A Hill-Sachs lesion or defect describes a fracture of the round head of bone at the top of the humerus (upper arm bone). Usually, the injury occurs when the person has his or her arm cocked back in a ball throwing motion. The shoulder is abducted (moved away from the body) and externally rotated.
In this position, the head of the humerus moves forward. With enough force and/or load, the forward movement can overcome the strength and restraint of the soft tissues holding the shoulder back. The joint capsule is stretched to the breaking point.
Once the soft tissues surrounding the shoulder have stretched enough to tear, then the shoulder can dislocate repeatedly. And with every dislocation, the damaged soft tissues give a little more until the shoulder is unstable and no longer stays in the shoulder socket (glenoid fossa). At the same time, the compression against the bone is enough to cause the fracture described as a Hills-Sachs lesion.
A small lesion or one that is oriented perpendicular (sideways) to the rim of the socket (glenoid rim) can be treated conservatively (without surgery). Rehab under the direction of a physical therapist may be all that is needed. Older adults are also usually directed toward nonoperative treatment. Even with small to mid-size lesions, rehab can be quite lengthy over a period of many months.
Larger lesions and bony defects that are parallel to the glenoid rim are usually just part of the total picture. In these more extensive injuries, other tissues (e.g., labrum, anterior capsule) are also damaged. Coexisting injuries like his require surgery to stabilize the shoulder and prevent worse shoulder instability.
Before a treatment plan can be determined, the surgeon takes a complete history, performs a physical examination, and orders imaging studies. X-rays, CT scans, MRIs, and ultrasound studies reveal the full extent of damage including location and direction of the lesion. Imaging studies also help identify the amount of bone loss for both the humeral head and the glenoid fossa.
Your best bet is to see an orthopedic surgeon for an evaluation. You may have something simple going on line a postural alignment issue or muscle imbalance. A short course of physical therapy may be all you need. But there could be a need for surgery to stabilize the shoulder at this point and only a surgeon can help you make that decision.