Posterior Shoulder Instability Score: Description and evaluation of a score for quantification of posterior shoulder instability

Background: Several scores are available for assessing and evaluating shoulder function, some of which include a portion for instability, but none is specifically designed for posterior shoulder instability. Because of this, the aim was to develop a score specifically for posterior shoulder instability and to validate this score in the second step. Methods: With the Posterior Shoulder Instability Score (POSI), a score was developed that assesses subjective and objective stability, range of movement, pain, and activities of daily living. To validate the score, 24 shoulders of 18 patients were examined by two shoulder specialists. Furthermore, the Constant score, ROWE score, and the WOSI score were assessed. Results: The interobserver reliability was r = 0.867 (95% CI 0.094–0.951). The two examiners showed an intraobserver reliability of r = 0.947 and r = 0.986. The POSI score correlated significantly with the subjective stability (r = 0.73; p < 0.0001) and the overall function of the shoulder (r = 0.78; p < 0.0001). Discussion: The newly developed POSI score showed good interobserver and excellent intraobserver reliability. With the validation, a high correlation between POSI and the overall function of the shoulder could be demonstrated. © 2017, Springer Medizin Verlag GmbH.