title: What's all that noise? The effect of co-morbidity on health outcome questionnaire results after knee arthroplasty.
abstract: BACKGROUND
  We modified the Charnley Classification for hips to facilitate its use with knee arthroplasty patients and investigated what affect the different classes of co-morbidity had on the results of a spectrum of outcome questionnaires.
  
  
  METHODS
  3600 patients from the Swedish Knee Arthroplasty Registry were surveyed by post with a variety of questionnaires ranging from multiple-item general health, to a single-item knee arthroplasty specific questionnaire. All patients also completed a co-morbidity questionnaire, from which a modified Charnley Classification was generated for each patient. We then investigated the correlation and relationship between the results of the questionnaires and the different classes of co-morbidity.
  
  
  RESULTS
  The results of the questionnaires tested varied significantly by Charnley Class, regardless of the specificity of the questionnaire used.
  
  
  CONCLUSIONS
  We suggest that co-morbidity should be taken into account in outcome studies utilizing general health or disease/site specific questionnaires.
authors.affiliation: Department of Orthopaedics, Lund University Hospital, SE-221 85 Lund, Sweden. Michael.dunbar@ort.lu.se
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Dunbar
authors.forename: Otto
authors.initials: O
authors.lastname: Robertsson
authors.forename: Leif
authors.initials: L
authors.lastname: Ryd
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000453:epidemiology* / Q000601:surgery; D012042:Registries; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology; D016896:Treatment Outcome