Autologous chondrocyte transplantation/implantation versus existing treatments

INTERVENTION: Arm 1: Autologous chondrocyte implantation (ACI) Arm 2: One 'conventional' treatment chosen by surgeon/ patient from following list: Debridement; Abrasion; Drilling; Microfracture; Mosaicplasty. Arm 1 (ACI) is further randomised to receive a patch made from either: a) Periosteum or b) Collagen membrane CONDITION: Orthopaedics ; Musculoskeletal Diseases ; Chondral defect(s) in the knee PRIMARY OUTCOME: Time to cessation of benefit: as defined when 2/3 assessment criteria show no improvement compared to preoperative assessment levels at least 12 months after surgery: ; 1. Independently assessed Lysholm Knee score; 2. Patient self‐assessed Lysholm Knee questionnaire; 3. Independent assessor's judgement based on impact on quality of life, physical examination and functional observation SECONDARY OUTCOME: Not provided at time of registration INCLUSION CRITERIA: Current inclusion criteria as of 09/11/2012: 1. Symptomatic chondral defect(s) on the medical or lateral femoral condyle, trochlea or patella suitable for either ACT or one of the existing conventional treatments (debridement, abrasion, drilling, microfracture, mosaicplasty) 2. Surgical treatment for the same defect carried out at least 12 months previously, that has not relieved symptoms 3. Not more than two defects, not kissing and total area not greater than 12cm2 4. Likely to comply with appropriate physiotherapy Previous inclusion criteria until 09/11/2012: 1. Symptomatic chondral defect(s) on the medical or lateral femoral condyle or trochlea suitable for either ACT or one of the existing conventional treatments (debridement, abrasion, drilling, microfracture, mosaicplasty) 2. Surgical treatment for the same defect carried out at least 12 months previously, that has not relieved symptoms 3. Not more than two defects, not kissing and