Effect of medial foot loading self-practice on lower limb kinematics in young individuals with asymptomatic varus knee alignment

Abstract

Background

Varus alignment of the knee is a risk factor for developing knee osteoarthritis. Recently, voluntary shifting the plantar pressure distribution medially (medial foot loading) during gait has been found to reduce knee adduction angle during stance, which may lower the joint load. However, it is not yet known whether such effect would persist after long-term self-practice. This study aimed to determine whether medial foot loading can be an effective self-care protocol for reducing the knee adduction angle.

Methods

Eight subjects with asymptomatic varus knee alignment were trained on medial foot loading once in a laboratory, then carried out as self-practice for 8 weeks outside the laboratory. Spatiotemporal gait parameters and lower limb joint kinematics data were collected during natural walking prior to the training (baseline walking), during the practice session immediately after the initial training (trained walking), and during natural walking after the self-practice period (post-practice walking).

Results

Participants walked significantly faster after the self-practice period with longer step length compared with the baseline. The knee adduction angle at initial contact, maximum angle during stance, and mean angle during a gait cycle were significantly decreased during both the trained and post-practice walking compared with baseline. The 8-week self-practice caused larger decrements in the three angles than the single training, but no significant differences were found between the two conditions.

Conclusions

Self-practice of medial foot loading walking could be an effective gait strategy to reduce the knee adduction angle. The effect could be sustained for individuals with asymptomatic varus knee alignment.

Introduction

Knee osteoarthritis (OA) is one of the most prevalent musculoskeletal disorders and has been a leading cause of physical disability, specifically among the elderly population [1], [2], [3]. In epidemiology studies, intrinsic factors including age, sex, obesity and local joint-specific factors such as lower limb malalignment have been associated with the occurrence or development of the disorder [4].

Among the known risk factors, the lower limb malalignment, specifically varus knee alignment has been known to incur abnormal load distribution across the knee joint and elevate the risk of the occurrence and progression of the OA in the medial compartment, even when controlling for other risk factors [5], [6], [7], [8], [9], [10]. In varus-aligned knees, the load-bearing axis, which is drawn from mid-femoral head to mid-ankle, passes medial to the knee and creates a moment arm to the centre of rotation of the knee joint at heel contact and during the stance phase of walking [11]. Walking with a more varus-aligned knee would produce a larger moment arm than that of a less varus-aligned knee, and individuals with more varus-aligned knees would be exposed to a greater external adduction moment and a compressive load on the medial compartment of the knee during their daily walking [12], [13], [14].

Several gait retraining protocols such as ‘medial knee thrust walking’ and ‘medial foot loading’ have been suggested to reduce the frontal plane moment arm by correcting the dynamic knee alignment during walking. The medial knee thrust walking requires trainees to intentionally push the knees medially during the stance phase of walking. The medial pushing of the knees can reduce the knee adduction angle directly, thereby reducing the moment arm, and it makes the trainee walk with less external adduction moment and load in the medial compartment of the knee [15], [16], [17]. While the medial pushing of the knee requires the trainee to alter primarily the knee joint kinematics, the medial foot loading requires the trainees to shift the plantar pressure medially during the stance phase by more eversion rotation of the ankle [18]. The eversion movement at the ankle and foot induces a valgus thrust of the knee that would decrease the frontal plane moment arm [19], [20]. Consequently, walking with medial foot loading reduces the external adduction moment and the knee joint load [18], [21], [22], [23].

The effectiveness of the two gait protocols in reducing the knee joint load has been confirmed in guided rehabilitation training by specialists or with real-time biofeedback systems [17], [21]. It has not yet been explored whether they can be used as self-training methods by asymptomatic individuals to correct their daily gait pattern and prevent the occurrence of knee OA. In the current study, our main interest was whether the intrinsic risk factor of knee OA could be lessened by modifying the daily gait pattern, and we chose the medial foot loading method as the daily gait training protocol. The medial knee thrust walking may pose a higher risk of knee pain or discomfort due to excessive medial knee pushing force while promoting increased femur internal rotation [24], [25]. Although it might be more efficient for the rehabilitation of knee OA, the employment of the method for daily self-practice by asymptomatic individuals may not be practical.

The main objective of this study, therefore, was to evaluate the effectiveness of the medial foot loading walking as self-care gait modification method for individuals with asymptomatic varus knee alignment by quantifying the changes in the knee adduction angle during walking after an 8-week self-practice period. It was hypothesized that the medial foot loading gait would reduce the knee adduction angle of individuals with asymptomatic varus knee alignment, and the change would persist after 8 weeks of self-practice in their daily life.