title: Proximal tibial bone density is preserved after unicompartmental knee arthroplasty.
abstract: BACKGROUND
  Bone mineral density (BMD) in the proximal tibia decreases after TKA and is believed to be a factor in implant migration and loosening. Unicompartmental knee arthroplasty (UKA) is a less invasive procedure preserving knee compartments unaffected by degeneration. Finite element studies have suggested UKA may preserve BMD and that implants of differing stiffnesses might differentially affect BMD but these notions have not been clinically confirmed.
  
  
  OBJECTIVE
  We therefore asked whether (1) proximal tibial BMD decreases after UKA, and (2) a cemented metal tibial component with a mobile polyethylene (PE) bearing would have greater BMD loss than a cemented PE tibial component.
  
  
  METHODS
  We prospectively followed 48 patients who underwent 50 UKAs using one of two implants: one with a cemented metal tibial baseplate and a mobile PE insert (n = 26) and one with a cemented all-PE tibial component (n = 24). In followup we assessed pain and function (Oxford Knee Score, SF-12, The Knee Society Score(©)) and radiographs. BMD changes were assessed using quantitative CT osteodensitometry performed postoperatively and at 1 and 2 years after the index procedure.
  
  
  RESULTS
  Mean cancellous BMD decreased 1.9% on the medial side and 1.1% on the lateral side. Mean cortical BMD was static, decreasing 0.4% on the medial side and increasing 0.5% on the lateral side. The greatest observed difference between implants for any region was 3.7%. There were no differences in pain or functional outcome scores.
  
  
  CONCLUSIONS
  BMD was preserved 2 years after UKA with no major differences seen between implant types.
authors: Department of Orthopaedics, Middlemore Hospital, Auckland, Manukau, 1640, New Zealand. bradleyr@windowslive.com
authors: Bradley I
authors: BI
authors: Richmond
authors: Simon V
authors: SV
authors: Hadlow
authors: Tim G
authors: TG
authors: Lynskey
authors: Cameron G
authors: CG
authors: Walker
authors: Jacob T
authors: JT
authors: Munro
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D018771:Arthralgia / Q000209:etiology; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation; D001696:Biomechanical Phenomena; D001843:Bone Cements / Q000627:therapeutic use; D015519:Bone Density; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D010149:Postoperative Pain / Q000209:etiology; D020959:Polyethylene; D011446:Prospective Studies; D011474:Prosthesis Design; D020127:Recovery of Function; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
chemical_list: D001843:Bone Cements; D020959:Polyethylene