Segmental variation in microstructure, matrix synthesis and cell proliferation in rabbit flexor tendon.

An experimental culture system was designed with the purpose of studying matrix synthesis and cell proliferation in the deep flexor tendon of the rabbit forepaw. Special attention was paid to differences between three consecutive defined segments of the tendon from the region of the tendon sheath. There were two fibrocartilaginous areas in the tendon, one in the dorsal part of the proximal segment and one in the volar part of the distal segment. The intermediate segment consisted of regular tendinous tissue. The dorsal aspect of the distal segment was further characterized by a cell rich area related to the entrance of the vinculum longum. Proteoglycan synthesis in vitro was higher in the proximal and distal segments than in the intermediate, while collagen synthesis was highest in the intermediate tendinous segment. Variations in collagen content were reflected in variations in collagen synthesis. The rate of cell proliferation was highest in the intermediate segment. Segmental biochemical characteristics correlated well with morphological variations of the deep flexor tendon. These variations may reflect an adaptation to different mechanical forces acting on the tendon. The segmental variations may also be relevant for the healing capacity of the flexor tendon.