The zero-plus first metatarsal and its relationship to bunion deformity.

The relationship between first metatarsal length and hallux valgus (HV) deformity was examined. Retrospectively, 210 randomly selected radiographic files were reviewed between 1988 and 1993. The morbid population consisted of 110 feet with HV deformities. The control population consisted of 100 healthy feet (no deformity). Seventy-seven percent of the patients with HV deformity had a first metatarsal length that was equal to or longer than the second metatarsal. This was defined as a zero-plus first metatarsal. Only 28% of the control population had this same proportion in length. Thus, prevalence of zero-plus first metatarsal was significantly associated with HV formation (chi(2)(1) = 51.15, P <.001). The mean first metatarsal protrusion distance was significantly higher in the bunion population (+1.58 mm) than in the control patients (-2.05 mm) (P <.001). The distribution of head shape differed significantly between the patients with HV and control patients; patients with HV had predominantly round heads (91%) and the control patients had predominantly square and square with a ridge heads (80%) (chi(2)(2) = 107.7, P <.001). All zero-plus first metatarsals in the HV population had a round first metatarsal head. Only 7.1% of the control patients had a round head with a zero-plus metatarsal. There was a positive relationship between the protrusion distance of the first metatarsal and the severity of the intermetatarsal angle, particularly in those patients with intermetatarsal angles ranging from 13 degrees to 20 degrees (P <.01). It was concluded that a zero-plus first metatarsal is a significant etiologic factor in the development of bunion deformity and should be part of the preoperative evaluation.