Dynamic Posterior Instability Test: A New Test for Posterior Glenohumeral Instability.

Abstract

Recurrent posterior shoulder instability has become an increasingly recognized cause of shoulder disability, especially among athletes. The presentation can be vague and therefore its clinical diagnosis is often overlooked. Few diagnostic tests exist and these tests are difficult to perform in an anxious and apprehensive patient. Many also lack high specificity and do not effectively distinguish posterior labral tears from other shoulder pathologies. As a result, the authors worked to develop a new test, the dynamic posterior instability test (DPIT). The purpose of this study was to describe the DPIT as well as a modified DPIT test and to evaluate the accuracy of these tests in detecting posterior labral pathology. It was hypothesized that the dynamic posterior instability test (DPIT) would improve accuracy in the evaluation of posterior labral tears. For a 9-month period, the DPIT and modified DPIT tests were performed on all patients evaluated for posterior instability of the shoulder. The records of all patients who had undergone a posterior labral repair (type VIII SLAP and posterior labral tears) were reviewed. The results of the DPIT and modified DPIT tests were compared to intra-operative findings. Anterior glenohumeral instability patients were also evaluated with these tests to serve as a control. Fifty-one patients had a positive and 3 patients had a negative DPIT test. Of the anterior instability patients, there was 1 positive and 19 negative test results. The sensitivity of the DPIT test was 94.4%, specificity 95%, the positive predictive value 0.98, and the negative predictive value 0.86. The results of the modified DPIT were the same as the DPIT test. The DPIT and modified DPIT tests provide a valuable new tool when combined with history and other physical examination findings improve the accuracy of diagnosis of posterior shoulder instability.