Experimental investigation of posterior elbow dislocation in a primate model

The purpose of this experimental study was to define the soft and bony tissues changes as the elbow joint dislocates posteriorly in a primate model. Sixty-six fresh arms were used in this study and were divided into two groups where manual and automated procedures were performed to address the mechanism of elbow dislocation. The first group called IA (50 arms) was tested using a special designed apparatus and was used for Instron machine whereas second group IB (16 arms) a manual dislocation by hyper-extending the elbow at the end of the tabletop was performed. An axial compressive load was applied on the distal forearm at a constant rate of 10 mm/min in group IA. The humerus was rigidly secured on a humeral plate at 90 degrees (3), 45 degrees (17), 30 degrees (13) and 0 degrees (17) of elbow flexion. Photographs and computer data recorded the changes in the soft tissue and bone at the elbow. It required on average 1960 N to dislocate the elbow in pronation with flexion (45, 30 degrees) compared to 1030 N for supination and the elbow flexion (45, 30 degrees). Three reproducible stages of dislocation from initiation to complete failure were observed when the elbow was flexed at 45 degrees or 30 degrees with forearm pronated or supinated.