The flexor hallucis longus is the most powerful of the long toe flexors, originating from the posterior fibula and travelling through a fibro-osseous tunnel behind the medial malleolus and then beneath the sustentaculum tali to reach the great toe. It is the tendon that powers the final push-off in walking, running, and jumping, and its dysfunction is a significant cause of both medial ankle pain and great toe stiffness in athletes.
| Origin | Posterior surface of the fibula (lower two-thirds) and adjacent interosseous membrane |
|---|---|
| Insertion | Plantar surface of the base of the distal phalanx of the great toe |
| Nerve Supply | Tibial nerve (L5, S1, S2) |
| Blood Supply | Fibular artery |
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It generates the powerful toe-off thrust at the end of the stance phase in running and jumping, storing elastic energy in the plantar fascia windlass mechanism and releasing it into propulsion. Its fibro-osseous tunnel behind the medial malleolus is a frequent site of both tenosynovitis and triggering.
FHL tenosynovitis behind the medial malleolus is a classic diagnosis in ballet dancers, producing posteromedial ankle pain with great toe movement that is reproduced by the FHL stretch test of passive great toe dorsiflexion with the ankle neutral. Stenosing tenosynovitis at the sustentaculum tali can produce a triggering or snapping great toe that catches during toe-off. FHL tendinopathy is also an underrecognised cause of heel pain in runners.
The FHL tendon is palpable behind the medial malleolus between the posterior tibial tendon anteriorly and the Achilles tendon posteriorly, and it can be felt tightening during active great toe plantarflexion.
Inflammation of the tendon sheath behind the medial malleolus producing posteromedial ankle pain with great toe movement, classic in ballet dancers and reproduced by passive great toe dorsiflexion.
Stenosing tenosynovitis at the sustentaculum tali causing a catching or clicking great toe during push-off that may require surgical release of the fibro-osseous tunnel in refractory cases.
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