From the case:
Hill-Sachs lesion - illustration
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Illustration of the posterior surface of the shoulder showing a subcoracoid dislocation of the humeral head, with impaction of the anterior glenoid rim into the posterior humeral head.
Case Discussion
With a Hill-Sachs lesion, the anterior glenoid rim acts as a hatchet, impacting the posterior surface of the humeral head to create the "hatchet deformity".