Validity of summing painful joint sites to assess joint-pain comorbidity in hip or knee osteoarthritis.
BACKGROUND
Previous studies in patients with hip and knee osteoarthritis (OA) have advocated the relevance of assessing the number of painful joint sites, other than the primary affected joint, in both research and clinical practice. However, it is unclear whether joint-pain comorbidities can simply be summed up.


METHODS
A total of 401 patients with hip or knee OA completed questionnaires on demographic variables and joint-pain comorbidities. Rasch analysis was performed to evaluate whether a sum score of joint-pain comorbidities can be calculated.


RESULTS
Self-reported joint-pain comorbidities showed a good fit to the Rasch model and were not biased by gender, age, disease duration, BMI, or patient group. As a group, joint-pain comorbidities covered a reasonable range of severity levels, although the sum score had rather low reliability levels suggesting it cannot discriminate well among patients.


CONCLUSIONS
Joint-pain comorbidities, in other than the primary affected joints, can be summed into a joint pain comorbidity score. Nevertheless, its use is discouraged for individual decision making purposes since its lacks discriminative power in patients with minimal or extreme joint pain.
Department of Psychology, Health & Technology, Arthritis Center Twente, University of Twente, Enschede, The Netherlands. L.siemons@utwente.nl
Liseth
L
Siemons
Peter M
PM
ten Klooster
Mart A F J
MA
van de Laar
Cornelia H M
CH
van den Ende
Thomas J
TJ
Hoogeboom
D015897:Comorbidity; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007596:Joints / Q000473:pathology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009426:Netherlands / Q000453:epidemiology; D015207:Osteoarthritis, Hip / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology; D020370:Osteoarthritis, Knee / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology; D010146:Pain / Q000175:diagnosis* / Q000453:epidemiology; D011594:Psychometrics / Q000379:methods; D015203:Reproducibility of Results; D057566:Self Report; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires