Elsevier

Clinical Biomechanics

Volume 14, Issue 10, December 1999, Pages 710-716
Clinical Biomechanics

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

https://doi.org/10.1016/S0268-0033(99)00025-XGet rights and content

Abstract

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.

Relevance

A reliable measure of whole body performance obtained during simple postural tasks, such as the root mean square in the medial–lateral plane, may be used to distinguish chronic low back pain patients as a group from a healthy population. Further uses may include the development and guidance of chronic low back pain treatment and evaluation of recovery progress.

Introduction

The evaluation of chronic low back pain (CLBP) is difficult due to the lack of suitable outcome measures available. The majority of CLBP studies have focussed on the trunk solely. However, the trunk is part of a system, the human body. In addition to specific trunk measures, performance of the entire body should be considered to guide treatment and measure progress during recovery. We were interested in evaluating the influence of CLBP on balance control as a measure of whole body performance.

Trunk specific CLBP assessment involves measurement of static and dynamic trunk extensor and flexor strength [1], [2], measurement of trunk extensor and flexor endurance [3], and quantification of the spinal range of motion [4]. Also muscle function including the fatiguability of the extensor musculature [5], [6], the magnitude of trunk muscle activation [7], [8], [9], the activation patterns of the trunk musculature [10], and the flexor-relaxation response [11] have been evaluated. A measure of whole body performance is balance which relies on three interacting sensory systems; vestibular, proprioceptive and visual. By challenging these systems their contribution to balance control can be studied. Vestibular input is challenged by tilting the head backwards [12] or by applying galvanic stimulation [13]. Proprioception can be altered by changing the support surface compliance (e.g. firm versus foam) or by activating muscle spindles through tendon vibration [14] and visual input can be varied by opened versus closed eyes [15]. The majority of balance control studies involve people with vestibular impairments [16], neurological disorders [17], and cerebellar syndromes [18]. Balance control of the elderly, whose balance may be impaired because of disease and aging, has been studied [19], [20].

Only a few balance control studies have been performed on chronic neck and back pain patients. McPartland et al. [21] found a decrease in balance control in chronic neck pain patients compared to healthy controls under various conditions in upright standing using force plate measures. Chronic pain patients frequently mention poor balance control [22]. A 30 s 1-leg stance test was designed in which the number of times the non-weight bearing foot touched the ground and the elapsed time to the first touch was recorded. Unfortunately, this test showed poor test-retest reliability. Byl and Sinnott [23] found that, in general, low back pain patients had greater postural sway compared to healthy controls under certain conditions in upright standing. Low back pain patients also positioned their centre of pressure (CoP) posterior to the healthy participants position and they were less likely to be able to balance on one foot with their eyes closed compared to healthy people.

The purpose of this study was 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. It was also determined whether balance measures were correlated with pain and disability reported by CLBP patients. Finally it was determined whether measures of balance control were reliable which is necessary to quantify postural control and to provide insight into changes related to CLBP.

Section snippets

Methods

Participants: Eight chronic low back pain patients, five males and three females, participated in this study (height 1.79 m, s.d.=0.11; age 38.4 yrs, s.d.=12.5). Inclusion criteria was the presence of back pain in the lumbar region with a duration of at least 3 months prior to testing. The patients recruited in this study reported a duration of back pain which far exceeded this inclusion criterion (mean 10.9 yrs of back pain, s.d.=10.2). Patients who reported specific balance problems (e.g.

Group differences

The mean performance of the CLBP patients was comparable to the mean performance of the healthy participants for the least challenging postural task (task 1). Fig. 1a shows the RMS in anterior–posterior direction (RMSx) which increased for CLBP patients when the eyes were closed during both the upright standing task (task 2) and lean forward task (tasks 6). However, the RMS in medial–lateral direction (RMSz) showed significant differences between the two groups in upright standing with the eyes

Discussion

The RMS of the centre of pressure in medial–lateral direction is a reliable and sensitive measure which can detect increases in postural sway of a group of CLBP patients compared to a healthy group during tasks which challenged visual input only (upright standing with the eyes closed; task 2) but especially during tasks which involved increased task complexity in addition to the removal of visual input (forward leaning with the eyes closed; task 6). Task 4, which challenged multiple balance

Conclusions

It was concluded that the RMSz in medial–lateral direction was reliable and sensitive enough to measure increased postural sway of CLBP patients as a group compared to a healthy population during tasks which challenged visual input only but especially during tasks which involved increased complexity in addition to challenged visual input (upright standing with the eyes closed and forward leaning with the eyes closed, respectively). Care must be taken when evaluating individual CLBP patients

Acknowledgements

We would like to thank Matthew Webster for his help during data collection and reduction. This study was supported by funding from the Canadian Memorial Chiropratic College in Toronto.

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