Adduction moment increases with age in healthy obese individuals.

There is a need to understand how obesity and aging interact to cause an increased risk of medial knee osteoarthritis (OA). This study tested whether the knee adduction and flexion moments increase with age in healthy normal-weight and obese adults, as well as the mechanism of this increase. We analyzed whether ground reaction force magnitude, knee alignment, step width, toe-out angle, body volume distribution, and limb position (knee position relative to the pelvis center) are associated with the adduction moment and whether these variables also change with age. Ninety-six healthy volunteers (60 normal-weight and 36 obese) were tested using marker-based gait analysis; knee alignment was based on marker positions during quiet standing. Adduction moment increased with age in obese (R(2) = 0.19), but not in normal-weight individuals (R(2) = 0.01); knee flexion moment did not change with age in either group. In the obese, only knee alignment and limb position were related to the adduction moment (R(2) = 0.19 and 0.51), but only limb position changed with age (R(2) = 0.26). The resulting increase in adduction moment suggests greater medial compartment loads, which may combine with elevated levels of inflammation to contribute to the increased risk of medial OA in this population.