title: Improvement of the bone-screw interface strength with hydroxyapatite-coated and titanium-coated AO/ASIF cortical screws.
abstract: OBJECTIVE
  To evaluate whether coating AO/ASIF screws with osteoconductive materials can improve bone-screw fixation.
  
  
  METHODS
  Ninety-six AO/ASIF 4.5-millimeter cortical screws were divided into four paired groups and implanted in the femurs and tibiae of six sheep: Group A = standard stainless steel screws; Group B = stainless steel screws coated with highly crystalline hydroxyapatite; Group C = stainless steel screws coated with low crystalline hydroxyapatite; Group D = titanium screws coated with titanium. The screws were implanted according to the standard AO technique to an insertion torque of 2,000 Newton-millimeters. Sheep were killed at one, three, and twelve months after surgery.
  
  
  METHODS
  Extraction torque was measured on six screws from each group selected at random at time of each euthanization. Morphologic analysis of the bone-screw interface was performed on the remaining screws.
  
  
  RESULTS
  At each euthanization the extraction torque of Group A was lower than that of the other groups (p < 0.0001). At three and twelve months the extraction torque of Group B was higher than that of Group D (p = 0.002). Morphologic results showed extensive bone-screw gap in Group A. Optimal osteointegration was observed in Groups B and C. Osteointegration of Group D was higher than that of Group A and lower than that of Groups B and C.
  
  
  CONCLUSIONS
  It was demonstrated that AO/ASIF screws coated with osteoconductive materials achieve optimal fixation strength, even in the early phase. This fixation strength was significantly higher than that of the standard screws.
authors.affiliation: Department of Orthopaedic Surgery, Bologna University, Rizzoli Institute, Bologna, Italy. a.moroni@ior.it
authors.forename: Antonio
authors.initials: A
authors.lastname: Moroni
authors.forename: Cesare
authors.initials: C
authors.lastname: Faldini
authors.forename: Michele
authors.initials: M
authors.lastname: Rocca
authors.forename: Susanna
authors.initials: S
authors.lastname: Stea
authors.forename: Sandro
authors.initials: S
authors.lastname: Giannini
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws; D020099:Coated Materials, Biocompatible; D004195:Disease Models, Animal; D017886:Durapatite; D005260:Female; D005264:Femoral Fractures / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D005592:Fracture Fixation; D017102:Fracture Healing / Q000502:physiology; D011897:Random Allocation; D012756:Sheep; D013718:Tensile Strength / Q000502:physiology*; D013978:Tibial Fractures / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D014025:Titanium; D019415:Torque
chemical_list: D020099:Coated Materials, Biocompatible; D017886:Durapatite; D014025:Titanium