Abstract: OBJECTIVE: Knee adduction moment and knee adduction angular impulse enlargement is the main biomechanical risk factor of knee osteoarthritis. According to the survey, a change in the foot progression angle could effectively change the motion mode of patients with knee osteoarthritis. However, the impact of toe-in and toe-out on knee adduction moment and knee adduction angular impulse in young and elderly patients did not reach a consensus. Therefore, this study comprehensively discussed the effect of foot progression angle on knee adduction moment and knee adduction angular impulse in different populations through meta-analysis and provided a reference for the treatment of knee osteoarthritis. 
METHODS: By June 2022, searches were conducted on Web of Science, Ebsco, PubMed and CNKI databases using “foot progression angle, knee adduction moment, knee adduction angular impulse, gait” as Chinese and English search terms. Self-controlled randomized controlled studies analyzing the effects of toe-in and toe-out on knee adduction moment bimodality and knee adduction angular impulse were included. The cochrane bias risk assessment tool was utilized to make a quality evaluation of the literature. Stata 15.1 software was used for subgroup analysis to determine the effect of foot progression angle on knee adduction moment and knee adduction angular impulse. Meta-regression analysis was used to further determine characteristics of outcome indicators (knee adduction moment, knee adduction angular impulse) changing with foot progression angle.
RESULTS: (1) A total of 15 self-control trials and 2 randomized controlled trials (455 subjects) were included in the meta-analysis. All of the included articles were of medium to high quality. (2) The meta-analysis results showed that the toe-in gait could reduce the first peak of knee adduction moment (SMD=-0.380, 95%CI:-0.710 to -0.060, P=0.022) and knee adduction angular impulse (SMD=-1.470, 95%CI:-2.160 to -0.770, P < 0.001) in young patients. The toe-out gait reduced the second peak of knee adduction moment (SMD=-0.720, 95%CI:-1.010 to -1.440, P < 0.001) in young patients. In addition, toe-in gait could reduce the first peak of knee adduction moment in elder patients (SMD=-0.550, 95%CI:-0.800 to -0.300, P < 0.001), but increase the second peak knee adduction moment of elderly (SMD=0.280, 95%CI:-0.010 to 0.560, P=0.047). The toe-out gait could decrease the second peak knee adduction moment in this population (SMD=-0.510, 95%CI:-0.830 to -0.190, P=0.002). (3) Meta-regression showed that the greater the toe-out in elderly patients, the lower the second peak knee adduction moment. 
CONCLUSION: (1) Toe-in reduced the first peak knee adduction moment and knee adduction angular impulse in young knee osteoarthritis patients aged 18 to 34 years. Since knee adduction moment and knee adduction angular impulse were associated with medial knee loading and knee osteoarthritis incidence, toe-in gait intervention may be a suitable rehabilitation strategy for young patients. (2) Toe-in increased the second peak of knee adduction moment in older knee osteoarthritis patients over 60 years of age, which may exacerbate knee osteoarthritis in this population. However, the second peak of knee adduction moment during walking in this population decreases as the toe-out increases, contributing to a reduction in medial knee loading, suggesting that older patients may consider using toe-out gait during walking.

Key words: knee osteoarthritis, knee soft tissue degeneration, young patient, older patient, toe-in, toe-out, knee adduction moment, knee adduction angular impulse, gait, meta-analysis