All shoulder dislocations cause some amount of bone damage. In the most common type of dislocation, the head of the humerus (upper arm bone) is forced forward and out of the shoulder socket. This is known as an anterior shoulder dislocation.
Even if the shoulder is reduced (head of the humerus is put back in the socket), the soft tissues around the shoulder have been overstretched. If the humeral head hits the rim of the socket with enough force, there can be damage to both areas (the humeral head and the glenoid rim). This type of injury is referred to as a Hill-Sachs lesion.
An engaging Hill-Sachs defect describes a situation in which the bone defect catches on the glenoid rim during shoulder motion. This is more common with large defects. And the end result is that the arc of motion as the humeral moves, slides, and glides in the socket is off biomechanically. The joint no longer matches up causing what’s referred to as an articular arc mismatch.
It is good that this problem has been identified before treatment. Studies show that it may not be enough to repair the torn or damaged soft tissues (tendons and ligaments) if there is also a bony defect. The soft tissue repair or reconstructive surgery is more likely to fail if the bony lesion(s) are not addressed as well. The patient ends up with a chronically dislocating shoulder from the abnormal shoulder biomechanics.
We hope this explanation helps you understand the surgeon’s explanation when looking at the CT scan together. Your treatment plan will depend on a number of variables including the presence of this type of Hill-Sachs lesion. Your age, activity level, severity of injury, and bone quality are some of the factors that must be evaluated when determining the best plan of care. Your surgeon may have some additional concerns or comments for you as well.