title: Periprosthetic bone mineral density changes after unicondylar knee arthroplasty.
abstract: BACKGROUND
  Unicompartmental knee arthroplasty (UKA) has received renewed interest in the last decade. UKA involves minor injury to soft tissues, limited removal of bone and delicate preservation of knee anatomy and geometry. In theory, UKA provides an opportunity to restore post-surgical knee kinematics to near normal.
  
  
  OBJECTIVE
  UKA leaves patellofemoral joint free to meet high mechanical forces with no stress-shielding and therefore might preserve bone mineral density (BMD).
  
  
  METHODS
  We studied 21 patients with osteoarthritis (OA), who had received medial compartment UKA at Kuopio University Hospital between October 1997 and September 2000. BMD was measured by dual-energy X-ray absorptiometry (DEXA), at baseline (within a week after surgery) and at intervals until 7 years.
  
  
  RESULTS
  DEXA results were reproducible. The highest rate of periprosthetic bone loss occurred during the first 3 months after UKA. The average loss in BMD was 4.4% (p = 0.039) in the femoral diaphysis and it ranged from 11.2% (p < 0.001) to 11.9% (p = 0.002) in the distal femoral metaphysis; however, BMD changes in these regions, from 2 years to 7 years, were nonsignificant. At the 1-year follow-up, the BMD of the medial tibial metaphysis had increased by 8.9% (p = 0.02), whereas those in the lateral tibial metaphysial (-2.4%) and diaphysial regions (-2.0%) did not change significantly.
  
  
  CONCLUSIONS
  UKA did not preserve periprosthetic BMD in the distal femoral metaphysis, whereas BMD changes in the tibial metaphysis were minor, consistent with a mechanical balance between the medial and lateral tibial compartments. LEVEL OF EVIDENCE 2B: Prospective case control study.
authors.affiliation: North Karelia Central Hospital, Joensuu Finland. Tarja.Soininvaara@uef.fi
authors.forename: Tarja A
authors.initials: TA
authors.lastname: Soininvaara
authors.forename: Kristiina A L
authors.initials: KA
authors.lastname: Harju
authors.forename: Hannu J A
authors.initials: HJ
authors.lastname: Miettinen
authors.forename: Heikki P J
authors.initials: HP
authors.lastname: Kröger
mesh_terms: D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D015519:Bone Density; D001862:Bone Resorption / Q000000981:diagnostic imaging; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D005500:Follow-Up Studies; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery; D010329:Patella / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D013977:Tibia / Q000000981:diagnostic imaging*; D013997:Time Factors