Measures of pain and physical function in patients with low back pain

Abstract

The main aim of this study was to determine whether experimentally induced pain (EXP) and simple tests of physical function can augment the assessment of patients with low back pain (LBP). A second aim was to determine the relationships between measures of pain and function in patients with low back problems attending an outpatient physical therapy clinic. Twenty-three subjects with LBP and 23 pain-free, age- and gender-matched subjects participated. The EXP threshold was measured on the arm and back using pressure and pinch dolorimeters. Clinical pain (CP) was measured with two numerical rating scales, one for pain intensity and one for pain unpleasantness. Physical function was measured using the self-report Roland and Morris Disability Questionnaire, a timed walk and a loaded reach test. Measures were obtained at entry into the study (baseline) and 2 and 6 weeks later. Comparisons of experimentally induced pain and physical function were made between groups, and over time using multivariate analyses of variance. Relationships between EXP thresholds, clinical pain and physical function were examined using Pearson's correlation coefficients. The EXP thresholds did not differ between the LBP and control groups but physical function was lower in the LBP patients. Patients walked significantly slower and had lower pain thresholds during a controlled spinal loading test than subjects in the control group. The intensity of clinical pain did not change over time, but CP unpleasantness declined significantly. The EXP threshold was not related to clinical pain, physical function or disability. Moderate and significant relationships were found between pain and disability at all times. Walking speed was well correlated with disability and moderately correlated with pain intensity. The results of this study suggest that the EXP threshold has limited clinical utility. Assessment of clinical pain should include a measure of the affective component of pain. Walking speed is a simple test of physical function that is correlated with self-reports of pain and disability.