Effects of three foot types on excessive pronation
Excessive pronation has been indicated as one of the major factors in a wide range of clinical symptoms in the lower extremity. Two of the foot deformities which lead to excessive pronation are forefoot varus and rearfoot varus. However, current biomechanical investigations of subtalar joint pronation do not identify causes of excessive pronation in their subjects and categorize them as one group "excessive pronators." The purpose of this study was to compare selected aspects of subtalar joint movement during barefoot walking in three foot types ( normal, forefoot varus, and rearfoot varus ) to the two groups: normal and excessive pronators which was combination of forefoot varus and rearfoot varus foot types. For this study, twenty normal feet, twenty forefoot varus feet and twenty rearfoot varus feet were studied using high-speed camera (100 Hz). After marking the lower posterior one-third of both legs, each subject walked on a 5 m-long stage away from the camera at a rate of 110 steps per minute. Following variables were measured: 1) rearfoot angle at heel strike (HS), at maximum pronation (Pmax), and at heel off (HO); 2) duration of the four events from HS to Pmax, HS to HO, HS to subtalar joint neutral (N), HS to toe off (TO); and 3) maximum pronation velocity. One-way analysis of variance (ANOVA) with a significance level of p<0.05 was used for data analysis. Results of this study indicated that the forefoot varus foot type had significantly greater rearfoot pronation angles at HS and Pmax compared to the rearfoot varus foot type. The length of time from HS to HO and HS to TO was significantly shorter in the forefoot varus foot type compared to the rearfoot varus foot type. No significant differences were found in the comparison between the normal group and the excessive pronator group. The excessive pronator group did not represent either the forefoot varus or the rearfoot varus foot motion characteristics. These findings demonstrated the need for future investigators to identify each foot type in pronation studies. Problems specific to each foot type can then be identified.