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Tennis elbow (TE) is a relatively common painful condition affecting the upper extremity. The aetiology is not known, but TE is most often seen in middle aged individuals using repetitive and forceful gripping at work or recreational activities, and is referred to overuse injuries. The pathogenesis is not known, but there are so-called degenerative changes in the wrist- and finger-extensor muscle origin (common extensor origin - CEO). The pain mechanisms involved have not been scientifically clarified.

The studies in the present thesis aimed to 1) evaluate the structure and blood flow using ultrasound (US) and colour Doppler (CD) examinations of the CEO in patients with TE, and in pain-free elbows, 2) evaluate the clinical effects of US- and CD-guided intratendinous injection treatment with the sclerosing substance polidocanol, 3) evaluate the long term (2 years) effects of injection treatment on the tendon structure and blood flow, and 4) investigate if there is a local production of sympathetic and parasympathetic signal substances in non-neural cells in the CEO.

Structural tendon changes and high blood flow was found in the CEO in patients with TE, but not in pain-free controls. Remaining structural changes and additional bone spur formation at the lateral epicondyle, but not high blood flow, were seen 2 years after successful injection treatment. In a randomised double-blind study, US- and CD-guided intratendinous injection treatment with sclerosing polidocanol or the local anaesthetic lidocaine combined with epinephrine, targeting the region with high blood flow, was found to reduce pain and increase grip strength in patients with TE. There were no differences in the outcome between the two treatment groups. A local production of catecholamines, but not acetylcholine, was found in fibroblasts in the CEO, in patients with TE.

This thesis presents results showing US and CD examinations to be useful methods to diagnose TE, and to evaluate structure and blood flow in the CEO after treatment. US- and CD-guided injection treatment targeting high blood flow in the region with structural changes can reduce pain symptoms in patients with TE. The localised high blood flow, and local production of catecholamines in the tendon cells in the CEO, might be involved in the pain mechanisms.