Hallucal rotation: a method of measurement and relationship to bunion deformity.

A method for measuring hallucal rotation or weightbearing tangential radiographs is described. Under controlled conditions using cadaver specimens, 10 degree changes in hallucal rotation were associated with a mean change in radiographically measured rotation of 10.6 degrees (S.D. = 2.3 degrees). A clinical study of 30 control patients and 39 patients presenting with a chief complaint of a bunion deformity was undertaken to assess the reliability of the measurement method. The overall reliability was high for both groups (r = 0.98). A significant difference was found between mean values for hallucal rotation in the two groups (P < 0.005). There is a modest association between increasing valgus deviation and increasing rotation of the hallux (r = 0.43, P < 0.01). This study suggests that bunion deformities involve variable degrees of axial and coronal plane rotations of the first metatarsophalangeal joint and that the concept of a planar "hallux valgus" deformity may insufficiently describe this three-dimensional clinical condition.