Tendoscopy of the Flexor Hallucis Longus Tendon

Abstract

The tendon of flexor hallucis longus (FHL) can present several pathologies along its course, including rupture, laceration, longitudinal tears, stenosing tenosynovitis and pigmented villonodular synovitis. The flexor hallucis longus is a bipennate muscle which extends to the posterior part of the ankle. The tendon of FHL courses from the fibro-osseous tunnel posterior to the talus and passes into the fibrocartilaginous tunnel under the sustentaculum tali. The tendon is connected to the flexor digitorum longus tendon at the master knot of Henry. Distal to the master knot of Henry, the FHL tendon passes into the fibro-osseous tunnel between the sesamoid bones and insert into the base of distal phalanx of the hallux. Most of the course of the FHL tendon is deep and difficult to approach surgically. Surgical exploration of the tendon requires extensive soft tissue dissection. The course of the flexor hallucis longus tendon is divided into three zones. Zone 1 is located behind the ankle joint, from the musculotendinous junction to the orifice of the tunnel underneath the sustentaculum tali. Zone 2 is located from the tunnel underneath the sustentaculum tali to the knot of Henry. Zone 3 is located from the knot of Henry to the tendon insertion to the base of the distal phalanx of the hallux.¹ Zone 2 tendon sheath can be subdivided into proximal fibrous sheath (Zone 2A) and distal fascial sheath (Zone 2B)² (Fig. 20.1). Using a different endoscopic approach to the each zone of the FHL tendon, the course of the tendon can be examined arthroscopically from the musculotendinous junction to its insertion.