Shoulder response characteristics and injury due to lateral glenohumeral joint impacts.

The objective of this study was to determine response characteristics and injury of the shoulder due to lateral impacts. The need for this data was heightened in the 1990s with increasing interest in harmonization of side impact standards, and questions regarding the measurement capabilities of dummies used in evaluating side impacts. A pneumatic impacting ram was employed in carrying out twentytwo lateral impacts to eleven unembalmed human cadavers at the level of the glenohumeral joint. Velocity of the ram at the time of impact was varied throughout the impacts from 3.5 to 7.0 m/sec, in an attempt to determine injury threshold. The cadavers were instrumented with tri-axial accelerometer blocks at ten locations in the shoulder region. Bony structures instrumented included the sternum, the first thoracic vertebra (T1), clavicles and scapulae. Output from the accelerometers was utilized to calculate impact forces and to exa mine the movement of the instrumented structures. Photographic target pins were inserted into the accelerometer blocks, thus permitting image analysis of the shoulder girdle displacement. Autopsies, radiographs, and magnetic resonance images (MRIs) were performed to document trauma that occurred as a result of the impact to the shoulder. Clavicles from the cadavers were subjected to bone density scans and threepoint bending tests. Results from these evaluations were used to assess and compare properties of bones of the upper extremities. Observations from autopsy, MRI, and radiography have shown looseness of the sternoclavicular joint and fracture of the distal clavicle to be the most common injuries. Significant findings include normalized shoulder forcedeflection curves and probability of injury distribution.