title: Superior sealing effect of hydroxyapatite in porous-coated implants: experimental studies on the migration of polyethylene particles around stable and unstable implants in dogs.
abstract: BACKGROUND
  Migration of wear debris to the periprosthetic bone is a major cause of osteolysis and implant failure. Both closed-pore porous coatings and hydroxyapatite (HA) coatings have been claimed to prevent the migration of wear debris. We investigated whether HA could augment the sealing effect of a porous coating under both stable and unstable conditions.
  
  
  METHODS
  We inserted porous-surfaced knee implants, with and without HA coating, in 16 dogs, according to a paired, randomized study design. 8 dogs had 2 implants inserted into each knee using a stable implant device and 8 dogs received 1 implant in each knee using a micromotion (500 microm) implant device. Implants had a peri-implant gap of 0.75 mm. We then injected polyethylene (PE) particles or a control solution into the knee joints on a weekly basis.
  
  
  RESULTS
  After 16 weeks, the rating of particles around stable implants was reduced by the HA coating froma median value of 2 (1-4) to 1 (0-1) (p = 0.01) and during micromotion from 3 (2-4) to 1 (0-3) (p = 0.002). HA-coated implants had superior bone ongrowth during stable and unstable conditions. We found no difference in bone ongrowth between PE-exposed and vehicle-exposed implants.
  
  
  CONCLUSIONS
  Compared to a pure plasma-sprayed porous coating, a layer of HA coating provides bettter bone ongrowth and protects the bone-implant interface against the migration of wear debris under both stable and unstable conditions.
authors.affiliation: Orthopedic Research Laboratory, Department of Orthopedics, Skejby Hospital, Denmark. ole_rahbek@hotmail.com
authors.forename: Ole
authors.initials: O
authors.lastname: Rahbek
authors.forename: Søren
authors.initials: S
authors.lastname: Kold
authors.forename: Knud
authors.initials: K
authors.lastname: Bendix
authors.forename: Søren
authors.initials: S
authors.lastname: Overgaard
authors.forename: Kjeld
authors.initials: K
authors.lastname: Søballe
mesh_terms: D000818:Animals; D020099:Coated Materials, Biocompatible; D004285:Dogs; D017886:Durapatite; D005548:Foreign-Body Migration / Q000209:etiology / Q000517:prevention & control; D007719:Knee Joint / Q000473:pathology / Q000601:surgery; D007720:Knee Prosthesis / Q000009:adverse effects*; D020959:Polyethylene; D016062:Porosity
chemical_list: D020099:Coated Materials, Biocompatible; D020959:Polyethylene; D017886:Durapatite