The effect of forefoot and arch posting orthotic designs on first metatarsophalangeal joint kinematics during gait.

STUDY DESIGN Repeated-measures analysis of variance. OBJECTIVE To examine the effect of 2 different orthotic posting designs on first metatarsophalangeal (first MTP) joint kinematics during gait. BACKGROUND Common orthotic designs used to control abnormal pronation incorporate the use of a medial post in the forefoot and/or rearfoot locations. Although this design may favorably alter rearfoot and lower-limb kinematics, the incorporation of a forefoot post has been theorized to negatively impact first MTP joint function by limiting hallux dorsiflexion during push off. An alternative design that has been proposed to be more favorable for function of the hallux and first metatarsal is the medial arch support. METHODS AND MEASURES Eighteen subjects with a mean age of 28.2 years (SD, 8.3 years) completed the study. All subjects were judged to have excessive pronation based on a clinical orthopaedic examination. Two different pairs of orthoses were custom molded for each subject. One design incorporated an extrinsic rearfoot and forefoot post and the second design had a high medial longitudinal arch in combination with an extrinsic rearfoot post. The "Flock of Birds" electromagnetic tracking device was used to collect 3-dimensional position and orientation data of 3 body segments (hallux, first metatarsal, and calcaneus) during the stance phase of walking for 3 conditions (no orthosis and each of the 2 different orthotic designs). A repeated-measures analysis of variance was used to assess differences in first MTP joint dorsiflexion at midstance and during the push-off period of gait, as well as metatarsal declination angle changes during relaxed stance. An exploratory regression analysis was used to investigate factors that related to the change in peak dorsiflexion for the orthotic conditions. RESULTS Peak first MTP joint dorsiflexion averaged between 38 degrees and 40 degrees across all conditions. Although slight increases in first MTP joint dorsiflexion values were noted with both types of orthotic designs, these differences were not significant at either phase of the stance cycle (P = .50). The metatarsal declination angle in relaxed stance significantly increased (P = .001) under both orthotic conditions. Considerable individual variability was present. For the rearfoot-forefoot posted orthosis, a change in the declination angle of the first metatarsal during relaxed stance with the orthosis was a significant nonlinear predictor of change in peak dorsiflexion during push off. CONCLUSIONS Foot orthoses that incorporate a medial forefoot post do not have a consistent negative effect of reducing first MTP joint dorsiflexion during walking.