Osteoarthritis (OA) causes degradation and deformities of joints, including knees, hips, hands, and feet. Approximately more than 55% of populations above 45 years and more than 70% of population above 70 years will develop OA in at least one joint. The symptoms are dominated by pain but also stiffness and swelling occur. There is currently no cure for OA, and the ultimate treatment is joint replacement surgery. However, there is an unmet need to identify other treatment options that may delay or avoid surgery.

Aquamid Reconstruction (AR) is a polyacrylamide hydrogel (PAAG) which is a non-degradable, highly visco-elastic synthetic gel, which is atoxic with durable effect and tissue-compatibility and well tolerated by mammal tissue by allowing in vivo vessel and fibrous in-growth. Experimental studies supported by histopathological observations have shown that AR exerts its effect via integration over time within the soft tissues, through a combination of vessel in-growth and molecular water exchange. Intra-articular injection of AR is expected to provide permanent pain relief and improve the functional ability through a cushioning or padding effect on the joint and thereby reduce symptoms and improve patients' quality of life.

The purpose of this study is to obtain information of the safety and effectiveness of AR in patients with OA of the knee.

Inclusion Criteria:

• Age > 18 years
• WOMAC pain score >/= 5
• Kellgren and Lawrence radiographic scoring >/= 1
• Signed informed consent form

Exclusion Criteria:

• Other diseases affecting the joints such as rheumatoid arthritis
• Actual or recurrent infections requiring intravenous antibiotic treatment within the last 30 days or oral antibiotic treatment within the last 14 days before inclusion
• Less than 12 weeks since injection of HA or corticosteroids in study-knee joint before treatment
• Pregnancy or lactation
• Not able to comply with the requirements of the study
• Previous alloplasty