Posterior Instability

Introduction

Posterior shoulder instability represents an array of disorders, ranging all the way from symptomatic subluxation (symptomatic, excessive translation of the humeral head on the glenoid) to multiple frank dislocation events. Posterior shoulder instability events are primarily subluxation events in nature, with complete dislocations comprising only 3% to 8%. ^, Posterior dislocations are significantly less common than anterior, with the percentage of posterior events accounting for 2% to 6% of all shoulder dislocation events. ^,

With advances in imaging and arthroscopy, the diagnosis of posterior shoulder instability has improved. In addition, there are some recent reports suggesting an increase in the prevalence of posterior shoulder instability based upon arthroscopic findings in surgical shoulder instability cohorts. However, the presence of a posterior labral tear does not necessarily denote posterior instability, as 36% of patients with instability are noted to have combined labral lesions at arthroscopy. Robinson reported the largest known series of posterior dislocations findings. A recent report on posterior instability in a collegiate athlete population showed that intercollegiate athletes were at highest risk, and those that participated in wrestling, rugby, and football had the highest rates of instability. Male athletes experience posterior instability at twice the rate of female athletes. As will be discussed, a complete history and physical examination are essential in the diagnosis of posterior instability, as 42% of posterior “instability” patients do not report instability symptoms, but rather pain only.