Altered Center of Pressure Dispersion and Regularity during Dual-Task Balance following Anterior Cruciate Ligament Reconstruction

Athletes demonstrate neuroplastic changes and altered neuromuscular control after anterior cruciate ligament reconstruction (ACLR). Conflicting reports of impaired balance and cognitive performance exist for dual-task balance following ACLR. Thus, significant gaps remain in understanding altered postural control strategies in this population. PURPOSE: To understand altered postural control strategies in ACLR individuals in the presence of sensory, motor, and cognitive challenges. METHODS: Fourteen ACLR (20.7±2.0 yr, 76.9±19.1 kg, 1.7±1.4 m, 6.7±1.9 Tegner) and 14 matched healthy control participants (CON) (21.2±1.4 yr, 75.4±15.3 kg, 1.7±1.5 m, 7.4±1.4 Tegner) were analyzed. Three 20-second trials of single-leg balance (ACLR limb, matched side for CON) were performed under the following conditions: eyes open (EO), eyes closed (EC), dual cognitive (DC), and dual motor (DM). DC involved mental addition every two seconds and DM required participants to catch a ball from a ball machine every 2 seconds. Traditional center of pressure (CoP) measures of 95% confidence ellipse area (EA) and medial-lateral root-mean-squared excursion (RMS_ml) were calculated after a 5 Hz 4th-order Butterworth low-pass filter. These measures were log transformed to satisfy model assumptions. Sample entropy (SEn, unitless) was also calculated for increment resultant CoP data after downsampling to 50Hz, without filtering. Linear mixed models included subject pair as a random effect and ACLR status, trial type, and ACLR * trial type as fixed effects. RESULTS: The ACLR group had increased CoP dispersion (e.g.,ln(EA): ACLR: 7.74 ± 0.78 mm2, CON: 7.47 ± 0.91 mm2, P = 0.003) and increased CoP signal regularity (SEn: ACLR: 0.78 ± 0.20, CON: 0.86 ± 0.23, P = 0.001). Significant interactions were also observed for SEn, EA, and RMS_ml that suggest the ACLR group impairments are most pronounced during the DC condition (e.g., 95% confidence interval for CON – ACLR for DC SEn: (0.03, 0.35), P = 0.01). CONCLUSION: Altered postural control is present following ACLR compared to healthy controls. A cognitively-challenging task resulted in greater ACLR-specific balance alterations compared to closing eyes or a motor dual-task. These findings are consistent with ACLR individuals adopting a more attentionally-focused approach to postural control.