Hill-Sachs Lesion: Understanding Its Appearance, Diagnosis, and Clinical Importance

What does a Hill-Sachs lesion look like?

A Hill-Sachs lesion appears as a cortical depression or "divot" on the posterolateral aspect of the humeral head, resulting from impact against the anterior rim of the glenoid during an anterior shoulder dislocation. On imaging, it typically presents as a characteristic indentation or impaction fracture of the bone.

Understanding the Hill-Sachs Lesion: A Core Concept

A Hill-Sachs lesion is a specific type of impaction fracture that occurs in the context of shoulder instability, most commonly following an anterior glenohumeral dislocation. To fully appreciate its appearance, it's crucial to understand its anatomical context and mechanism of injury.

• Definition: Named after Harold Hill and Maurice Sachs, who described it in 1940, it is an osteochondral defect—meaning it involves both bone and cartilage—on the posterior aspect of the humeral head.
• Mechanism of Injury: When the shoulder dislocates anteriorly, the humeral head (the ball part of the joint) is forced out of the glenoid (the socket). As it displaces, the relatively soft posterior portion of the humeral head impacts and scrapes against the hard, bony anterior rim of the glenoid. This forceful impact creates a compression fracture or indentation, forming the Hill-Sachs lesion.
• Anatomical Context: The shoulder joint is a ball-and-socket joint, comprising the head of the humerus and the glenoid fossa of the scapula. Its inherent mobility makes it prone to dislocation. The lesion's typical location on the posterolateral aspect of the humeral head is a direct consequence of this specific dislocation mechanism.

The Visual Signature: What Imaging Reveals

The appearance of a Hill-Sachs lesion is primarily determined through medical imaging. While physical examination might reveal signs of shoulder instability, the lesion itself is an internal bony defect requiring specialized visualization.

• General Appearance: Visually, it manifests as a depression, indentation, or flattened area on the otherwise smooth, spherical surface of the humeral head. The size and depth can vary significantly, ranging from a subtle cortical defect to a large, prominent divot that can affect a substantial portion of the humeral head's articular surface.

• Imaging Modalities:

  • X-ray: While not always definitive, a Hill-Sachs lesion can sometimes be identified on plain radiographs, particularly on specific views like the "internal rotation AP view" or the "Stryker notch view." It may appear as a cortical defect or flattening on the posterolateral aspect of the humeral head. However, smaller lesions can be easily missed.
  • MRI (Magnetic Resonance Imaging): This is often considered the gold standard for visualizing Hill-Sachs lesions and associated soft tissue injuries. MRI provides detailed images of bone and soft tissues. On MRI, the lesion appears as a well-defined focal signal change or depression in the bone, often accompanied by bone marrow edema (swelling within the bone) in acute cases, indicating recent trauma. MRI can accurately assess the size, depth, and volume of the lesion, as well as its proximity to the articular surface. It also effectively identifies co-occurring injuries, such as Bankart lesions (damage to the anterior glenoid labrum).
  • CT (Computed Tomography) Scan: CT scans are excellent for evaluating bony structures. They provide detailed cross-sectional images and can be used to create 3D reconstructions of the humeral head and glenoid. On a CT scan, the Hill-Sachs lesion appears as a clear bony indentation or defect, allowing for precise measurement of its dimensions and assessment of any associated bone loss. This is particularly useful in surgical planning.
  • Arthroscopy: During a surgical procedure (arthroscopy), the surgeon can directly visualize the humeral head. The Hill-Sachs lesion appears as a visible indentation or gouge on the posterior aspect of the articular cartilage and underlying bone. This direct visualization confirms the diagnosis and allows for assessment of its engagement with the glenoid.

• Key Characteristics to Look For:

  • Location: Always on the posterolateral aspect of the humeral head.
  • Shape: Typically a concave defect, ranging from a shallow divot to a deep groove.
  • Size: Varies greatly, from a few millimeters to several centimeters in length and depth. Larger lesions are more clinically significant.
  • Bone Changes: May show signs of bone marrow edema (acute injury) or sclerosis (chronic injury) on MRI, or clear cortical disruption on CT.

Clinical Presentation and Associated Injuries

While the Hill-Sachs lesion itself is a structural defect, its presence is often linked to the clinical presentation of shoulder instability.

• Symptoms: Patients typically present with a history of shoulder dislocation, followed by recurrent instability, pain, and a feeling of apprehension when the arm is moved into positions of external rotation and abduction. The lesion contributes to this instability by allowing the humeral head to "engage" with the anterior glenoid rim more easily, leading to re-dislocation.
• Associated Injuries: Hill-Sachs lesions rarely occur in isolation. They are frequently accompanied by other injuries resulting from the same dislocation event, most notably:
  • Bankart Lesion: A tear of the anterior-inferior labrum, often with a fracture of the anterior glenoid rim (bony Bankart). This is the "other half" of the instability equation, as the Hill-Sachs lesion on the humeral head engages with the Bankart lesion on the glenoid.
  • Capsular Tears: Damage to the ligaments and capsule surrounding the shoulder joint.

Why Understanding Its Appearance Matters

The detailed understanding of a Hill-Sachs lesion's appearance is not merely academic; it has profound implications for diagnosis, treatment, and prognosis.

• Accurate Diagnosis: Visual identification on imaging is crucial for confirming the cause of recurrent shoulder instability.
• Treatment Planning: The size, depth, and "engaging" nature of the Hill-Sachs lesion (i.e., whether it consistently catches on the glenoid rim during movement) significantly influence treatment decisions.
  • Conservative Management: Smaller, non-engaging lesions may be managed with rehabilitation focusing on rotator cuff strengthening and proprioception.
  • Surgical Intervention: Larger or engaging lesions, especially in active individuals, often necessitate surgical repair to restore stability. Techniques like remplissage (filling the defect with soft tissue) or bone grafting may be used to address the lesion directly, often in conjunction with Bankart repair.
• Prognosis and Recurrence Risk: A larger Hill-Sachs lesion is a significant risk factor for recurrent shoulder dislocation. Its presence and characteristics help clinicians predict the likelihood of future instability episodes and guide patient counseling.

Conclusion

A Hill-Sachs lesion, while an internal bony defect, has a distinct and recognizable appearance on medical imaging. It presents as a characteristic indentation on the posterolateral humeral head, a direct result of an anterior shoulder dislocation. Understanding its visual signature, particularly on MRI and CT scans, is fundamental for accurate diagnosis, comprehensive treatment planning, and effective management of shoulder instability, guiding interventions that range from targeted rehabilitation to complex surgical reconstruction. For fitness professionals and kinesiologists, recognizing the implications of this lesion is vital for guiding safe and effective exercise progression for individuals recovering from shoulder injuries.