The shoulder joint, a ball-and-socket mechanism, allows for an impressive range of motion, making it one of the most mobile joints in the human body. This flexibility, however, also makes it susceptible to various injuries, particularly dislocations. When the head of the humerus (upper arm bone) is forced out of its socket (the glenoid, part of the shoulder blade), it can lead to additional damage within the joint. One such consequence of a shoulder dislocation is the formation of a Hill-Sachs lesion.
The Nature of a Hill-Sachs Lesion
A Hill-Sachs lesion is specifically an osseous defect, often described as a “dent” or “divot,” located on the posterolateral (back and outer) aspect of the humeral head. This defect represents an impaction fracture, meaning it occurs when one bone forcefully impacts another. It is a direct result of trauma, particularly associated with instability or dislocation of the glenohumeral joint.
This bony indentation affects the smooth, rounded surface of the humeral head, which normally articulates within the glenoid socket. While it is a bony injury, it is often found alongside other soft tissue damage within the shoulder.
The Mechanism of Formation
A Hill-Sachs lesion typically forms during an anterior shoulder dislocation, which is the most common type. This occurs when the arm is forced into excessive abduction (away from the body) and external rotation. During this traumatic event, the humeral head is driven out of the glenoid cavity.
As the humeral head dislocates forward, its relatively soft bone impacts forcefully against the harder anterior rim of the glenoid. The resulting indentation is the characteristic Hill-Sachs lesion, indicating a dislocation has occurred, even if the joint has been reset.
Recognizing and Confirming a Hill-Sachs Lesion
A Hill-Sachs lesion may sometimes be asymptomatic, or its symptoms can overlap with those of the initial shoulder dislocation, including severe pain, weakness, and limited arm movement. Patients might also report a feeling of instability, apprehension, or recurrent dislocations. The potential for repeat dislocations increases with the size of the bone defect.
Diagnosis begins with a thorough medical history and physical examination, where provocative maneuvers may reveal apprehension. However, confirming a Hill-Sachs lesion often relies on imaging techniques. X-rays are usually the initial assessment and can detect larger lesions, with specific views being particularly useful for visualization. For a more detailed evaluation, computed tomography (CT) scans provide precise measurements of the lesion’s size and depth, offering detailed bony anatomy. Magnetic resonance imaging (MRI) assesses associated soft tissue injuries like labral tears and capsular damage, while also visualizing the Hill-Sachs lesion itself.
Management and Outlook
The approach to managing a Hill-Sachs lesion depends on several factors, including the lesion’s size, its location, the patient’s arm mobility, and the extent of any associated glenoid bone loss. For smaller lesions, typically those involving less than 20% of the humeral head, conservative management is often the first step. This non-surgical approach focuses on physical therapy to strengthen the muscles supporting the shoulder, such as the rotator cuff and scapular stabilizers, and activity modification to reduce the risk of further injury.
Surgical intervention becomes necessary for larger or symptomatic lesions, especially those contributing to recurrent shoulder instability. One common arthroscopic procedure is Remplissage, a French term meaning “to fill in”. In this technique, the infraspinatus tendon and posterior capsule are secured into the Hill-Sachs defect, effectively filling the indentation and preventing the humeral head from “engaging” or catching on the glenoid rim during movement.
For cases with significant bone loss from the glenoid socket, the Latarjet procedure may be performed. This involves transferring a piece of bone, typically from the coracoid process, to augment the glenoid, restoring stability. For very large defects or severe damage, bone grafting or even shoulder replacement might be considered.
The general outlook for individuals with a Hill-Sachs lesion is positive with appropriate treatment and rehabilitation. Following a comprehensive rehabilitation program, which often includes strengthening exercises and progressive resistance training, is important for improving shoulder function and reducing the risk of future dislocations. While recurrence of dislocation is possible, particularly in younger individuals or athletes, tailored treatment plans aim to restore stability and enable a return to daily activities.