The most common complication of an acute shoulder dislocation is recurrence. This complication occurs because the capsule and surrounding ligaments are stretched and deformed during the dislocation. Age is the most important indicator for prognosis; dislocations recur in approximately 90% of teenagers.
Another common complication following dislocation is fracture. The most common type is a Hill-Sachs lesion or compression fracture of the posterior humeral head. Fractures of the proximal humerus, greater tuberosity, coracoid, and acromion have also been described.
Rotator cuff tears also commonly occur as a result of shoulder dislocations, and the frequency of this complication increases with age. This complication can be expected in 30-35% of patients aged 40 years or older. Slow progression in return to active function following shoulder dislocation in a middle-aged patient should warrant a workup for a rotator cuff tear.
Vascular injuries are rare, but they do occur, especially in older patients. Vascular injuries are more common with inferior dislocations and usually involve a branch of the axillary artery.
Nerve injuries are much more common than vascular injuries, especially with anterior or inferior dislocations. The axillary nerve is the nerve injured most often and may be crushed between the humeral head and the axillary border of the scapula or injured by traction from the humeral head. Axillary nerve injury has been reported in as many as 33% of acute anterior dislocations.