The subacromial space is the narrow functional compartment between the inferior surface of the acromion and coracoacromial arch above and the rotator cuff and greater tuberosity below. The subacromial bursa, which is the largest bursa in the body, occupies this space and allows smooth gliding of the rotator cuff under the arch during shoulder elevation. The normal subacromial space measures 7-14 mm on radiograph.
Subacromial impingement syndrome (shoulder impingement) results from mechanical compression of the subacromial contents during shoulder elevation, particularly the supraspinatus tendon and the subacromial bursa. The Neer, Hawkins-Kennedy, and empty can tests reproduce impingement. MRI demonstrates bursal swelling, rotator cuff partial tears, and the acromion morphology that may narrow the space. Corticosteroid injection into the subacromial space is both diagnostic and therapeutic. Arthroscopic subacromial decompression creates more space by resecting the bursa and inferior acromion.
Narrowing of the subacromial space from acromion morphology, AC joint osteophytes, bursal hypertrophy, or rotator cuff tendon thickening compresses the supraspinatus and bursa during arm elevation, producing arc pain and weakness, managed by physiotherapy, subacromial injection, and arthroscopic decompression for refractory cases.
Progressive subacromial compression and mechanical wear produce partial then full-thickness rotator cuff tears, with MRI demonstrating the tear pattern, bursal-side vs. articular-side location, and tendon retraction, guiding whether surgical repair is indicated.
