Etiology

Rotator cuff tears can result from an acute traumatic event, repetitive or vigorous overhead activity (such as throwing a baseball or lifting heavy objects), or chronic, age-related degeneration. They can be considered the final stage of a continuum of pathology and clinical symptoms referred to as rotator cuff tendinopathy.

The extreme external and internal rotation stresses of the thrower's shoulder predispose the cuff (particularly the undersurface and interlaminar areas) to significant strain with repetitive throwing. This leads to eventual articular-sided rotator cuff tears and, occasionally, intratendinous tears (PAINT lesion) with full-thickness tears occurring in some cases.[10]​ An episode of vigorous overhead activity, such as painting and overhead lifting, may incite subacromial bursitis or tendonitis symptoms, which can be prodromes to breakdown and failure of the rotator cuff.

The space between the undersurface of the acromion and the superior aspect of the humeral head (the impingement interval) is maximally narrowed in a normal patient with abduction of the shoulder. Impingement of the rotator cuff against the coracoacromial arch can result from any condition that further narrows this space. Anatomically, this space is affected by the morphology of the undersurface of the acromion: type I (flat), type II (curved), and type III (curved with an anterior hook).[11] Both extrinsic compression and loss of rotator cuff competency can lead to impingement. For example, cadaveric studies have described an increased incidence of rotator cuff tears in patients with a type II or III acromion. However, there is evidence to suggest that age-related degeneration of the rotator cuff compromises its humeral head depression function, thereby leading to "impingement" against the acromial arch, irrespective of acromial morphology.[11][12]​ Rotator cuff tendinopathy is preferred to impingement when explaining rotator cuff degeneration.​[12]

Pathophysiology

Tears associated with classic rotator cuff tendinopathy classically start on the bursal surface or within the tendon substance. A common factor leading to tendinopathy is diminished tendon blood supply due to aging. Because of the poor blood supply in the area along the rotator cuff insertion, especially the anterior supraspinatus, and the critical stresses placed on this area, attritional and intrinsic tears commonly begin in this location.[13]

Intrinsic tendon fiber breakdown due to repetitive or vigorous overhead motion preferentially occurs on the articular side of the cuff due to "hypertwist" of the rotator cuff fiber pattern, caused by excessive rotation. Subtle shoulder instability can result in microtrauma to the cuff, which undergoes excessive strain due to heightened eccentric loads. Internal impingement, whereby the undersurface of the rotator cuff can become impinged between the superior glenoid and greater tuberosity, is the result of excessive anterior shoulder laxity, posterior capsular tightness, or scapular dyskinesis.[14]​ Accordingly, there is an increased association between undersurface rotator cuff tears and labral disorders, especially superior labrum anterior posterior (SLAP) tears.

Modern imaging techniques and arthroscopy have helped to replace the nonspecific diagnosis of "impingement" with specific diagnoses of rotator cuff tendinosis, partial tear, and complete tear. These refined terms better reflect the degree of damage to the rotator cuff.[15][16]

Classification

Cofield classification of rotator cuff tears[1]

  • Small <1 cm

  • Medium 1-3 cm

  • Large 3-5 cm

  • Massive >5 cm

Partial-thickness rotator cuff tears[2]

  • Grade 1: partial tear <3 mm deep

  • Grade 2: partial tear 3-6 mm deep

  • Grade 3: partial tear >6 mm deep

Snyder classification of partial rotator cuff tears[3]

Location of tear

  • A - Articular surface

  • B - Bursal surface

Severity of tear

  • 0 - Normal cuff with smooth coverings of synovium and bursa

  • I - Minimal superficial bursal or synovial irritation or slight capsular fraying in a small, localized area; usually <1 cm

  • II - Actually fraying and failure of some rotator cuff fibers in addition to synovial, bursal, or capsular injury; usually 1-2 cm

  • III - More severe rotator cuff injury, including fraying and fragmentation of tendon fibers, often involving the entire surface of a cuff tendon (most often the supraspinatus); usually 2-3 cm

  • IV - Very severe partial rotator tear that usually contains a sizable flap tear in addition to fraying and fragmentation of tendon tissue and often encompasses more than a single tendon; usually >4 cm

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