Beyond the tissue: the relationship between structure, function, and pain in Achilles tendinopathy

Introduction: Achilles tendinopathy (AT) is a highly prevalent, disabling and oftenpersistent musculoskeletal complaint, commonly affecting athletic and non-athletic populations. To date, attempts to explain the pathoaetiology of tendinopathy have utilised theoretical models and paradigms, predominantly focusing on the contribution of structural factors, or changes in the physical properties of the tendon. Although structural factors may play an important role in the mediation pain associated with AT, the persistent nature of AT suggests that it is a multifactorial disorder, involving a complex interaction of numerous interlinking variables. Understanding the relative contribution of structure, function and pain, and the possible relationship between these factors may improve our understanding of AT. The aims of this doctoral thesis are to investigate if alterations in tendon structure are associated with the development of pain, examine the relationship between pain and function in AT, and explore the factors associated with clinical improvements following a 12 week loading intervention. Methods: In the first part of the thesis (Chapter 2), two systematic reviews were completed. Study I investigated the reliability and degree of error associated with quantifying tendon size using ultrasound imaging. Study II reviewed the literature exploring the relationship between alterations in tendon structure and the development of future Achilles or patellar tendinopathy. The second part of the thesis, (Chapter 3) explored the degree and nature of functional deficits in AT by performing a systematic review and meta analysis. The final part of the thesis, (Chapter 4) outlines the results of a pilot intervention study investigating the factors associated with clinical outcomes following a 12 week loading intervention. Finally, a qualitative study explored the beliefs and experiences of people with AT. 2 Results: Study I demonstrated that US imaging displays good-excellent inter and intrarater reliability, as well as demonstrating a low degree of measurement error in quantifying tendon size throughout a range of upper and lower limb tendons. A systematic review and meta-analysis performed in study II demonstrated tendon abnormalities were associated with a 5 fold increased risk of developing Achilles or patellar tendinopathy in asymptomatic athletes. In Chapter 3, a systematic review and meta-analysis highlighted people with AT display altered strength profile across the entire strength spectrum using a range of outcome measures. Results from a pilot intervention in Chapter 4 suggest clinical improvements in pain and function following 12-week loading intervention may be attributed to change in a range number of factors. The remaining study in Chapter 4 highlighted the impact of AT on psychosocial factors. Conclusion: The finding of this doctoral thesis indicates that AT is a multifactorial musculoskeletal disorder, involving a complex interaction between structure, function, and pain. The relative contribution of each factor may vary between individuals. Results of the included studies appears to suggest that future research should investigate the pathoaetiology, prediction and designing of interventions in AT from a multifactorial perspective.