Examination of corticospinal and spinal reflexive excitability during the course of postoperative rehabilitation after anterior cruciate ligament reconstruction

OBJECTIVE: To investigate corticospinal and spinal reflexive excitability and quadriceps strength in healthy athletes and athletes after anterior cruciate ligament reconstruction (ACLR) over the course of rehabilitation. DESIGN: Prospective cohort study. METHODS: Eighteen athletes with ACLR and 18 healthy athletes, matched by sex, age, and activity, were tested at (1) 2 weeks after surgery, (2) the "quiet knee"time point, defined as full range of motion and minimal effusion, and (3) return to running, defined as achieving a quadriceps index of 80% or greater. We measured (1) corticospinal excitability, using resting motor threshold (RMT) and motor-evoked potential amplitude at a stimulator intensity of 120% of RMT (MEP120) to the vastus medialis, (2) spinal reflexive excitability, calculating the ratio of the maximal Hoffmann reflex to the maximal M-wave to the vastus medialis, and (3) isometric quadriceps strength. RESULTS: The ACLR group had higher RMTs in the nonsurgical limb and higher MEP120 in the surgical limb at all time points. The healthy-athlete group did not have interlimb differences. The RMT was positively associated with quadriceps strength 2 weeks after surgery; MEP120 was associated with quadriceps strength at all time points. CONCLUSION: Compared to healthy athletes, athletes after ACLR had altered corticospinal excitability that did not change from 2 weeks after surgery to the time of return to running.