Whiplash injury results in persistent pain and disability for a significant number of individuals. Clinically, these individuals present with a complex presentation of physical features (including central hyperexcitability and motor dysfunction) and psychological manifestations (e.g. psychological distress, pain catastrophization and posttraumatic stress symptoms) that may be resistant to conservative care. Understanding this complex symptom presentation is made challenging by the inability of current diagnostic imaging techniques to clearly identify potential pathoanatomical causes for these symptoms. Nevertheless, anatomical structures contributing to chronic whiplash associated disorders (WAD) have been identified in clinical and basic science research. Diagnostic facet joint injections implicate the cervical facet joint as the most likely anatomical structure responsible for neck pain in individuals with chronic WAD. Basic science research has also provided empirical evidence of a possible association between nociception in the cervical facet joints and the clinical features of WAD, in particular behavioural hypersensitivity (quantified pain response following stimulation with a non-noxious stimulus).
Individuals with cervical facet joint-mediated pain respond favourably to radiofrequency neurotomy (RFN), with significant reductions in neck pain and psychological distress. Yet it is unknown whether persistent cervical facet joint nociception contributes to the clinical features evident in individuals with chronic WAD, and whether effective modulation of this nociception through RFN improves these features. There has been no detailed study of the relationship between cervical facet joint nociception and the variety of clinical features demonstrated in individuals with chronic WAD. The primary aim of this thesis was to determine if the physical and psychological manifestations of chronic WAD could be effectively modulated through successful response to RFN. The null hypothesis was that reducing nociception via successful RFN would not result in improvements in central nociceptive processing, motor function or psychological features of chronic WAD.
A series of studies was undertaken to test the hypothesis for this body of research. Data were collected using a range of clinical psychophysical, physical and psychological tests pertinent to chronic WAD: thermal and pressure pain thresholds (PPT), nociceptive reflex threshold (NFR), cervical range of movement (ROM) and cranio-cervical flexion test (CCFT); and questionnaires of self-reported pain (visual analogue scale: VAS) and disability (neck disability index: NDI), general well being (general health questionnaire (GHQ-28), pain catastrophization (PCS) and psychological distress (Post Traumatic Stress Diagnostic Scale: PDS).
Study 1 compared the outcome of these tests between participants, aged 18-65 years, who successfully responded to diagnostic facet joint injections (n=58); individuals who did not respond (n=32), and healthy controls (n=30). The results demonstrated no differences in clinical features between those who responded and did not respond to cervical facet joint injections, with both groups significantly differing from the healthy controls. Both WAD groups demonstrated generalized sensory hyperexcitability, loss of neck ROM and increased sternocleidomastoid muscle activity during the CCFT, and similar psychological features, although increased pain catastrophizing was evident in the group who did not respond to the facet injections.
Studies 2-4 focussed on the individuals who responded to diagnostic facet joint blockade and proceeded to RFN. For these studies, participants attended the research laboratory at two time periods prior to RFN (after the diagnostic facet joint injections had been performed when original symptoms returned: t(1); and then immediately prior to RFN being performed – approximately 12 months later: t(2)); and then at one- (t(3)) and three-months (t(4)) post-RFN and finally when pain returned (t(5)). The clinical measurements were taken at each time point. The results indicated that following RFN, most physical and psychological measures improved significantly, apart from post traumatic stress symptoms (Study 2 and 3). Upon the subsequent return of the participants’ neck pain, most physical (except PPTs and CCFT electromyography) and psychological measures returned to pre-RFN values (Study 4).
Study 5 investigated whether any physical or psychological clinical manifestations predicted a successful response (defined as a Global Rating of Change questionnaire score of ≥ 4) to RFN. The results of this study indicated that lower levels of disability or pain catastrophizing independently predicted a successful response.
The null hypothesis for this body of research was rejected. The results suggested that peripheral nociception contributes to central hyperexcitability, motor dysfunction and psychological manifestations (except post-traumatic stress symptoms) of chronic WAD. These results provide further knowledge of processes underlying chronic WAD. The finding that peripheral nociception is one of the drivers of central hyperexcitability, motor dysfunction and psychological manifestations in chronic WAD is a vital step forward towards more effective management for this difficult patient group, allowing healthcare providers to provide patients with appropriate treatment options, especially when conservative therapy has failed.