title: Fixation of a double-coated titanium-hydroxyapatite focal knee resurfacing implant: a 12-month study in sheep.
abstract: OBJECTIVE
  Focal cartilage lesions according to International Cartilage Repair Society (ICRS) grade 3-4 in the medial femoral condyle may progress to osteoarthritis. When treating such focal lesions with metallic implants a sound fixation to the underlying bone is mandatory. We developed a monobloc unipolar cobalt-chrome (Co-Cr) implant with a double coating; first a layer of commercially pure titanium (c.p.Ti) on top of which a layer of hydroxyapatite (HA) was applied. We hypothesised that such a double coating would provide long-lasting and adequate osseointegration.
  Unilateral medial femoral condyles of 10 sheep were operated. The implants were inserted in the weight-bearing surface and immediate weight-bearing was allowed. Euthanasia was performed at 6 (three animals) or 12 months (six animals). Osseointegration was analysed with micro-computer tomography (CT), light microscopy and histomorphometric analyses using backscatter scanning electron microscopy (B-SEM) technique.
  
  
  RESULTS
  At 6 months one specimen out of three showed small osteolytic areas at the hat and at 12 months two specimens out of six showed small osteolytic areas at the hat, no osteolytical areas were seen around the peg at any time point. At both time points, a high total bone-to-implant contact was measured with a mean (95% confidence interval - CI) of 90.6 (79-102) at 6 months and 92.3 (89-95) at 12 months, respectively.
  
  
  CONCLUSIONS
  A double coating (Ti + HA) of a focal knee resurfacing Co-Cr implant was presented in a sheep animal model. A firm and consistent bond to bone under weight-bearing conditions was shown up to 1 year.
authors.affiliation: Department of Orthopaedics, Karolinska University Hospital, Stockholm, Sweden; Institution of Clinical Sciences, Intervention and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden. Electronic address: nicolas.martinez-carranza@karolinska.se.
authors.forename: N
authors.initials: N
authors.lastname: Martinez-Carranza
authors.affiliation: Department of Orthopaedics, Karolinska University Hospital, Stockholm, Sweden; Institution of Clinical Sciences, Intervention and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden.
authors.forename: H E
authors.initials: HE
authors.lastname: Berg
authors.affiliation: Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
authors.forename: A-S
authors.initials: AS
authors.lastname: Lagerstedt
authors.affiliation: Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Nurmi-Sandh
authors.affiliation: Schupbach Ltd, Service and Research Laboratory for Histology, Electron Microscopy and Micro CT, Horgen, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Schupbach
authors.affiliation: Episurf Medical, Stockholm, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Ryd
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000473:pathology / Q000601:surgery*; D020099:Coated Materials, Biocompatible; D004195:Disease Models, Animal; D017886:Durapatite / Q000494:pharmacology*; D005260:Female; D005500:Follow-Up Studies; D007719:Knee Joint / Q000473:pathology / Q000601:surgery*; D007720:Knee Prosthesis; D008855:Microscopy, Electron, Scanning; D016348:Osseointegration / Q000502:physiology*; D011474:Prosthesis Design; D019919:Prosthesis Implantation; D011897:Random Allocation; D012756:Sheep; D034561:Sheep, Domestic; D013997:Time Factors; D014025:Titanium; D016896:Treatment Outcome; D016474:Weight-Bearing; D055114:X-Ray Microtomography
chemical_list: D020099:Coated Materials, Biocompatible; D017886:Durapatite; D014025:Titanium
keywords: Focal cartilage lesion; Focal knee resurfacing; Metal implants; Osseointegration; Sheep animal model