Intensity of chronic pain modifies postural control in low back patients

Abstract

OBJECTIVE: Some recent studies have provided evidence that alteration in central motor control may have causative impact on the emergence and sustenance of chronic pain. We hypothesized that comparison of postural control between patients with high (HP) and low pain (LP) level would display intergroup differences in favour of the LP group lending support for the postulated relationship between altered cortical function and pain. METHODS: Motivated by this concept, we investigated postural control in 36 subjects with chronic low back pain (CLBP) stratified into two groups according to the reported rest pain intensity on a numerical rating scale: LP group (n = 16) and high pain (HP) group (n = 20). The pressure pain threshold (PPT) of selected muscles was assessed on the involved and uninvolved sides. Body balance was investigated on hard or soft surface using postural performance. RESULTS: As regards pain measurements, the PPT of muscles was lower in HP than in LP (P < 0.05), without differences between the involved and uninvolved sides. Results indicated that patients in HP group relied more on visual input on hard surface than those in LP group (P <0.05). Changing the stance condition from hard surface to foam decreased sway entropy in LP (P < 0.001), accounting for higher cognitive investment in balance control, while HP had the same level of sway entropy. CONCLUSIONS: Body balance measurements seemed to confirm the hypothesized role of the altered executive function in the CLBP problems, with a further support from pain assessment that indicated central sensitization. Patients with higher self-reported pain level displayed deficit in the postural adaptability to environmental challenge and lower level of postural automaticity.