Perceptual Changes in People with Shoulder Pain: Motor Imagery, Left/Right Judgement and Sensory Tactile Thresholds

Abstract

Shoulder pain is one of the most common musculoskeletal problems for which people seek health care advice and management, and according to the World Health Organisation, musculoskeletal problems disorders are the second largest cause of disability worldwide. Shoulder pain can become persistent and one example of this is frozen shoulder (adhesive capsulitis), a chronic and disabling shoulder problem. The diagnosis of shoulder complaints including frozen shoulder is difficult, and not without controversy, as there are currently no gold standard diagnostic tests. The treatment of shoulder complaints including frozen shoulder is similarly debated in the literature. This lack of consensus in diagnoses and treatment of shoulder complaints implies that new methods of assessment and treatment are required. A large body of work has implicated the role of the brain in chronic pain conditions. Neuroplastic changes associated with chronic pain can be assessed directly, for example, by the neuroimaging of sensory or motor cortex changes. Neuroplastic changes associated with chronic pain can also be inferred indirectly by behavioural experiments. These include motor imagery tasks such as the left/right judgement task, and tactile acuity tasks like the two-point discrimination threshold test. The first part of thesis systematically reviews the literature surrounding the left/right judgement task in chronic pain conditions to determine if motor imagery is affected in people with chronic pain. This revealed a notable gap in the left/right judgement task literature, as no study had yet assessed motor imagery in people with shoulder pain. The second part of this thesis describes the development of a shoulder specific left/right judgement task, its validity and reliability, which was the first step to address this gap in the literature. In the third part of this thesis this new shoulder specific motor imagery test was then applied to a self-selected sample of people with shoulder pain, and then to a clinician confirmed cohort of people with frozen shoulder. Motor imagery was found to be affected in the frozen shoulder group, and one possible explanation for this is that central processes and cortical proprioceptive representations were altered in this group. In a second behavioural experiment, a tactile acuity task – the two point discrimination test – was employed in the frozen shoulder cohort, and the results demonstrated side to side differences in two point discrimination. Again, this could be interpreted as further implication of somatosensory cortical changes in this group. Taken together, these findings of motor imagery impairment and tactile acuity deficits in people with persistent shoulder pain (frozen shoulder) imply sensorimotor cortical alterations in this group. Moreover, these findings raise the possibility that cortically targeted treatments – that have proven successful in other conditions such as complex regional pain syndrome, and shown promise in chronic low back pain – may be beneficial in the management of frozen shoulder.