title: An investigational study on the healing process of anterior spinal arthrodesis using a bioactive ceramic spacer and the change in load-sharing of spinal instrumentation.
abstract: METHODS
  Ceramic anterior lumbar interbody arthrodesis was performed using an in vivo sheep model. Observations of fusion status and the load-sharing of spinal instrumentation were studied at sequential intervals for 1 year after surgery.
  
  
  OBJECTIVE
  To elucidate the healing process of spinal arthrodesis performed with a bioactive ceramic spacer and the change in load-sharing of anterior spinal instrumentation.
  
  
  BACKGROUND
  With the improved development of spinal instrumentation, anterior spinal arthrodesis has become a standard spinal reconstruction technique; however, the mechanistic basis underlying the healing process is not well documented. Moreover, it remains unclear how load-distribution through the fusion mass and spinal instrumentation change throughout the healing process.
  
  
  METHODS
  Using 24 sheep, a two-level anterior lumbar interbody fusion (L2-L3, L4-L5) was performed using a smooth surface and a porous surface-modified bioactive ceramic, with each segment instrumented using a one-rod anterior spinal instrumentation system. Four animals each were killed at 2, 4, 8, 12, 24, and 52 weeks after surgery. Postmortem analysis included quantification of anterior rod strain under multidirectional flexibility testing and radiographic and histologic analyses of the arthrodesed segments.
  
  
  RESULTS
  From 0 to 8 weeks after surgery, the bending strain of the rod gradually decreased despite no obvious bone formation. From 8 to 24 weeks after surgery, the rod strain markedly decreased with the development of bridging trabeculated bone formation between vertebral bodies. After 24 weeks after surgery, minimal changes were observed in rod strain; however, the fusion mass volumetrically increased with corresponding facet joint atrophy. The porous surface-modification of ceramic did not influence the histologic healing process, despite the improvement of interface osseous union rate.
  
  
  CONCLUSIONS
  In anterior spinal arthrodesis, spinal instrumentation is mainly exposed to bending stress, with decreased load-sharing with corresponding development of the spinal fusion. Continuous bone remodeling of the anterior fusion mass results in concurrent decreases in spinal instrumentation and posterior spinal element load-transmission. The principal healing mechanism of ceramic anterior interbody spinal fusion is not an osseous union between the ceramic and vertebral body, but bridging bone formation around the ceramic, which directly connects the vertebral bodies above and below the disc.
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Sapporo, Japan. takamasa@med.hokudai.ac.jp
authors.forename: Masahiko
authors.initials: M
authors.lastname: Takahata
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kotani
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Abumi
authors.forename: Manabu
authors.initials: M
authors.lastname: Ito
authors.forename: Takashige
authors.initials: T
authors.lastname: Takada
authors.forename: Akio
authors.initials: A
authors.lastname: Minami
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kaneda
mesh_terms: D000818:Animals; D001174:Arthrodesis; D001696:Biomechanical Phenomena; D018786:Bone Substitutes; D002516:Ceramics; D004867:Equipment Design; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D009984:Orthopedic Fixation Devices; D012756:Sheep; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing; D014945:Wound Healing
chemical_list: D018786:Bone Substitutes