Effect of Muscle Compensation on Knee Instability during ACL-Deficient Gait

Kevin B. Shelburne; Michael R. Torry; Marcus G. Pandy

Disclosures

Med Sci Sports Exerc. 2005;37(4):642-647. 

In This Article

Abstract and Introduction

Purpose: The purpose of this investigation was to determine whether an isolated change in either quadriceps or hamstrings muscle force (quadriceps avoidance and hamstrings facilitation, respectively) is sufficient to stabilize the ACL-deficient (ACLd) knee during gait.
Methods: A three-dimensional model of the lower limb was used to calculate anterior tibial translation in the intact and ACLd knee during gait. The model was then used to predict the amount of quadriceps and hamstrings force needed to restore anterior tibial translation (ATT) in the ACLd knee to an intact or maximum allowable level.
Results: It was possible to reduce ATT in the ACLd knee to the level calculated for the intact knee by increasing the magnitude of hamstrings force (a hamstrings facilitation pattern). Although this strategy decreased the knee extensor moment calculated for walking, the effect was much less than that obtained when quadriceps force was reduced. Reducing quadriceps force to restore normal ATT resulted in complete elimination of the knee extensor moment (a quadriceps avoidance pattern); however, this strategy was insufficient to restore ATT to the level calculated for the intact knee over portions of the gait cycle.
Conclusion: The model simulations showed that increased hamstrings force was sufficient to stabilize the ACLd knee during gait. Reduced quadriceps force was insufficient to restore normal ATT for portions of the gait cycle.

Stability of the knee during walking is determined by the balance of muscle, ligament, joint contact, and ground reaction forces applied to the leg. Muscles, in particular, are able to actively adapt to changes in external and intraarticular loading conditions to maintain knee stability during locomotion. Indeed, many gait analysis studies have identified specific muscular adaptations in the walking patterns of chronic ACL-deficient (ACLd) individuals.[3,4,9,17] Some studies have shown that ACLd individuals adapt their gait patterns either by reducing the extensor moment at the knee in stance (a quadriceps reduction pattern[6,9,11,28] or by eliminating it altogether (a quadriceps avoidance pattern.[3,4] One possible explanation for the observed decrease in knee extensor moment is an adaptive change in thigh muscle force, brought about by the need to reduce anterior tibial translation (ATT) in the ACLd knee. Support for this idea is provided by EMG data acquired during gait, which show an increase in the level of hamstrings activation concomitant with a decrease in the magnitude of knee extensor moment.[26,31] Because the quadriceps and hamstrings apply opposite (anterior and posterior) shear forces to the tibia[13,20,27] it is widely acknowledged that control of these muscles may be adapted to stabilize the knee during dynamic weightbearing activity. What is not known, however, is whether an isolated change in either quadriceps or hamstrings muscle force is sufficient to stabilize the ACLd knee during gait.

Although many studies have applied computer modeling and simulation to understand muscle coordination of walking[1,5,34] to our knowledge only one has quantified the effect of muscle compensation on knee instability in ACLd gait. Using a two-dimensional model of the lower limb, Liu and Maitland[15] found that 56% of peak isometric hamstrings force was necessary to restore ATT in the ACLd knee to the amount observed in normal gait. Their analysis was performed for a single instant of the gait cycle (heel strike) and considered only the effect of hamstrings muscle action on ATT when people walked at their preferred (normal) speeds.

The overall goal of the present study was to test the hypothesis that an isolated change in either quadriceps or hamstrings muscle force is sufficient to stabilize the ACLd knee during walking. A three-dimensional (3D) model of the lower limb was used to calculate muscle, ligament, and joint-contact forces at the knee during gait. The model simulations were designed to address two questions. First, can isolated changes in quadriceps or hamstrings muscle force stabilize the ACLd knee during walking, and if so, what changes in muscle force are needed to provide knee stability? Second, how do quadriceps and hamstrings muscle adaptations affect the net extensor moment developed at the knee during gait?

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