title: Flexibility and fatigue evaluation of oblique as compared with anterior lumbar interbody cages with integrated endplate fixation.
abstract: OBJECTIVE
  This study was undertaken to quantify the in vitro range of motion (ROM) of oblique as compared with anterior lumbar interbody devices, pullout resistance, and subsidence in fatigue.
  
  
  METHODS
  Anterior and oblique cages with integrated plate fixation (IPF) were tested using lumbar motion segments. Flexibility tests were conducted on the intact segments, cage, cage + IPF, and cage + IPF + pedicle screws (6 anterior, 7 oblique). Pullout tests were then performed on the cage + IPF. Fatigue testing was conducted on the cage + IPF specimens for 30,000 cycles.
  
  
  RESULTS
  No ROM differences were observed in any test group between anterior and oblique cage constructs. The greatest reduction in ROM was with supplemental pedicle screw fixation. Peak pullout forces were 637 ± 192 N and 651 ± 127 N for the anterior and oblique implants, respectively. The median cage subsidence was 0.8 mm and 1.4 mm for the anterior and oblique cages, respectively.
  
  
  CONCLUSIONS
  Anterior and oblique cages similarly reduced ROM in flexibility testing, and the integrated fixation prevented device displacement. Subsidence was minimal during fatigue testing, most of which occurred in the first 2500 cycles.
authors.affiliation: Excelen Center for Bone and Joint Research, Minneapolis, Minnesota;
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Freeman
authors.affiliation: Excelen Center for Bone and Joint Research, Minneapolis, Minnesota;
authors.forename: William J
authors.initials: WJ
authors.lastname: Camisa
authors.affiliation: Midwest Spine Institute, Stillwater, Minnesota; and.
authors.forename: Glenn R
authors.initials: GR
authors.lastname: Buttermann
authors.affiliation: Pinnacle Orthopaedics, Marietta, Georgia.
authors.forename: James R
authors.initials: JR
authors.lastname: Malcolm
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology*; D001860:Bone Plates; D002102:Cadaver; D005221:Fatigue; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000601:surgery; D008297:Male; D008875:Middle Aged; D018583:Pliability / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013123:Spinal Fusion / Q000295:instrumentation
keywords: DEXA = dual-energy x-ray absorptiometry; IPF = integrated plate fixation; ROM = range of motion; fatigue; interbody cage; interbody device; lumbar spine biomechanics; pullout testing; subsidence