Elsevier

Journal of Biomechanics

Volume 46, Issue 1, 4 January 2013, Pages 122-128
Journal of Biomechanics

Toe-in gait reduces the first peak knee adduction moment in patients with medial compartment knee osteoarthritis

https://doi.org/10.1016/j.jbiomech.2012.10.019Get rights and content

Abstract

The first peak of the knee adduction moment has been linked to the presence, severity, and progression of medial compartment knee osteoarthritis. The objective of this study was to evaluate toe-in gait (decreased foot progression angle from baseline through internal foot rotation) as a means to reduce the first peak of the knee adduction moment in subjects with medial compartment knee osteoarthritis. Additionally, we examined whether the first peak in the knee adduction moment would cause a concomitant increase in the peak external knee flexion moment, which can eliminate reductions in the medial compartment force that result from lowering the knee adduction moment. We tested the following hypotheses: (a) toe-in gait reduces the first peak of the knee adduction moment, and (b) toe-in gait does not increase the peak external knee flexion moment. Twelve patients with medial compartment knee osteoarthritis first performed baseline walking trials and then toe-in gait trials at their self-selected speed on an instrumented treadmill in a motion capture laboratory. Subjects altered their foot progression angle from baseline to toe-in gait by an average of 5° (p<0.01), which reduced the first peak of the knee adduction moment by an average of 13% (p<0.01). Toe-in gait did not increase the peak external knee flexion moment (p=0.85). The reduced knee adduction moment was accompanied by a medially-shifted knee joint center and a laterally-shifted center of pressure during early stance. These results suggest that toe-in gait may be a promising non-surgical treatment for patients with medial compartment knee osteoarthritis.

Introduction

Symptomatic knee osteoarthritis (OA) affects 12% of adults over age 60 years (Dillon et al., 2006) and its prevalence is projected to increase as life expectancy and obesity rates rise (Elders, 2000). The medial compartment of the knee is affected ten times more often than the lateral compartment, likely due to greater medial compartment loading during walking (Ahlback, 1968, Schipplein and Andriacchia, 1991). The external knee adduction moment (KAM) during walking gait is a surrogate measure of medial compartment loading (Zhao et al., 2007, Birmingham et al., 2007). The KAM typically has two peaks: a first peak during early stance and a second peak during late stance. The first, and the larger, peak in the KAM has been linked to the presence (Hurwitz et al., 2002), severity (Sharma et al., 1998), and progression (Miyazaki et al., 2002) of knee OA.

Gait modifications to lower the KAM have been suggested as a conservative treatment for patients with medial compartment knee OA. The foot progression angle is defined by the angle between the foot vector (calcaneous to the second metatarsal) and the line of progression (Rutherford et al., 2008). In normal gait, the foot progression angle is around 5°, indicating toes pointing slightly outward (Rutherford et al., 2008, Guo et al., 2007). Toe-out gait, defined as an increase in foot progression angle from baseline through external foot rotation (Wang et al., 1990, Jenkyn et al., 2008), reduces the second peak of the KAM but not the first peak (Guo et al., 2007, Lynn and Costigan, 2008, Lynn et al., 2008, Fregly et al., 2008). During stair climbing, toe-out gait reduces the second peak KAM but increases the first peak (Guo et al., 2007). Toe-in gait, defined as a decrease in foot progression angle from baseline through internal foot rotation, has been studied comparatively less. Lynn and Costigan (2008) reported that toe-in gait reduced the first peak KAM in healthy adults, while Lin et al. (2001) reported that toe-in gait did not change the first peak KAM and increased the second peak KAM in healthy children.

Gait modifications that are designed to alter the KAM can also change the external knee flexion moment, which may alter joint contact force (Walter et al., 2010). It is possible that gait modifications may decrease the KAM while simultaneously increasing the external knee flexion moment. An increased external knee flexion moment necessitates greater force development by the quadriceps and can eliminate reductions in the medial compartment force brought about by a reduced KAM (Walter et al., 2010). Thus, there is motivation to develop gait modifications for patients with medial-compartment knee OA that lower the first peak KAM without increasing the peak external knee flexion moment.

The mechanism linking changes in foot progression angle to changes in the KAM is not fully understood. It is thought that toe-out gait causes the center of pressure to move laterally, shifting the line of action of the ground reaction force toward the knee joint center (Guo et al., 2007, Jenkyn et al., 2008). This change could reduce the lever arm of the ground reaction force (Hunt et al., 2006) and reduce the magnitude of the KAM; however, experimental data supporting this theory have not been reported. A prior study, in which subjects were instructed to make modifications only to the foot progression angle and separately to make modifications only to the frontal plane tibia angle, found that foot progression and frontal plane tibia angles were moderately correlated (r=0.60, Shull et al., 2010). This suggests that an instructed change in foot progression angle could be accompanied by a frontal plane tibia angle change, which could shift the knee joint center medially for toe-in gait. Thus, it may be too simplistic to assume that changes in the KAM from an altered foot progression angle arise from a change in the center of pressure alone.

We undertook this study to determine the effect of toe-in gait on the first peak knee adduction moment and the peak external knee flexion moment in patients with medial compartment knee osteoarthritis. We hypothesized that: (a) toe-in gait reduces the first peak knee adduction moment, and (b) toe-in gait does not increase the peak external knee flexion moment. We expected that reductions in the knee adduction moment would occur as the knee joint center moved medially and the center of pressure moved laterally, thereby reducing the lever arm of the ground reaction force vector.

Section snippets

Subjects

Twelve subjects (Table 1) with symptomatic, medial-compartment knee OA participated in this study after giving informed consent in accordance with Stanford University's Institutional Review Board. A priori pairwise sample size calculation (power: 95%, alpha: 5%), based on a cohort of healthy subjects from a previous study (Shull et al., 2011), was used to determine that twelve subjects were sufficient to detect a 10% reduction in the KAM. To be included, subjects were required to have

Results

Subjects, on average, reduced their foot progression angle by 5° (p<0.01) during toe-in trials compared to baseline walking trials (Fig. 1, Table 2). Toe-in gait reduced the first peak of the KAM (p<0.01) by an average of 13% (Fig. 2, Table 2). Toe-in gait did not change the ground reaction force vector magnitude (p=0.30) but shortened the lever arm of the ground reaction force vector (p<0.01) by an average of 13% (Fig. 2, Table 2). The tibia angle was not significantly different, though it

Discussion

The purpose of this study was to determine whether toe-in gait reduces the first peak of the KAM without increasing the peak external knee flexion moment in patients with medial compartment knee OA. In support of our first hypothesis, toe-in gait significantly reduced the first peak of the knee adduction moment, which occurred as the knee joint center shifted medially and the center of pressure shifted laterally. The second hypothesis was also supported; toe-in gait did not increase the peak

Conflict of interest statement

None of the authors had any conflict of interest regarding this manuscript.

Acknowledgments

The authors would like to thank Dr. Stuart Goodman for advice and for his assistance in recruiting knee OA patients for this study. This work was supported by the National Science Foundation through the Human-Centered Computing program, grant #1017826.

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