Workplace analysis for regional pain syndrome: the development and application of posture measurement model and cervical assessement tools for reducing the risk of regional pain syndrome

Work-related musculoskeletal disorders are widespread in industrialised countries and represent a serious work-related health concern. Work-related musculoskeletal disorder is an umbrella term used to describe a wide range of specific and non-specific complaints. It includes regional pain syndrome (RPS) and fibromyalgia (FM), which are regional and general chronic non-specific musculoskeletal pain syndromes, respectively. Non-specific pain syndromes are common in the general population. Sufferers experience significant chronic pain and discomfort. Unfortunately, a definitive aetiology for these syndromes is still unclear. Knowledge about causative factors would be very helpful in assessing risks associated with the onset of these pain syndromes. It is believed by rheumatologists that chronic non-specific musculoskeletal pain syndromes are caused by dysfunctional pain modulation. Augmentation of pain stimulus, via mechanisms of peripheral and possibly central sensitisation, are believed to play a critical important role in the pain manifestations associated with RPS and FM. However, this information has not been effectively conveyed to other disciplines. The ergonomics community has not recognised the potential neurogenic basis for chronic musculoskeletal pain. Hypersensitivity of the pain system in chronic musculoskeletal pain, including the dorsal horn cells in the central nervous system, has not been greatly discussed by this discipline. In addition, the rheumatology and pain physiology fields have not investigated to a great extent the potential contribution of workplace ergonomic risk factors to the onset of non-specific pain syndromes, including RPS and FM. Consequently, it is not clear how workplace ergonomic exposures may act as aetiological factors in chronic musculoskeletal pain. There is significant opportunity for the disciplines of ergonomics, rheumatology and pain physiology to combine knowledge when examining the associations between workplace ergonomic risk factors, dysfunction of the pain system and non-specific musculoskeletal pain. This thesis uses knowledge from these different research fields to explore the relationship between the specific ergonomic risk factors of poor and static working posture and the development of RPS and FM characteristics. The literature is initially examined for possible aetiological factors of RPS and FM. Putative pathophysiological peripheral and central pain mechanisms involved with RPS and FM are reviewed. Research conducted in this thesis showed that exposure to poor and static working postures, particularly of the cervical spine region, increased pain sensitivity and selfreported pain in healthy people. Furthermore, it was demonstrated that the work action characteristics of a task significantly influenced pain sensitivity. The work action characteristics of the neck were varied during a computer based work task and this intervention significantly changed the amount of pain sensitivity and self-reported pain. Hence, the postures and actions of the neck can be very important in changing how the pain system modulates pain. Long-term exposure to the postures and actions described in this research increased the risk of RPS developing and, therefore, should not be undertaken as part of daily work. It was concluded that pathophysiological pain mechanisms should be included as risk factors for chronic musculoskeletal pain. This research added to the limited understanding of the relationship between ergonomic postural risk factors and change in pain sensitivity. As well, this research supported the measurement of pain sensitivity in ergonomic work investigations, a measurement that is not normally used by ergonomists in workplace investigations. More research is needed to inform the development of better ergonomic guidelines (including better workplace analysis tools), with the ultimate goal of decreasing the risk of development of non-specific musculoskeletal pain. A new posture measurement system was developed specifically for this research. This tool assisted in understanding the postural and action characteristics of the computer task. This system utilised an electromagnetic tracking system to measure the motion and posture of participants. A computer application was developed that applied kinematic transformations to convert raw data from the tracking system to meaningful postural data. This custom computer application assessed the actions of the measured task based on a pre-determined motion-time standard, and displayed the results both textually and through animation. As motion-time standards are based on manual assessment methods, the new posture measurement system and computer application represented a significant advancement for work action analysis. There is potential for this advanced tool to assist ergonomists in understanding the posture and work action characteristics of a work task. In this thesis, particular attention was also paid to cervical spinal factors. The concept of 'spinal dysfunction' and its importance in the aetiology of RPS and FM was explored. A new device was developed in this thesis for the measurement of cervical stiffness and mechanical pressure pain, to assess cervical spine function. This device was used in an experiment to explore cervical spinal stiffness and pain in both FM patients, chronic neck pain patients, and healthy participants. Results from the pain measurements, and other clinical measures, supported the hypothesis that the symptomatic participants had dysfunction of the axial musculoskeletal system in the cervical spine. The conclusion from this research was that abnormalities of spinal function and aberrant pain modulation mechanisms in the symptomatic participants (possibly including central pain factors) may be associated with clinical features characteristic of RPS and FM. Consequently, spinal dysfunction is possibly a factor involved in the aetiology of chronic non-specific musculoskeletal pain syndromes.