Athletes After ACLR Demonstrate Asymmetries In Cortical Silent Period

PURPOSE: Cortical excitability (facilitation and inhibition) is altered after ACLR and contributes to worse quadriceps strength after ACLR. Previous work has examined cortical inhibition via short-interval intracortical inhibition (SICI), which reflects postsynaptic inhibitory signaling. Cortical spinal period is a temporal measure of intracortical inhibition that has yet to be explored in participants after ACLR. The purpose of this study is to determine the difference between limbs in cortical silent period in participants 4-8 months post-ACLR. We hypothesize longer silent periods measured on the surgical limb compared to the nonsurgical limb. METHODS: Eleven participants (6 male), 5.3 ± 1.3 months post-ACLR completed testing for active motor threshold (AMT) using an isokinetic dynamometer and transcranial magnetic stimulation. Six stimulations were delivered at 120% AMT to determine silent period. Custom matlab code calculated silent period as the duration following stimulation that electromyography (EMG) activity remained below the pre-stimulus EMG activity. Paired samples t-tests were used to determine differences between the surgical and non-surgical limb. RESULTS: There was a significant between-limb difference (p = 0.049) in cortical silent period, with longer silent periods on the surgical limb (103.5 ± 26.6 ms) compared to the nonsurgical limb (95.4 ± 19.1 ms). CONCLUSION: Participants exhibited longer silent periods on the surgical limb compared to the nonsurgical limb, indicating greater intracortical inhibition to the surgical limb. This is consistent with previous work that identified cortical excitability asymmetries after ACLR contributing to quadriceps weakness. Future work should continue to investigate cortical silent periods in this population and compare those after ACLR to uninjured participants.