Anterior Shoulder Instability, Its Anatomy and Associated Lesions

João, a shoulder surgeon, starts with epidemiology. The glenohumeral joint is the most commonly dislocated joint, about 90% of dislocations are anterior, and recurrence reaches 72 to 95% under age 20. Patients over 40 recur less but are at risk of rotator cuff tears, greater tuberosity fractures and nerve injury. Instability is classified by direction, cause, timing and the amount of glenoid, humeral or bipolar bone loss. The anatomy section covers the small glenoid contact area, the superior, middle and inferior glenohumeral ligaments and the positions where each restrains the humeral head, humeral retroversion, the labrum and the suction effect of negative intra-articular pressure, shown in his own dissections. Dynamic stability depends on the rotator cuff, proprioception from capsular mechanoreceptors and scapular muscle timing. He then reviews associated lesions: rotator cuff tears in older patients, Bankart lesions in 80 to 90% of traumatic cases, bony Bankart fractures, critical glenoid bone loss above 20 to 25%, Hill-Sachs defects and the on-track and off-track glenoid track concept.