The purpose of this study is to compare the effects of platelet rich plasma, whole blood and saline vehicle on the natural course of lateral epicondylitis.

Lateral epicondylitis, also known as "tennis elbow", is the most common work-related disease of the upper extremity. Usually it has favorable natural healing-tendency, but sometimes it is responsible for long-lasting disability. The pathogenesis of this disease has remained unclear, however it has been speculated that the role of inflammation is smaller than previously believed. Instead, anatomical and vascular factors may play a much greater role. The evidence for the operative treatment is lacking, and the conservative treatment is therefore preferred. The conservative treatment used to rely largely on corticosteroid injections to the extensor muscle insertions. However, it has been shown that corticosteroids, in fact, tend to increase the subjective pain in the long run. Several studies -- most of them unfortunately underpowered -- have been carried out to find an efficient conservative treatment to this disease, but none of them has turned out to be significantly better than others. During the last couple of years, platelet rich plasma (PRP) has been used as a treatment in several musculoskeletal diseases (e.g. fracture healing, cartilage regeneration, wound healing). PRP is a substance centrifuged from patient own blood. There are a couple of studies regarding the use of PRP in lateral epicondylitis. The results are mostly positive; however it has not been thoroughly shown that it would be more effective than patient's whole blood. The hypothesis of this study is that PRP is more effective in the treatment of lateral epicondylitis than whole blood or saline vehicle injection. The primary outcome measures are pain (VAS) and the Disabilities of the Arm, Shoulder and Hand -score (DASH).

Inclusion Criteria:

• The duration of symptoms over 3 months
• Primary conservative treatment (physiotherapy, NSAID, ...) has been tried

Exclusion Criteria:

• Significant systemic diseases
• Any surgical operation of the particular elbow