title: Disability in end-stage knee osteoarthritis.
abstract: OBJECTIVE
  To examine the attributes of disability in end-stage knee osteoarthritis (OA) by analyzing the relationships between self-reported disability and objectively measured physical function after controlling pain, personal characteristic factors, and pathophysiological factors.
  
  
  METHODS
  The present study adopted a cross-sectional design. The subjects (n=88, aged 60-80 years) were scheduled for primary unilateral total knee arthroplasty (TKA) due to knee OA. Self-reported disability and pain were measured with the Western Ontario and McMaster Universities OA Index (WOMAC) and the RAND 36-item Health Survey 1.0 (RAND-36). Physical performance tests included a 15-m walk test and stair performance. Knee isometric muscle strength was measured. A clinical examination included analyses of comorbidity, body mass index (BMI), and a detailed knee examination: The flexion range of motion (ROM) was measured; the presence of varus/valgus malalignments and antero-posterior laxity was assessed. Radiographs were analyzed with the Kellgren-Lawrence grading scale.
  
  
  RESULTS
  In the linear regression model the WOMAC pain score, antero-posterior laxity of the knee, age, and BMI accounted for 54.8% of the variance in the WOMAC function score. In the bivariate analyses the WOMAC function score had a positive correlation with the 15-m walk (r(s)=0.32, p=0.003), stairs up (r(s)=0.40, p=0.001), and stairs down (r(s)=0.38, p=0.001) tests, and a negative correlation with RPT extension (r(s)=-0.45, p < 0.001) and RPT flexion (r(s)=-0.39, p=0.001) of the affected side and RPT flexion (r(s)=-0.39, p <0.001) of the contralateral side. The results of the physical performance tests also correlated with the RAND-36 Physical function (PF) score. Comorbid diseases and pain deteriorated the results of the physical performance tests and self-reported disability. Female gender deteriorated the results of the physical performance tests and the RAND-36 PF, but not the WOMAC function score. Malalignments, restriction in the flexion ROM of the knee, and the radiologic severity of knee OA did not affect self-reported disability.
  
  
  CONCLUSIONS
  Pain, BMI, and antero-posterior laxity of the knee joint were major attributes of self-reported disability. The negative effect of comorbid diseases and female gender on health-related quality of life was significant. The results of objectively measured physical performance tests correlated with self-reported disability.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Oulu University Hospital, Oulu, Finland. anna-maija.kauppila@oulu.fi
authors.forename: Anna-Maija
authors.initials: AM
authors.lastname: Kauppila
authors.forename: Eero
authors.initials: E
authors.lastname: Kyllonen
authors.forename: Paula
authors.initials: P
authors.lastname: Mikkonen
authors.forename: Pasi
authors.initials: P
authors.lastname: Ohtonen
authors.forename: Vesa
authors.initials: V
authors.lastname: Laine
authors.forename: Pertti
authors.initials: P
authors.lastname: Siira
authors.forename: Jaakko
authors.initials: J
authors.lastname: Niinimaki
authors.forename: Jari P A
authors.initials: JP
authors.lastname: Arokoski
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D004185:Disability Evaluation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D051346:Mobility Limitation; D009765:Obesity / Q000150:complications*; D020370:Osteoarthritis, Knee / Q000150:complications* / Q000503:physiopathology; D010146:Pain / Q000150:complications*; D010147:Pain Measurement; D011187:Posture; D011788:Quality of Life; D016059:Range of Motion, Articular; D012720:Severity of Illness Index; D012737:Sex Factors