MAGNETIC RESONANCE IMAGING OF THE CERVICAL EXTENSOR MUSCULATURE IN PERSISTENT WHIPLASH ASSOCIATED DISORDERS (WAD): RELATIONSHIP WITH SIGNS AND SYMPTOMS OF CHRONIC WAD

Ongoing pain and disability is not uncommon in 20-60% of persons following a whiplash injury. A number of causes for symptom persistence have been suggested, but current diagnostic imaging techniques have not clearly identified pathoanatomical causes. As a result, there continues to be long-standing acrimony about whether persistent pain is attributable to a salient structural physical pathology or to other underlying processes. Nevertheless qualitative observations have been made on MRI of fatty infiltrate in the sub-occipital extensor muscles in chronic neck disorders and these have been aligned with a decrease in standing balance and EMG abnormalities in the rectus capitis posterior minor muscles reasoned to be related to a denervation of the C1 dorsal ramus. However there has been no systematic quantitative evaluation of the presence of fatty infiltrate in the extensor muscles in chronic whiplash and no detailed study of the relationship of any fatty infiltrate to symptomatic and physical features. The aim of this thesis was to establish a MRI measure to quantify muscle/fat constituents in cervical extensor muscles as well as to investigate any relationship between musculature degeneration (fatty infiltrate, atrophy) and sensory, physical or psychological features in female subjects with chronic whiplash associated disorders (WAD). This thesis reports a series of studies which make up this body of research. A conventional MRI measure was developed to analyze signal intensities for cervical extensor muscular fat content. Clinical tests which have shown to characterize the chronic condition were also examined: thermal and pressure pain thresholds, cervical range of movement (ROM), joint position error (JPE), and questionnaires of self-reported pain and disability (neck disability index (NDI); dizziness handicap inventory (DHI)); general well being (general health questionnaire (GHQ-28), Short-Form-36 (SF-36) and psychological stress (Impact Events Scale (IES); Tampa Scale of Kinesophobia (TSK) were collected. Comparison was made between 79 female subjects, aged 18-45 years with chronic WAD and 34 healthy female controls of similar ages. A final study was conducted in which subjects with chronic insidious onset neck pain were examined to assess whether the findings of fatty infiltrate were peculiar to chronic WAD or were generic to chronic neck pain disorders. The outcomes of the studies present the development of a reliable MRI measure for cervical muscle/fat constituents as well as muscle morphometry. It was determined that age, body mass index and activity levels did not influence muscular alterations in both asymptomatic and symptomatic subjects. Physical, sensory, motor and psychological impairments were found in subjects with chronic WAD but not in healthy controls or insidious onset neck pain. The presence of muscular degeneration was identified in subjects with chronic WAD. It was widespread involving all extensor muscles, but higher indices of fatty infiltrate were found in the sub-occipital and multifidus muscles, especially at the C3 level. Nevertheless the fatty infiltrate was not strongly related to clinical features, with only marginal relationships being observed between cervical ROM, JPE, thermal/pressure thresholds and psychological stress. Nevertheless all of the WAD subjects demonstrated widespread fatty infiltrate in combination with impairments that typically characterize the chronic condition, suggesting that chronic WAD represents a complex, debilitated state. Widespread fatty infiltrate was not found in subjects with insidious onset neck pain, suggesting this is a feature characteristic of WAD. The mechanisms for the development of fatty infiltrate in chronic WAD could not be determined from this thesis but its presence underpins the need to further utilize advanced MRI techniques to better determine the origin behind these changes. This research is a vital step forward towards a more accurate identification and diagnosis for those who continue to suffer in the long-term following a whiplash injury. Future research should include a more heterogenous sample of whiplash subjects to determine if fatty infiltrate is unique to those with chronic symptoms or a general feature of the condition regardless of recovery. It is also imperative to conduct a longitudinal study to establish the temporal development of fatty infiltrate following whiplash and these studies should include male subjects to determine gender differences. Early recognition of these muscular changes in tandem with clinical tests may ultimately assist in the diagnosis and hence contribute towards the development of treatments aimed at lessening the transition from acute to chronic pain following whiplash injury