Changes in tibiofemoral forces due to variations in muscle activity during walking

Abstract

Muscles induce large forces in the tibiofemoral joint during walking and thereby influence the health of tissues like articular cartilage and menisci. It is possible to walk with a wide variety of muscle coordination patterns, but the effect of varied muscle coordination on tibiofemoral contact forces remains unclear. The goal of this study was to determine the effect of varied muscle coordination on tibiofemoral contact forces. We developed a musculoskeletal model of a subject walking with an instrumented knee implant. Using an optimization framework, we calculated the tibiofemoral forces resulting from muscle coordination that reproduced the subject's walking dynamics. We performed a large set of optimizations in which we systematically varied the coordination of muscles to determine the influence on tibiofemoral force. Model-predicted tibiofemoral forces arising with minimum muscle activation matched in vivo forces measured during early stance, but were greater than in vivo forces during late stance. Peak tibiofemoral forces during late stance could be reduced by increasing the activation of the gluteus medius, uniarticular hip flexors, and soleus, and by decreasing the activation of the gastrocnemius and rectus femoris. These results suggest that retraining of muscle coordination could substantially reduce tibiofemoral forces during late stance.

Keywords: coordination; knee; muscle activity; tibiofemoral force; walking.

© 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Figures

Figure 1

(A) Musculoskeletal model of the human legs and torso. The tibiofemoral and patellofemoral joints were modeled as planar joints with translations and rotations coupled to the knee flexion angle (B). Forces in the quadriceps (B, dark red) were transmitted through the patella to the tibia (see Methods section for details).

Figure 2

Stance-phase tibiofemoral forces predicted using a musculoskeletal model and muscle coordination strategies that minimize muscle activation squared (dashed black line) and tibiofemoral forces (solid gray line). The minimum tibiofemoral force represents the smallest compressive tibiofemoral force the model generated while still reproducing the measured walking kinematics and kinetics. Measured in vivo forces (solid black line) are shown.

Figure 3

The effect of varying activation of individual muscles on predicted tibiofemoral forces shown for the most influential muscles. The shaded area represents the range of predicted tibiofemoral forces due to varying the activation of each muscle. For each muscle, the boundary indicated by w = 0 corresponded to the optimization for which the muscle activity weight of that muscle was set to zero in the objective function. This objective function permitted the muscle to activate without penalty. The model predictions that minimize uniformly-weighted muscle activations squared (dashed black lines) are shown.

Figure 4

Maximum change in peak tibiofemoral force due to activation of a muscle or muscle group during the late stance phase of walking. The maximum change was calculated as the difference between peak tibiofemoral forces obtained from the static optimizations with w = 0 (promote activity) and w = 100 (prohibit activity) for that muscle or muscle group. Note that increasing the activation of gluteus medius greatly decreased the tibiofemoral force, whereas increasing the activation of the gastrocnemius increased tibiofemoral force. The changes in peak tibiofemoral force during the late stance of walking were minimal for the muscles not shown.

Figure 5

Model-predicted activations of the nine most influential muscles produced by optimizations with varied muscle activity weights. For each muscle, activity ranged from 0 (no activity) to 1 (maximum activity). A muscle activity weight of w = 100 (dotted blue) prohibited the muscle from activating, while w = 0 (solid red) allowed the muscle to activate freely. The range of muscle activity used by the model (the area between the dotted blue and solid red lines) resulted in a corresponding variation in tibiofemoral forces (Fig. 3). Filtered electromyography (EMG) signals, measured from the subject during the same trial of normal walking, are provided for comparison. EMG was not measured from the psoas major or iliacus muscles.