Pathology and pathogenesis of the intratendinous tearing of the rotator cuff viewed from en bloc histologic sections.

Histologic sections from 17 en bloc surgical specimens were studied to clarify the pathogenesis of intratendinous tears of the rotator cuff. The specimens consisted of the bony insertion, the partially torn area, and the musculotendinous junction of the supraspinatus tendon. An intratendinous tear alone was present in two patients, and was associated with bursal side cuff tears in seven patients and joint side cuff tears in eight. There were 13 men and 4 women, whose average age was 49.8 years. Trauma was noted in all intratendinous tears and combined intratendinous and joint side cuff tears and in two of the seven patients who had intratendinous plus bursal side tears. All patients exhibited clinical evidence of subacromial impingement. Histologic sections were stained with azan and hematoxylin and eosin. Microscopically, the sections demonstrated several abnormalities in addition to degeneration. The intratendinous tears was located in the midlayer of the tendon in 15 specimens and eccentrically in two, the axis of which were parallel to tendon fibers in all. The intratendinous tears continued to local disruptions of the enthesis in 11 cases. The inner surface of the tear appeared smooth in 16 specimens. Despite the presence of granulation tissue and vessel proliferation near the intratendinous tears, there was no evidence of closure of the defect in any specimen. Intratendinous tears develop between superficial and deep layers of the degenerated rotator cuff. Shear within the tendon appears to be responsible in pathogenesis. Concomitant subacromial bursitis is very common.