Treatment of Cartilage Lesions in Flanders Today

Inclusion Criteria: * Symptomatic single cartilage lesions of the femur condyles * Size of the lesion, determined by MRI: between 1-2 cm² for the group who will receive conservative treatment between 2-5 cm² for the group who will have surgery \- Mechanical joint pain, assessed by a 100 mm Visual Analogue Scale: \> 40 mm for the conservative group, \> 60 mm for the operative group * Agree to stop using analgetics and NSAID's 2 weeks before the First respond of the surveys, and 2 weeks before the second respond of the surveys. Only paracetamol (4g/day) is allowed. * men and women, women have to use contraceptive to avoid pregnancies. * age between 18 - 50 years Exclusion Criteria: * participation in concurrent trials * participation in previous trials within 3 months * subjects with HIV, hepatitis, syphilis * malignancy * alcohol and drug abuse * poor general health condition as judged by the investigator * osteochondritis dissecans * advanced osteoarthritis (kellgren 2-4) * known allergy to penicillins and gentamicin or presence of multiple severe allergies * complex ligamentous instability of the knee * lateral meniscus lesion or more than 50% resection of medial meniscus * Varus or valgus misalignment exceeding 3° (kissing lesions out) * Mosaicplasty (OATS) * Microfracture performed less than 1 year before baseline * Received hyaluronic acid intra-articular injections into the afflicted knee within the last six months of baseline * Taking specific OA drugs, such as chondroitin sulphate, diacerein, capsaicin within two weeks of the baseline visit * Corticosteroid therapy by systemic or intra-articular route within the last month of baseline or intramuscular or oral corticosteroids within the last two 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 disease in the target joint: septic arthritis, inflammatory joint disease, hematochrosis, collagen gene mutations * Current diagnosis of osteomyelitis * A blood result showing liver enzymes more than two times the upper limit of normal or any other result that in the clinical investigator's mind is important clinically * CRP level greater than 10g/l * Unwilling to participate in post-operative rehabilitation protocol