The reliability and validity of pain threshold measurements in osteoarthritis of the knee.

The purpose of this study was to examine the reliability and validity of measuring pain threshold (PT) of persons with osteoarthritis (OA) of the knee. The PTs of women with and without OA of the knee were measured on 3 occasions at 6 sites at the knee with a pressure dolorimeter. Subjects with OA also recorded their pain on a visual analogue scale (VAS) and on the McGill Pain Questionnaire (MPQ). The reliability coefficients for repeated measures of PT varied from 0.61 to 0.91 in the OA group and from 0.71 to 0.90 in the control group. PT was lower in the OA group at all sites. Only the control group demonstrated significant differences between sites. The correlations between PT and measures of pain intensity were poor. It is concluded that the measurement of PT at the knee distinguishes OA from healthy controls, and that it has moderate reliability. However, it cannot substitute for a measure of pain intensity.