High frequency of posterior and combined shoulder instability in young active patients

The purpose of this study was to describe the epidemiology and demographics of surgically treated shoulder instability stratified by direction. We hypothesized that there would be an increased frequency of posterior and combined shoulder instability in our population compared with published literature. Secondarily, we assessed preoperative magnetic resonance imaging (MRI) reports to determine how accurately they detected the pathology addressed at surgery.

A retrospective review was conducted at a single facility during a 46-month period. The study included all patients who underwent an operative intervention for shoulder instability. The instability in each case was characterized as isolated anterior, isolated posterior, or combined, according to pathologic findings confirmed at arthroscopy. The findings were retrospectively compared with official MRI reports to determine the accuracy of MRI in characterizing the clinically and operatively confirmed diagnosis.

A consecutive series of 231 patients (221 men, 10 women) underwent stabilization for shoulder instability over 46 months. Patients were a mean age of 26.0 years. There were 132 patients (57.1%) with isolated anterior instability, 56 (24.2%) with isolated posterior instability, and 43 (18.6%) with combined instability. Overall, MRI findings completely characterized the clinical diagnosis and arthroscopic pathology in 149 of 219 patients (68.0%).

The rate of posterior and combined instability in an active population is more common than has been previously reported, making up more than 40% of operatively treated instability, including a previously unreported incidence of 19% for combined instabilities. In addition, MRI was often incomplete or inaccurate in detecting the pathology eventually treated at surgery.