Inclusion Criteria:

1. Symptomatic cartilage or osteochondral defects
2. One or more International Cartilage Repair Society (ICRS) Grade III or IV chondral or unsalvageable osteochondral defects located on the femoral condyles and/or trochlea amenable to treatment with the surgical procedure determined at randomization (MACI or microfracture).

1. Concurrent ICRS Grade I and II defects are acceptable on the tibia if they remain untreated (or are treated with debridement only) at the time of study treatment.

2. Participants with a potentially re-attachable osteochondral fragment, identified by magnetic resonance imaging (MRI) and that has not previously been repaired, may be consented to the study and undergo baseline assessments per protocol and prior to confirmatory arthroscopy (Visit 2). At arthroscopy, an attempt will be made to reattach the osteochondral fragment. If this is successful, the participant will be excluded from the study and deemed an intra-operative screen failure. If the attempted reattachment fails and no other exclusion criteria apply, the participant may continue in the PEAK study: a MACI biopsy will be taken, the participant will be randomized and treated per protocol.

Exclusion Criteria:

1. Any surgery on the target knee joint within 6 months prior to Screening (not including diagnostic arthroscopy)
2. Previous investigational drug or device use within 3 months prior to Screening
3. Avascular necrosis of the target knee (other than potential OCD lesion to be treated)
4. Participants with uninvolved open growth plates where the surgery necessitates crossing the growth plate, or where the depth of the lesion crosses the growth plate
5. ICRS Grade III or IV chondral or unsalvageable osteochondral defects located on the tibia or any lesion that is bipolar to the index lesion
6. Malalignment requiring concurrent osteotomy to correct tibial-femoral or patella-femoral alignment (prior guided growth treatment is not exclusionary)
7. Symptomatic musculoskeletal conditions in the lower limbs that could impede measurement of efficacy for the target knee joint
8. Concomitant inflammatory disease or other conditions that affects the joints (eg, rheumatoid arthritis, metabolic bone disease, psoriasis, symptomatic chondrocalcinosis)
9. Known history of septic arthritis in the index knee joint
10. Current malignancy or treatment for malignancy within the past 5 years
11. Known history of hypersensitivity to gentamicin, other aminoglycosides, or products of porcine or bovine origin
12. Females who are pregnant or lactating
13. Participants who, in the opinion of the Investigator, have significant medical or psychosocial problems that warrant exclusion. Examples of significant problems included but are not limited to:

1. Any condition that has potential for negatively impacting intra or postoperative course
2. Conditions that limit compliance with rehabilitation program
3. Any condition that has potential for significantly limiting participant's ability to assess postoperative knee function
4. Any condition, psychiatric or otherwise, that would preclude informed consent/assent, consistent follow-up, or compliance with any aspect of the study
5. Participant is currently abusing drugs or alcohol or, in the opinion of the Investigator, at high risk for poor compliance