The effect of hallux sesamoid excision on the flexor hallucis longus moment arm.

Surgical treatments for chronic, painful hallux sesamoid disorders typically involve partial or complete resection of 1 or both sesamoids. Although these approaches generally result in satisfactory symptom relief, their effect on biomechanical function of the major hallux flexors is not completely understood. The effects of selective sesamoid resections on the effective tendon moment arm of the flexor hallucis longus tendon were evaluated. Twelve fresh frozen cadaver first rays were each mounted in a device that held rigid the metatarsal. A ramp-controlled displacement of an MTS ram supplied a functional load input force to the flexor hallucis longus. The components of the resultant output force necessary to resist the input flexor hallucis longus force were transduced simultaneously by a multicomponent load cell. Subsequently, 3 progressively more extensive seasamoid resections were done: (1) distal hemiresection, (2) complete resection, and (3) resection of both sesamoids. Six specimens were tested with the medial sesamoid removed first and 6 with the lateral sesamoid removed first. Statistical analysis showed that significant decreases in the effective tendon moment arms occurred with full medial sesamoid resection, full lateral sesamoid resection, and resection of both the medial and lateral sesamoids.