A Multi-Segment Foot Model Analysis on Normal, Pes Planus and Pes Cavus Feet and Ankle Kinetics

This study focuses on testing a clinically practical multi-segment foot model, in an optical motion capture laboratory, to analyse foot kinetics and the medial longitudinal arch (MLA) of the foot. The foot kinetics are analysed for differences between a control group with a normal/neutral arch foot anatomy, and two patient groups, one with a low arch in the foot (pes planus) and one with a high arch in the foot (pes cavus). The multi-segment foot model assesses four segments of the foot: hindfoot, midfoot, forefoot, and hallux. The joint moments for all segments in the x-axis (plantarflexion/dorsiflexion in the sagittal plane), y-axis (internal/external rotation in the transverse plane), z-axis (inversion/eversion in the frontal plane), and joint power in the sagittal plane were analysed for a full gait cycle, as well as the MLA height-to-length ratio. This study analysed ten adults with normal/neutral arch anatomy, five adults with pes planus, and three adults with pes cavus. Participants had auto-reflective markers placed on anatomical locations of the body, which were tracked by the optical motion capture cameras as the participants walked across a force plate at their typical walking speed. This multi-segment foot model precisely determined differences in the kinetics of the normal/neutral arch anatomy group and the two patient groups. The normal/neutral arch anatomy group showed agreement with other published multi-segment kinetic foot models, as well as strong test-retest relatability (r > 0.7), and all groups showed strong within-participant reliability. The model determined that the pes cavus group experiences a higher MLA height-to-length ratio throughout the gait cycle than the normal/neutral arch anatomy group and larger power in the forefoot and hindfoot during the push-off phase of gait. In contrast, the pes planus group experiences a lower MLA height-to-length ratio than the normal/neutral arch anatomy group, and lower power in the midfoot and hindfoot during the push-off phase of gait. The model is determined to be clinically practical and relevant for testing foot kinetics and evaluating differences between control and patient populations.