Biomechanical quantitative study in hallux valgus deformity associated with the second metatarsalgia

Objective To study the relation between the pressure in forefoot and the second metatarsalgia in hallux valgus deformity, finally to quantitatively analyze the pressure under the second metatarsal head which is a dangerous factor leading to second metatarsalgia. Methods Three groups volunteered for this study by a self-devised foot pressure measurement system： fifty-eight normal subjects （116 feet） without pain and deformity in foot, thirty-two patients （45 feet） with hallux valgus and pain only under the second metatarsal head, fifty-six patients （102 feet） with hallux valgus without symptoms of metatarsalgia. The percentage of pressure to weight was the criteria for data analysis. First the pressures under second metatarsal head among three groups were compared with each other. Secondly we used case-control study to identify whether it was high pressure that was likely to result in metatarsalgia. Finally we compared the pressure interval under second metatarsal head among three groups to define the pressure interval which might be a dangerous factor to second metatarsalgia. Results 1）The pressure beneath the second meatatarsal head in patients with metatarsalgia was the highest in the three groups （P〈 0.05）. 2） In case-control study, we calculated the odds ratio of the high pressure between the group with metatarsalgia and that without symptom. The odds ratio was larger than three. The low limit of 95% confident interval of the odds was larger than one. 3） The pressure under second metatarsal in the group with second metatarsalgia existed in the interval between 5.20% to 7.29% of body weight. Conclusion The increased pressure under metatarsal head is the dangerous factor leading to metatarsalgia. If the pressure under the second metatarsal head increases beyond 5.20% of weight, metatarsalgia will be happened at the region. Key words: Hallux valgus;  Biomechanics;  Metatarsal bones;  Pain;  Pressure