Shoulder instability

Abstract

Shoulder stabilizers are categorized as mid-range and end-range stabilizers. The mid-range stabilizers are the negative intraarticular pressure, the concavity-compression effect created by the glenoid concavity, muscle contraction forces across the glenohumeral joint, and scapular inclination. The end-range stabilizers are the capsuloligamentous structures, such as the superior, middle, and inferior glenohumeral ligaments, which become tight at a specific end range. Glenoid bone loss is observed in 71–90% of shoulders with anterior instability. The critical size of glenoid bone loss is demonstrated to be 25% of the glenoid width. If the bony defect of the glenoid exceeds this critical size, either free bone grafting or coracoid transfer, such as the Latarjet procedure, is necessary. Hill-Sachs lesions also need to be taken into consideration. When the arm is moved along the end range of motion, the glenoid creates a contact zone on the humeral head (the glenoid track). If a Hill-Sachs lesion extends out of this glenoid track, there is a risk of engagement and dislocation. Therefore, a Hill-Sachs lesion that extends out of the glenoid track needs to be treated surgically. There are two methods: (1) covering the defect either with bone or soft tissue, or (2) limiting external rotation. In shoulders with an engaging Hill-Sachs lesion (the Hill-Sachs lesion extends medially over the medial margin of the glenoid track), treatment is required if a glenoid defect is equal to or greater than 25% of the glenoid width. If the Hill-Sachs lesion is still engaging after treatment of the glenoid defect, repair is indicated. If the glenoid defect is less than 25%, treatment for either the Hill-Sachs lesion or the glenoid defect is required.