A Hill-Sachs injury to the shoulder can occur due to a shoulder dislocation, resulting in a Hill-Sachs lesion or a Hill-Sachs deformity of the head of the humerus bone (the upper arm bone).As the bones in the shoulder joint dislocate, the round humeral head (the ball on the top of the arm bone) can strike the edge of the glenoid bone (the socket) with force. This creates a compression fracture in the humeral head. A small divot in the bone is often seen on MRI, and larger Hill-Sachs injuries may also be seen on an X-ray.
Source:Verywell Health