Measurement of first-ray mobility in normal vs. hallux valgus patients.

Hypermobility of the first ray is one causative factor in development of hallux valgus and an important factor in the treatment of hallux valgus, but measuring first-ray motion is difficult. There are two known ways of measuring first-ray motion. One is measuring the bony angle on the lateral foot X-ray using a modified Coleman block. The other is using devices. However, neither is suitable for clinical application. We introduce a simple, fast and easy way of measuring first-ray range of motion. Using this method, we compared the first-ray motion between a normal group and a hallux valgus group. Forty normal and 60 hallux valgus patients were included in the measurement. We measured the first-ray range of motion in the following way: with one hand we held the 2nd, 3rd, 4th, and 5th rays at the metatarsal head level with a simple right-angled indicator. With the other hand, we held the first ray at the metatarsal head level using a simple right-angled device, such as a scale. Keeping the other rays fixed, we moved the first ray up and down and recorded the average distance (d) 10 times to reduce intra-measurement differences. We also measured and recorded the first metatarsal length (L) on the anteroposterior foot X-ray film. Finally, we calculated the first-ray range of motion (alpha) using the above data. We also measured the hallux valgus angle and intermetatarsal angle in the hallux valgus patient group. With this method, the average first-ray motion was 10.3 degrees in the normal group and 12.9 degrees in the hallux valgus patient group. If we define 14 degrees, (that is, above the 95th percentile in the normal group) as having hypermobility, 38% of hallux valgus patients had first ray hypermobility. There was no correlation between first-ray hypermobility and either hallux valgus angle or intermetatarsal angle.