Hallux saltans due to stenosing tenosynovitis of flexor hallucis longus: dynamic sonography and arthroscopic findings.

Triggering of the toes is rare, with isolated cases reported in the literature involving predominantly the flexor hallucis longus (FHL) tendon, a condition known as "hallux saltans" (HS). We report the dynamic sonographic findings of a 42-year-old female with a 2-month history of ankle pain and triggering of right hallux, consistent with HS. Sonography demonstrated tenosynovitis and focal thickening of FHL at the level of hindfoot, with a fibrous band adjacent to the tendon. Dynamic ultrasound showed triggering and snapping of FHL tendon during hallux flexion and extension, respectively. We present comprehensive documentation of this rare entity, including sonographic still images and cine clips, as well as correlation with arthroscopic surgical findings.