Orthoses posted in both the forefoot and rearfoot reduce moments and angular impulses on lower extremity joints during walking

Abstract

The purpose of the present study was to determine the effects of orthoses designed to support the forefoot and rearfoot on the kinematics and kinetics of the lower extremity joints during walking. Fifteen participants volunteered for this study. Kinematic and kinetic variables during overground walking were compared with the participants wearing sandals without orthoses or sandals with orthoses. Orthoses increased knee internal abduction moment during late stance and knee abduction angular impulse, and reduced the medial ground reaction force during late stance, adduction free moment, forefoot eversion angle, ankle inversion moment and angular impulse, hip adduction angle, hip abduction moment, and hip external rotation moment and angular impulse (p<0.05). Orthoses decreased the torsional forces on the lower extremity and reduced the loading at the hip during walking. These findings combined with our previous studies and those of others suggest that forefoot abnormalities are critically important in influencing lower extremity kinematics and kinetics, and may underlie some non-traumatic lower extremity injuries.

Introduction

It has been claimed that the varus foot, through anatomic and functional constraints (McPoil and Knecht, 1985, Root et al., 1977), results in an everted calcaneus, excessive subtalar joint pronation, knee abduction, hip adduction and lower extremity internal rotation during gait (Michaud, 1993, Tiberio, 1987, Tiberio, 1988). These abnormal motions caused by the varus foot have often been considered risk factors for running injury (Ferber et al., 2009, Hamill et al., 1999, McClay and Manal, 1998, Messier and Pittala, 1988). Most orthoses designed to prevent excessive pronation focus on controlling rearfoot motion. Nevertheless, a forefoot varus abnormality is considered a ‘destructive foot’ because of its proposed mechanism to cause prolonged excessive pronation in the late stance phase which could affect lower leg biomechanics during gait, create abnormally high torques in the lower extremity and lead to chronic knee, hip and pelvic injury (Holt and Hamill, 1995, Michaud, 1993, Tiberio, 1988). Supporting this supposition, Gross et al. (2007) found that elderly individuals with a large forefoot varus in non-weight bearing had a two times greater incidence of hip osteoarthritis and a five times greater risk for total hip replacement.

Recent evidence (Monaghan et al., 2013) has shown that individuals with large forefoot varus (>15°), at foot contact measured relative to the ground plane (Holt and Hamill, 1995), had a greater range and duration of pronation during stance than those with less forefoot varus. Since such increased and prolonged pronation is claimed to affect the relative motions among the lower extremity joints and stress the hip joint (Michaud, 1993, Tiberio, 1988), this would provide a potential mechanism for the hip pathology observed by Gross et al. (2007). In contrast to the forefoot posture, the rearfoot posture was not related to the amount or timing of pronation (Monaghan et al., 2013) or the incidence of hip osteoarthritis and/or total hip replacement (Gross et al., 2007).

Investigations of the effectiveness of orthoses in walking have largely been limited to those designed to control rearfoot motion, with results showing equivocal effects on the motion of the foot (Eng and Pierrynowski, 1994, Ferber and Benson, 2011, McCulloch et al., 1993, Novick and Kelley, 1990, Zifchock and Davis, 2008). One experiment indicated a decrease in moments at the foot (Nester et al., 2003), and reduction of knee frontal plane motion (Eng and Pierrynowski, 1994). The only study that investigated the kinetics of proximal joints in walking showed no effects on the knee and hip (Nester et al., 2003). However, orthoses utilizing medial posting have done so only in the rearfoot with some extended distally to a point proximal to the first metatarsal head. This design may not provide sufficient control during late stance as orthoses posted up to the metatarsophalangeal joint line have dynamical effects only from foot contact to mid-stance (MacLean et al., 2006). Once the heel leaves the ground and the body weight transfers to the forefoot, a rearfoot orthosis will not be effective in controlling the pronation in a varus forefoot undergoing a large pronatory torque (Holt and Hamill, 1995). To date, however, there have been no studies investigating the effects of orthoses with medial posting that extended through the forefoot to the end of the first toe during walking either in the foot or in the more proximal joints. In the studies that reported forefoot posting, that posting extended only to the first metatarsal head.

The purpose of this study was to examine the effects of custom-made orthoses posted in both the forefoot (extended to and including the first toe) and rearfoot on lower extremity kinematics and kinetics during walking. It was hypothesized that such orthoses would diminish the theorized effects of increased and late pronation on lower extremity biomechanics, by: (a) reducing foot eversion, knee internal rotation and hip adduction and internal rotation motions, (b) increasing knee adduction motion, (c) affecting ankle inversion, knee abduction and external rotation, and hip abduction and external rotation moments and angular impulses.