title: Lumbar disk herniation: do MR imaging findings predict recurrence after surgical diskectomy?
abstract: OBJECTIVE
  To retrospectively evaluate if the degree of disk degeneration and disk herniation volume at magnetic resonance (MR) imaging are risk factors for recurrent disk herniation.
  
  
  METHODS
  The institutional review board permits such retrospective studies, and individual informed consent was not required. MR imaging findings obtained before initial diskectomy in 30 patients (mean age, 42.8 years; 10 women, 20 men) with recurrent disk herniation (study group) and 30 patients (mean age, 42.2 years; nine women, 21 men) without recurrence for at least 2 years after surgery (control group) were compared. Disk degeneration was assessed on T2-weighted sagittal MR images with a five-point grading system (grade I indicated no degeneration; grade II, horizontal hypointense bands within disk; grade III, inhomogeneous disk with intermediate signal intensity; grade IV, no distinction between inner and outer parts of disk; and grade V, collapsed hypointense disk). Disk herniation was classified as representing protrusion, extrusion, or sequestration. The volume of both the affected intervertebral disk and the herniated disk material was measured. Qualitative and quantitative analyses were performed by two readers. The chi(2) test was used for comparison of categorical variables. For comparison of disk degeneration and volumes between patients with and those without recurrence, a paired two-tailed t test was used. Odds ratios based on the extent of disk degeneration were calculated for the entire sample.
  
  
  RESULTS
  Advanced disk degeneration (grades IV and V) was significantly less frequent in the study group than in the control group (P < .006). The risk of recurrent disk herniation decreased by a factor of 3.4 for each increase in grade of disk degeneration (odds ratio: 3.58; 95% confidence interval: 1.3, 9.6; P = .011). Mean disk herniation volume as a percentage of intervertebral disk volume was 10.59% +/- 3.41 in the study group and 11.56% +/- 3.84 in the control group. This difference was not significant (P = .31).
  
  
  CONCLUSIONS
  Minor disk degeneration but not herniation volume represents a risk factor for the recurrence of disk herniation after diskectomy.
authors.affiliation: Center for Spinal Surgery and Department of Radiology, University of Zurich, Balgrist Hospital, Forchstrasse 340, CH-8008 Zurich, Switzerland.
authors.forename: Claudio
authors.initials: C
authors.lastname: Dora
authors.forename: Marius R
authors.initials: MR
authors.lastname: Schmid
authors.forename: Achim
authors.initials: A
authors.lastname: Elfering
authors.forename: Marco
authors.initials: M
authors.lastname: Zanetti
authors.forename: Juerg
authors.initials: J
authors.lastname: Hodler
authors.forename: Norbert
authors.initials: N
authors.lastname: Boos
mesh_terms: D000328:Adult; D017586:Diskectomy; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007403:Intervertebral Disc / Q000473:pathology*; D007405:Intervertebral Disc Displacement / Q000175:diagnosis / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011183:Postoperative Complications / Q000175:diagnosis* / Q000601:surgery; D012008:Recurrence; D012086:Reoperation; D012189:Retrospective Studies; D018570:Risk Assessment; D013128:Spinal Osteophytosis / Q000175:diagnosis