The patient has a decreased acromiohumeral interval noted on radiograph of the shoulder. This distance can be measured from the undersurface of the acromion to the superior portion of the humerus. Increased distance suggests inferior subluxation, which can result from a shoulder dislocation or proximal humerus fracture. Decreased distance suggests a rotator cuff tear. An intact rotator cuff places an inferiorly directed force to the humeral head relative to its position on the glenoid. A balance of intact supraspinatus, infraspinatus, teres minor, and subscapularis tendons allows for concentric rotation of the humeral head in the glenoid.
A massive rotator cuff tear may cause superior humeral head migration from the unopposed contraction of the deltoid. A rotator cuff tear also causes loss of negative pressure in the glenohumeral joint and the release of normal synovial fluid out of the joint. With chronic massive rotator cuff tearing, the acromion can often articulate with the humeral head. Decreasing acromiohumeral interval found on serial radiographs is a sign of progressive rotator cuff disease. A decreased acromiohumeral interval is the start of the rotator cuff arthropathy cascade whereby articular cartilage is gradually lost and arthritis becomes evident. A loss of dynamic stabilization of the shoulder causes repetitive trauma to the articular cartilage, resulting in arthritis.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
References
- Nam D, Maak TG, Raphael BS, Kepler CK, Cross MB, Warren RF. Rotator cuff tear arthropathy: evaluation, diagnosis, and treatment: AAOS exhibit selection. J Bone Joint Surg Am. 2012;94(6):e34.
- Ecklund KJ, Lee TQ, Tibone J, Gupta R. Rotator cuff tear arthropathy. J Am Acad Orthop Surg. 2007;15(6):340-349.
