Effect of foot supports on knee joint loading

Abstract

Knee pain is one of the most prevalent problems that impairs knee functions. Mechanical loading is one of the most important determinants of knee pain. Changing the alignment of lower limb may vary knee loading. Clinicians prescribe wedged insoles primarily for pain-relieving. However, how wedged insoles influence the load transfer through foot-ankle-knee have not been fully elucidated. The purpose of this study is to systematically understand the effectiveness of wedged insoles on lower-limb alignment and knee loading. Experimental gait analysis and multi-body model of wedged lower-limbs were used. Six different wedges were analyzed for their effects on the center of pressure, joint angles and the joint moments. Ten healthy female subjects participated in this experiment. Their gait patterns were assessed with six different wedged conditions: forefoot lateral wedge (LF), forefoot medial wedge (MF), rearfoot lateral wedge (LR), rearfoot medial wedge (MR), full-length lateral wedge (LW) and full-length medial wedge (MW) in addition to a control flat insole (FF). They walked with a controlled cadence of 120 step/min and were assigned with random insole each time. Gait was monitored using Motion Analysis System with eight infrared cameras and two force platforms. Forty-four reflective markers were attached on the pelvis, thigh, shank, forefoot and rearfoot segment, to monitor lower extremity motion. The multi-body musculoskeletal model was developed using OpenSim (SimTK.org) to estimate the joint and major muscle forces at the knee. The gait data were input into this model to obtain the joint and muscle forces during walking. The kinematic and kinetic data were analyzed by one-way repeated measures analysis of variance. The results showed that LW and MF shifted the center of pressure laterally up to 0.18% foot width. The first peak knee adduction moment was reduced by an average of 8.75% in all wedged insole conditions. For the second peak, the knee adduction moment was reduced by 34.00% in the LW condition and by 9.80% in the MW condition, while the moment was increased in the MR group (1.96%). It was suggested that certain medial wedge could be used in the treatment of knee osteoarthritis. All conditions had an apparent relationship between the peak angles of forefoot dorsiflexion and the ankle eversion moment, between the ankle eversion moment and the ankle inversion angle and between the ankle inversion and the peak knee adduction moment. The data showed that the changes in knee adduction moment occurred due to the combined effects of increased forefoot dorsiflexion angle and decreased ankle inversion angle. These findings suggested that knee joint kinematics and kinetics were altered not only by the knee locomotion during walking, but also by responses of other parts of the lower limb, such as the ankle and forefoot, that responded to the influence of the wedged insoles. Adjusting the forefoot angle and the ankle moment were more efficient for reducing knee adduction moment compared to adjusting the center of pressure. These adjustments could be made by custom orthoses. Ankle joint and foot compensation should be considered when using wedged insoles. Current findings indicated that proper-wedged support decreased peak knee adduction moment and might alleviate knee pain around the medial compartment where OA often occurs. These results provide information for designing foot supports for footwear and knee orthoses as well as providing information for the input and validations for computational models.