Hallux valgus and hypermobility of the first ray: facts and fiction.

The aetiology of hallux valgus with regard to stability of the first metatarsocuneiform joint has historically been subject to much debate. Associations between the magnitude of the intermetatarsal angle and the hallux valgus angle have previously been established. Metatarsocuneiform joint coronal plane mobility is necessary for a concomitant increase in both of these angles. Although metatarsocuneiform joint hypermobility has been implicated in the development of a hallux valgus deformity, isolated sagittal plane instability has thus far not been proven to be a definitive cause.