title: Is the lateral jack-knife position responsible for cases of transient neurapraxia?
abstract: OBJECTIVE
  The lateral jack-knife position is often used during transpsoas surgery to improve access to the spine. Postoperative neurological signs and symptoms are very common after such procedures, and the mechanism is not adequately understood. The objective of this study is to assess if the lateral jack-knife position alone can cause neurapraxia. This study compares neurological status at baseline and after positioning in the 25° right lateral jack-knife (RLJK) and the right lateral decubitus (RLD) position.
  
  
  METHODS
  Fifty healthy volunteers, ages 21 to 35, were randomly assigned to one of 2 groups: Group A (RLD) and Group B (RLJK). Motor and sensory testing was performed prior to positioning. Subjects were placed in the RLD or RLJK position, according to group assignment, for 60 minutes. Motor testing was performed immediately after this 60-minute period and again 60 minutes thereafter. Sensory testing was performed immediately after the 60-minute period and every 15 minutes thereafter, for a total of 5 times. Motor testing was performed by a physical therapist who was blinded to group assignment. A follow-up call was made 7 days after the positioning sessions.
  
  
  RESULTS
  Motor deficits were observed in the nondependent lower limb in 100% of the subjects in Group B, and no motor deficits were seen in Group A. Statistically significant differences (p < 0.05) were found between the 2 groups with respect to the performance on the 10-repetition maximum test immediately immediately and 60 minutes after positioning. Subjects in Group B had a 10%-70% (average 34.8%) decrease in knee extension strength and 20%-80% (average 43%) decrease in hip flexion strength in the nondependent limb. Sensory abnormalities were observed in the nondependent lower limb in 98% of the subjects in Group B. Thirty-six percent of the Group B subjects still exhibited sensory deficits after the 60-minute recovery period. No symptoms were reported by any subject during the follow-up calls 7 days after positioning.
  
  
  CONCLUSIONS
  Twenty-five degrees of right lateral jack-knife positioning for 60 minutes results in neurapraxia of the nondependent lower extremity. Our results support the hypothesis that jack-knife positioning alone can cause postoperative neurological symptoms.
authors.affiliation: Orthopedic Pain Specialists, Santa Monica;
authors.forename: Diana Margarita
authors.initials: DM
authors.lastname: Molinares
authors.affiliation: Orthopedic Pain Specialists, Santa Monica;
authors.forename: Timothy T
authors.initials: TT
authors.lastname: Davis
authors.affiliation: Orthopedic Pain Specialists, Santa Monica;
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Fung
authors.affiliation: Departments of Neurosurgery and Orthopedic Surgery and Spine Center, Keck Medicine of USC, Los Angeles;
authors.forename: John Chung-Liang
authors.initials: JC
authors.lastname: Liu
authors.affiliation: Athletic Physical Therapy, Westlake Village; and.
authors.forename: Stephen
authors.initials: S
authors.lastname: Clark
authors.affiliation: Athletic Physical Therapy, Westlake Village; and.
authors.forename: David
authors.initials: D
authors.lastname: Daily
authors.affiliation: The Spine Institute, Santa Monica, California.
authors.forename: James M
authors.initials: JM
authors.lastname: Mok
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery; D008297:Male; D009043:Motor Activity / Q000502:physiology; D056888:Patient Positioning; D011187:Posture / Q000502:physiology*; D055815:Young Adult
keywords: 10Max test = 10-repetition maximum test; MIS = minimally invasive surgical; RLD = right lateral decubitus; RLJK = right lateral jack-knife; jack-knife; neurapraxia; positioning complications; tEMG = triggered electromyography; technique