Operant Conditioning of Corticospinal Pathways Following Anterior Cruciate Ligament Reconstruction and Total Knee Arthroplasty

Abstract

Reduced corticospinal excitability has been theorized to contribute to quadriceps dysfunction after knee injury and surgery. Current rehabilitation methods do not directly target corticospinal pathways, which may limit recovery. Operant conditioning is an emerging approach that can address this issue; however, whether it can improve quadriceps function is unclear. Further, dosage parameters used during operant conditioning (i.e., stimulus intensity and number of trials) appear to be selected arbitrarily and lack empirical support. Given the importance of appropriate dosage for intervention efficacy, sub-optimal dosage parameters may limit therapeutic benefits. Therefore, this dissertation aimed to: 1) determine the feasibility and effect of dosage parameters (intensity, number of trials) on the ability to increase corticospinal excitability following anterior cruciate ligament (ACL) reconstruction and total knee arthroplasty (TKA) and 2) evaluate the effect of operant conditioning on quadriceps function following ACL reconstruction. This dissertation consists of four studies. In Study 1, we evaluated the reliability of the motor evoked responses elicited by transcranial magnetic stimulation in ACL reconstructed individuals. We found that raw motor evoked torque (MEPTORQUE) and motor evoked potentials (MEPEMG) demonstrated good reliability. However, MEPTORQUE generally demonstrated higher reliability than MEPEMG, regardless of the normalization method. Findings from Study 1 support the use of MEPTORQUE as a suitable target variable for upregulating quadriceps corticospinal excitability after knee surgery. In Study 2, we tested: 1) the ability of individuals with ACL reconstruction to up-condition quadriceps corticospinal excitability in a single session and 2) the influence of stimulus intensity on changes in corticospinal excitability following ACL reconstruction. We found that ACL reconstructed individuals improved their corticospinal excitability within a single session, which were paralleled by acute neural adaptations. However, the ability to up-condition and the associated neural adaptations were not influenced by stimulus intensity. Findings from Study 2 indicate that operant conditioning is a feasible intervention for improving corticospinal excitability after ACL reconstruction, and any of the stimulus intensities (100/120/140% of active motor threshold) tested are suitable for future interventions. In Study 3, we tested the effect of multiple training sessions on 1) the ability to increase corticospinal excitability and 2) quadriceps strength and voluntary activation following ACL reconstruction. We found that the conditioning group significantly improved their corticospinal excitability during training whereas the sham-conditioning group did not. Both groups also improved quadriceps strength and voluntary activation in the reconstructed leg. Findings from Study 3 suggest that ACL reconstructed individuals can improve their corticospinal excitability and that operant conditioning has the potential to improve quadriceps function after ACL reconstruction. In Study 4, we tested: 1) the ability of individuals with TKA to up-condition quadriceps corticospinal excitability within a single session and 2) the influence of stimulus intensity and number of trials on changes in corticospinal excitability after TKA. We found that individuals with TKA were able to improve their corticospinal excitability, which was paralleled by acute neural adaptations in the corticospinal pathway. However, the ability to up-condition and the associated neural adaptations were not influenced by stimulus intensity. In addition, individuals with TKA did not improve their corticospinal excitability after 75 trials, but succeeded following 150 and 225 trials, indicating that 150 trials is sufficient for acute neural adaptations. Collectively, this dissertation establishes the feasibility and optimal dosage of operant up-conditioning and its ability to successfully improve corticospinal excitability following ACL reconstruction and TKA.