title: Neural Excitability Alterations After Anterior Cruciate Ligament Reconstruction.
abstract: BACKGROUND
  Neuromuscular dysfunction is common after anterior cruciate ligament reconstruction (ACL-R). However, little is known about quadriceps spinal-reflex and descending corticomotor excitability after ACL-R. Understanding the effects of ACL-R on spinal-reflex and corticomotor excitability will help elucidate the origins of neuromuscular dysfunction.
  
  
  OBJECTIVE
  To determine whether spinal-reflex excitability and corticomotor excitability differed between the injured and uninjured limbs of patients with unilateral ACL-R and between these limbs and the matched limbs of healthy participants.
  
  
  METHODS
  Case-control study.
  
  
  METHODS
  Laboratory.
  
  
  METHODS
  A total of 28 patients with unilateral ACL-R (9 men, 19 women; age = 21.28 ± 3.79 years, height = 170.95 ± 10.04 cm, mass = 73.18 ± 18.02 kg, time after surgery = 48.10 ± 36.17 months) and 29 participants serving as healthy controls (9 men, 20 women; age = 21.55 ± 2.70 years, height = 170.59 ± 8.93 cm, mass = 71.89 ± 12.70 kg) volunteered.
  
  
  METHODS
  Active motor thresholds (AMTs) were collected from the vastus medialis (VM) using transcranial magnetic stimulation. We evaluated VM spinal reflexes using the Hoffmann reflex normalized to maximal muscle responses (H : M ratio). Voluntary quadriceps activation was measured with the superimposed-burst technique and calculated using the central activation ratio (CAR). We also evaluated whether ACL-R patients with high or low voluntary activation had different outcomes.
  
  
  RESULTS
  The AMT was higher in the injured than in the uninjured limb in the ACL-R group (t27 = 3.32, P = .003) and in the matched limb of the control group (t55 = 2.05, P = .04). The H : M ratio was bilaterally higher in the ACL-R than the control group (F1,55 = 5.17, P = .03). The quadriceps CAR was bilaterally lower in the ACL-R compared with the control group (F1,55 = 10.5, P = .002). The ACL-R group with low voluntary activation (CAR < 0.95) had higher AMT than the control group (P = .02), whereas the ACL-R group with high voluntary activation (CAR ≥ 0.95) demonstrated higher H : M ratios than the control group (P = .05).
  
  
  CONCLUSIONS
  The higher VM AMT in the injured limbs of ACL-R patients suggested that corticomotor deficits were present after surgery. Higher bilateral H : M ratios in ACL-R patients may be a strategy to reflexively increase excitability to maintain voluntary activation.
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill; Departments of.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Pietrosimone
authors.affiliation: Kinesiology and Health Promotion and.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Lepley
authors.affiliation: Department of Kinesiology and Health, Northern Kentucky University, Highland Heights;
authors.forename: Hayley M
authors.initials: HM
authors.lastname: Ericksen
authors.affiliation: Department of Kinesiology and.
authors.forename: Amy
authors.initials: A
authors.lastname: Clements
authors.affiliation: Division of Orthopaedics, University of Toledo, OH.
authors.forename: David H
authors.initials: DH
authors.lastname: Sohn
authors.affiliation: Rehabilitation Sciences, University of Kentucky, Lexington;
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Gribble
mesh_terms: D016118:Anterior Cruciate Ligament / Q000502:physiology / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D011184:Postoperative Period; D052097:Quadriceps Muscle / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D013127:Spinal Nerves / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: knee; quadriceps muscles; transcranial magnetic stimulation; voluntary activation
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