Complex varus elbow instability: a terrible triad model.

Hypothesis The terrible triad is a debilitating injury that involves elbow dislocation with injury to the lateral collateral ligament (LCL) complex, the radial head, and the coronoid process. This study investigated the role of these components in varus stability of the elbow. Materials and methods We investigated the role of these components in varus stability of the elbow using 10 cadaveric fresh frozen upper extremities. The testing order allowed each of four states to be tested (intact, LCL complex deficient or repaired, radial head resected or replaced) at two flexion angles and multiple coronoid resection levels. Values for restraining load (newtons [N]) at 1.5 cm of varus displacement were obtained on a materials testing machine. Results Beyond a 50% loss of the coronoid process, neither repair of the LCL nor replacing the radial head alone resulted in a statistically significant increase in varus stability. For a loss of the coronoid process between 67-75%, repair of the LCL and replacement of the radial head showed improved stability over repair alone, or radial head replacement alone. For loss of the coronoid beyond 75%, even repair of the LCL and replacement of the radial head did not improve varus stability of the elbow. Conclusion These findings provide a biomechanical basis for aggressive treatment of coronoid fractures as a component of the terrible triad injury. Levels of evidence Basic science study.