Variations in the quality of uncalcified fibrocartilage at the insertions of the extrinsic calf muscles in the foot.

It has been suggested that fibrocartilage at entheses (tendon-bone junctions) prevents collagen fibres bending at the hard tissue interface. We have investigated this function by exploring the relationship between the presence or amount of fibrocartilage at the attachments of the major extrinsic muscles in the foot, and the extent to which these tendons bend near their entheses during movement. The tendons were taken from each of 5 formalin-fixed dissecting room cadavers and prepared for routine histology, and sections were collected systematically throughout the blocks. Tendons that attached to the tarsus and metatarsus had fibrocartilaginous entheses, but those attached to the phalanges had fibrous entheses. In all tarsal and metatarsal tendons, the fibrocartilage was significantly thicker (P < 0.05) in the deepest part of the enthesis. Here the greatest amount of fibrocartilage was in the Achilles tendon (mean thickness +/- S.E.M.: 1560 +/- 161 microns). There were moderate amounts at the medial cuneiform attachment of tibialis anterior (533 +/- 82 microns), peroneus brevis (472 +/- 64 microns) and tibialis posterior (454 +/- 26 microns), small quantities at the first metatarsal attachment of tibialis anterior (104 +/- 14 microns) and peroneus longus (21 +/- 8 microns), but only traces at the attachments of the flexor and extensor tendons of the phalanges. The differences can be related to variations in the freedom of movement of the tendons near their attachments. This depends on the extent to which the tendons are bound by retinacula and the range of movement of the joint nearest the enthesis. The results suggest that more 'mobile' tendons have more fibrocartilage.(ABSTRACT TRUNCATED AT 250 WORDS)