The structure and vascular pattern of the human tibialis anterior tendon was investigated using injection
techniques, light and transmission electron microscopy and immunohistochemistry. From the well
vascularised peritenon, blood vessels penetrate the tendon tissue and anastomose with a longitudinally
oriented intratendinous network. The distribution of blood vessels within the tibialis anterior tendon was
not homogenous. The posterior part of the tendon had a complete vascular network that extends from the
musculotendinous junction to the insertion at the first metatarsal and medial cuneiform bones. In the
anterior half, the tissue was avascular in a zone with a length of 45–67 mm. This zone was covered by a
single layer (∼30 μm) of oval shaped cells. Transmission electron microscopy showed that these cells have
the characteristics of chondroid cells. This region was stained by Alcian blue at pH 1 which indicates a high
concentration of acid glycosaminoglycans and immunohistochemical staining for chondroitin-4-sulphate,
chondroitin-6-sulphate and aggrecan was positive. However, immunostaining for the typical cartilage specific
type II collagen within this zone was negative. The location of the avascular zone corresponds to the region
where the tibialis anterior tendon wraps around the superior and inferior retinacula which serve as fibrous
pulleys. This is the region where most spontaneous ruptures of the tibialis anterior tendon occur. The
presence of fibrocartilage within gliding tendons is a functional adaptation to compressive and shearing
forces. In contrast to reports from the literature about the structure of gliding tendons wrapping around a
bony pulley, the gliding zone of the tibialis anterior tendon has only a narrow layer of chondroid cells and
proof of type II collagen is lacking.