Pathologic evidence of degeneration as a primary cause of rotator cuff tear.

Histopathologic, histochemical, and morphometric studies were done on 80 medial stumps of torn rotator cuff tendons to clarify the cause of tears. A high prevalence and diffuse distribution of degenerative changes were observed in the rotator cuff tendons including thinning and disorientation of collagen fibers, myxoid degeneration, hyaline degeneration, chondroid metaplasia, calcification, vascularproliferation, and fatty infiltration. No distinct inflammatory reaction was observed.