STROBOSCOPIC VISUAL DISRUPTION EFFECTS ON RUNNING BIOMECHANICS BETWEEN POST-OPERATIVE ACLR PATIENTS AND HEALTHY CONTROLS

Abstract

Objective: To examine the extent to which the use of SVFD elicits differences in somatosensory function during loading while running between individuals at least two years post ACLR compared to Healthy Controls. Methods: Running biomechanics of 74 (37 ACLR and 37 healthy control) participants all between the 18-45 years old. were evaluated. Participants performed 6 trials running at a velocity of 4.0 m/s  10% at each strobe level. Running trials were completed under 3 conditions: normal vision (S3), low SVFD (S3), and high SVFD (S7). The ACLR limb was individually matched to CON via leg dominance. Kinematics were collected at 240 Hz via 3D motion capture system (Vicon, Colorado, USA); kinetics were collected at 960 Hz using a force plate (AMTI, Massachusetts, USA). A 2 x 3 (between and within participants) mixed ANOVA design. Two groups (IV1:ACLR and CON groups) completed testing for running under normal conditions and two SVFD conditions (IV2). Gait-related loading biomechanical variables, particularly those associated with ACLR dysfunction and/or OA, with a focus on joint moments and power, served as dependent variables.Results: KAM RATE at the S0 strobe setting was significantly different (P=0.04) between ACLR and MATCHED. No other variables were significantly different between groups for any strobe levels. Comparing strobe settings within the ACLR and MATCHED groups, ACLR participants demonstrated a significant decrease in maximum vertical ground reaction force (VGRF - scaled for body mass: (n/kg)) and the peak rate of knee adduction moment (KAM RATE - calculated as the peak KAM divided by the time to reach peak KAM following initial contact during stance) while under strobe conditions. Notably, there was no significant difference in peak knee adduction moment (KAM) between ACLR and MATCHED for any of the three strobe settings nor between any of the strobe settings within either ACLR or MATCHED. There were no significant differences between strobe settings within the MATCHED group for any of the variables examined: VGRF, peak KAM, and KAM RATE. Conclusion: Individuals who have undergone ACL reconstruction on average more than 8 years prior, displayed underloading with regards to VGRF and KAM RATE when visual disruption was applied. Within the CON group, there were no signs of change in loading the knee while under visual disruption. These findings support a growing body of research suggesting that persistent long-term loading deficits following ACLR, which likely increase the risk for PTOA, may be due to overreliance on visual feedback and deficits in sensorimotor function.