Analysis of Shoulder Ligament Injury Potential in Automotive Rear-End Impacts

The potential for injury to the acromioclavicular (AC) and coracoclavicluar (CC) ligaments as potential sequelae of rear-end collisions is examined. In the current study, rear-end impact data from four crash tests were analyzed to quantify and bound forces applied to the shoulder of the Hybrid III 50^th percentile male occupant seated in the target vehicle. Two potential scenarios for AC and CC ligament loading were examined: 1) relative motion between the clavicle and shoulder due to belt loading on the shoulder and torso, and 2) compression of the humerus into the glenoid fossa due to locked arms on the steering wheel. Assumptions were made for the shoulder load calculations to obtain a conservative upper bound of loads that could be applied to the AC and CC ligaments. With the target vehicle at rest, the bullet vehicle speeds were 5, 10, 15, and 20 mph, yielding target vehicle changes in velocity (delta-V) of 3.9, 6.5, 8.9 and 12.2 mph. In all tests, the occupant moved initially rearward relative to the vehicle until accelerated forward by forces transmitted through the seat. For the 50^th percentile male, the AC and CC ligament forces for Scenarios 1 and 2 ranged from 38–90 N and 71–462 N. Force values calculated were less than reported force at failure of the AC and CC ligament. The forces and occupant kinematics associated with rear-end, low-speed collisions are not likely to result in AC or CC ligament injury.