This is a phase III, multicenter, open-label, randomized controlled trial of ChondroCelect® in an Autologous Chondrocyte Implantation (ACI) procedure compared to the procedure of microfracture (MF) in the repair of symptomatic cartilage lesions of the knee. Eligible patients attended two screening visits and were booked for arthroscopy approximately 2 weeks later. At that time, patients were randomized to either ACI with ChondroCelect® or to MF, a procedure in which the subchondral bone is perforated to allow a bloodcloth to form scar tissue. Patients randomized to MF had the procedure performed at the time of their arthroscopy; those randomized to ACI with ChondroCelect® had their cells harvested during the arthroscopy and then returned to the clinic approximately 4 weeks later for an open knee procedure, during which the ACI procedure using ChondroCelect® was performed. Patients subsequently followed the same rehabilitation program and had follow-up assessments up to 12 months post-surgery. The 12-month visit was the end-of-study visit for the TIG/ACT/01/2000 protocol. Subject to satisfying the eligibility criteria, patients who had participated in the initial 12 month trial could enter the extension trial. The 12-month visit for the initial study was the baseline visit for the extension study. During the extension study, patients have follow-up assessments up to 60 months post-surgery.

see above

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