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When considering the possible causes of rotator cuff disease, mechanical impingement of the rotator cuff is considered the most common recognizable source of recurring pain and disability in the active population. Neer’s classic work  served to organize the clinician’s approach to rotator cuff disease and, most importantly, to define rotator cuff pathology as a spectrum of disease ranging from reversible edema to cuff fiber failure.

Primary impingement occurs at the anterior one third of the acromion and coracoacromial arch. The mechanical stresses endured by the rotator cuff, as well as its poor vascular design, both dynamic and static, have been well documented. Additional factors influencing rotator cuff pathology include acromial shape, slope, coracoacromial ligament size, postfracture deformity, os acromiale  and acromioclavicular joint spurring . Snyder  has recently reported on the “keeled” acromion, a particularly pernicious acromial variant associated with rotator cuff injury.

Functional abnormalities, such as asynchronous shoulder motion, posterior capsular contractures, scapular dyskinesia, glenohumeral instability, and distant neurological injury leading to weakness can also adversely affect the rotator cuff on a secondary basis with increased impingement forces concentrated in the subacromial space.

Impingement may occur from a direct mechanical insult, usually the result of an acromial excrescence excoriating the bursal aspect of the rotator cuff . However, another plausible injury cascade begins with intrinsic cuff failure, leading to insufficient humeral head depression and subsequent superior migration with creation of a traction spur within the coracoacromial ligament as a secondary phenomenon.

The cause for intrinsic cuff failure can range from fatigue on an overuse basis to underlying shoulder instability or superior labral pathology, injuries that have been associated with internal impingement and articular sided cuff failure. Regardless of etiology, a narrowed or stenotic supraspinatus outlet poses continued risk to the rotator cuff.

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