44-year-old female with persistent left shoulder complaints since a skiing accident in February, approximately five months earlier. Symptoms are mainly provoked in higher degrees of anteflexion. The clinical question concerns persistent posttraumatic shoulder pain despite an otherwise largely normal shoulder ultrasound.
Ultrasound examination of the shoulder is predominantly normal. The rotator cuff tendons, long head of the biceps tendon, and subacromial-subdeltoid bursa show no clinically relevant abnormalities that fully explain the symptoms.
The main abnormality is located around the acromioclavicular joint. At rest, the AC joint shows a normal joint space and normal height relationship between the clavicle and acromion. There is no relevant increase in joint fluid. However, during dynamic assessment with the cross-arm maneuver, instability of the AC joint is visible.
At the sternoclavicular joint, there appears to be a positional change, with the medial clavicle on the affected side positioned slightly more anteriorly and appearing more prominent.
In addition, a unilateral circular soft tissue structure is visible on the affected side, approximately 3 cm from the shoulder head. This structure has a fibrous, probably muscular pattern with a medial-to-lateral fibre orientation. It is not visible in the same way on the contralateral side. Based on its location and fibre direction, it may represent the subclavius muscle, but the exact nature of this structure cannot be determined with certainty by ultrasound.
The overall appearance may fit with posttraumatic disruption of the clavicular chain, with dynamic AC joint instability and possible additional sternoclavicular or subclavicular soft tissue involvement.
1. Final diagnosis
Predominantly normal shoulder ultrasound, without relevant rotator cuff, biceps tendon, or bursial pathology. Dynamic instability of the AC joint is present during the cross-arm maneuver, without clear static malalignment or relevant joint effusion at rest. There is also suspicion of sternoclavicular positional change, with more anterior prominence of the medial clavicle on the affected side.
2. Differential diagnosis
The primary diagnosis is posttraumatic dynamic AC joint instability, possibly after a low-grade AC ligament injury with preserved resting alignment. Additional differential diagnoses include sternoclavicular sprain, sternoclavicular subluxation, or chronic posttraumatic positional change of the medial clavicle. The unilateral muscular-appearing subclavicular structure may represent a more prominent or reactive subclavius muscle, posttraumatic soft tissue change, organized hematoma, local swelling, scar tissue, anatomical variant, or another soft tissue structure.
3. Teaching points
Dynamic ultrasound can reveal AC joint instability that may not be visible during static assessment. A normal AC joint position at rest does not exclude symptomatic dynamic instability, especially after trauma. In patients with persistent pain during higher anteflexion, the full clavicular chain should be considered, including the AC joint, sternoclavicular joint, subclavicular soft tissues, and scapulothoracic mechanics. Uncertain unilateral soft tissue findings should be described cautiously and correlated clinically.
4. Injury/disease information
Posttraumatic AC joint instability may follow a direct fall or traction injury to the shoulder girdle and can cause pain during cross-body movement, elevation, or loaded overhead positions. Sternoclavicular joint involvement may alter clavicular mechanics and contribute to persistent symptoms, although ultrasound has limited ability to assess the deeper and bony aspects of this joint. Specialist clinical reassessment may be useful when symptoms persist after several months. CT can assess bony alignment of the sternoclavicular joint and clavicle, while MRI may be helpful for ligamentous injury, subclavicular soft tissue pathology, or an unclear soft tissue structure. Urgent medical evaluation is required if there are symptoms such as dyspnea, swallowing difficulty, vascular symptoms, progressive swelling, neurological deficit, or concern for posterior sternoclavicular dislocation.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
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