Hallux valgus due to cuneiform-metatarsal instability.

We present a biomechanical rationale for the treatment of severe hallux valgus deformity by realignment and arthrodesis of the first cuneiform metatarsal (CM) joint. We think that this severe hallux valgus deformity represents instability at the CM-1 articulation, since normal motion at that joint is very small. A forefoot compression test was used to assess the foot preoperatively. This was found not only to realign the first metatarsal, but also to align the metatarsophalangeal joint. A surgical procedure has evolved to include a transverse screw between the first and second metatarsal bases, as well as a second screw from first cuneiform to first metatarsal base, along with a small-volume bone graft of the CM-1 articulation. This is a modern variant of the Lapidus procedure.