title: Evaluation of hydroxyapatite ceramic vertebral spacers with different porosities and their binding capability to the vertebral body: an experimental study in sheep.
abstract: OBJECTIVE
  The aim of this study was to evaluate the degree of bone ingrowth and bonding stiffness at the surface of hydroxyapatite ceramic (HAC) spacers with different porosities in an animal model and to discuss the ideal porous characteristics of these spacers for anterior spinal reconstruction.
  
  
  METHODS
  Twenty-one adult sheep (age 1-2 years, mean weight 70 kg) were used in this experiment. Surgery consisted of anterior lumbar interbody fusion at L2-3 and L4-5, insertion of an HAC spacer (10 x 13 x 24 mm) with three different porosities (0, 3, and 15%), and single-rod anterior instrumentation. At 4 and 6 months postoperatively, the lumbar spines were harvested. Bonding conditions at the bone-HAC spacer interface were evaluated using neuroimages and biomechanically. A histological evaluation was also conducted to examine the state of bone ingrowth at the surface of the HAC spacer. Biomechanical testing showed that the bonding strength of HAC at 6 months postoperatively was 0.047 MPa in 0% porosity spacers, 0.39 MPa in 3%, and 0.49 MPa in 15% porosity spacers. The histological study showed that there was a soft-tissue layer at the surface of the HAC spacer with 0% porosity. Direct bonding was observed between bone and spacers with 3 or 15% porosity. Micro-computed tomography scans showed direct bonding between the bone and HAC with 3 or 15% porosity. No direct bonding was observed in HAC with 0% porosity.
  
  
  CONCLUSIONS
  Dense (0%) HAC anterior vertebral spacers did not achieve direct bonding to the bone in the sheep model. The HAC vertebral spacers with 3 or 15% porosity showed proof of direct bonding to the bone at 6 months postoperatively. The higher porosity HAC spacer showed better bonding stiffness to the bone.
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Sapporo, Japan. maito@med.hokudai.ac.jp
authors.forename: Manabu
authors.initials: M
authors.lastname: Ito
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kotani
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hojo
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Abumi
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kadosawa
authors.forename: Akio
authors.initials: A
authors.lastname: Minami
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D018786:Bone Substitutes; D002516:Ceramics; D016009:Chi-Square Distribution; D004195:Disease Models, Animal; D017886:Durapatite; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008422:Materials Testing; D016062:Porosity; D034561:Sheep, Domestic; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical; D013499:Surface Properties; D014057:Tomography, X-Ray Computed
chemical_list: D018786:Bone Substitutes; D017886:Durapatite