Full length articleAn exploratory study examining factors underpinning postural instability in older adults with idiopathic neck pain
Introduction
The cervical spine plays a critical role in sensorimotor function. Abundant cervical mechanoreceptors are important in integrating multisensory afferent input from the vestibular, visual, proprioceptive and central nervous systems (CNS). Individuals with NP have demonstrated sensorimotor disturbances, amongst which is the negative impact of NP on postural stability [1]. Of greater relevance is that older adults with NP have demonstrated poor dynamic postural stability placing them at a higher risk of falls [2]. The potential serious consequences of falls and the burden it imposes on public health [3] highlights the need for a comprehensive assessment to inform intervention for this population. Unfortunately, there is limited understanding of the fundamental mechanisms underlying NP related postural control deficits.
Because of the multi-sensory complex nature of postural control, it is important to explore whether other factors that might negatively impact on postural stability such as physical activity levels, lower limb sensory and motor function, and vestibular and visual function are different in older adults with and without NP. First, level of physical-activity has been negatively associated with onset of NP [4]. Lower levels of physical activity may be associated with poorer lower limb function such as reduced strength and flexibility [5] and consequently contribute to a decrease in postural stability in older adults with NP. In particular, big toe flexor strength [6], range-of-motion [7], light touch sensation [8] and ankle vibration sense [9] have been closely associated with postural stability in older adults. Second, a disruption in the dynamics between the intimately blended systems involved in sensorimotor control could be expected in older adults with neck pain (NP) [1]. This is not only due to diminished cervical proprioception but also a progressive decline in vestibular, visual and CNS function with ageing. Moreover, vestibular dysfunction and specific to vision, deficits in visual contrast sensitivity, have been associated with increased falls risk [10], [11], hence supporting the need to explore vestibular and visual function in older adults with NP.
As a preliminary step towards understanding mechanisms contributing to the development of postural control deficits in older adults with NP, in addition to clinically relevant balance measures and standard centre-of-pressure (CoP) measures, we will use analytical techniques of wavelet analysis. This technique decomposes the postural sway data into multiple independent frequency distinct bandwidths each hypothesised to identify with physiological significance of postural movements associated with muscular proprioception (1.56–6.25 Hz) [12], cerebellar (0.39–1.56 Hz) [12], vestibular (0.10–0.39 Hz) [13] and visual (<0.10 Hz) [14] systems.
Given the aforementioned background, this cross-sectional, exploratory study sought to understand the mechanisms underlying postural control deficits in older adults with and without NP by (i) comparing several features that might relate to impaired postural stability but not directly related to the cervical spine to determine their influence, including level of physical-activity, lower limb, vestibular and visual function, as well as (ii) employing the use of wavelet analysis of standing balance. We hypothesized differences between groups in the level of physical-activity, lower limb, vestibular and visual function and that wavelet analysis will demonstrate changes in frequency measures in the NP group.
Section snippets
Participants
This cross-sectional study involved 84 older adults with (n = 35, mean age 69.63 ± 6.3 years) and without (n = 49, mean age 69.5 ± 4.9) idiopathic NP. Participants aged 60 years and older were recruited using convenience sampling. Participants were given an option of location of testing; either at the research laboratory or at their residence. Participants were included in the NP group if they reported chronic NP for ≥3 months, neck disability index (NDI) of ≥10% (worst) and neck-related pain intensity
Statistical analysis
Descriptive analyses compared demographic and clinical characteristics between groups. Wilcoxon-Mann-Whitney or Welch-t tests compared continuous data and Fisher’s Exact, Chi square or linear by linear tests was used to test for differences in proportions. Regression analysis was performed to adjust for potential confounding variables (number of co-morbidities, BMI and fall history). All statistical calculations were performed using the STATA version 11.0 statistical software. Statistical
Results
Table 1 compares the demographic and clinical characteristics between groups. Physical-activity level, lower limb motor and sensory function, vestibular function and visual contrast sensitivity were similar in both groups (p > 0.05). Older adults with NP obtained poorer ABC (p = 0.01), lower DGI (p = 0.02) and higher DHI scores (p < 0.01). By design, older adults in the NP group showed significantly higher NDI compared to healthy controls (p < 0.001). Number of co-morbidities and BMI showed trends
Discussion
In this exploratory cross-sectional study, we compared various physical function tests and characteristics in older adults with and without NP. Contrary to our hypothesis, there were no significant differences in physical activity level, big toe strength, ankle range-of-motion, lower limb light touch and vibration sense, vestibular function and visual contrast sensitivity. In addition, the NP group had lower balance confidence (p = 0.01) and greater dizziness handicap (p < 0.01). As expected, older
Limitations
The results of this study must be interpreted in the light of our study limitations. Firstly, whilst the vestibular tests selected were clinically relevant, they may lack precision to detect subtle deficits in eye movement, and may increase the likelihood of under reporting vestibular impairments. Nevertheless, subjects with obvious vestibular pathology were excluded from the study. Secondly, given the way the DHI was structured, misinterpretation of questions to represent the neck problem and
Conclusion
In conclusion, the results of our study indicate that NP related postural control deficits in older adults may not be associated with the level of physical-activity, lower limb motor and sensory function, vestibular function and visual contrast sensitivity. The changes in postural activity are most likely due to NP and associated musculoskeletal impairments altering cervical proprioceptive input to the sensorimotor control system. Wavelet analysis suggests, sensory reweighting was in place to
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgements
We are grateful to all participants who volunteered for this study.
June Quek received a PhD scholarship funded by Singapore General Hospital. Author RAC is supported by a National Health and Medical Research Council R.D. Wright Biomedical Fellowship (#1090415). This played no role in any aspect of the study. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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References (36)
Sensorimotor disturbances in neck disorders affecting postural stability, head and eye movement control
Man. Ther.
(2008)- et al.
New insights into neck-pain-related postural control using measures of signal frequency and complexity in older adults
Gait & Posture
(2014) - et al.
ISB Clinical Biomechanics Award 2009: toe weakness and deformity increase the risk of falls in older people
Clin. Biomech.
(2009) - et al.
Comparative reliability and validity of chronic pain intensity measures
Pain
(1999) - et al.
Normative values of vibratory perception in 530 children, juveniles and adults aged 3–79 years
J. Neurol. Sci.
(1998) - et al.
ISB Clinical Biomechanics Award 2009: toe weakness and deformity increase the risk of falls in older people
Clin. Biomech.
(2009) - et al.
Validity and reliability of the Nintendo Wii Balance Board for assessment of standing balance
Gait Posture
(2010) - et al.
Standing balance post total knee arthroplasty: sensitivity to change analysis from four to twelve weeks in 466 patients
Osteoarthritis Cartilage
(2017) Human balance and postural control during standing and walking
Gait Posture
(1995)- et al.
Assessment of standing balance deficits in people who have undergone anterior cruciate ligament reconstruction using traditional and modern analysis methods
J. Biomech.
(2014)