Operant Upconditioning of the Quadriceps Motor Evoked Torque as a Means to Improve Quadriceps Function After ACL Reconstruction.

Abstract

Background: Diminished corticospinal excitability is theorized to contribute to poor quadriceps function after anterior cruciate ligament (ACL) reconstruction. Operant conditioning of the motor evoked torque (MEP_TORQUE) is a promising approach capable of improving corticospinal excitability. However, it is unknown whether increasing corticospinal excitability can improve quadriceps function after a short-term operant conditioning intervention in patients with reconstructed ACL.

Hypothesis: After ACL reconstruction, patients would demonstrate increases in quadriceps strength, voluntary activation, and corticospinal excitability after a 2-week operant conditioning intervention.

Study design: Randomized controlled clinical trial.

Level of evidence: Level 1.

Methods: A total of 22 patients with reconstructed ACL were randomized into 1 of 2 groups: group 1 received 2 weeks of operant conditioning training on the reconstructed leg to improve their transcranial magnetic stimulation (TMS)-elicited MEP_TORQUE responses (COND); group 2 received 2 weeks of TMS only (SHAM-COND). Quadriceps strength, voluntary activation, and corticospinal excitability on the reconstructed leg were evaluated before and after the 2-week intervention. Within-session changes in corticospinal excitability were also evaluated during the training sessions.

Results: The COND group demonstrated a significantly higher within-session percent increase in MEP_TORQUE during training compared with the SHAM-COND group, paralleled by a significant increase in corticospinal excitability after the 2-week intervention. In addition, quadriceps strength and voluntary activation improved on the reconstructed leg after the 2-week intervention, regardless of group.

Conclusion: Operant conditioning training can elicit improvements in corticospinal excitability after ACL reconstruction; however, improvements in quadriceps strength and voluntary activation seem not to be attributed solely to operant upconditioning training.

Clinical relevance: Operant conditioning is a promising approach to improve corticospinal excitability after ACL reconstruction. However, optimizing the delivery of operant conditioning protocols by potentially increasing the dosage of operant conditioning and intervening earlier after surgery may be needed to translate these changes to improvements in quadriceps function.