The major objective of this study is to evaluate the efficacy of the MACT versus the AMT for the treatment of large cartilage defects in patellofemoral and femorotibial injuries.

Knee cartilage injuries are common, especially in young active adults, and have the potential to progress to osteoarthritis if left untreated, which would disable a large part of the population with joint functionality loss.The issue with knee cartilage remains in the fact that the tissue has very limited healing potential as it contains no blood vessels allowing a supply in cells for a proper regeneration. Many surgical techniques have been developed for cartilage repair, however, traditional methods have shown their limitations, especially in the case of large defects. More importantly, there is no consensus on novel surgical techniques. Therefore, the choice of a proper cartilage treatment becomes crucial Worldwide, because the aging population is increasing rapidly and there is a need to remain functional and independent as long as possible.

The overall objective of the present study is to compare two advanced surgical techniques for the treatment of large defects in cartilage: one technique consists of a more conventional and widely used approach, which stimulates the natural repair of the tissue by making micro-holes in the bone, allowing the recruitment cells from the underneath bone marrow and stabilize them with a membrane to repair the defect (technique called enhanced microfracture or AMT); and the other technique called MACT, consists of taking patients own cartilage cells from a small biopsy and growing them on a membrane to form a cartilage tissue in vitro, which is then implanted surgically at the location of the injury. This second technique has the advantage of cellular assistance in the surgery enabling to improve the regeneration.

The purpose of this study is to determine which technique (AMT or MACT) is the most appropriate to treat large cartilage injuries, in order to propose the best therapeutic option depending on the severity, size and location of the injury in the joint to the patient.

Inclusion Criteria:

• Patients aged between 15-50 years
• Symptomatic chondral and osteochondral defect, grade III and IV according to the ICRS classification, and size between 2.5 and 15 cm2
• Failure of a conservative treatment
• Patient in good general condition, documented by an ASA score ≤ 2 (American Society of Anesthesiologists)
• Patient considered compliant and able to participate in rehabilitation and pre- and post-operative follow-up
• Consent to participate in the study

Exclusion Criteria:

• All inflammatory and synovial pathologies
• Diffuse or mirror lesions
• An unfavorable biomechanical environment
• Obesity grade II or higher, with a BMI>35 kg/m2
• Active smoking/ active drug dependency (hard drugs)
• Poor compliance
• The patient is already part of another clinical trial that may compromise the present study
• Vulnerable populations (except minors aged 15-18 years)
• Presence of open growth plate (15-18 years)
• Pregnancy or planned pregnancy during the study (MRI-related contra-indication)
• Proven allergy to penicillin and gentamicin (for MACT group) and porcine collagen (for both groups)

For final inclusion, an additional exclusion criteria will be assessed after randomization:

- Positive to HIV, HBV, HCV, syphilis.