Balance in chronic low back pain patients compared to healthy people under various conditions in upright standing

Objective. To determine whether balance responses of chronic low back pain patients differed from healthy controls under various upright standing conditions which challenged the balance system. Methods. Eight chronic low back pain patients and eight controls performed seven postural tasks which involved manipulation of visual, vestibular, and proprioceptive input as well as body orientation. The unbiased root mean square, the mean power frequency and the mean position of the centre of pressure were calculated from force plate readings. A pain scale and two questionnaires were used to evaluate the severity of disability and the scores were correlated with the force plate measures. The reliability of the force plate measures was determined. Results. A significant increase in the root mean square in the medial-lateral direction for the chronic low back pain patients as a group was found during tasks which involved removal of vision, especially when combined with increased task complexity. The root mean square and mean power frequency in the medial-lateral plane were reliable for the majority of the tasks. Conclusion. The root mean square in the medial-lateral direction was reliable and sensitive enough to measure an increase in postural sway of chronic low back pain patients as a group compared to healthy controls when the task involved increased complexity and removal of visual information. (C) 1999 Elsevier Science Ltd. All rights reserved.