Patterns and Mechanisms of Traumatic Elbow Dislocations

Thanks to You Tube we now know that elbow dislocations don't occur the way previous investigations using cadavers led us to believe. In the past, researchers had no choice but to rely on cadavers (human bodies preserved after death) to study the patterns and mechanisms of elbow dislocation. And those studies suggested that forces placed on the flexed (or bent) elbow led to traumatic elbow dislocation.

But a review of 62 You Tube videos clearly showed that most acute elbow dislocations occur when the elbow is extended (relatively straight). A closer look at all aspects of elbow dislocation revealed some interesting information.

For example, more than two-thirds (68 per cent) of cases, the forearm is pronated (palm down) with shoulder abduction (arm away from the side). That makes sense because the person is usually reaching the arm out to brace from a fall.

The body is rotated inwardly with the palm planted on the floor or ground. The result is external rotation of the forearm. The arm is also usually forward with load and impact translated from the hand through the wrist and forearm to the elbow. Of course, the force must be enough to overcome stabilizing structures like ligaments (e.g., medial collateral ligament).

Dislocation events filmed and available on You Tube tend to be from sporting events such as wrestling (most common), skateboarding, martial arts, football, basketball, and weightlifting. Less often, elbow dislocations associated with rugby, gymnastics, and rollerblading were presented. After analysis of all the videos, there were four distinct patterns of elbow dislocation based on shoulder position, elbow position, and direction of the force.

The most common pattern (half of all acute elbow dislocations) is as described above: shoulder flexed and abducted (arm forward and out to the side) with the elbow pronated and extended (palm down and straight). The pattern is one of axial force (up through the forearm) and from the outside of the elbow inward toward the body (called a valgus force). Valgus and axial forces are enough in this pattern to tear the medial collateral ligament on the inside of the elbow (side next to the body). Wrestlers and football players had this pattern of elbow dislocation.

One-third of the cases were with shoulder extension and abduction and forearm supination (palm up) and extension. Once again, the loading forces were axial and valgus (through the forearm and across the elbow). This pattern was most often seen in inline skaters. Other much less common patterns (usually in weightlifters) were variations and combinations of these two patterns.

In summary, cadaver studies do not accurately mimic true force, pattern, and mechanisms of acute elbow dislocations. As this collection of You Tube videos showed, the key differences are not only position of the arm but also (and most especially) biomechanical stability of the anterior portion of the medial collateral ligament.

The authors do acknowledge the limitations of using You Tube videos as evidence of these observations. They suggest further study to prove whether the presence of medial collateral ligament instability before the dislocation injury may be a contributing factor. It is possible that ligamentous instability is part of the cause and effect rather than just a result of deforming forces from the fall.

References: Joseph J. Schreiber, MD, et al. An Online Video Investigation Into the Mechanism of Elbow Dislocation. In The Journal of Hand Surgery. March 2013. Vol. 38A. No. 3. Pp. 488-497.