Arthritis Research UK Pain Centre

Measuring intermittent and constant osteoarthritis knee pain

Moreton BJ, Wheeler M, Walsh DA, Lincoln NB. Rasch analysis of the intermittent and constant osteoarthritis pain (ICOAP) scale. Osteoarthritis and Cartilage 2012, 20(10), 1109-1115.

Key findings and importance of study

Many pain questionnaires measure overall pain experienced by people. Such tools may, however, fail to detect differences in the type of pain experienced. We tested a questionnaire that measures intermittent and constant pain, and found that it is an accurate measure of pain in people with knee osteoarthritis. As a result, we are now able to measure osteoarthritis pain more precisely.



ICOAP* is the first questionnaire to consider Intermittent and Constant OsteoArthritis Pain reported by patients. Constant pain is described as “pain that is there all the time, although it may vary in intensity”, and intermittent as “pain that comes and goes”. However, concerns have been raised over the ability of the ICOAP to measure these different types of pain reliably.

*Hawker et al., 2008 


Aim of the study

We wanted to examine whether the ICOAP questionnaire can measure intermittent and constant pain separately, or whether the total score should be used as a general measure of pain.

How the study was carried out

People with knee osteoarthritis were recruited from hospital clinics and a previous study, and asked to take part in a postal survey which included the ICOAP and other questionnaires. Results from the ICOAP were analysed and compared with another questionnaire (SF-36 pain subscale) using a statistical method called Rasch analysis.

What the study found

We approached 474 people for this study and 175 took part in the survey (37% response rate). Ninety-one of the respondents were female and 84 male, and the average age was 66.

We found that the ICOAP questionnaire is an accurate measure of intermittent and constant pain in people with knee osteoarthritis. We also found that separate scores for these two types of pain were better measures than a total score for general pain. It is therefore recommended that researchers and clinicians wishing to use this questionnaire refrain from using the total score.

Significance of the study to Pain Centre’s research

This study is part of the Pain Centre’s work to compile a set of questionnaires that can be used to measure the complex and diverse nature of pain in osteoarthritis.





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