Lateral elbow pain can be difficult to diagnose because of the different pathologies or combinations of pathologies that can cause this clinic. Although lateral epicondylitis is the most common cause of lateral elbow pain, symptoms of radial tunnel syndrome may masquerade as lateral epicondylitis or they can be seen together with rate of 21-41%. The aim of the study is; to evaluate the presence of radial tunnel syndrome in the patients who have resistant lateral epicondylitis.

Lateral epicondylitis (LE), also known as "tennis elbow," is an overuse syndrome of the common extensor tendon (CET), predominantly affecting the extensor carpi radialis brevis. History and physical examination including manual provocation tests are key elements for the diagnosis.

Ultrasound imaging of the CET is an important complementary method to the clinical diagnosis of LE. It provides information about the severity of the disease with evidence of tendon thickening, focal/diffuse areas of decreased echogenicity in the tendon, epicondylar cortical irregularity or spur formation, and increased vascularity in case of local inflammation depicted by power- Doppler imaging.

Radial tunnel syndrome (RTS) is a dynamic/intermittent compression neuropathy of the radial nerve, where different structures can potentially compress the nerve. Local inflammatory and/or vascular changes (scarring, fibrosis), which are seen in LE may lead to compression of the radial nerve or its branches (especially the deep branch) at the radial tunnel. While RTS can often be the cause of refractory LE, some patients with LE actually have RTS concomitantly. The diagnosis of RTS is difficult/controversial due to inconclusive findings on electrophysiological tests and its close relationship with LE. Ultrasound is a superior imaging modality that can be used as an adjunct to electromyography for the evaluation of peripheral nerve problems. It can be used to diagnose compression neuropathies and to identify the entrapment site of the nerve. For the exact diagnosis of RTS complete relief should be achieved with a nerve block at the radial tunnel. Patients who have RTS coexisting with LE (18-43%) usually experience incomplete relief.

The purpose of the study is; to evaluate the RTS and LE with physical examination, special clinical tests, electrophysiological and ultrasonographic examinations and, to confirm the presence of RTS accompanying LE with the evaluation of clinical findings after the posterior interosseous nerve and lateral epicondyle diagnostic injections.

Inclusion Criteria:

1. Aged 18-65 years
2. Had persistent lateral elbow pain at least 6 months' duration with suspected lateral epicondylitis
3. Be able to understand enough Turkish to complete the outcome questionnaire
4. Patients whose informed consent was obtained for paticipation in the study

Exclusion Criteria:

1. Fibromyalgia
2. History of surgery in the elbow
3. History of fracture that cause the deformity at radius/ulna
4. Pregnancy or breastfeeding
5. Inflammatuar arthropathy in upper extremities
6. Osteoarthritis in the upper extremities
7. Neurological disabilities that effect the upper extremity functions
8. Cervical radiculopathy that effect the level of C6-C7