Functional hallux rigidus in the rheumatoid foot.

Hallux rigidus results from arthritic involvement of the first metatarsophalangeal joint. The authors have observed loss of motion at this joint in patients with rheumatoid arthritis in the absence of hallux valgus or joint destruction. A hyperextension deformity of the interphalangeal joint has also been observed, with a painful callus beneath it. The first metatarsophalangeal joint appears normal on roentgenograms, and passive motion of the joint is normal when it is examined clinically. The loss of first metatarsophalangeal motion is functional, and stems from muscle spasm of the great toe intrinsic muscles in an effort to relieve pressure on the lesser metatarsal heads. The interphalangeal hyperextension may develop secondary to "functional hallux rigidus."