Open Access Research article

Validity of summing painful joint sites to assess joint-pain comorbidity in hip or knee osteoarthritis

Liseth Siemons15*, Peter M ten Klooster1, Mart A F J van de Laar12, Cornelia H M van den Ende3 and Thomas J Hoogeboom4

Author Affiliations

1 Department of Psychology, Health & Technology, Arthritis Center Twente, University of Twente, Enschede, The Netherlands

2 Department of Rheumatology, Arthritis Center Twente, Medisch Spectrum Twente, Enschede, The Netherlands

3 Department of Rheumatology, Sint Maartenskliniek, Nijmegen, The Netherlands

4 Department of Epidemiology, CAPHRI, CCTR; Maastricht University Medical Centre +, Maastricht, The Netherlands

5 Department of Psychology, Health & Technology, Faculty of Behavioural Sciences, University of Twente, PO Box 217, 7500, AE, Enschede, the Netherlands

For all author emails, please log on.

BMC Musculoskeletal Disorders 2013, 14:234  doi:10.1186/1471-2474-14-234

Published: 9 August 2013



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.


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.


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.


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.

Hip or knee osteoarthritis; Joint-pain comorbidities; Rasch analysis; Sum score; Validity