Quadriceps neural alterations in anterior cruciate ligament reconstructed patients: A 6‐month longitudinal investigation

<jats:p>The purpose of this investigation was to evaluate differences in quadriceps corticospinal excitability, spinal‐reflexive excitability, strength, and voluntary activation before, 2 weeks post and 6 months post‐anterior cruciate ligament reconstruction (<jats:styled-content style="fixed-case">ACLr</jats:styled-content>). This longitudinal, case‐control investigation examined 20 patients scheduled for <jats:styled-content style="fixed-case">ACLr</jats:styled-content> (11 females, 9 males; age: 20.9 ± 4.4 years; height:172.4 ± 7.5 cm; weight:76.2 ± 11.8 kg) and 20 healthy controls (11 females, 9 males; age:21.7 ± 3.7 years; height: 173.7 ± 9.9 cm; weight: 76.1 ± 19.7 kg). Maximal voluntary isometric contractions (<jats:styled-content style="fixed-case">MVIC</jats:styled-content>), central activation ratio (<jats:styled-content style="fixed-case">CAR</jats:styled-content>), normalized <jats:styled-content style="fixed-case">H</jats:styled-content>offmann spinal reflexes, active motor threshold (<jats:styled-content style="fixed-case">AMT</jats:styled-content>), and normalized motor‐evoked potential (<jats:styled-content style="fixed-case">MEP</jats:styled-content>) amplitudes at 120% of <jats:styled-content style="fixed-case">AMT</jats:styled-content> were measured in the quadriceps muscle at the specific time points. <jats:styled-content style="fixed-case">ACLr</jats:styled-content> patients demonstrated bilateral reductions in spinal‐reflexive excitability compared with controls before surgery (<jats:italic>P</jats:italic> = 0.02) and 2 weeks post‐surgery (<jats:italic>P</jats:italic> ≤ 0.001). <jats:styled-content style="fixed-case">ACLr</jats:styled-content> patients demonstrated higher <jats:styled-content style="fixed-case">AMT</jats:styled-content> at 6 months post‐surgery (<jats:italic>P</jats:italic> ≤ 0.001) in both limbs. No <jats:styled-content style="fixed-case">MEP</jats:styled-content> differences were detected. Quadriceps <jats:styled-content style="fixed-case">MVIC</jats:styled-content> and <jats:styled-content style="fixed-case">CAR</jats:styled-content> were lower in both limbs of the <jats:styled-content style="fixed-case">ACLr</jats:styled-content> group before surgery and 6 months post‐surgery (<jats:italic>P</jats:italic> ≤ 0.05) compared with controls. Diminished excitability of spinal‐reflexive and corticospinal pathways are present at different times following <jats:styled-content style="fixed-case">ACLr</jats:styled-content> and occur in combination with clinical deficits in quadriceps strength and activation. Early rehabilitation strategies targeting spinal‐reflexive excitability may help improve postoperative outcomes, while later‐stage rehabilitation may benefit from therapeutic techniques aimed at improving corticospinal excitability.</jats:p>