Gait Biomechanics in Individuals Meeting Sufficient Quadriceps Strength Cutoffs after Anterior Cruciate Ligament Reconstruction

Abstract

Context: Quadriceps weakness is associated with disability and aberrant gait biomechanics after anterior cruciate ligament reconstruction (ACLR). Strength-sufficiency cutoff scores, which normalize quadriceps strength to the mass of an individual, can predict who will report better function after ACLR. However, whether gait biomechanics differ between individuals who meet a strength-sufficiency cutoff (strong) and those who do not (weak) remains unknown. Objective: To determine whether vertical ground reaction force, knee-flexion angle, and internal knee-extension moment differ throughout the stance phase of walking between individuals with strong and those with weak quadriceps after ACLR. Design: Case-control study. Setting: Laboratory. Patients or Other Participants: Individuals who underwent unilateral ACLR .12 months before testing were dichotomized into strong (n = 31) and weak (n = 116) groups. Main Outcome Measures: Maximal isometric quadriceps strength was measured at 908 of knee flexion using an isokinetic dynamometer and normalized to body mass. Individuals who demonstrated maximal isometric quadriceps strength ≥3.0 Nmkg-1 were considered strong. Three-dimensional gait biomechanics were collected at a self-selected walking speed. Biomechanical data were time normalized to 100% of stance phase. Vertical ground reaction force was normalized to body weight (BW), and knee-extension moment was normalized to BW 3 height. Pairwise comparison functions were calculated for each outcome to identify between-groups differences for each percentile of stance. Results: Vertical ground reaction force was greater in the weak group for the first 22% of stance (peak mean difference [MD] = 6.2% BW) and less in the weak group between 36% and 43% of stance (MD = 1.4% BW). Knee-flexion angle was greater (ie, more flexion) in the strong group between 6% and 52% of stance (MD = 2.38) and smaller (ie, less flexion) between 68% and 79% of stance (MD = 1.08). Knee-extension moment was greater in the strong group between 7% and 62% of stance (MD = 0.007 BW 3 height). Conclusions: Individuals with ACLR who generated knee-extension torque ≥3.0 Nmkg-1 exhibited different biomechanical gait profiles than those who could not. More strength may allow for better energy attenuation after ACLR.