Age-dependent associations between asymmetric cumulative knee adductor load and medial meniscus extrusion

This study aimed to investigate the differences in medial meniscus extrusion (MME) between lower limbs with higher and lower loading in healthy young and elderly individuals. Sixty-two participants (young, n = 31; elderly, n = 31) were enrolled. The increase in MME (ΔMME) was calculated as the difference between supine and one-leg standing positions evaluated by ultrasonography. The knee adduction moment impulse was calculated using a three-dimensional motion analysis system synchronized with force plates. The cumulative knee adductor load (CKAL) was calculated as the product of the impulse and daily steps. Lower limbs were referred to the 'lower' and 'higher' sides based on CKAL value and the asymmetry index (ASI) of CKAL was calculated. In only the elderly group, a significant difference in ΔMME between the limbs (lower, 0.3 ± 0.2 mm; higher, 0.6 ± 0.3 mm, p < 0.01) was observed. The interaction between CKAL and ASI was associated with ΔMME from the linear mixed model (B = 0.09, 95% confidence intervals = 0.02-0.15, 1 SD increment for both values) in the elderly group. These findings indicate that asymmetric knee joint loading is associated with greater meniscal extrusion in elderly individuals.