The shape of the metatarsal head as a cause of hallux abductovalgus.

The curvature of the 1st metatarsal head was evaluated on 100 radiographs by calculating the functional angle of the joint surface. This measure of curvature varied positively with the degree of hallux abductovalgus (HAV). Using measures of correlation it was found that in males, the association was linear (r2=0.39, p<0.001). In females, a linear relationship was identified only after logarithmic transformation of the data (r2=0.25, p<0.001). Comparison of the functional angle between males and females showed a significant difference (t=-5.03, df=98, p<0.001).