Endoscopic Release of the Flexor Hallucis Longus Tendon at Posterior Ankle for Management of Checkrein Deformity of the Great Toe, Second Toe, and Third Toe.

Checkrein deformity is rare and involves entrapment or fixed tethering of the flexor hallucis longus (FHL) in the posterior foot, just proximal to the flexor retinaculum of the ankle, and causes the "constant length phenomenon" of FHL. The clinical presentation is a dynamic flexion deformity of the great toe characterized by flexion contracture of the interphalangeal joint with mild extension contracture of the metatarsophalangeal joint, causing difficulty in walking since in the stance phase of gait, the hallux is forced into plantar flexion and impinges onto the ground. Because the FHL tendon has some interconnection to the tendons of the flexor digitorum longus at the master knot of Henry, deformities of the second and third toes are sometimes seen. There is no standard surgical treatment for checkrein deformity. Surgical release of the FHL muscle or release/lengthening of the FHL tendon has been proposed. The purpose of this Technical Note is to report the endoscopic release of the FHL tendon at the posterior ankle for management of checkrein deformity of the great toe, second toe, and third toe.