Knee instability after acute ACL rupture affects movement patterns during the mid-stance phase of gait

Abstract

The purpose of this study was to identify gait asymmetries during the mid-stance phase of gait among subjects with knee instability ("non-copers") after acute anterior cruciate ligament (ACL) rupture. Twenty-one non-copers with acute, isolated ACL injury ambulated at their intentional walking speed as kinetic, kinematic, and electromyographic (EMG) data were collected bilaterally. Lower extremity movement patterns and muscle activity were analyzed during the mid-stance and weight acceptance phases of stance. When compared to the uninjured limb, subjects exhibited lower sagittal plane knee excursions and peak knee angles, and higher muscle co-contraction on the injured limb. There was a lower knee flexion moment at peak knee extension, a trend for the knee contribution to the total support moment to be lower, and a higher ankle contribution to the total support moment on the injured limb. There were differences in the magnitude of muscle activity which included higher hamstring activity and lower soleus activity on the injured limb. Changes in quadriceps, soleus, and hamstring muscle activity on the injured limb were identified during weight acceptance that had not previously been reported, while hip compensation for a lower knee contribution to the total support moment has been described. Non-copers consistently stabilize their knee with a stiffening strategy involving less knee motion and higher muscle contraction. The variable combination of muscle adaptations that produce joint stiffness, and the ability of both the ankle and the hip to compensate for lower knee control indicate the non-coper neuromuscular system may be more malleable than previously believed.

Figure 1. Sagittal Plane Knee Kinematics

Injured (solid line) and uninjured limb (dashed line) sagittal plane knee motion during stance. Sagittal plane knee excursion and peak knee angles were significantly lower on the injured limb compared to the uninjured limb during weight acceptance (*) and mid-stance (**).

Figure 2. Muscle Co-Contraction Indexes During Mid-Stance (A) and Weight Acceptance (B)

VLLH and VMMH indexes are significantly greater on the injured limb compared to the uninjured limb (*) during both intervals.

Figure 3. Sagittal Plane Knee Moments

Injured (solid line) and uninjured limb (dashed line) sagittal plane knee moments during stance. Peak knee flexion (*) and peak knee extension (**) moments on the injured limb were significantly lower compared to the uninjured limb.

Figure 4. Percent Support Moment Contribution For The Hip, Knee, And Ankle

(A) The ankle contribution to the total support moment is significantly greater on the injured limb (*), and there was a trend for the knee contribution to the total support moment to be lower on the injured limb compared to the uninjured limb. (B). The hip contribution to the total support moment was significantly greater on the injured limb (*) while the knee contribution to the total support moment was significantly lower on the injured limb (**) compared to the uninjured limb.