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Scand J Med Sci Sports. 2015 Dec;25(6):828-39. doi: 10.1111/sms.12435. Epub 2015 Feb 18.

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

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Department of Kinesiology and Health Promotion, University of Kentucky, Lexington, Kentucky, USA.
Department of Rehabilitation Sciences, University of Kentucky, Lexington, Kentucky, USA.
Biodynamics Research Laboratory, Department of Kinesiology, University of North Carolina at Charlotte, Charlotte, North Carolina, USA.
Department of Rehabilitation Sciences, University of Toledo, Toledo, Ohio, USA.
Department of Orthopedic Surgery, University of Toledo, Toledo, Ohio, USA.
Department of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.


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 (ACLr). This longitudinal, case-control investigation examined 20 patients scheduled for ACLr (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 (MVIC), central activation ratio (CAR), normalized Hoffmann spinal reflexes, active motor threshold (AMT), and normalized motor-evoked potential (MEP) amplitudes at 120% of AMT were measured in the quadriceps muscle at the specific time points. ACLr patients demonstrated bilateral reductions in spinal-reflexive excitability compared with controls before surgery (P = 0.02) and 2 weeks post-surgery (P ≤ 0.001). ACLr patients demonstrated higher AMT at 6 months post-surgery (P ≤ 0.001) in both limbs. No MEP differences were detected. Quadriceps MVIC and CAR were lower in both limbs of the ACLr group before surgery and 6 months post-surgery (P ≤ 0.05) compared with controls. Diminished excitability of spinal-reflexive and corticospinal pathways are present at different times following ACLr 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.


Knee injury; muscle inhibition; neuromuscular function; transcranial magnetic stimulation

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