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

CONTEXT Quadriceps weakness is associated with disability and aberrant gait biomechanics following anterior cruciate ligament reconstruction (ACLR). Strength sufficiency cutoff scores, that normalize quadriceps strength to the mass of an individual, are capable of predicting individuals who will report better function following ACLR. Yet, it remains unknown if gait biomechanics differ between individuals who meet a strength sufficiency cutoff (strong) compared to those who do not (weak). OBJECTIVE Determine if vertical ground reaction force (vGRF), knee flexion angle (KFA) and internal knee extension moment (KEM) differ between strong and weak individuals with an ACLR throughout stance phase of walking. DESIGN Comparison-control. SETTING Laboratory Participants: Individuals who received unilateral ACLR ≥12 months prior to testing were dichotomized into strong (n=31) and weak groups (n=116). MAIN OUTCOME MEASURES Maximal isometric quadriceps strength was collected at 90° of knee flexion using an isokinetic dynamometer and normalized to body mass. Individuals demonstrating ≥3.0Nm/kg 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. vGRF were normalized to body weight (BW), and KEM was normalized to BW*height. Pairwise comparison functions were calculated for each outcome to identify between-group differences for each percentile of stance. RESULTS vGRF was significantly greater in weak participants for the first 22% of stance (average difference of 6.2% BW) and lesser in weak participants between 36-43% of stance (1.4% BW). KFA was significantly greater (i.e., more flexion) in strong participants between 6-62% of stance (2.3°) and lesser (i.e., less flexion) between 68-79% of stance (1.0°). KEM was significantly greater in strong participants between 7-62% of stance (0.007 BW*height). CONCLUSIONS ACLR individuals able to generate knee extension torque ≥3.0Nm/kg exhibit different biomechanical gait profiles compared to weak individuals, which may allow for better energy attenuation following ACLR.