Emergent care / stabilization: It is important to identify and reduce a posterior shoulder dislocation first and then address the reverse Hill-Sachs lesion, if present and symptomatic.

Causes / typical injury mechanism:

• A reverse Hill-Sachs lesion (RHSL), also called a McLaughlin lesion, is an impaction fracture of the anteromedial humeral head resulting from a posterior shoulder dislocation.
• The most common cause of dislocation is trauma, such as falling on an outstretched hand from a bicycle. Other mechanisms of this injury include direct trauma to the shoulder or violent muscle contractions related to epileptic seizures and electrocution.
• Chronic posterior shoulder instability is more common than frank dislocation. Repetitive posterior-directed loads forcing the humeral head against the edge of the glenoid can also result in an RHSL.

Classic history and presentation:

• The patient typically presents with a history of chronic posterior shoulder instability, which may have begun at a young age after an acute posterior shoulder dislocation or as a result of high-impact pushing sports such as football or bench-pressing. Less commonly, the patient presents acutely with a first-time posterior shoulder dislocation or with a chronically stiff shoulder after a remote event when dislocation was missed.
• On examination, the patient has limited shoulder external rotation, flexion, and abduction. Pain is reproduced with a wall push-up.

Prevalence:

• Posterior shoulder dislocation is a rare injury, comprising 2%-5% of all shoulder dislocations.
• RHSLs are observed in up to 90% of acute, first-time, traumatic posterior shoulder dislocations.
• The typical age of patients is between 35 and 67 years.
• Males are more commonly affected.

Risk factors:

• History of posterior shoulder dislocation.
• Young age at the time of the first instability episode.
• Chronic posterior shoulder instability.
• Activities with a posteriorly directed force on the humeral head – bench-pressing, football, wrestling, gymnastics, swimming, etc.
• Osteonecrosis of the humeral head.
• Glenohumeral arthritis.
• Epilepsy and other seizure disorders.
• Glenoid retroversion.

Pathophysiology: An RHSL occurs when a posteriorly directed axial load on the upper extremity drives the humeral head against the posterior edge of the glenoid, denting the head's anteromedial articular surface. The force needed to create an RHSL is significantly greater than the force needed to create an anterior HSL. A significant defect could lock the dislocated joint and prevent reduction or make the joint susceptible to future dislocations if positioned so that the defect engages with the edge of the glenoid (ie, in flexion, adduction, and internal rotation).

Grade / classification system: 

• Type 1 – Unlocked dislocations associated with small RHSLs.
• Type 2 – Locked dislocation associated with large RHSLs.
• Type 3 – Chronic locked dislocations associated with very large RHSLs.