Immunohistochemistry of the enthesis organ of the human Achilles tendon.

Background: The insertional region of the Achilles tendon includes: the fibrocartilage of the enthesis at the tendon-bone junction, the sesamoid fibrocartilage in the deep surface of the tendon, and the periosteal fibrocartilage covering the superior tuberosity of the calcaneus. The mechanism by which compressive stress and low oxygen concentration modulate the phenotypical expression of cartilaginous cells in mesenchymal tissue is still unknown. Tenascin-C isoform, with its anti-adhesive properties, has been hypothesized to have a role in cellular adaptation to compression.