An online video investigation into the mechanism of elbow dislocation

Acute elbow instability leading to dislocation is thought to be a spectrum initiated by an injury to the lateral stabilizing structures of the elbow. Previous cadaveric studies have shown elbow dislocations to occur in flexion. The purpose of this study was to analyze videographic evidence of the deforming forces and upper extremity position during elbow dislocations. We sought to corroborate previous biomechanics studies with in vivo observations.

We included 62 YouTube.com videos with a clear videographic view of an elbow dislocation. Three senior elbow surgeons independently evaluated arm position at the time of dislocation, along with the suspected deforming forces at the elbow based on these positions.

Of the 62 visualized elbow dislocation events, the vast majority (92%) dislocated at or near full extension. The most common arm positions were forearm pronation (68%) with shoulder abduction (97%) and forward flexion (63%). The typical elbow deforming forces were a valgus moment (89%), an axial load (90%), and progressive supination (94%). We identified 4 discrete patterns of arm position and deforming forces.

Acute elbow dislocations in vivo occur in relative extension irrespective of forearm position, a finding distinct from previous cadaveric studies. The most common mechanism appears to involve a valgus moment to an extended elbow, which suggests a requisite disruption of the medial collateral ligament, the known primary constraint to valgus force. These videographic findings suggest that some acute elbow dislocations may result from acute valgus instability and therefore are distinct in nature and mechanism from posterolateral rotatory instability. This information could lead to improved understanding of the sequence of structural failure, modification of rehabilitation protocols, and overall treatment.