Degenerative change and rotator cuff tears. An anatomical study in 160 shoulders of 80 cadavers.

In order to determine the effects of friction and rubbing in the development of rotator cuff tear, we studied 160 shoulders of 80 cadavers (age at death 43-93 years, mean 69.3 years). Seventy-two cadavers were fixed with formalin and eight were fresh cadavers. The surface of the cuff and the undersurface of the acromion were observed macroscopically. Eight shoulders of fresh cadavers were examined by scanning electron microscopy. Ninety-eight specimens (61%) showed degenerative changes of the supraspinatus tendon. The number of tendons with degeneration and tear increased from the fifth to sixth decade of life, and the size of the tear increased with age. However, there was no sustained increase in the incidence with aging from the age of 60 to 90 years, and the percentage with degenerative changes of the cuff remained at approximately 60% in each decade. Ninety-six specimens (60%) showed degeneration of the subacromial surface. The percentage with degeneration of the undersurface of the acromion remained at approximately 60% from the sixth to ninth decade. There was a significant correlation between the severity of the changes in the rotator cuff and the subacromial surface. Scanning electron microscopy showed changes suggesting effects of friction and rubbing on the rotator cuff, such as regularly arranged wool-like spherical structures on the surface of the tendon and rounded ruptured ends of the tendon fibers. These results indicate that degenerative change of the rotator cuff is aggravated by a friction and rubbing mechanism with the undersurface of the acromion and leads to development of a complete tear.