This study aims to compare arthroscopic resection (surgical intervention) versus infiltration of cytokine rich serum (CRS) (proteins derived from the patient's own blood) for the treatment of lateral epicondylitis (LE).

Lateral epicondylitis (LE) is a common debilitating condition that affects the extensor muscles of the forearm at its junction with the lateral humeral epicondyle. This pathology is commonly treated by a surgical intervention. However, advances in research have allowed the discovery of new and less invasive techniques for its treatment, for example the infiltration of cytokine rich serum.

The aim of the study is to compare the common treatment of this pathology, arthroscopic resection (surgical intervention) with a new technique, infiltration of cytokine rich serum (CRS) (proteins derived from the patient's own blood) with respect to medium and long-term pain reduction.

The study will include a total of 86 patients. Patients will be included by randomization into two groups:

• GROUP 1: 43 patients will be treated with 2 infiltrations of cytokine rich serum.
• GROUP 2: 43 patients will be treated by a regular surgical treatment consisting of arthroscopic resection.

The main objective of this study is to evaluate the efficacy of CRS as compared to arthroscopic resection in reducing pain in the medium term (6 months) in patients with chronic lateral epicondylitis.

Inclusion Criteria:

• Over 18 years of age
• Patients with persistent pain (EVA > 5) at lateral epicondyle level of at least 3 months duration.
• Patients with a diagnosis of chronic lateral epicondylitis confirmed with a complementary diagnostic test such as Echo or MRI.
• Availability to follow the study protocol for up to 24 months.
• Patients with the ability to understand study information and give informed consent.
• Patients who sign informed consent.
• Normal hematologic parameters.

Exclusion Criteria:

• Local infection present.
• Patients who have been treated with corticosteroid infiltrations in the same area in the past 4 months.
• Patients who have received treatment with growth factors, PRP, cytokines, or new drug treatments in the same area in the last 12 months.
• Pregnancy or breast-feeding.
• Neoplastic disease.
• Patients being treated with immunosuppressants (medical evaluation).
• Patients undergoing arthroscopic surgery of the same elbow.
• Active liver disease.
• Immunosuppressive or immunodeficiency states.
• Coagulation deficit or abnormalities.
• Thrombocytopenia.
• Treatment with anticoagulants.
• Difficulty understanding and following study procedures.
• Participation in a clinical trial with medications.