The effect of ankle position on the exam for first ray mobility

PURPOSE: The clinical assessment of first ray motion in the sagittal plane, as originally described by Morton, is difficult to quantify. Different reports have shown inconsistent values and variability between the manual exam and examination using an external measuring device. The authors hypothesize that when performing a manual examination for evidence of increased first ray motion, the magnitude of first ray mobility varies as the position of ankle dorsiflexion/plantarflexion varies. METHODS: Using an external caliper (a modified Klaue device), the authors quantified first ray motion in reference to variable ankle positions in a group of normal patients, a group of patients with untreated moderate and severe hallux valgus, a group who had undergone a successful metatarsophalangeal joint arthrodesis for hallux valgus, and a small group who had previously undergone a plantar fasciectomy. A total of 119 feet (109 patients) were measured. In addition to first ray motion, radiographic data were compared between groups. RESULTS: With the ankle in the neutral dorsiflexion position, the mean first ray motion was 4.9 mm for the control group, 7.0 mm for the hallux valgus group, 4.4 mm for the metatarsophalangeal fusion group, and 7.7 mm for the plantar fasciectomy group. There was a significant decrease (p < .05) in first ray motion when the ankle was moved to the dorsiflexed position for all four groups. There was a significant increase in first ray motion when the ankle was moved to the plantarflexed position (p < .01) for all groups except the plantar fasciectomy group. No significant difference in first ray motion was observed for the plantar fasciectomy group between the neutral and plantarflexed ankle positions (p < .05). CONCLUSION: The exam for first ray mobility is influenced by the position of the ankle and may explain the discrepancy between the manual exam and measurement with an external device. Recommendations for the manual exam of first ray mobility are given.