Pressure pain thresholds in patients with chronic nonspecific low back pain

BACKGROUND: The lumbar back and hip muscles are important for a normal functioning of the human spine and they are considered to be of etiological significance in chronic nonspecific low back pain (nCLBP). Inactivity and a lower level of physical activity in patients with nCLBP may change muscle characteristics and may be associated with pain and disability. Pressure algometry has been found to be non-invasive, efficient and reliable in the exploration of physio-pathological mechanisms involved in muscle pain syndromes. The subjective characteristic of the pressure pain thresholds (PPTs) cannot be avoided once it is the very objective of the measurement, i.e. the minimum pain perceptible by the person, is a subjective factor. Most studies have revealed gender differences between PPTs, with females showing lower thresholds. OBJECTIVE: to determine whether demographic variables and PPTs, are related pain intensity and a disability in patients with nCLBP. METHODS: One hundred and twenty-four patients with nCLBP were included in the study. The Visual Analogue Scale (VAS) and the Roland-Morris Questionnaire for Low Back Pain (RM) were used to evaluate the intensity of pain and degree of disability. The PPT was performed from L1 up to S2 dermatomes, at the muscles over the Gluteus medius, minimus and maximus, including a point located at the level of the piriformis, at the Quadratus lumborum, at the Iliopsoas and points of reference located at the level of the L1 up to L5 ligaments. The pain intensity was assessed by visual analogue scale (VAS) and the lumbar function by Roland Morris questionnaire (RM). Multiple linear regression models were used for both the VAS and the RM. RESULTS: No significant differences were found between the PPTs measured at either left or right limb. The mean VAS value was 7.3 (+/- 1.5) and the RM score was 14.2 (+/- 5.3). The PPT-values showed significant negative correlations to the VAS and the RM. The highest correlation between the mean VAS and PPT-values were found at the level of the Gluteus medius (r = -0.34, p < 0.001), which was the only measurement correlated to the intensity of pain (r(2) = 0.11, p < 0.001). The RM was correlated to the BMI, the level of education and the PPT values at the level of the Iliopsoas muscle and the L4-L5 supraspinous ligament. CONCLUSIONS: This study showed that most PPT values are correlated to the VAS and the RM. Nevertheless, the variability explained by PPT values and demographic characteristics was low for pain intensity and function.