Prolonged Load Carriage Impacts Magnitude and Velocity of Knee Adduction Biomechanics

Introduction: Adopting knee adduction biomechanics during prolonged load carriage, a common military occupational activity, may increase service members knee osteoarthritis (OA) risk. Although service members reportedly increase knee adduction motions and moments during prolonged load carriage, it is unknown if either body borne load or walk duration increases velocity of knee adduction biomechanics, and subsequent knee OA risk. Varus thrust and alignment are also related to greater knee OA risk, yet it is unknown whether varus thrust and/or alignment are related to magnitude and velocity of knee adduction biomechanics during prolonged load carriage. Purpose: To determine whether body borne load and walk duration impacted magnitude and velocity of knee adduction biomechanics, or whether increases in knee adduction biomechanics are related to knee varus thrust or alignment. Methods: Seventeen participants (11 male/6 female, 23.2 ± 2.9 yrs, 1.8 ± .09 m, 71.0 ± 12.1 kg) had knee adduction biomechanics quantified while walking 1.3 m/s for 60 minutes with three body borne loads (0 kg, 15 kg, and 30 kg). Specifically, peak, average and maximum velocity, as well as time to peak, for knee adduction angle and moment, and varus thrust (first 16% of stance) were calculated at minutes 0, 30, and 60 of the load carriage task. Static knee alignment was calculated as the frontal plane knee projection angle. Statistical Analysis: Participants were defined as varus thrust (VT, n=8) or control (CON, n=9). Then, each knee adduction measurement was submitted to a repeated measures ANCOVA to test the main effect and interaction between body borne load (0 kg, 15 kg, and 30 kg), time (minutes 0, 30, and 60), and group (VT and CON), with static alignment considered a covariate. Results: A significant 3-way interaction for maximum varus thrust velocity (p=0.014), revealed the VT group exhibited greater maximum velocity at minutes 0 through 60 (p ≤ 0.038) with the 0 kg load, and minutes 0 and 60 (p ≤ 0.043) with the 15 kg load. Significant load by group interactions for magnitude (p=0.008) and average velocity (p=0.013) of varus thrust, and maximum KAA velocity (p=0.041) revealed VT participants exhibited larger and faster varus thrust and knee adduction angle than the CON group with the 0 kg and 15 kg loads (p < 0.050). Additionally, both magnitude and maximum velocity of KAM increased with the addition of load (p=0.009 and p=0.004), and walk duration increased magnitude of varus thrust (p=0.044). Static alignment was not a significant covariate for any knee adduction measure (p > 0.05). Conclusion: During prolonged load carriage participants adopted larger, faster knee adduction biomechanics, potentially increasing risk of knee OA. The VT group exhibited greater knee OA risk, and larger, faster knee adduction motions when walking with the lighter (0 kg and 15 kg) loads; while CON adopted increases in knee adduction biomechanics related to knee OA with the heavy (30 kg) load.