Adhesive Capsulitis of the Shoulder MRI Findings
The term “frozen shoulder” is used synonymously with adhesive capsulitis. Women in their 50s-70s are most commonly diagnosed with adhesive capsulitis (1). The pathophysiology of an adhesive capsulitis is inflammation of the synovial surface of the GH joint (3). There is also fibroblast proliferation in both the axillary recess and rotator cuff interval (5). Histologic samples have shown thickening of the capsule and synovium (3).
Patients with a frozen shoulder typically complain of shoulder pain and a decrease in their shoulder range of motion (1). Clinical exam can be difficult because patients can have concurrent calcific tendonitis, subacromial bursitis, and GH arthritis. As a result, MRI has been used to help aid in diagnosis.
The relevant anatomy when evaluating an MRI for adhesive capsulitis is the rotator interval, the coracohumeral ligament, and the axillary pouch (1).
Patients typically have painful inflammatory capsules of the joint capsule secondary to inflammation in the glenohumeral ligaments (2). Thickening of both the rotator interval and coracohumeral ligament have a high specificity for the diagnosis of adhesive capsulitis (1). The rotator interval is a triangular space that is bordered by the supraspinatus tendon, subscapularis tendon, coracoid process and long head of the biceps tendon (8). The coracohumeral ligament aids in restraining external rotation (4).
Thickness of the rotator interval >3mm and coracohumeral ligament > 4mm are the thresholds used for diagnosis (1). On MRI, the rotator cuff interval appears hypointense in a patient with adhesive capsulitis.
Providers also need to look for capsular and synovial thickening (1). Thickness of the joint capsule can be measured on a T2-weighted fat suppression coronal oblique view (4). A thickness >4mm on a coronal oblique T2-weighted fat suppression image has a high specificity for adhesive capsulitis (1).
Signal change within the subcoracoid fat triangle is also diagnostic of adhesive capsulitis (2). The subcoracoid fat triangle can be visualized on a sagittal oblique image seen below (9).
A frozen shoulder can be a debilitating condition causing nighttime pain and restriction in shoulder range of motion. Diagnosis is difficult and can be aided with MRI. Typical MRI findings include thickening of the axillary joint capsule, subcoracoid fat signal change, coracohumeral ligament thickening, and rotator cuff interval thickening. Treatment options go beyond the scope of this review.
By Gregory Rubin, DO
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