title: Load rate of facet joints at the adjacent segment increased after fusion.
abstract: BACKGROUND
  The cause of the adjacent segment degeneration (ASD) after fusion remains unknown. It is reported that adjacent facet joint stresses increase after anterior cervical discectomy and fusion. This increase of stress rate may lead to tissue injury. Thus far, the load rate of the adjacent segment facet joint after fusion remains unclear.
  
  
  METHODS
  Six C2-C7 cadaveric spine specimens were loaded under four motion modes: Flexion, extension, rotation, and lateral bending, with a pure moment using a 6° robot arm combined with an optical motion analysis system. The Tecscan pressure test system was used for testing facet joint pressure.
  
  
  RESULTS
  The contact mode of the facet joints and distributions of the force center during different motions were recorded. The adjacent segment facet joint forces increased faster after fusion, compared with intact conditions. While the magnitude of pressures increased, there was no difference in distribution modes before and after fusion. No pressures were detected during flexion. The average growth velocity during extension was the fastest and was significantly faster than lateral bending.
  
  
  CONCLUSIONS
  One of the reasons for cartilage injury was the increasing stress rate of loading. This implies that ASD after fusion may be related to habitual movement before and after fusion. More and faster extension is disadvantageous for the facet joints and should be reduced as much as possible.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Bao-Qing
authors.initials: BQ
authors.lastname: Pei
authors.affiliation: Department of Orthopedics, Beijing Chao-Yang Hospital, Beijing 100020, China.
authors.forename: Jin-Cai
authors.initials: JC
authors.lastname: Yang
authors.forename: Yong
authors.initials: Y
authors.lastname: Hai
authors.forename: De-Yu
authors.initials: DY
authors.lastname: Li
authors.forename: Shu-Qin
authors.initials: SQ
authors.lastname: Wu
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D066298:In Vitro Techniques; D008159:Lumbar Vertebrae / Q000503:physiopathology; D016059:Range of Motion, Articular / Q000502:physiology; D013123:Spinal Fusion / Q000009:adverse effects*; D013131:Spine / Q000503:physiopathology*