title: Neurophysiological changes during shortening osteotomies of the spine.
abstract: BACKGROUND
  Kyphotic deformities with sagittal imbalance of the spine can be treated with spinal osteotomies. Those procedures are known to have a high incidence of neurological complications, in particular at the thoracic level. Motor evoked potentials (MEPs) have been widely used in helping to avoid major neurological deficits postoperatively. Previous reports have shown that a significant proportion of such cases present with important transcranial MEP (Tc-MEP) changes during surgery with some of them being predictive of postoperative deficits.
  
  
  OBJECTIVE
  Our aim was to study Tc-MEP changes in a consecutive series of patients and correlate them with clinical parameters and radiological changes.
  
  
  METHODS
  Retrospective case notes study from a prospective patient register.
  
  
  METHODS
  Eighteen patients undergoing posterior shortening osteotomies (nine at thoracic and nine at lumbar levels) for kyphosis of congenital, degenerative, inflammatory, or post-traumatic origin were included.
  
  
  METHODS
  Loss of at least 80% of Tc-MEP signal expressed as the area under the curve percentual change, of at least one muscle.
  
  
  METHODS
  We studied the relation between outcome measure (80% Tc-MEP loss in at least one muscle group) and amount of posterior vertebral body shortening as well as angular correction measured on computed tomography scans, occurrence of postoperative deficits, intraoperative blood pressure at the time of the osteotomy, and hemoglobin (Hb) change.
  
  
  RESULTS
  All patients showed significant Tc-MEP changes. In particular, greater than 80% MEP loss in at least one muscle group was observed in five of nine patients in the thoracic group and four of nine patients in the lumbar group. No surgical maneuver was undertaken as a result of this loss in an effort to improve motor responses other than verifying the stability of the construct and the extent of the decompression. Four patients developed postoperative deficits of radicular origin, three of them recovering fully at 3 months. No relation was found between intraoperative blood pressure, Hb changes, and Tc-MEP changes. Severity of Tc-MEP loss did not correlate with postoperative deficits. Shortening of more than 10 mm was linked to more severe Tc-MEP changes in the thoracic group.
  
  
  CONCLUSIONS
  Transcranial MEP changes during spinal shortening procedures are common and do not appear to predict severe postoperative deficits. Total loss of Tc-MEP (not witnessed in our series) might require a more drastic approach with possible reversal of the correction and wake-up test.
authors: Department of Orthopedic Surgery, Centre Hospitalier Universitaire Vaudois, Avenue Pierre Decker 4, 1011 Lausanne, Switzerland. Electronic address: cschizas@hotmail.com.
authors: Constantin
authors: C
authors: Schizas
authors: Department of Neurosurgery, Centre Hospitalier Universitaire Vaudois, Avenue du Bugnon 46, 1011 Lausanne, Switzerland.
authors: Etienne
authors: E
authors: Pralong
authors: Department of Neurosurgery, Centre Hospitalier Universitaire Vaudois, Avenue du Bugnon 46, 1011 Lausanne, Switzerland.
authors: Damien
authors: D
authors: Debatisse
authors: Department of Orthopedic Surgery, Centre Hospitalier Universitaire Vaudois, Avenue Pierre Decker 4, 1011 Lausanne, Switzerland.
authors: Gerit
authors: G
authors: Kulik
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007738:Kyphosis / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D010027:Osteotomy / Q000009:adverse effects* / Q000379:methods; D013904:Thoracic Vertebrae / Q000503:physiopathology / Q000601:surgery*; D016896:Treatment Outcome
keywords: Intraoperative monitoring; Kyphosis; Sagittal imbalance; Spinal deformities; Spinal osteotomy