Influence of the Hardness of Insoles on the Abductor Hallucis Muscle in Baxter's Entrapment: A Cross-Over Randomized Study.

Background: The etiology and diagnosis of heel pain are complex and multifactorial, and it has been reported that Baxter's entrapment is responsible for up to 20% of foot disorders. The most conservative treatment of Baxter's entrapment has been the use of custom insoles. Electromyography was considered an effective test to assess muscle activity. The aim of this study was to test the use of insoles of different hardness on muscle activity of the abductor hallucis muscle in subjects with entrapment of the lateral branch of the external plantar nerve. Methods: 18 subjects (7 women and 11 men) diagnosed with nerve entrapment of the first branch of the lateral plantar nerve were recruited. Muscle activity of the adductor hallucis muscle was analyzed with insoles of different hardness in static and dynamic situations using electromyographic evaluation. Results: The statistical analysis did not show statistically significant differences in the muscle activity of the abductor hallucis muscle in the static position, with and without plantar orthoses (p>0.05), in contrast, in dynamic situations statistically significant differences were found between groups (p<0.01). Conclusions: The use of a hard insole decreases the maximum peak muscular activity of the abductor hallucis muscle in subjects with Baxter's nerve entrapment in walking conditions.