title: Does spinal kyphotic deformity influence the biomechanical characteristics of the adjacent motion segments? An in vivo animal model.
abstract: METHODS
  In an in vivo sheep model, the effects of spinal fusion and kyphotic deformity on the neighboring motion segments were analyzed.
  
  
  OBJECTIVE
  To investigate the effects of spinal fusion and kyphotic deformity on the adjacent motion segment.
  
  
  BACKGROUND
  The in vivo effects of kyphotic deformity on the neighboring motion segments have not been investigated in any studies.
  
  
  METHODS
  Eighteen sheep were equally randomized into three groups based on surgical procedure: L3-L5 in situ posterolateral fusion (n = 6) L3-L5 kyphotic posterolateral fusion (n = 6), and surgical exposure alone (n = 6). After a 16-week survival period, the adjacent motion segment changes were analyzed radiographically, biomechanically, and histologically.
  
  
  RESULTS
  The kyphosis group showed 5.0 degrees +/- 2.6 degrees and 1.7 degrees +/- 1.8 degrees compensatory hyperlordosis at L2-L3 and L5-L6, respectively, compared with surgical exposure and in situ posterolateral fusion, the kyphotic posterolateral fusion significantly influenced cranial adjacent motion segment biomechanics by inducing more stiffness in the posterior ligamentous complex (P < 0.05) and increasing lamina strain under flexion-extension loading (P < 0.05). Results of histologic analysis showed significant degenerative changes of the L2-L3 facet joints in the kyphosis group.
  
  
  CONCLUSIONS
  It is inferred that in the kyphosis group, compensatory hyperlordosis at the cranial adjacent level leads to lordotic contracture of the posterior ligamentous complex. The increased lamina strain, exhibited by the in situ group under flexion-extension, was further increased in the kyphosis group, indicating higher load transmission through the posterior column. Significant degenerative changes of the cephalad adjacent facet joints observed in the kyphosis group served to corroborate the biomechanical data. These results indicate that a kyphotic deformity may lead to facet joint contracture and facet arthritis and may serve as the origin of low back pain at the cranial adjacent level.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Union Memorial Hospital, Baltimore, USA. ODAITR@aol.com
authors.forename: I
authors.initials: I
authors.lastname: Oda
authors.forename: B W
authors.initials: BW
authors.lastname: Cunningham
authors.forename: R A
authors.initials: RA
authors.lastname: Buckley
authors.forename: M J
authors.initials: MJ
authors.lastname: Goebel
authors.forename: C J
authors.initials: CJ
authors.lastname: Haggerty
authors.forename: C M
authors.initials: CM
authors.lastname: Orbegoso
authors.forename: P C
authors.initials: PC
authors.lastname: McAfee
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004195:Disease Models, Animal; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D007738:Kyphosis / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D009038:Motion; D011859:Radiography; D011897:Random Allocation; D013123:Spinal Fusion