Increased Rate of Posterior Shoulder Instability in Young Active Patients (SS-10)

Abstract

Posterior shoulder instability is significantly less common than anterior shoulder instability and is often difficulty to diagnose. While most patients with anterior shoulder instability complain of instability, patients with posterior shoulder instability often complain of shoulder pain and decreased athletic performance. Older studies have reported that posterior instability makes up 2 – 5 % of all shoulder instability. A recent study from the United States Military Academy, reported a higher 10% of posterior shoulder instability during 1 academic year. In our population, the incidence of posterior shoulder instability is significantly higher than the previously reported in the literature. A retrospective review was conducted at an active sports medicine referral military medical center with three sports medicine fellowship-trained orthopaedic surgeons between July 1, 2010 and June 30, 2011. Medical records were reviewed for patients who underwent operative intervention for shoulder instability. Patients were categorized by their direction of instability: anterior, posterior, or other (anterior & posterior or multidirectional). One hundred patients underwent operative intervention for shoulder instability during the one year period. There were 95 males and 5 females with a mean age of 26.2 years of age. There were 60 patients with anterior instability, 22 patients with posterior instability, and 18 patients categorized as other. In our study, posterior instability is significantly more common at a rate of 22% of all shoulder instability compared to 10% that was the highest rate reported in the literature. It is most commonly seen in males involved in overhead or contact sports. The most common etiology of posterior instability is believed to be secondary to repetitive microtrauma. The significantly higher prevalence of posterior shoulder instability in our study may be secondary to the young active military population who are involved in very demanding mandatory physical training where push-up and pull-ups are required for their job. Another reason for the higher prevalence may be secondary to the difficulty in diagnosing patients with posterior instability. While patients with anterior instability can usually recall a specific dislocation or subluxation, patients with posterior instability are less likely to have one specific traumatic dislocation or subluxation and often complain of vague shoulder pain, weakness, and decrease in athletic performance. This constellation of symptoms can be common in young active patients. Interestingly, anterior instability only comprised 60% of all shoulder instability. We believe that posterior shoulder instability is much more commonly than previously reported and that thorough evaluation for posterior instability is critical for patients complaining of shoulder pain.