Side-to-Side Differences in Varus Thrust and Knee Abduction Moment in High-Functioning Individuals With Chronic Anterior Cruciate Ligament Deficiency

Abstract

Background: There is evidence that frontal plane knee joint motion plays a crucial role in the pathogenesis of knee osteoarthritis, yet investigation of individuals with chronic anterior cruciate ligament–deficient (ACLD) knees remains sparse. Purpose: To investigate (1) if individuals with chronic ACLD knees demonstrate higher biomechanical measures of medial knee load as compared with their anterior cruciate ligament–intact (ACLI) knees, (2) if differences in static knee alignment of the ACLD knee will demonstrate a difference in the magnitude of biomechanical measures of medial knee load when compared with the ACLI knee, and (3) the side-to-side concordance of varus thrust among individuals with chronic ACLD knees. Study Design: Descriptive laboratory study. Methods: Participants were sourced from a metropolitan orthopaedic surgeon group. Those who met the inclusion criteria and agreed to participate underwent a 3-dimensional gait analysis assessment to measure knee adduction moment (KAM), knee flexion moment (KFM), KAM peaks, KAM impulse, and varus thrust. Frontal plane knee static alignment was measured with a digital inclinometer fixed to medical calipers. The participants were divided according to their static knee alignment (neutral, varus, and valgus) for subgroup analysis. Peak knee angular velocity and frontal plane knee angle were used to establish if a participant was walking with a knee thrust. An individual was deemed to have knee thrust during gait if the largest frontal plane knee movement coincided with the peak knee angular velocity that occurred within the first 30% of stance phase. Results: Forty-five participants were recruited. The mean (SD) time from injury was 34.5 (55.6) months. ACLD knees did not demonstrate higher mean KAM and KFM (P > .5) or early-stance peak KAM (P = .3-.8) and KAM impulse (P = .3-.9) as compared with ACLI knees as a whole group or when the varus, neutral, and valgus alignment subgroups were investigated separately. Twenty-three percent (n = 9) of the participants had a varus thrust at the ACLD or ACLI knee, 44% (n = 4) had a varus thrust at the ACLD knee, and 22% (n = 2) had varus thrust at both knees. Conclusion: There were no side-to-side differences in mean KAM and KFM and early-stance peak KAM and KAM impulse among high-functioning individuals with chronic unilateral ACLD knees. There was a low prevalence of varus thrust among high-functioning individuals with chronic unilateral ACLD knees.