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.