Hallux valgus, first metatarsal pronation and collapse of the medial longitudinal arch--a radiological correlation.

In a previous study we developed a model to assess first metatarsal pronation based on the position of the inferior tuberosity of its base and showed a significant relationship between first metatarsal pronation and the intermetatarsal angle (r=0.69, p<0.001). The present study was undertaken to correlate first metatarsal pronation with the height of the medial longitudinal arch in an attempt to define the clinical significance of this new finding. The weight-bearing anteroposterior and lateral radiographs of the feet of 50 patients (100 feet; 36 females patients of mean age 38 years, 14 males patients of mean age 40 years) were reviewed, and in each case, the patient's age, sex, intermetatarsal angle, amount of first metatarsal pronation and medial longitudinal arch angle were recorded by independent observers. A significant relationship was demonstrated between first metatarsal pronation and the height of the medial longitudinal arch (r=0.93, p<0.0001). Less marked association was observed between intermetatarsal angles and first metatarsal pronation (r=0.71, p<0.001). Multivariate analysis of patient age, sex, intermetatarsal angle and medial longitudinal arch angle against metatarsal pronation showed that the single most dominant variable affecting metatarsal pronation was the height of the medial longitudinal arch.