The study aims to investigate the natural course and the results of operative treatment of chronic tennis elbow (TE). Chronic is defined as symptoms having lasted for more than a year. The investigators will also study the effect of pain catastrophising on the subjective outcome, the patient acceptable symptomatic state and the response shift phenomenon in TE. The study will also ascertain the feasibility of a multi-center randomised, controlled trial (RCT), and test and refine the co-operation and interaction of the planned RCT centers.

Objectives:

1. To study the natural course of tennis elbow/spontaneous recovery of chronic (lasting for over 12 months) tennis elbow and the results of surgery in a pragmatic setting.
2. To investigate the patients' expectations of the treatment, and define the patient acceptable symptomatic state, or PASS, in tennis elbow.
3. To investigate the effect of pain behaviour on treatment results and PASS.
4. To delineate the existence of a potential "response shift" -phenomenon in patients with a tennis elbow.
5. To determine the feasibility of a prospective, placebo-controlled, randomised trial by finding out the actual number of patients in each center and those that may be suitable for the FINITE-RCT. The investigators will also test the functioning and response of the planned outcome measures in this environment and for this purpose.

Study setting The study is carried out as a prospective open-label multi-center cohort study.

The study was originally planned with a follow-up up to 10 years, but the cost-benefit of the long term follow-up was evaluated after the completion of one year data collection, and the decision was made to shorten the follow-up to include two year data, but no further follow-ups.

Inclusion Criteria:

1. Clinically diagnosed tennis elbow defined as: Pain on the lateral side of the elbow, made worse by pressure applied on the lateral epicondyle of the humerus and during resisted extension of the wrist or when making a fist with the elbow joint straight.
2. Duration of symptoms over 10 months
3. Age between 35 and 60 years
4. Ability to fill in Finnish questionnaires
5. Written informed consent

Exclusion Criteria:

1. Earlier fracture or dislocation in the elbow joint area

2. Earlier surgical treatment of the same elbow joint

3. Congenital deformity in the elbow

4. Systemic muscle, tendon, nerve or joint disease

5. Other problems causing pain the elbow joint:

   1. Pain in the medial epicondyle of the elbow
   2. Pain in the biceps muscle tendon
   3. Painful snapping or crepitus of elbow joint
   4. Instability of elbow joint (table top, posterolateral drawer test)

6. A passive movement limitation of more than 10 degrees in the elbow joint

7. Abnormal finding in an elbow joint X-ray. An elbow joint X-ray is a routine examination of elbow symptoms.

All patients who seek advice or treatment at the outpatient clinics of the centers taking part in the study will be assessed for eligibility. Those fulfilling the criteria defined below will be asked to participate.