THE ROLE OF CONTEXTUAL FACTORS ON HEALTHCARE OUTCOMES OF MUSCULOSKELETAL PAIN

Musculoskeletal pain is a highly prevalent and disabling condition usually presenting with physical function loss and incurring substantial health care costs. The burden of musculoskeletal pain is expected to increase over the next decades due to the aging population and increasing obesity globally. In Europe, the prevalence of musculoskeletal pain is reported to range from 12% to approximately 30%, with research reporting the prevalence of disability-adjusted life years for musculoskeletal conditions having increased 60% between 1990 and 2010. The two most common causes of musculoskeletal pain worldwide are osteoarthritis and non-specific low back pain. Contextual factors related to health conditions may range from lifestyle factors (e.g. practice of physical activity, obesity, food intake, and smoking) to people’s individual characteristics (e.g. sex, genetic factors, and predisposing conditions). The broad aim of this thesis was to investigate the role of specific contextual factors, namely obesity, sex, diabetes, level of physical activity and existing comorbidities on the prevalence, prognosis and management of musculoskeletal pain. One of the most disabling conditions, especially in the elderly population, is osteoarthritis. Despite the potential benefits of surgical interventions for the management of osteoarthritis and the influence of patient characteristics on the disease progression, there is controversial evidence on the association between lifestyle characteristics, namely obesity and physical activity participation, on the clinical outcomes of surgical procedures. Chapter Two presents a systematic review with meta-analysis of 62 cohort studies. This meta-analysis shows that pre-surgical obesity is associated with worse clinical outcomes of hip or knee arthroplasty in terms of pain, disability and complications in patients with osteoarthritis. Due to lack of relevant studies, the impact of physical activity participation is still unclear. Another important cause of disability worldwide is low back pain. It is estimated to have a point prevalence of around 18.3%, a 30-day prevalence of 30.8% and a lifetime prevalence of 84%. Sex is also one contextual factor believed to influence prevalence of low back pain. Chapter Three presents a co-twin control study aiming to quantify the association between sex and prevalence of low back pain. The discordant-pair twin analyses showed, however, no significant association. These results have challenged previous views on the role of sex as a predisposing factor for the development of low back pain. Currently, diabetes is also one of the most commonly reported chronic diseases and patients with low back and neck pain will often report the co-existence of type 2 diabetes. The nature and magnitude of this link was, however, still under-investigated. In this context, Chapter Four presents a meta-analysis of studies assessing the association between type 2 diabetes and the presence of neck, low back or spinal pain (i.e. concurrent back and neck pain). The results suggest that diabetes and low back pain or neck pain are significantly associated. A direct causal link between them is however, unlikely. Recent research shows that exercise, either alone or in combination with education, is an effective strategy to prevent new onset of low back pain. In Chapter Five we have established whether the level of physical activity participation before an acute episode of low back pain predicts recovery within the following 12 months. The findings of this cohort study show that pre-pain levels of physical activity participation are not a significant predictor of recovery from low back pain. Finally, Chapter Six presents a study addressing the effect of comorbidities on the rate of hospital complications for people with low back pain and sciatica. The study used hospital admitted patient data and the analyses on the potential association between comorbidities and hospital complications were adjusted for patient-level (e.g. sex, age) and health care-level (e.g. type of hospital or access to private health insurance) characteristics. The multivariate logistic regression analyses showed that presence of cardiovascular, respiratory and renal comorbidities were independently associated with higher rates of in-hospital complications. The evidence presented in this thesis has established the role of a range of important contextual factors on the prevalence, prognosis and management of people with musculoskeletal pain.