The effect of foot orthotics on the initiation of plantar surface loading.
INTRODUCTION:: Little information exits concerning the effect, if any, foot orthoses have upon how the foot is loaded during normal walking. The purpose of this study was to determine if there was a difference in the initiation of forefoot loading with different densities of foot orthoses. METHODS:: Ten volunteers (5 men, 5 women) between the age of 23 and 43 years (mean=30.3 yrs) participated in this study. None of the subjects had a history of congenital deformity, hallux valgus, malleolar torsion or a history of injury or pain to either lower extremity 12 months prior to the start of the investigation. Two different pair of foot orthoses were provided to each subject in the study. One pair consisted of UCO-BKS medium width foot orthoses with a durometer rating of 55-60 (Shore A gauge). Forefoot and/or rearfoot wedging was applied to these orthoses if indicated from a physical examination. This orthotic condition was labeled RIGID. The second pair consisted of UCO-BF foot orthoses with a durometer rating of 30-35 (Shore A gauge). This orthotic condition was labeled SOFT. In addition to the foot orthoses, each of the 10 subjects were fitted with the same type of footwear (Reebok Boston Road). Following a 'break-in' period for the footwear and orthotics, each subject walked along a 12 m walkway with the EMED PEDAR insole placed inside their shoes. A total of 10 consecutive walking trials were collected at each subject's self-selected speed. Using the NOVELWin MASKS program, the plantar surface of the forefoot was divided into 3 different areas, Lateral, Central and Medial. The time of initiation of loading for each of these masks was then determined. Reliability of the loading initiation times was determined using type (2,1) intraclass correlation coefficients. Differences between the three forefoot areas were determined using a one-way, repeated measuresANOVA and Tukey's post hoc analysis, if indicated. An alpha level of 0.05 was used for all tests of statistical significance. RESULTS:: The ICC values for the initiation of loading in the forefoot were in excess of.936. The result of theANOVA test revealed that the medial forefoot is loaded significantly earlier with a RIGID foot orthotic compared to either the SHOE ONLY or SOFT foot orthotic condition. This earlier loading caused a reversal of the normal loading sequence of plantar pressure in the forefoot during walking. DISCUSSION:: Previous studies have reported that approximately 10 degrees of forefoot movement, independent to hindfoot motion occurs during the loading response of walking. An additional 3 degrees has been shown to occur from the end of the loading response to mid-stance. It would appear from the findings of this study that rigid orthoses prevent this normal independent movement between the forefoot and hindfoot, since the rigid orthoses cause earlier loading of the medial forefoot. The soft orthoses permitted the same lateral to medial forefoot loading pattern also observed in barefoot walking. CONCLUSION:: The results of this study indicate that the use of a rigid foot orthosis inside a shoe, alters the timing of forefoot loading during walking. These findings suggest that the use of soft orthoses permit a more normal forefoot to hindfoot movement pattern during the loading phase of walking.
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