Author: Tom Walsh
Walsh, Tom, 2018 Obesity and foot pain: Studies of non-mechanical and mechanical mechanisms, Flinders University, College of Medicine and Public Health
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Musculoskeletal pain is common, it is a leading cause of burden of disease and it is strongly associated with obesity. There is a particularly high prevalence of frequent, disabling musculoskeletal pain in the feet in the community, affecting nearly one in four adults aged over 45 years in Australia and the United States of America. Whilst much attention is directed towards the effect of obesity causing mechanical overload of single regions, there is a growing body of evidence that highlights the systemic effects of obesity, including non-mechanical factors such as inflammation and a reduction in psychological health that may manifest as pain throughout the human body, including the feet.
This thesis examines the relationship between obesity and foot pain.
The systemic effects of obesity are largely attributed to the metabolic activity of adipose tissue. Adipose tissue secretes a variety of cytokines and inflammatory mediators that have been linked with joint disease and also a deterioration in psychological health. Given excessive adipose tissue is not merely a passive load, it does question the usefulness of measuring body weight as opposed to body composition, when there is clear heterogeneity in the metabolic activity of both adipose tissue and lean tissue. The association between musculoskeletal pain and body fat was reviewed and analysed in a systematic review and meta-analysis (chapter 2). The systematic review suggested that the volume or percentage of body fat is an important distinction when considering the effect of obesity on pain across multiple sites in the body including the foot. Whether body fat or inflammatory mediators / adipokines were associated with pain was also investigated in a secondary analysis of a community cohort (chapter 3). The results of this study suggested that participants with higher body fat (and depression) had increased risk of having prevalent and future foot pain. Whether the location of fat or different aspects of psychological health were important factors for foot pain was investigated for both the presence and the severity of foot pain (chapter 4). This study again reinforced that psychological health and body fat are both associated with foot pain.
Despite the known association of obesity and foot pain, there has been very limited research on the effects of weight loss on foot pain. As a means of analysing a group that is over-represented with foot pain, a cohort of people awaiting bariatric surgery were recruited. This study was able to analyse both the role of weight loss and the impact of baseline depression and body composition on a change in foot pain (chapter 5), finding that bariatric surgery was associated with a reduction in foot pain, while baseline body composition was significantly associated with a change in foot pain, independent of bariatric surgery.
The mechanical effects of body weight on foot pain were also studied. The association of foot pain with small changes in both body weight and regional plantar pressures were explored longitudinally over two-year period (chapter 6). This was the first study to explore the temporal relationships between plantar pressure and foot pain. Plantar pressure data from the bariatric cohort in chapter 5 was used to determine the impact of mechanical and non-mechanical factors in both baseline and a change of foot pain (chapter 7). These studies on plantar pressures, which also included foot posture, do not support a strong association between foot posture and foot pain.
Clinicians should be aware that musculoskeletal foot pain is associated with obesity through mechanisms beyond mechanical overload and local foot changes. Foot pain, psychological health and obesity are a triad of factors, each amplifying the other. As both obesity and foot pain (and hence depression) increase in the community, improving the understanding of how this relationship exists and how this may be overcome is discussed.
The association of obesity with foot pain is not surprising, but the studies that comprise this thesis highlight factors that are beyond mechanical overload.
Keywords: Obesity, Musculoskeletal, Foot, Pain
Subject: Musculoskeletal Medicine thesis
Thesis type: Doctor of Philosophy
Completed: 2018
School: College of Medicine and Public Health
Supervisor: Prof E Michael Shanahan