title: Changes in bone mineral density of the distal femur after total knee arthroplasty: a 7-year DEXA follow-up comparing results between obese and nonobese patients.
abstract: OBJECTIVE
  Periprosthetic femoral bone mineral density (BMD, g/cm2) decreases after total knee arthroplasty (TKA) as a result of the stress-shielding phenomenon. It is not known whether obesity has an effect on this phenomenon or not. The aim of this study was to assess long-term periprosthetic BMD changes after TKA and compare whether there is a difference between obese and nonobese patients.
  
  
  METHODS
  A total of 69 TKAs in 61 patients were performed, and BMD measurements of the distal femur were followed up to 7 years postoperatively. The patients were divided into two study groups according to their body mass index, and the groups were compared in relation to BMD and functional outcome.
  
  
  RESULTS
  The mean of periprosthetic bone loss during the 7-year follow-up varied from 10.3% to 30.6% depending on the region of interest (p<0.0005). The highest bone-loss rates were detected during the first three postoperative months. A total of 26 patients were categorized as obese with a body mass index value of ≥30 kg/m2. The obese patients' total periprosthetic BMD was higher at both baseline (8.6%) and 7 years after operation (p=0.05) (15.2%).
  
  
  CONCLUSIONS
  Periprosthetic bone loss around the femoral component continued for up to 7 years postoperatively. The loss of bone density was not associated with any negative clinical outcome in this study, but periprosthetic bone loss was of a smaller quantity in the obese which is probably due to higher weight induced stresses on bone.
authors.affiliation: Central Finland Central Hospital, Jyväskylä, Finland; University of Eastern Finland, Kuopio, Finland. Electronic address: jaakko.jarvenpaa@fimnet.fi.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Järvenpää
authors.affiliation: University of Eastern Finland, Kuopio, Finland; North Karelia Central Hospital, Joensuu, Finland.
authors.forename: Tarja
authors.initials: T
authors.lastname: Soininvaara
authors.affiliation: Department of Orthopaedics and Traumatology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Kettunen
authors.affiliation: Department of Orthopaedics and Traumatology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Miettinen
authors.affiliation: University of Eastern Finland, Kuopio, Finland; Department of Orthopaedics and Traumatology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Kröger
mesh_terms: D015502:Absorptiometry, Photon; D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D015519:Bone Density / Q000502:physiology*; D001862:Bone Resorption / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009765:Obesity / Q000503:physiopathology*; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery; D011446:Prospective Studies
keywords: BMD; Obesity; Stress shielding; TKA