RCT of ChondroCelect® (in an ACI Procedure) vs Microfracture in the Repair of Cartilage Defects of the Knee

Inclusion Criteria: * Signed patient informed consent * Symptomatic cartilage single lesion of the femoral condyle * Lesion on femoral condyle between 1 and 5 cm² * Agree to participate actively in a strict rehabilitation protocol and follow-up programme * Agree to only use paracetamol mono-or combination preparation (max 4g/d) and Non-Steroidal Anti Inflammatory Drugs (NSAIDS) during the study and to discontinue this medication 2 weeks before the baseline visit and the follow-up visits. The use of paracetamol mono-preparation (max 4g/d) is allowed up to one week before the baseline visit and the follow-up visits. * Females of childbearing age should use a proven method to prevent pregnancy Exclusion Criteria: * Participation in concurrent trials * Participation in previous trials within 3 months * Subjects with hepatitis, HIV or syphilis * Malignancy * Alcohol or drug (medication) abuse * Poor general health as judged by Investigator * Clinically relevant second cartilage lesion on the patella * Patellofemoral cartilage lesion * Osteochondritis Dissecans (OCD) : recent OCD (within 1 year before baseline), depth of lesion \> 0.5cm, subchondral slerosis * Advanced osteoarthritis (OA) : radiographic atlas of OA grade 2-3 * Known allergy to gentamicin or penicillins (or presence of multiple severe allergies) * Complex ligamentous instability of the knee * Meniscal transplant * Meniscal suture with meniscal arrows (ipsilateral) * Meniscus resection : if \< 1 yr before baseline - lateral meniscus resection or medial meniscus resection of more than 50%. If \> 1 yr before baseline - ipsilateral meniscus resection of more than 50%, controlateral meniscus resection of more than 50% if ipsilateral meniscus is not intact, combination of medial and lateral meniscus resection and one of both \> 50%. * Varus or valgus malalignment of more than 5° * Mosaicplasty * Microfracture performed less than 1 yr before baseline * Having received hyaluronic acid intra-articular injections in the affected knee within the last 6 months of baseline * Taking specific OA drugs such as chondroïtin sulfate, diacerein, n-glucosamine, piascledine, capsaicin within 2 weeks of the baseline visit * Corticosteroïd treatment by systemic or intra-articular route within the last month of baseline or intramuscular or oral corticosteroïds 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 * Any evidence of the following diseases in the target joint : septic arthritis, inflammatory joint disease, gout, recurrent episodes of pseudogout, Paget's disease of bone, ochronosis, acromegaly, hemochromatosis, Wilson's disease, primary osteochondromatosis, heritable disorders, collagen gene mutation * Current diagnosis of osteomyelitis * 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