummies. Methods: Thirty-three fresh human shoulders were harvested and boneligament-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 (Fig 1). One quasi-static rate (0.1 %/sec) and two high rates were used in this study. The two high rates (40,000 %/sec and 15,000 %/sec) were determined by analyzing ligament strain rates in the shoulder finite element model [1] subjected to three different test conditions (Heidelberg sled test, FMVSS 214 test, and IIHS side impact test. The acromioclavicular and sternoclavicular ligaments were tubular in cross section and cross sectional area was obtained by measuring the thickness around the ligament circumference with a fine gauged needle and micrometer.