Causes / typical injury mechanism: Flexor hallucis longus (FHL) tendonitis is caused by chronic friction of the tendon resulting from repetitive plantarflexion, os trigonum irritation, acute trauma to the foot, or entrapment of the FHL muscle body in the tarsal tunnel.

Classic history and presentation: The common presentation consists of difficulty fully flexing the hallux when the ankle is maximally dorsiflexed.

Risk factors: Exposure to repeated plantarflexion or hyperflexion of the ankle. FHL tendonitis commonly presents in athletes, such as ballerinas, who repeatedly subject their ankle to extreme ranges of motion. However, this condition can also present in the general population.

Pathophysiology: FHL tendonitis is characterized by inflammation of the tendon sheath, with the presence of inflammatory fluid, caused by acute trauma or chronic friction of the FHL tendon.