Radiographic assessment of the second metatarsal: measure of first ray hypermobility.

Hypermobility of the first metatarsal cuneiform joint has been implicated as a cause of the hallux valgus deformity. The objective definition of hypermobility at this joint, however, has not been clearly defined. We used a modified Coleman block test to accentuate motion at the first metatarsal cuneiform joint in order to measure physiologic limits of motion in vivo. This motion was compared with radiographic analysis of the feet, which included the hallux valgus angle, intermetatarsal angle, and medial cortical thickening at the midshaft of the second metatarsal. This assessment was performed on 100 feet (50 right feet and 50 left feet in 50 patients). The average intermetatarsal angle was 8.7 degrees (range, 4-14 degrees), the average hallux valgus angle was 11 degrees (range, 4 degrees of varus to 30 degrees of valgus), and the average midshaft medial cortical thickness was 3.2 mm (range, 2.0-5.5 mm). Pearson's correlation coefficient was calculated to compare these factors. The relationship between variables was found to be small (r < or = 0.2). Motion was noted to occur in the normal foot at this joint and a range of normal values for medial cortical thickness was identified.