Towards an understanding of motor system impairments in individuals with unilateral lateral epicondylalgia

Abstract

Human grip is commonly used in sport and recreational activities and involves the coordinated activation of forearm muscles. Lateral epicondylalgia (LE) is a common musculoskeletal disorder that involves pathology of the tendon of extensor carpi radialis brevis (ECRB) at its insertion onto the lateral epicondyle of the humerus. LE presents clinically as pain provoked by gripping activities and has a major impact on function. This results in days off work and time off sport. Despite considerable research into the pathophysiology of LE, it remains poorly understood whether forearm muscles activity is altered during gripping in individuals with LE. This thesis aimed to comprehensively understand the extent of current knowledge and provide new data of activity of the wrist/forearm muscles in LE.Study 1 clarifies the current understanding of muscle activity in LE by way of systematic review with quantitative analysis. This review identified that studies of individuals with LE revealed altered motor unit morphology, abnormal patterns of muscle activity during resisted wrist extension and tennis strokes, fewer cortical peaks and less distance between cortical representation of muscles (mapped with transcranial magnetic stimulation), and delayed activation of wrist extensor muscles during gripping, when contrasted to pain-free controls. The latter finding was also present on the asymptomatic limb.Importantly, this systematic review identified limited understanding of gripping despite the clinical importance of this task in provocation of LE. The only study that had investigated muscle activity during this task had severe limitations that compromise the interpretation of the results. Limitations included the use of surface electromyography (which does not record from individual muscles), and performance of sustained contraction with high grip force (50% maximum voluntary contraction), which is likely to be provocative of pain in some individuals with LE.On the basis of some evidence of sensorimotor changes in the asymptomatic limb of individuals with unilateral LE, Study 2 was conducted as a systematic review with meta-analysis to determine the extent bilateral differences in sensorimotor function between individuals with unilateral tendinopathy and pain-free controls. Study 2 identified evidence for several sensory and motor system differences, ii and evidence for tendon pathology in the asymptomatic limb of individuals with other unilateral tendinopathies (Achilles tendinopathy) but not LE when contrasted to pain-free controls.On the foundation that tendon pathology was present in asymptomatic limb of individuals with Achilles tendinopathy, Study 3 investigated whether there was a greater prevalence of tendon pathology of the asymptomatic common extensor tendon of individuals with LE than pain-free controls. Unlike the findings in the Achilles tendon, Study 3 did not identify greater tendon pathology in the asymptomatic limb of individuals with unilateral LE than that present in the tendons of pain-free individ...