The purpose of this investigation was to test the German version of the intermittent and constant osteoarthritis pain score (ICOAP) in patients with advanced knee osteoarthritis. The ICOAP measures pain with 12 items divided in the two subscales "pain which comes and goes" and "permanent pain".
The reliability, the validity, the sensitivity to change, the practicability and the acceptance of this questionnaire were investigated in 120 patients with advanced knee osteoarthritis necessitating a total knee replacement. Retest reliability was determined in a subsample of 29 patients prior to hospital admission. Convergent construct validity was assessed by comparing the results of the ICOAP subscales and the overall score to the pain scales of the Western Ontario and McMasters University osteoarthrosis score (WOMAC) and the knee-injury and osteoarthrosis outcome score (KOOS). Sensitivity to change was determined by comparing the results of the ICOAP prior to admission with those assessed at discharge from hospital as well as 3 months after knee replacement surgery. To quantify the strength of associations between the ICOAP scales and the measures of validity as well as to test its reliability the Spearman correlation coefficient was calculated with an absolute value of "r" indicating the strength of a relationship. Sensitivity to change was assessed with an analysis of variance of the score results at the three different times of assessment. A p value of < 0.5 was regarded to be significant.
The reliability of this questionnaire was high, retest reliability ranged between r = 0.57-0.67, for the overall score as well as for the subscales. As a further criterion of reliability the internal consistency of the questionnaire was high as well, with r = 0.81-0.9. In comparison to the WOMAC pain scale, there was a concordance with r = 0.67 (overall score) and r = 0.68 (subscales). The pain scale of the KOOS correlated highly to the ICOAP scales. It ranged between r = 0.64 and r = 0.91. The review of sensitivity to change of this questionnaire showed a significant (p < 0.5) decrease of pain within three months after implantation of a total knee arthroplasty for the overall score as well as for both subscales. The median significantly decreased from 30.37 to 12.93 % for the overall score and from 16.77 to 7.07 or, respectively, 13.59 to 5.86 for the subscales. Practicability is given and the acceptancy in patients was high, with no drop-outs during this study.
With the validated German version of the ICOAP a questionnaire is available now which accurately measures pain in patients with advanced knee osteoarthritis.