title: Effect of anular repair on the healing strength of the intervertebral disc: a sheep model.
abstract: METHODS
  The intervertebral disc, in a sheep model, was used to assess the effect of directly repairing three different anular incisions on the subsequent healing strength of the intervertebral disc.
  
  
  OBJECTIVE
  To assess whether directly repairing an anular defect, made at the time of lumbar discectomy, could influence the healing rate and strength of the anulus fibrosus.
  
  
  METHODS
  Twenty-four sheep underwent a retroperitoneal approach to five lumbar disc levels. An anular incision, followed by partial discectomy was done at each exposed level. Anular incisions used in this study consisted of 1) a straight transverse slit, 2) a cruciate incision, and 3) a window or box excision. Healing strength was measured at three time intervals: 2 weeks, 4 weeks, and 6 weeks. Each anular incision type was performed on 30 lumbar discs, 10 discs in each time interval. Five discs in each time interval underwent direct repair, and five discs were left unrepaired to heal as controls. The sheep were killed at 2, 4, and 6 weeks after surgery. The lumbar spines were removed en bloc, and the intervertebral discs were subjected to pressure-volume testing to assess the anular strength of repaired versus unrepaired disc injuries at each time interval.
  
  
  RESULTS
  Statistical analysis was performed to evaluate the effects of healing time, incision technique, and repair on the pressure-volume characteristics of the involved discs. Pressure-volume testing showed trends of stronger healing for repaired discs, but at no time interval was any significant difference found between repaired and nonrepaired anular strength. Of the nonrepaired discs, the box incision was only 40 to 50% as strong as the slit or cruciate incised discs during early healing.
  
  
  CONCLUSIONS
  Direct repair of anular incisions in the lumbar spine does not significantly alter the healing strength of the intervertebral disc after lumbar discectomy.
authors.affiliation: Department of Orthopaedic Surgery, William Beaumont Hospital, Royal Oak, Michigan, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Ahlgren
authors.forename: W
authors.initials: W
authors.lastname: Lui
authors.forename: H N
authors.initials: HN
authors.lastname: Herkowitz
authors.forename: M M
authors.initials: MM
authors.lastname: Panjabi
authors.forename: J P
authors.initials: JP
authors.lastname: Guiboux
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004195:Disease Models, Animal; D017586:Diskectomy / Q000379:methods*; D007403:Intervertebral Disc / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D007405:Intervertebral Disc Displacement / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D011312:Pressure; D012756:Sheep; D014945:Wound Healing / Q000502:physiology*