OBJECTIVES: To evaluate relationships between patient-reported outcomes and lower extremity biomechanics associated with risk for second ACL injury among individuals with ACL reconstruction (ACLR). DESIGN: Cross-sectional study. SETTING: Research laboratory. PARTICIPANTS: 20 individuals with primary, unilateral ACLR (10 female, age = 20.1 ± 2.0 years, median time from surgery = 29.6 [IQR = 9.1-53.3] months). MAIN OUTCOME MEASURES: Participants completed the International Knee Documentation Committee Subjective Knee Evaluation, Tampa Scale of Kinesiophobia (TSK-11), and Veterans RAND 12-Item Health Survey. Three-dimensional biomechanics were evaluated at peak vertical ground reaction force (vGRF) and as peak kinematic and kinetics within the first 100 ms of landing from a drop vertical jump. RESULTS: Higher TSK-11 scores associated with lesser hip flexion angles (r = -.723, P <
.002), lesser knee flexion angles (r = .561, P = .010), and greater internal knee abduction moments (ρ = -.606, P = .005) at peak vGRF. These relationships remained significant when correcting for multiple tests and controlling for time from surgery and biological sex. CONCLUSIONS: Kinesiophobia, but not self-reported knee function or health-related quality of life, is associated with aberrant landing biomechanics when the largest magnitudes of vertical force were applied to the knee. Individuals with greater kinesiophobia may adopt a stiffer landing profile with increased medial knee compartment loading, potentially increasing risk for second ACL injury.