Biomechanical gait evaluation of the immediate effect of orthotic treatment for flexible flat foot

Flexible flat foot subjects attending the prosthetics and orthotics units come with prescriptions from orthopaedic surgeons for arch supports. Usually a pair of thermoformed plastic inserts are fabricated and fitted to treat the patients. However the effect of the orthotic treatment is not yet clear. A motion analysis system with two video cameras placed on the lateral and rear sides of the subject together with one force platform was used to investigate the immediate effects of the orthotic treatment. The force platform collected force data and the two cameras captured two-dimensional displacement data of the lower limb. Eight subjects, all having an arch index (AI) larger than 3.0 participated in the study. For each subject, three successful steps on the force platform were videotaped for both the shod (with shoe only) and the orthotic (with shoe and orthosis) conditions. The kinetic variables were normalized to individual body weight and averaged for each subject. A Paired t-test was conducted to analyse sample means of matched pairs between the shod and the orthotic conditions. The results showed changes in displacement data with relatively little change in the collected force data. The modified UCBL shoe insert evaluated significantly affected the orientation and movements of the subtalar joint, ankle joint and knee joint. These immediate effects reduced the degree and duration of abnormal pronation during the stance phase and thus had the potential for decreasing strain in the plantar ligaments and reducing abnormal tibial rotation which may be therapeutic for the foot.