Effects of custom and semi-custom foot orthotics on second metatarsal bone strain during dynamic gait simulation.

BACKGROUND

Stress fractures of the lower extremity are common in military and running populations. Research on the effectiveness of orthotics in modifying bone strain is limited. Our hypothesis was that custom and semi-custom foot orthotics would equally decrease bone strain of the second metatarsal.

MATERIALS AND METHODS

Eight cadaver specimens were cast for two types of orthotics, a custom and semi-custom device, using neutral plaster casts. Cadaver specimens, mounted to a dynamic gait simulator, walked over a force platform while force and bone strain data were collected. Peak bone strains, strain rates and tendon forces during the stance phase for each condition were analyzed using repeated measures analysis of variance and effect sizes.

RESULTS

Condition effects were present for tension strain, shear strain, compression rate and shear rate. Specifically, custom orthotics significantly decreased the aforementioned bone strains and strain rates (< or = 0.01 for all) and the semi-custom orthotic decreased tension strains and shear strain rates (p = 0.05 and 0.03, respectively). The effect of custom and semi-custom devices only differed significantly for compression and shear strain (p= 0.04 and 0.02, respectively) with custom orthotics having a greater effect.

CONCLUSION

Both custom and semi-custom orthotics modified the second metatarsal bone strain and strain rate. The use of custom orthotics during simulated walking decreased second metatarsal bone strains and strain rates more effectively than semi-custom orthotics.

CLINICAL RELEVANCE

Orthotics may minimize the strain magnitudes and rates of the second metatarsal in walking and therefore are a feasible treatment option for the treatment and prevention of stress injury to the second metatarsal.