The purpose of this thesis was to understand the implications of ultrasound in the assessment of flexor tendon shear to establish its role in carpal tunnel syndrome. An in vitro and in vivo approach was used to examine ultrasound “shear” between the tendon and adjacent tenosynovium. Ultrasound shear is defined by the relative displacement between the tendon and tenosynovium, and has been considered a surrogate measure of tendon shear. However, the mechanical implications of relative displacement are not well understood. In Chapters 2 and 3, an in vitro approach was used to compare ultrasound to direct measurements of tendon displacement and tendon shear. Chapter 2 demonstrated the validity of colour Doppler ultrasonography in the evaluation of tendon displacement. Chapter 3 assessed the relationship between ultrasound shear and mechanical tendon shear using frictional work. We dispelled the notion that ultrasound shear represents tendon shear by showing it only captures the viscoelastic stretch of the tenosynovium in tendon shear; missing surface friction from neighbouring anatomical structures in the carpal tunnel. However, measuring viscoelastic resistance in tendon motion is important for the development of pathological fibrosis and thickening of the tenosynovium, a characteristic finding in carpal tunnel syndrome. In Chapter 4 we further established the clinical utility of ultrasound in vivo by showing ultrasound shear discriminated carpal tunnel syndrome symptomatic individuals from the healthy population. Ultrasound measures progressed with symptoms suggesting an etiological progression of fibrosis and thickening with carpal tunnel syndrome. This thesis concluded that ultrasound only partially represents tendon shear with the viscoelastic component, but underscored the clinical implications. Ultrasound provides a non-invasive assessment of viscoelastic resistance that will be highly valuable for our understanding of the role of wrist and hand motion in the etiology of injury with potential applications in the diagnosis of carpal tunnel syndrome. / Thesis / Master of Science in Kinesiology