This trial aims to evaluate the safety and effectiveness of different doses of the patient's own fat stromal cells in the treatment of severe osteoarthritis of the knee joint. The study is being undertaken at the University Hospital Montpelier in France and at the Orthopädische Klinik in Wurzburg, Germany. The study plans to enrol a total of 18 subjects with moderate to severe osteoarthritis of the knee, at both centres between April 2000 trial and April 2014. Stromal cells will be harvested from fat obtained by liposuction of the subjects and injected into their knees. The subjects will be divided into three groups that receive three strengths concentrations of cells. Participants will be monitored for complications and assessed for changes in their clinical condition. The study is expected to be completed by April 20015.