Knee Joint Loading Distribution With Vest-borne Loads

Abstract

Vest borne loads increase tibiofemoral joint (TFJ) contact forces, but the TFJ contact forces do not always increase proportionally to the increase in load (Lenton et al., 2018). It is unclear if and how increase in TFJ contact forces are attenuated during load carriage.PURPOSE: To determine the effects of load carriage on total, medial (MTFJ), and lateral (LTFJ) tibiofemoral joint contact forces, and to determine if increases in joint loads are attenuated via gait adaptations. METHODS: Twelve young, healthy adults (6 males [BMI = 22.19] and 6 females [BMI = 20.38]; 22 + 1.6 yrs), walked for 5 minutes per condition at 1.4 m·s-1 on an instrumented treadmill while carrying vest borne loads of 0%, 15%, and 30% body weight during 3D motion capture. Hip, knee, and ankle kinematic and kinetic data were used as inputs to an inverse-dynamics informed musculoskeletal model of axial TFJ contact force. Kinematic and TFJ contact force comparisons were made via repeated measures ANOVA. RESULTS: From 0% load to 15% and from 0% to 30%, total peak TFJ increased 14% and 32% (3.44 vs 3.92 vs 4.55 body weights (BW) p < 0.001); peak MTFJ increased 12% and 26.5% (2.42 vs 2.72 vs 3.05 BW, p < 0.001); peak LTFJ increased 13% and 38% (1.29 vs 1.46 vs 1.79 BW, p < 0.001), and leg stiffness decreased 10% and 28% (7.17 vs 6.46 vs 5.10 N/mm, p < 0.001), respectively. CONCLUSION: Young, healthy participants do not attenuate the increase in total and medial knee joint contact forces with increasing magnitude of load carriage. They respond to load by decreasing joint stiffness through small increases in dorsiflexion, knee flexion, and hip flexion, which does increase shock absorption and assists with energy transfer (Kinoshital, 1985). These minor increases in flexion coupled with increases in vertical ground reaction forces led to the approximately proportional relative percent increase in TFJ and MTFJ as compared to the increase in load. However, the increase in LTFJ from 0% load to 30% load was 8% greater indicating a disproportional increase in the lateral compartment, assuming that “disproportional” is greater or less than 5%. Further research should investigate if greater increases in load magnitude continue to lead to proportional increases in total TFJ and MTFJ, and disproportional increases LTFJ, especially in military populations who frequently carry heavy loads.