Changes in Capsule Function Following Anterior Dislocation Elucidate the Need for Standardized Clinical Exams to Diagnose Shoulder Instability

The anteroinferior glenohumeral capsule (anterior band of the inferior glenohumeral ligament (AB-IGHL), axillary pouch) limits anterior translation, particularly in positions of external rotation, and as a result is frequently injured during anterior dislocation. [1,2] A common capsular injury is permanent tissue deformation, however, the extent and effects of this injury are difficult to evaluate as the deformation cannot be seen using diagnostic imaging. In addition, clinical exams to diagnose this injury are not reliable [3] and poor patient outcome still exists following repair procedures. [4] Previous experimental models have observed increased joint mobility following permanent tissue deformation. [5] While other models have quantified the permanent deformation using nonrecoverable strain [6], no model has correlated the amount of tissue damage to altered capsule function. Understanding the relationship between the extent of tissue damage and changes in capsule function following anterior dislocation could aid surgeons in diagnosing and treating anterior instability. Therefore, the objectives of this work were to 1) quantify the nonrecoverable strain in the anteroinferior capsule resulting from an anterior dislocation and 2) evaluate capsule function (strain distribution in anteroinferior capsule, anterior translation) during a simulated clinical exam at three joint positions, in the intact and injured joint.