Inclusion Criteria:  Being able to provide signed and dated informed consent form.  Scheduled for one of the following surgical treatments  Surgery that involves the harvest of cartilage tissue as part of the treatment, thus creating a fresh cartilage defect, which is then left to heal naturally. Examples of such surgery are autologous chondrocyte implantation (ACI) and mosaicplasty. Autologous stromal cell implantation (ASCI), as part of the ASCOT randomised clinical trial.  Exclusion Criteria:  Inadequate understanding of verbal explanations or written information given in English, or having special communication needs. Chronic severe renal insufficiency Anything that would preclude the individual's full compliance with or completion of the study.