Shoulder Dislocation Explained – Anatomy, Causes, Lesions, and Treatment

Join this channel to support the channel https://www.youtube.com/channel/UCOHfqHMhHvfQCYJDXfpSAiw/join Shoulder dislocation refers to displacement of the head of the humerus from the glenoid cavity of the scapula. The acromioclavicular joint, or AC joint, when injured, is referred to as a shoulder separation. Shoulder dislocation is different from shoulder separation. The image shows shoulder separation on the left and shoulder dislocation on the right. In the proximal humerus, you can identify the head, shaft, greater tuberosity, and lesser tuberosity. The rotator cuff muscles attach around these structures: the subscapularis attaches to the lesser tuberosity, while the supraspinatus, infraspinatus, and teres minor attach to the greater tuberosity. The axillary nerve can be injured during shoulder dislocation. The most common associated lesions include: Bankart lesion Hill-Sachs lesion Rotator cuff tear (in elderly patients) Axillary nerve injury Fracture of the greater or lesser tuberosity The shoulder joint is formed between the humeral head and the glenoid cavity. The labrum, attached to the glenoid, reinforces the socket and acts as a bumper within the joint capsule, deepening the cavity by approximately 50%. In shoulder dislocation, injury to the labrum results in a Bankart lesion. This lesion is associated with a high recurrence rate, especially in young patients, and is found in approximately 80–90% of those with traumatic unilateral dislocation (TUBS). A Bankart lesion may be fibrous or bony, involving avulsion of the anterior labrum and the anterior band of the inferior glenohumeral ligament from the anteroinferior glenoid. A bony Bankart occurs in about 50% of patients with recurrent dislocation. Glenoid bone loss greater than 20–25% results in significant instability, making soft tissue repair alone insufficient. In such cases, bony augmentation (e.g., Latarjet procedure or iliac crest bone graft) is required. The most accurate study to assess glenoid bone loss is a CT scan with 3D reconstruction. When bone deficiency exceeds 20–25%, arthroscopic repair often fails, and Latarjet surgery is indicated—especially in cases of inverted pear-shaped glenoids. Rotator cuff tears occur more frequently in elderly patients with shoulder dislocation—approximately 30% over age 40 and up to 80% over age 60. If a young patient cannot lift the arm after reduction, suspect axillary nerve palsy. If the patient is older, suspect a rotator cuff tear. A Hill-Sachs lesion occurs when the humeral head impacts the anteroinferior glenoid rim, creating a defect on the posterior-superior aspect of the humeral head. It appears in about 80% of acute dislocations and 25% of traumatic subluxations. For large Hill-Sachs defects ( more than 25%), a Remplissage procedure is performed—suturing the posterior capsule and infraspinatus tendon into the defect. In posterior shoulder dislocation, the lesser tuberosity may be fractured. If the dislocation is less than six months old and the reverse Hill-Sachs lesion involves less than 40% of the humeral head, open reduction with subscapularis transfer (McLaughlin procedure) is recommended. A HAGL lesion (humeral avulsion of the inferior glenohumeral ligament) is uncommon and often missed. It typically occurs in high-energy or sports injuries and, if unrecognized, can lead to recurrent instability. MRI shows irregularity in the inferior recess (pouch). The anterior inferior glenohumeral ligament prevents anterior translation of the humeral head at 90° abduction and external rotation (the apprehension position). Injury causes anterior instability. The posterior inferior glenohumeral ligament limits posterior translation at 90° flexion and internal rotation. Anterior labral tears are visible on axial MRI views and are enhanced by contrast dye. Apprehension testing confirms anterior instability. Posterior labral tears cause more pain than instability and can be diagnosed clinically using the Jerk or Kim test. Posterior shoulder dislocation occurs most commonly after seizures or electric shock, because internal rotators (subscapularis, latissimus dorsi, pectoralis major) are stronger than the external rotators. Normal labral variants—such as a sublabral foramen or Buford complex—should not be repaired, as this may restrict motion, particularly external rotation. This video explains the anatomy and key injuries associated with shoulder dislocation to help improve understanding of the mechanisms, diagnosis, and related complications.