The purpouse of this study is to determine the efficacy and safety of chondroitin sulphate conventional treatment in patients with both knee osteoarthritis and plaque psoriasis.

Inclusion Criteria:

• Primary knee OA according to ACR criteria;
• OA of radiological stages 1 to 3 according to Kellgren-Lawrence;
• VAS of pain ≥30;
• PASI ≥ 5.

Exclusion Criteria:

• Known allergy to chondroitin sulphate;
• Other bone and articular diseases such as chondrocalcinosis, Paget's disease, rheumatoid arthritis, psoriatic arthritis, acromegaly, hemochromatosis, Wilson's disease;
• Patients with skin conditions that could interfere in the clinical trial evaluation