The aim of the study is to compare the 6 months clinical outcome of the treatment with a single intra-articular collagen injection versus a single placebo (saline solution) infiltration in the infiltrative treatment of knee osteoarthritis. The evaluation will be performed through clinical, subjective and objective assessments.

204 patients affected by knee osteoarthritis will be included in a double-blinded randomized controlled trial. Patients in the experimental group will be treated with a single intra-articular injection of collagen (solution of low molecular weight peptides derived from hydrolyzed collagen) instead patients in the control arm, will be treated with a single intra-articular injection of placebo (saline solution). All patients will be evaluated by clinical examination before the infiltrative procedure and they will follow-up at 1,3,6 months. During the follow-up visits ,will be evaluated the inflammatory status of the knee by thermographic assessment and questionnaires, filled out by patients, will be utilized for clinical evaluations. After 6 months, patients in the control arm (saline solution injection), have the possibility to cross-over into the treatment arm (collagen) in which case they will be followed for an additional 6 months.

Inclusion Criteria:

1. Unilateral involvement;
2. Signs and symptoms of degenerative pathology of knee cartilage;
3. Radiographic and MRI signs of degenerative pathology of the knee cartilage (Kellgren-Lawrence 1-4 grades);
4. Failure, defined as the persistence of symptoms, after at least one course of conservative treatment (pharmacological, physiotherapeutic or infiltrative treatment);
5. Ability and consent of patients to actively participate in clinical follow-up;

Exclusion Criteria:

1. Patients who have undergone intra-articular injections of another substance in the previous 6 months;
2. Patients undergoing knee surgery within the previous 12 months;
3. Patients with malignant neoplasms;
4. Patients with rheumatic diseases;
5. Patients with diabetes;
6. Patients with hematologic diseases (coagulopathies);
7. Patients on anticoagulant therapy;
8. Patients with metabolic disorders of the thyroid gland;
9. Patients abusing alcoholic beverages, drugs or medications;
10. Body Mass Index > 35;
11. Pregnant or lactating women.
12. Patients with established hypersensitivity to bovine collagen or vitamin C.
13. Patients with joint or peri-articular infections, emarto, erythema, or psoriatic patches in the knee joint area

his is a double-blind randomized controlled trial with 1:1 allocation. Patients, healthcare professionals who assess clinical and functional outcomes (outcome assessors) and professionals who analyze the data will be "blinded."