title: Open versus endoscopic lumbar pedicle screw fixation and posterolateral fusion in a sheep model: a feasibility study.
abstract: BACKGROUND
  Conventional open procedures for lumbar pedicle screw instrumentation are often associated with significant morbidity resulting in longer postoperative recovery and hence have led to the advent of less invasive techniques of spinal instrumentation and fusion.
  
  
  OBJECTIVE
  This study compares lumbar pedicle screw fixation and posterolateral fusion using endoscopic and open techniques in a sheep model.
  
  
  METHODS
  Endoscopic and open techniques of lumbar pedicle screw instrumentation and posterolateral fusion are compared in a sheep model (12 sheep in each group). The safety and fusion outcome are assessed by postoperative computed tomography (CT) scans performed at 6 months.
  
  
  METHODS
  Twelve sheep underwent bilateral L4-L5 pedicle screw fixation and posterolateral fusion by means of endoscopic instrumentation and another 12 sheep by means of conventional open technique. For posterolateral fusions, an autologous iliac crest bone or bone graft substitute (Healos/MP52; Orquest, Mountain View, CA) was used on either the animal's left or right side. The animals were euthanized 6 months after surgery and the lumbar spines were harvested. Pedicle dimensions and screw insertion angles were measured and the two techniques were compared using CT and image analysis software. Pedicle screw misplacement was detected by means of direct inspection and CT scan, and fusions were evaluated by CT scans.
  
  
  RESULTS
  The endoscopic group's screw insertion angle was more convergent, corresponded more closely to the human pedicle angle and was less variable than in the open technique. Three of the endoscopic group's 48 screws were misplaced medially, whereas in the open technique, 5 screws were misplaced laterally. Posterolateral bone fusion masses were palpable 6 months after surgery for both the autologous bone grafts and graft substitutes. There were no complications. The ratio of screw to pedicle diameter was approximately 0.6, greater than in human studies.
  
  
  CONCLUSIONS
  Despite differences between pedicle dimensions and screw angles, most screws could be inserted into the sheep pedicle using endoscopic or open techniques. Bone fusion was successful in both groups. Thus, minimally invasive, endoscopic transpedicular screw-plate fixation and posterolateral fusion is feasible, and as effective as the conventional open technique.
authors.affiliation: Department of Neurosurgery, Stanford University School of Medicine, 300 Pasteur Drive, R-201, Stanford, CA 94305-5327, USA.
authors.forename: Tae-Ahn
authors.initials: TA
authors.lastname: Jahng
authors.forename: Tsai-Sheng
authors.initials: TS
authors.lastname: Fu
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Kim
mesh_terms: D000818:Animals; D001863:Bone Screws; D004724:Endoscopy; D005240:Feasibility Studies; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D019060:Minimally Invasive Surgical Procedures; D011859:Radiography; D012756:Sheep; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*