Histopathology of the supraspinatus tendon in rotator cuff tears.

BACKGROUND: Causes of rotator cuff pathology are poorly understood. HYPOTHESIS: Macroscopically intact supraspinatus tendon may show profound light microscopy changes. These changes may be the pathogenic precursor to a subsequent rotator cuff tear. STUDY DESIGN: Comparative laboratory study. METHODS: Tendon samples were harvested from 88 individuals (49 men, 39 women; mean age, 58.2 years) who had sustained a rotator cuff tear and underwent arthroscopic repair of the lesion, and from 5 male patients who died of cardiovascular events (mean age, 69.6 years). A full-thickness supraspinatus tendon biopsy specimen was harvested en bloc within the arthroscopically intact middle portion of the tendon between the lateral edge of the tendon tear and the muscle-tendon junction. Slides stained with hematoxylin and eosin were interpreted twice by the same observer using a semiquantitative grading scale assessing fiber structure and arrangement, rounding of the nuclei, regional variations in cellularity, increased vascularity, decreased collagen stainability, and hyalinization. Intraobserver reliability of the subscore readings was calculated. RESULTS: The mean pathologic sum-score of ruptured tendons was significantly greater than the mean pathologic score of control tendons (15.66 +/- 1.82 vs 3.7 +/- 2.31, P = .001). Within each specific category of tendon abnormalities, the control and ruptured tendons were significantly different (chi(2) test); all variables were significantly different (Mann-Whitney U test