Gait retraining to reduce the knee adduction moment through real-time visual feedback of dynamic knee alignment
Introduction
The lifetime risk of symptomatic knee osteoarthritis (OA) is nearly 50% (Murphy et al., 2008). Therefore, preventative strategies targeting mechanical risk factors are important to develop. As a mechanical factor, varus knee alignment has been linked to incident medial knee OA (Brouwer et al., 2007), likely due to higher-than-normal medial knee joint forces (Andriacchi, 1994). As a surrogate measure for medial knee forces, the knee external adduction moment (KEAM) is often studied. The KEAM has been found to be 40% greater in varus-aligned, healthy knees than in normally aligned knees, values similar to those with established medial OA (Barrios et al., 2009a). The KEAM is also predictive of radiographic disease progression in diseased knees (Miyazaki et al., 2002).
A number of gait modifications are associated with a reduced KEAM. A 33% decrease in walking velocity reduces the KEAM by 10% (Mundermann et al., 2004). Increased foot progression angle reduces the second peak of the KEAM, but not the larger first peak (Andrews et al., 1996, Teichtahl et al., 2006, Lin et al., 2001, Guo et al., 2007, Hurwitz et al., 2002, Rutherford et al., 2008). Ipsilateral trunk lean can reduce the KEAM by 65% (Mundermann et al., 2008). However, this pattern appears abnormal and may increase the risk for back problems. Finally, Fregly et al. (2007), Fregly (2008) used a dynamic optimization method in a case study to derive a KEAM-minimizing gait pattern. The alterations involved pelvic obliquity and axial rotation, and flexion at the hip, knee and ankle to produce a ‘medial thrust’ of the knee. Reductions in the KEAM ranged from 39% to 50% (2007). In a follow-up case study using a force-measuring knee replacement, medial contact forces were reduced by 16% (Fregly et al., 2009).
Hip-driven alterations may be another approach to KEAM reduction. Previously, Davis (2005) described a case study in which a runner with patellofemoral pain was able to reduce her dynamic knee valgus by increasing hip external rotation and abduction. Based on these directional relationships, the opposite changes of increasing hip internal rotation and adduction may reduce knee adduction. As knee adduction angle and moment are correlated (Barrios et al., 2009b), these kinematics might reduce the KEAM.
A notable limitation of the previous gait modification studies is the lack of systematic training. Systematic training should lead to improved retention of the learned pattern, especially if extrinsic feedback mechanisms are initially provided to facilitate learning (Blandin et al., 2008), then later removed to help internalize the task (Winstein, 1991). As a gait pattern is internalized, performance should require less effort and feel more natural.
Therefore, our purpose was to test a KEAM-reducing gait retraining program in varus-aligned, healthy individuals. We expected increases in hip adduction and internal rotation would drive reductions in knee adduction and the KEAM both post-training and after 1 month. We also hypothesized that natural gait patterns would shift over time due to internalization of the learned pattern. Finally, with training, we hypothesized that the gait modification would require less effort and feel more natural.
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Subjects
A sample size calculation for comparing the KEAM between sessions was conducted based on pilot work, using a reduction of 0.08 N m/(kg m). The analyses suggested that eight subjects would be sufficient (Cohen, 1988). Subjects were recruited from a university setting. Informed consents in accordance with the University of Delaware’s Institutional Review Board were obtained.
All subjects were between 18 and 35 years of age, fit and healthy. Subjects were excluded if they reported any history of knee
Results
The subject demographics are presented in Table 1. Seven of the eight subjects were male. All subjects were healthy, asymptomatic and completed the protocol without any adverse events. Soreness over the ipsilateral greater trochanter was reported by two subjects in the beginning of the protocol, which resolved by the third session.
Comparing the post-training modified gait data to baseline, a 20% average reduction (p=0.027) in peak KEAM was seen (Table 2). The modified KEAM pattern during early
Discussion
The primary purpose of this experiment was to examine the effectiveness of a systematic gait retraining program aimed at reducing the KEAM. Young and healthy varus-aligned individuals were targeted as they are predisposed for incident knee OA, but have a greater ability to learn novel locomotor tasks than older individuals (van Hedel et al., 2004). In this study, the male cohort bias was notable and unplanned, but seems to suggest that varus malalignment is more prevalent in males. The training
Conflict of interest statement
There are no financial and personal relationships with other people or organizations that could inappropriately influence (bias) this work. This work was approved by the appropriate ethical committees related to the University of Delaware and the subjects gave informed consent to the work.
Acknowledgements
This study was supported by the American Society of Biomechanics student grant-in-aid award, and National Institutes of Health shared instrumentation grant 1 S10 RR022396-01.
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