Shoulder Center Saar
Diagnosis of shoulder instability: soft tissue injuries and bony lesions
The shoulder is the most mobile joint in the human body, making it prone to instability. This instability can be due to soft tissue injuries or bone defects, often resulting from a dislocation or chronic stress. Precise diagnosis is crucial to identify the underlying pathology and determine the optimal treatment strategy.
Classification and basics of shoulder instability
Shoulder instability can occur due to trauma, overuse, or anatomical abnormalities. A proven classification system is the FEDS (Frequency, Etiology, Direction, Severity) classification system. It takes into account the frequency of instability episodes (solitary, occasional, frequent), their cause (traumatic or atraumatic), the direction of the instability (anterior, posterior, or inferior), and the severity (subluxation or complete dislocation). This system enables rapid and effective classification of symptoms, which is crucial for further diagnosis and treatment planning.
| Frequency | Episodes per year One-time: 1 episode Occasionally: 2-5 episodes Frequently: > 5 episodes |
| Etiology | traumatic atraumatic |
| Direction | forward: anterior downward: inferior backward: posterior |
| Severity | subluxation Dislocation |
Imaging: The key to diagnosis
Choosing the right imaging technique is essential for assessing shoulder instability!
A simple X-ray is definitely not sufficient to diagnose pathologies that occur in a dislocation or cause chronic instability! Magnetic resonance imaging (MRI) offers excellent opportunities to visualize soft tissue damage and has established itself as the gold standard.
Since in addition to soft tissue injuries, bony lesions are also responsible for instability, computed tomography (CT) is often recommended. Computed tomography with 3D reconstruction is the standard for visualizing bony defects. The 3D reconstruction allows for the visualization of the glenoid surface by subtracting the humeral head, thus demonstrating even minor bone loss. Furthermore, a Hill-Sachs deformity can also be optimally visualized and measured.
Newer MRI techniques with 3D sequences offer promising alternatives, especially for patients who would be exposed to radiation from CT. Ultrasound diagnostics can also be used for dynamic testing and rotator cuff assessment.
Soft tissue injuries as a cause of shoulder instability
The soft tissues of the shoulder include the labrum, capsule, glenohumeral ligaments, and rotator cuff. Injuries to these structures often lead to instability, especially after trauma.
Labral and capsule injuries are common findings in patients with anterior instability. A typical injury is the Bankart lesion, in which the anteroinferior (front-bottom) labrum tears away from the glenoid (socket). This lesion often occurs after a primary dislocation.
Another common pathology is the SLAP (Superior Labrum Anterior to Posterior) lesion, which occurs primarily in overhead athletes such as volleyball or tennis players. Diagnosis is primarily performed using magnetic resonance imaging (MRI) with contrast medium, which provides high-resolution images of the soft tissue structures. In cases of doubt or for surgical planning, a diagnostic arthroscopy may be necessary.
Dynamic stability disorders often affect the rotator cuff. These muscles are crucial for the active stabilization of the joint. Chronic damage to the rotator cuff, which is more common in older patients, can also contribute to instability.
Bony lesions: types and clinical significance
Bone defects resulting from dislocations or chronic stress are a common cause of recurrent shoulder instability. Defects of the glenoid and humeral head are particularly relevant.
Glenoid Defects arise from anteroinferior dislocations (front-downward dislocations) in which part of the glenoid is worn away. Such defects alter the shape of the glenoid socket, reducing the ability to center the humeral head. Studies show that defects of more than 20% of the glenoid width lead to a significantly increased recurrence rate after soft tissue repair alone. For accurate assessment, computed tomography (CT) with 3D reconstruction is the gold standard. The Glenoid Track Concept helps estimate the risk of recurrent dislocations by evaluating whether the humeral head lies within the weight-bearing area of the glenoid.
Another common problem is the Hill-Sachs lesion, a dent in the posterolateral humeral head that occurs during a dislocation. These lesions are particularly problematic when combined with a glenoid defect, as they further reduce joint stability. Accurate assessment is also performed using CT or MRI. Dynamic assessment during arthroscopy can help identify "engaging" lesions, in which the defect engages the glenoid when the arm is moved.
Modern diagnostic concepts: On- and off-track lesions
A key advance in the diagnosis of shoulder instability is the On- and off-track concept. This concept evaluates whether a Hill-Sachs lesion lies within (on-track) or outside (off-track) the weight-bearing area of the glenoid. Off-track lesions have an increased risk of causing recurrent instability and often require specific surgical treatment.
Conclusion
The diagnosis of shoulder instability requires precise clinical and imaging evaluation to accurately characterize soft tissue and bony lesions. Concepts such as the Glenoid track model and on- and off-track classification enable a more precise prediction of the risk of recurrence and optimized treatment planning. Modern diagnostic approaches allow for individually tailored treatments that restore long-term shoulder function and stability.