title: Range of movement correlates with the Oxford knee score after total knee replacement: A prediction model and validation.
abstract: BACKGROUND
  Patient reported outcome measures are widely used in the evaluation of outcomes after Total Knee Replacement (TKR) in joint registries and large studies. The aim of this study was to assess the relationship between the Oxford knee score (OKS) and range of motion (ROM) after TKR, and to construct and validate prediction models of ROM from the measured OKS.
  
  
  METHODS
  Eight hundred sixty patients reviewed five years postoperatively and 273 patients reviewed nine to 10 years postoperatively completed an OKS. Of these, 808 (94%) and 226 (83%) patients, respectively, had a complete dataset (knee extension and ROM) and formed the study cohort.
  
  
  RESULTS
  Regression analysis demonstrated a significant correlation between the OKS and ROM (r=0.38, p<0.001) after adjusting for other confounding variables (age, sex, body mass index, and knee extension). A prediction model was constructed and validated using a second cohort of 226 patients at nine to 10 years after their TKR. Intraclass correlation demonstrated good reliability (r=0.60, 95% CI 0.47 to 0.69) between predicted and actual measured ROM for this group. However, when the OKS is used in isolation the reliability of the predicted ROM is diminished (intraclass correlation r=0.41, 95% CI 0.24 to 0.55).
  
  
  CONCLUSIONS
  The OKS is an independent predictor of ROM after TKR. It is also possible to predict ROM from the OKS, but the reliability of this is improved when other independent predictors such as age, gender, body mass index (BMI) and degree of knee extension are also acknowledged.
authors.affiliation: Department of Orthopaedics and Trauma, Victoria Hospital, Hayfield Road, Kirkcaldy, Fife KY2 5AH, United Kingdom. Electronic address: julian.maempel@nhs.net.
authors.forename: Julian F
authors.initials: JF
authors.lastname: Maempel
authors.affiliation: Department of Orthopaedics and Trauma, Victoria Hospital, Hayfield Road, Kirkcaldy, Fife KY2 5AH, United Kingdom.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Clement
authors.affiliation: Department of Orthopaedics and Trauma, Victoria Hospital, Hayfield Road, Kirkcaldy, Fife KY2 5AH, United Kingdom.
authors.forename: Ivan J
authors.initials: IJ
authors.lastname: Brenkel
authors.affiliation: Department of Orthopaedics and Trauma, Victoria Hospital, Hayfield Road, Kirkcaldy, Fife KY2 5AH, United Kingdom.
authors.forename: Phil J
authors.initials: PJ
authors.lastname: Walmsley
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D006305:Health Status Indicators; D006801:Humans; D008962:Models, Theoretical; D020370:Osteoarthritis, Knee / Q000601:surgery*; D000071066:Patient Reported Outcome Measures; D011379:Prognosis; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D016896:Treatment Outcome
keywords: Oxford knee score; Range of motion; Total knee replacement