title: Electrophysiological evidence of functional improvement in the corticospinal tract after laminoplasty in patients with cervical compressive myelopathy: clinical article.
abstract: OBJECTIVE
  Cervical laminoplasty is a surgical procedure for cervical compressive myelopathy (CCM), and satisfactory outcomes have been reported. However, few reports have examined the pathophysiology of improvements in spinal cord function. The aim of this study was to investigate the variation in central motor conduction time (CMCT) before and after cervical laminoplasty in patients with CCM.
  
  
  METHODS
  Motor evoked potentials (MEPs) following transcranial magnetic stimulation and compound muscle action potentials (CMAPs) and F-waves following electrical stimulation of the ulnar and tibial nerves at the wrist and ankle were measured from the abductor digiti minimi muscle (ADM) and abductor hallucis muscle (AH) in 42 patients with CCM before and 1 year after cervical laminoplasty. The peripheral conduction time (PCT) was calculated as follows: (latency of CMAPs + latency of F-waves - 1)/2. The CMCT was calculated by subtracting the PCT from the onset latency of the MEPs. The CMCT recovery ratio was defined and calculated as the ratio of CMCT values 1 year after surgery to those before surgery. The CMCT data were analyzed as longer or shorter CMCT between the patients' right and left ADMs and AHs. The Japanese Orthopaedic Association (JOA) score for cervical myelopathy was obtained as a clinical outcome before and 1 year after surgery. The recovery rate (RR) 1 year after surgery was calculated using the following formula: (postoperative JOA score 1 year after surgery - preoperative JOA score)/(17 - preoperative JOA score) × 100. Correlations among CMCT parameters, patient age, JOA score, and RR were determined.
  
  
  RESULTS
  The longer and shorter CMCTs from the ADM (longer, p = 0.000; shorter, p = 0.008) and the longer CMCT from the AH (longer, p = 0.000) before surgery decreased significantly 1 year after surgery; the shorter CMCT from the AH did not significantly differ (shorter, p = 0.078). The mean JOA score before surgery was 10.1 ± 3.0 and improved significantly to 12.9 ± 2.7 at 1 year after surgery (p = 0.000). The mean CMCT recovery ratio and RR were 0.91 ± 0.18 and 0.43 ± 0.27, respectively. The longer/shorter CMCT parameters in the ADM and AH before or 1 year after surgery correlated significantly with the JOA score both before and 1 year after surgery. The CMCT recovery ratio from the longer CMCT in the ADM correlated significantly with the RR (r = - 3090, p = 0.011). There were no significant correlations between age and any CMCT parameters or CMCT recovery ratios.
  
  
  CONCLUSIONS
  These results suggest that cervical laminoplasty improves corticospinal tract function 1 year after surgery, which may be one of the reasons for the JOA score improvements in patients with CCM. The degree of improvement in corticospinal tract function did not correlate with patient age in this case series. The results demonstrated quantitative evidence of the pathophysiology of functional recovery in the corticospinal tract following cervical laminoplasty in patients with CCM.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima City, Hiroshima, Japan.
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Nakanishi
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Tanaka
authors.forename: Naosuke
authors.initials: N
authors.lastname: Kamei
authors.forename: Ryo
authors.initials: R
authors.lastname: Ohta
authors.forename: Yuki
authors.initials: Y
authors.lastname: Fujioka
authors.forename: Takeshi
authors.initials: T
authors.lastname: Hiramatsu
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ujigo
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Ochi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000503:physiopathology* / Q000601:surgery*; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007796:Laminectomy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009431:Neural Conduction / Q000502:physiology*; D020127:Recovery of Function; D013117:Spinal Cord Compression / Q000503:physiopathology* / Q000601:surgery*; D016896:Treatment Outcome
keywords: ADM = abductor digiti minimi muscle; AH = abductor hallucis muscle; CCM = cervical compressive myelopathy; CMAP = compound muscle action potential; CMCT = central motor conduction time; JOA = Japanese Orthopaedic Association; MEP = motor evoked potential; PCT = peripheral conduction time; RR = recovery rate; SCEP = spinal cord evoked potential; TMS = transcranial magnetic stimulation; central motor conduction time; cervical myelopathy; laminoplasty; motor evoked potentials; surgical outcome; transcranial magnetic stimulation