title: Long-term survival of cemented distal femoral endoprostheses with a hydroxyapatite-coated collar: a histological study and a radiographic follow-up.
abstract: BACKGROUND
  The objective of this study was to examine the degree of osteointegration into a hydroxyapatite-coated collar and relate this finding to aseptic loosening in patients with a distal femoral replacement used to treat primary bone cancer. Our hypothesis was that the implant collar would increase osteointegration and reduce the rate of aseptic implant loosening.
  
  
  METHODS
  Sixty-one patients treated with a primary cemented distal femoral prosthesis between 1992 and 2001 were included in this study. The mean duration of follow-up was 8.5 years (range, two to eighteen years). Extracortical bone growth into the grooved hydroxyapatite-coated collar was quantified radiographically. Histological sections through four hydroxyapatite-coated collars and four implants with no collar, retrieved following amputation due to local recurrence or at autopsy at a mean of 3.5 years (range, 1.4 to 6.1 years) after implantation, were evaluated as well.
  
  
  RESULTS
  Five (8%) of the implants were revised because of aseptic loosening, 3% of the implants fractured, and 3% were revised because of infection. Six limbs (10%) required amputation because of local tumor recurrence. On radiographs, osteointegration into the collar was seen to have occurred in 70% of the patients and did not correlate with sex, age, diagnosis, or length of time postoperatively. Histological analysis showed mature lamellar bone within the grooves of the hydroxyapatite-coated collar, and bone was observed in direct contact with the hydroxyapatite coating. Extracortical bone failed to make direct contact with the surface of the implants manufactured without a collar.
  
  
  CONCLUSIONS
  The use of cemented distal femoral massive bone tumor prostheses with a hydroxyapatite-coated collar located at the shoulder of the implant was followed by a low (8%) rate of revision due to aseptic loosening. The use of hydroxyapatite grooved collars may lead to osteointegration of the implant shoulder (collar) and may reduce the rate of aseptic loosening.
authors.affiliation: John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, Division of Surgery and Interventional Science, University College London, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, United Kingdom. m.coathup@ucl.ac.uk
authors.forename: Melanie Jean
authors.initials: MJ
authors.lastname: Coathup
authors.forename: Vineet
authors.initials: V
authors.lastname: Batta
authors.forename: Robin C
authors.initials: RC
authors.lastname: Pollock
authors.forename: William J
authors.initials: WJ
authors.lastname: Aston
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Cannon
authors.forename: John A
authors.initials: JA
authors.lastname: Skinner
authors.forename: Timothy W R
authors.initials: TW
authors.lastname: Briggs
authors.forename: Paul S
authors.initials: PS
authors.lastname: Unwin
authors.forename: Gordon William
authors.initials: GW
authors.lastname: Blunn
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001859:Bone Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D020099:Coated Materials, Biocompatible; D017886:Durapatite; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D016348:Osseointegration / Q000502:physiology*; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D011859:Radiography; D016896:Treatment Outcome
chemical_list: D020099:Coated Materials, Biocompatible; D017886:Durapatite