Is there a relationship between pain intensity and postural sway in patients with non-specific low back pain?

Seventy-seven patients with non-specific low back pain and a matching number of healthy controls were enrolled. Center of pressure parameters were measured by three static bipedal standing tasks of 90 sec duration with eyes closed in narrow stance on a firm surface. The perceived pain intensity was assessed by a numeric rating scale (NRS-11), an equal number of patients (n = 11) was enrolled per pain score.Generally, our results confirmed increased postural instability in pain sufferers compared to healthy controls. In addition, regression analysis revealed a significant and linear increase in postural sway with higher pain ratings for all included COP parameters. Statistically significant changes in mean sway velocity in antero-posterior and medio-lateral direction and sway area were reached with an incremental change in NRS scores of two to three points.COP mean velocity and sway area are closely related to self-reported pain scores. This relationship may be of clinical use as an objective monitoring tool for patients under treatment or rehabilitation.Increased postural sway is well documented in patients suffering from non-specific low back pain (NSLBP) [1] and a variety of theories exist regarding the effect of NSLBP on body sway. Postural control mechanisms are believed to be affected by damage to sensory tissues in the lumbar spine and trunk [2]. This deterioration of proprioceptive information reduces the accuracy of the sensory integration processes resulting in an imprecise estimation of the center of mass position [3], thereby inhibiting compensatory center of pressure (COP) shifts.Acute "pain interference" [4] has also been proposed as a possible cause with discharge from high-threshold nociceptive afferents in the low back interfering with spinal motor-pathways [5] and the motor cortex [6]. In addition, pain may cause an increased pre-synaptic inhibition of muscle afferents [7] and affect the central modulation of proprioceptive spindles of muscles [8],