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Flexor Hallucis Longus

- Anatomy:
    - origin: distal 2/3 of posterior fibula, interosseous membrane and adjacent intermuscular septum; (see deep posterior compartment)
    - tendon passes through posterior aspect of fibro-osseous tunnel, plantar midfoot (knot of Henry);
    - insertion:
            - plantar surface of base of distal phalanx of greater hallux (FHL tendon passes between medial and lateral sesamoid bones at MP joint;)
            - prior to inserting on the base of the distal phalanx, the FHL passes beneath the sustentaculum in an oblique manner;
    - action:
            - flexes great toe at the foot;
            - assists in plantar flexion of the foot at the ankle;
            - synergist: flexor hallucis brevis;
    - nerve supply: tibial nerve, S1 > S2 > L5; (see innervation)

- Injury to FHL following Tibial Fracture: (see tibial frx)
    - McKeever has described the checkrein deformity of the great toe that may occur after fracture of the distal third of the tibia;
    - flexor hallucis longus adheres to callus at the fracture site so that its tendons forms a bowsring between this point and the site of
           insertion on the tendon into the great toe;
    - thus when ankle is dorsiflex, the great toe is sharply flexed, but when the ankle is plantar flexed, the interphalangeal joint extends completely;

- FHL Tendonitis:  
    - tendon pathology my consist of stenosing tenosynovitis, pseudocyst, or tendon tear;
          - tendon cyst tends to be soft and movable over the posteromedial ankle;
    - Ballet dancing is a predisposing condition (as dancers go from flat foot to the en pointe position);
    - tendinitis of the FHL tendon is rarely seen in activities other than ballet dancing, in which extreme plantar flexion is necessary;
    - contributing causes of the tendonitis may be due to anomalous FHL musculature at the entrance to the tunnel;
    - diff dx: posterior impingement, symptomatic os trigonium, Achilles tendonitis, and tarsal tunnel syndrome;
          - at the midfoot attempt to distinguish FHL tenderness from the underlying plantar fascia;
    - clinical findings:
          - swelling, pain, and tenderness posterior to the medial malleolus;
          - triggering and pain along tendon sheath may occur with toe flexion;
          - dorsiflexion of the great toe may be reduced when the ankle is placed in dorsiflexion;
          - observe ease of flexion/extension of the great toe when the ankle lies in plantarflexion and dorsiflexion;
    - non operative treatment:
          - steroid injection is contra-indicated due to proximity of N/V bundle;
    - operative treatment:
          - consider medial approach, made posterior to the medial malleolus at the the level of the superior border of calcaneus;
          - FHL is identified just anterior to the Achilles tendon;
          - identify the N/V bundle and the underlying FHL tunnel;
          - flex and extend the great toe to identify the tunnel, and attempt to palpate for a nodule;
          - release the posteromedial aspect of the tunnel down to the level of the sustentaculum tali;
          - ensure that there is unrestricted motion of the FHL;
          - look for a longitudinal rent in the FHL tendon;
          - consider remvoal of an os trigonium is one is present

Sesamoid disorders and treatment. An update.

Stenosing tenosynovitis of the flexor hallucis longus tendon and posterior impingement upon the os trigonum in ballet dancers

Lacerations of the flexor hallucis longus in the young athlete.  

Flexor hallucis longus tendon injury in dancers and non dancers

Tenosynovitis of the flexor hallucis longus: a clinical study of the spectrum of presentation and treatment.

Distal anatomical relationship of the flexor hallucis longus and flexor digitorum longus tendons.