Low back pain and postural control, effects of task difficulty on centre of pressure and spinal kinematics
Introduction
Postural control (PC) of the trunk when standing is regarded essential to keep or regain one's body position for stability and orientation, within challenging environments [1]. Postural control strategies are described as a feedback mechanism derived by the interaction of sensory input and adapted motor output [1]. Postural control strategies on firm ground with open eyes predominantly use peripheral or ankle strategies for the sagittal plane [2], [3]. In contrast the frontal plane control-mechanisms are described as proximal or hip loading/unloading strategies [3]. In a recent review changes in postural control sway excursions in patients with non-specific low back pain (NSLBP) compared to asymptomatic controls were inconsistently reported in previous studies [4]. Some studies showed impaired postural control in the presence of LBP with increased body sway, sway velocity and loss of balance [5], [6] others did not find any differences in body sway or sway velocity [7], [8]. Possible reasons for these contradictory reports are the differences in tasks and conditions used in those studies [7], [9], [10]. Most studies evaluate centre of pressure (COP) movements using force plate technology [5], [8], [11]. However, range and velocity of segmental adaptations in thoracic, lumbar and hip segments cannot be described by COP variables, as only kinematic models can adequately account for segmental and directional strategies [6], [9], [10], [12], [13], [14], [15]. One recent study used additional kinematic measurements to evaluate hip and trunk control strategies in the sagittal plane while standing [5], [8]. Two electrogoniometers were placed over the first thoracic vertebra and the second sacral vertebra. They assessed sagittal plane kinematics and the mean position of the trunk. They found, that patients with LBP have larger forward trunk inclination during demanding PC tasks. Further kinematic measurements of body segments might even better discern differences in PC strategies of LBP patients and asymptomatic controls.
To date, no research evaluated movements of the thoracic and lumbar spine and the hip in the frontal and sagittal plane parallel with COP measurements during standing PC tasks.
Therefore the aim of this study was to examine the sway of the thoracic and lumbar spine, the hip and COP during three standing tasks conditions with increasing PC requirements in patients with NSLBP and asymptomatic controls. The research questions were (a) does the presence of LBP affects sway and sway velocity and are PC strategies different in asymptomatic controls and those with NSLBP, (b) how does changing the task difficulty in terms of visual and surface condition influences sway and sway velocity of the thoracic and lumbar spine, the hip and COP.
Section snippets
Subjects
Participants between 18 and 65 years were recruited at physiotherapy-practices, the university campus and by newspaper advertisements. Included were patients with NSLBP for longer than 4 weeks with at least moderate disability, defined as an Oswestry-disability-index (ODI) >8% and a low level of having biopsychosocial risk factors defined with less than 4 points in the STarT Back Screening tool [16], [17]. Excluded were subjects with specific LBP, vertigo or disturbance of the equilibrium,
Results
Fifty-seven patients with NSLBP and 22 asymptomatic controls from the local area were included (Table 1).
Subjects completed all tests with the exception of condition 3 (Blind-Foam). Three asymptomatic controls and four patients with NSLBP could not remain in the required position for 60 s.
Due to technical problems with the sensors there were two missing values in the variables of the hip and lumbar spine, respectively (1 patient, 1 control). Technical problems with the balance board led to
Discussion
Different adaptation strategies in postural control between NSLBP patients and asymptomatic controls were found for frontal plane variables of the trunk when the visual condition changed from open eyes to blindfold. This indicates that NSLBP patients need adaptive PC strategies using trunk movements, while in control subjects, hip loading/unloading strategies and a stable trunk suffices. Significant gender and age effects were demonstrated, with less MADpos and slower MADvel in men in six out
Conclusion
The current study states that increasing standing tasks difficulties affect COP, hip and spine control strategies in both sagittal and frontal planes. The frontal plane postural control mechanism measured directly on the spine using inertial movement sensor technology, differ between NSLBP patients and asymptomatic controls, when visual condition changes. These differences could not be detected by COP measurements alone and are valid, if the stance width is small, i.e. feet together. Mean
Acknowledgements
This work was supported by the Commission of Technology and Innovation of Switzerland, 12413.1. PFES.ES. The authors would like to thank All participating subjects, Valentine L. Marcar for English revision and Hocoma AG, Switzerland, for providing the Valedo Research Software and technical support.
Conflict of interest statement
None of the authors are aware of any financial or personal relationships with other people or organisations that could improperly influence this work.
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