Prospective observational study of 6 months of follow-up, of national and multicenter scope with medical device with CE marking and according to the usual clinical practice.

In addition, due to the observational design of the clinical investigation, no assignment of the patients will be made to any specific study group, but will be carried out in accordance with the usual clinical practice, not applying any intervention other than the usual one in this type of care practice and always in accordance with current clinical guidelines and recommendations and with the indications authorized in Spain.

Patients will be recruited by specialists and will be followed for 6 months under the conditions of usual clinical practice.

Inclusion Criteria:

1. Patients of both sexes and over 18 years.
2. Patients with a previous diagnosis of primary knee osteoarthritis according to ACR criteria and who have a knee x-ray performed during the previous 18 months.
3. Patients who attend a control clinic for primary osteoarthritis of symptomatic knee.
4. Patients with pain equal to or greater than 4 on the VAS scale.
5. Patients who have been prescribed an injection of Pronolis® HD as part of the usual clinical practice.
6. Patients who have given their written informed consent to participate in the clinical investigation.
7. Patients for whom there is a reasonable expectation of follow-up during the development of clinical research.
8. Patients who understand and can complete the questionnaires and do not have cognitive impairment that prevents it.

Exclusion Criteria:

1. Patients with known intolerance to hyaluronic acid.
2. Patients with hypersensitivity to intraarticular injections.
3. Patients who present with infection in the knee joint.
4. Patients presenting with a skin disorder or infection in the area of injection or systemic.
5. Coagulation disorders that contraindicate puncture.
6. Patients who have been prescribed intra-articular injection in both knees.
7. Patients diagnosed with autoimmune rheumatologic diseases or connective diseases.
8. Patients diagnosed with microcrystalline diseases.
9. Patients with traumatic history in the study joint.
10. Patients with a surgical history in the study joint.
11. Pregnant or breastfeeding women.

The study population will be made up of subjects of legal age diagnosed with primary knee osteoarthritis who have pain equal to or greater than 4 measured by VAS.

All patients included in this clinical investigation must have been duly informed by the investigator about the investigation procedure and its objectives.