Autologous Mesenchymal Stem Cells vs. Chondrocytes for the Repair of Chondral Knee Defects

Inclusion Criteria: * Symptomatic focal articular cartilage lesion on the medial femoral condyle * Lesion on femoral condyle between 1 and 5 cm² * ICRS Grade III/IV * Stable knee * Signed patient informed consent Exclusion Criteria: * Clinically relevant member malalignment (\> 5 degrees) * Non stable knee * Inflammatory joint disease * Knee surgery in the last year (transplant, suture or resection of the meniscus, mosaicplasty, microfracture) * Participation in concurrent trials or in the previous 3 months * Subjects with hepatitis, HIV or syphilis * Malignancy in the previous 5 years * Alcohol and/or drug abuse * Poor general health as judged by Investigator * Clinically relevant second cartilage lesion on the patella * Patellofemoral cartilage lesion * Known allergy to gentamicin or penicillins (or presence of multiple severe allergies) * Having received hyaluronic acid intra-articular injections in the affected knee within the last 6 months of baseline * Taking specific OA drugs such as chondroitin sulfate, diacerein, n-glucosamine, piascledine, capsaicin within 2 weeks of the baseline visit * Corticosteroid treatment by systemic or intra-articular route within the last month of baseline or intramuscular or oral corticosteroids within the last 2 weeks of baseline * Chronic use of anticoagulants * Uncontrolled diabetes * Any concomitant painful or disabling disease of the spine,hips or lower limbs that would interfere with evaluation of the afflicted knee * Any clinically significant or symptomatic vascular or neurologic disorder of the lower extremities * Liver enzymes (SGOT, SGPT, Alkaline Phosphatase) of more then two times the upper limit of normal or any other result that is clinically important according to the Investigator * CRP \> 10 mg/l