Assessment of chronic pain behaviour: reliability of the method and its relationship with perceived disability, physical impairment and function.

The aim of the present study was to develop a reliable assessment of pain behaviour performed during the execution of a range of functional assessment measures. For the initial reliability study 18 subjects (consecutive referrals) were assessed. Subjects were observed and videotaped during a variety of physical tasks and demonstrations of pain behaviour were recorded; the videotapes were scored by two independent observers on two occasions. The relationships between pain behaviour, distress and physical function and impairment were also investigated in a group of 51 patients with chronic back pain. Self-report of disability and pain intensity were assessed using the Finnish version of Oswestry disability questionnaire and the pain visual analogue scale (VAS). Depression and somatic perception were assessed using the modified Zung and modified somatic perception questionnaire. The Tampa scale for kinesiophobia was used to evaluate fear of movement and (re)injury. The results of the intra- and interobserver reliability study demonstrate good to excellent levels of agreement. The exception was facial expression (kappa 0.29), which was excluded from the final instrument. There was a strong correlation between pain behaviour and subjective pain report and disability (p < 0.01). The correlations between total pain behaviour and performance of physical function tasks is striking (p < 0.01). Subjective disability was analysed by means of multiple regression analysis. Pain measured on the VAS was the most important variable explaining 36% of the variance, pain behaviour and pain combined explained 48% of the variance for self reported disability. In conclusion, this functional videobased assessment of pain behaviour is a reliable measure of pain behaviour. The total scores for pain behaviour correlate with tasks that involve the back; tests involving upper limbs were not affected. This test is suitable for the assessment of those with pain problems specifically involving the back. Furthermore, in the group studied pain and pain behaviour were the two most important determinants of self-reported disability.