title: Medial unicompartmental knee arthroplasty: does tibial component position influence clinical outcomes and arthroplasty survival?
abstract: BACKGROUND
  In several recent studies, unicompartmental knee arthroplasty (UKA) produced better functional outcomes than did total knee arthroplasty with 10-year prosthesis survival rates greater than 95%. Nevertheless, UKA is still widely viewed as producing inconsistent results. Tibial component loosening is the leading cause of failure. We consequently sought to identify tibial component position criteria associated with outcomes of medial UKA.
  
  
  METHODS
  We conducted a retrospective multicentre study of 559 medial UKAs performed between 1988 and 2010 in 421 patients (262 females and 159 males) with a mean age of 69.51±8.72 years at surgery. We recorded the following radiographic parameters: joint space height, obliquity and slope of the tibial implant, whether the tibial component was perpendicular to the femoral component, and lower limb malalignment. The International Knee Society (IKS) score was used to assess clinical outcomes. Mean follow-up at re-evaluation was 5.17±4.33 years.
  
  
  RESULTS
  The mean 10-year prosthesis survival rate was 83.7±3.5%. Factors associated with decreased prosthesis survival were a greater than 2-mm change in joint space height, a greater than 3° change in tibial component obliquity, a slope value greater than 5° or a change in slope greater than 2°, and more than 6° of divergence between the tibial and femoral components. Residual mechanical varus of 5° or more was also associated with mechanical failure. The only factor associated with worse functional score values was joint space elevation by more than 2mm.
  
  
  CONCLUSIONS
  The high level of accuracy required for optimal positioning of the tibial component during medial UKA indicates a need for considerable technical expertise and emphasises the conservative nature of the procedure. Optimal positioning is crucial to restore normal knee kinematics and to prevent implant wear and lesions to adjacent compartments.
  
  
  METHODS
  IV, retrospective study.
authors.affiliation: Service de chirurgie orthopédique I, hôpital Trousseau, CHRU de Tours, avenue de la République, Chambray-lès-Tours, Tours cedex 9, France.
authors.forename: R
authors.initials: R
authors.lastname: Chatellard
authors.forename: V
authors.initials: V
authors.lastname: Sauleau
authors.forename: M
authors.initials: M
authors.lastname: Colmar
authors.forename: H
authors.initials: H
authors.lastname: Robert
authors.forename: G
authors.initials: G
authors.lastname: Raynaud
authors.forename: J
authors.initials: J
authors.lastname: Brilhault
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000295:instrumentation; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000209:etiology*; D016059:Range of Motion, Articular; D020127:Recovery of Function; D012189:Retrospective Studies; D013977:Tibia / Q000601:surgery; D016896:Treatment Outcome