Lateral elbow tendinopathy: towards a better understanding of its multifactorial nature and the role of isometric exercise

Abstract

Lateral elbow tendinopathy (LET) is a common musculoskeletal disorder that presents as pain over the lateral elbow during activities involving repetitive gripping. Although its clinical presentation appears reasonably straightforward, its pathophysiology is not completely understood, in particular the mechanisms underlying pain, disability and prognosis. Studies that have investigated sensory, motor and psychological factors have mostly been of cohorts of unilateral LET without comorbid musculoskeletal pain. This research may not be representative of the broader LET population with comorbid pain who commonly present in primary care. Isometric exercise is commonly used as a way of reducing pain in tendinopathy, although its true efficacy in LET remains unclear. A better understanding of the effect and potential mechanisms of isometric exercise in LET may help guide its use in the management of LET. The aims of this thesis were to investigate sensory, motor and psychological factors associated with pain, disability and prognosis in a broader LET cohort with possible comorbid musculoskeletal pain, and the efficacy of isometric exercise in LET. Study 1 investigated potential differences in comorbid pain, sensory, and psychological features between individuals with and without LET, and between LET individuals with different levels of pain and disability. This study identified widespread multi-modal hyperalgesia and a high prevalence of comorbid pain in individuals with LET compared to those without LET. This study also found that individuals with more severe pain and disability demonstrated greater impairments in the form of greater widespread cold hyperalgesia, localised mechanical hyperalgesia, pain catastrophising, kinesiophobia and number of pain sites compared to those with less severe symptoms. Findings of this study implicate the involvement of mechanisms that are associated with nociplastic and not just nociceptive pain in LET and may help explain the poorer outcomes found in those with severe pain and disability. Study 2 investigated the predictive capacity of comorbid pain, sensory, and psychological features on pain and disability at 6 and 12 months in individuals with LET. Pain and disability at 6 months were predicted by baseline pain and disability, and pain self-efficacy. Baseline pain and disability, pain-free grip strength and having 3 or more comorbid pain sites were predictive of pain and disability at 12 months. These findings suggest that the assessment of pain and disability, pain self-efficacy and number of comorbid pain sites may aid in the early identification of individuals with LET at risk of poorer prognosis.To address the limited understanding of pain-related impairments associated with sustained isometric function of the wrist extensors in LET, study 3 first investigated whether time to failure and pain response to a sustained low-load isometric contraction of the wrist extensors were different between individuals with and without LET, and between LET individuals with different pain characteristics. This study showed decreased time to failure and greater pain following sustained isometric contraction in individuals with LET compared to those without LET, and greater impairment in LET individuals with greater disability and pain sensitivity. Study 3 then investigated whether responses to sustained isometric contraction could predict disability at 6 and 12 months in individuals with LET. The findings indicate responses to sustained isometric contraction were not associated with disability at 6 and 12 months.Study 4 investigated the effect of an 8-week unsupervised isometric exercise program compared to a wait-and-see approach on pain, disability, global improvement and pain-free grip strength in individuals with LET. As a secondary aim, the effect of isometric exercise on pain sensitivity was also investigated to explore potential mechanisms of effect. Findings of this study showed that unsupervised isometric exercise was effective in improving pain and disability, but not perceived rating of change and pain-free grip strength when compared to a wait-and-see approach at 8 weeks. In addition, no group differences were observed in measures of pain sensitivity. On the basis of only one out of three primary outcomes being significantly different following isometric exercise, it is unlikely that this form of exercise is effective as a sole treatment for LET.