PROTEOGLYCANS OF HUMAN ROTATOR CUFF TENDONS

Rotator cuff and biceps tendons that appeared grossly normal were proc ured from adult cadavers without a history of shoulder problems. These tendons were analyzed for the amount and type of glycosaminoglycan, t ype of proteoglycan, and histology. When compared with the distal/tens ional region of biceps tendon, the glycosaminoglycan content of supras pinatus, infraspinatus, and subscapularis tendons was 2.5-fold higher and the glycosaminoglycan content of the proximal/compressed region of biceps tendon was 3-fold higher. The ratio of hyaluronic acid to chon droitin sulfate/dermatan sulfate in all three cuff tendons was approxi mately 1. Rotator cuff tendons contained large proteoglycan similar to aggrecan, as demonstrated by sodium dodecyl sulfate-polyacrylamide ge l migration, elution from Sepharose CL-4B, and content of both chondro itin sulfate and keratan sulfate chains. Both decorin and biglycan wer e also present, as demonstrated by migration in sodium dodecyl sulfate -polyacrylamide gels and core protein immunoreactivity. In contrast, d ecorin was the only proteoglycan prominent in distal/tensional regions of biceps tendon. Histological analysis showed layers of loosely orga nized, alcian blue stained material running between the longitudinal c ollagen fiber bundles. The proteoglycan content of rotator cuff tendon s was similar to fibrocartilage in tendons that have been subjected to compressive loads in situ. This suggests that cells of normal adult r otator cuff tendons have adapted to loads distinct from pure tension. However, the histological organization did not resemble mature fibroca rtilage. The increased amount of proteoglycan in rotator cuff tendons may serve to separate and lubricate collagen bundles as they move rela tive to each other during normal shoulder motion.