True compression of pelvic fractures under lateral impact

To promote the understanding of pelvic fracture mechanism and make more accurate evaluation of maximal deformity at the moment of fracture, kinematic response of pelvis to lateral impact and the difference between peak and final displacement were investigated.

A total of three human cadaver pelves were seated uprightly on a sled test table, explored to horizontal lateral impact by a 22.1-kg impactor at a speed of 5.2, 4.0, and 4.8 m/s. Kinematic data of pelvic osseous interesting points (POIP) were measured by the motion capture system. Trajectories of POIP, duration of impact, and deflection of pelvis were calculated as well as rotational movement of pelvis was evaluated. After impact, autopsy and CT scan were made to validate the motion capture data.

The peak deflection of pelvis under lateral impact was 31.9, 30.1, and 18.5%, while final deflection was 19.6, 13.8, and 13.8%. The final deflection was only 61.5, 45.9, and 74.46% of the peak deflection.

In clinical practice, pelvic fracture displacement tends to be underestimated. The peak compression can be 1.3-2.2 times of final compression appearing on images in hospital. Clinicians shall give adequate estimation of displacement and related injuries.