Orthopedics & Sports Medicine
What Is MACI Knee Cartilage Repair?
Published · Haute MD Editorial Team
MACI (autologous cultured chondrocytes on porcine collagen membrane) is an FDA-approved implant made from a patient's own knee cartilage cells. The cells are grown in a lab, seeded onto an absorbable collagen membrane, and surgically placed over a damaged area of knee cartilage. FDA prescribing information says MACI is indicated "for the repair of symptomatic, single or multiple full-thickness cartilage defects of the knee with or without bone involvement in adults." The label also states that effectiveness in joints other than the knee, and safety and effectiveness in patients over 55, have not been established. MACI is made by Vericel Corporation. FDA first approved it on December 13, 2016, and in August 2024 added arthroscopic delivery for smaller lesions. This guide is general information, not medical advice.
At a glance
What is it?: An autologous cellularized scaffold: your own cultured chondrocytes on a resorbable porcine Type I/III collagen membrane, at least 500,000 cells per cm². What is it approved for?: Symptomatic, single or multiple, full-thickness cartilage defects of the knee, with or without bone involvement, in adults. Not established: Effectiveness in joints other than the knee; safety and effectiveness over age 55. How many surgeries?: Two stages: a cartilage biopsy (may be arthroscopic), then implantation weeks later. Time between stages: The label says "on average" 6 weeks; cells can be held until a surgery date is agreed. Open or arthroscopic?: Arthrotomy or arthroscopy; arthroscopic delivery is for lesions up to 4 cm² that are reachable arthroscopically (added Aug. 2024). Rehab: A physician-prescribed rehabilitation program is recommended and is part of the label. FDA status: Biologics license BLA 125603; original approval Dec. 13, 2016.
How MACI works: the two-stage process
Stage 1 — Biopsy. The surgeon takes at least two small full-thickness cartilage samples from a lesser load-bearing area of the same knee. The label says the procedure may be performed arthroscopically, typically when the diagnosis is confirmed. The samples are shipped for manufacturing, where the patient's own cells are expanded and placed on the collagen membrane to make the implant. Stage 2 — Implantation. The surgeon prepares the defect and trims the MACI implant to its size and shape, cell side down. More than one implant can be used for more than one defect. Implantation is done through an open incision (arthrotomy) or, for lesions up to 4 cm² that are accessible, arthroscopically. Not every biopsy leads to an implant. The label tells patients that MACI may not be possible if the biopsy is of insufficient quality, the cells don't grow, or the expanded cells don't meet quality requirements.
Who MACI is (and isn't) labeled for
Labeled population: adults with symptomatic, full-thickness cartilage defects of the knee. Contraindications listed on the label: Known hypersensitivity to gentamicin, other aminoglycosides, or products of porcine or bovine origin. Severe osteoarthritis of the knee (Kellgren-Lawrence grade 3 or 4) Inflammatory arthritis, inflammatory joint disease, or uncorrected congenital blood-coagulation disorders. Prior knee surgery within 6 months, excluding the biopsy or a procedure to prepare the knee for MACI. Inability to cooperate with a physician-prescribed post-surgical rehabilitation program. Assessed before or with MACI (label warning 5.3): local inflammation or infection, meniscal problems, ligament instability, and misalignment should be evaluated and treated before or at the same time as implantation. Widespread arthritis is a different problem from a focal cartilage defect. For that context see What Is Osteoarthritis? and What Is Knee Replacement Surgery?.
What the clinical trial on the label showed
The label describes SUMMIT, a 2-year, prospective, multicenter, randomized, open-label trial. It enrolled 144 patients aged 18 to 54 with at least one symptomatic Outerbridge grade III or IV focal defect on the femoral condyles and/or trochlea, and randomized them to MACI or microfracture. Per the label: At week 104, KOOS pain and function (sports and recreational activities) scores improved in both groups, and improvement was statistically significantly greater with MACI (p = 0.001). In a responder analysis, 87.5% of MACI patients versus 68.1% of microfracture patients had at least a 10-point improvement in both scores. In a 3-year extension study (128 patients), mean scores remained stable through year 5 in both groups. The proportion of patients needing at least one subsequent surgical procedure on the treated knee within 2 years was similar (8.3% MACI, 9.7% microfracture). These are the label's trial results, not a prediction for any individual patient.
Risks and side effects (from the label)
Most frequent adverse reactions (≥5%): arthralgia (joint pain), tendonitis, back pain, joint swelling, and joint effusion. Serious adverse reactions reported: arthralgia, cartilage injury, meniscus injury, treatment failure, and osteoarthritis. Warnings: the risk of malignancy in the biopsy or implant area is unknown. Biopsy tissue and implants are not routinely tested for transmissible infectious diseases. Final sterility results aren't available at shipping. Pregnancy: because implantation requires invasive surgery, use in pregnancy is not recommended. Patients should be counseled on graft complications, subsequent procedures, and treatment failure.
Recovery and rehabilitation
The label recommends a physician-prescribed rehabilitation program "that includes early mobilization, joint range of motion, and weight bearing" to promote graft maturation and reduce the risk of graft delamination, blood clots, and joint stiffness. Weight-bearing and strengthening progress in stages. Return to recreational and sporting activity should be decided with your healthcare professionals. The label gives no universal return-to-sport date, and neither does this guide.
Questions to ask an orthopedic surgeon about MACI
Is my problem a focal, full-thickness cartilage defect, or more widespread arthritis? Where is the defect, and how large is it? Am I a candidate for arthroscopic delivery (≤4 cm²) or an open procedure? Do I have meniscus, ligament, or alignment problems that need treatment first or at the same time? Am I within the labeled population (adult, and how does my age relate to the over-55 limitation)? What happens if my biopsy cells don't meet quality standards? What does the rehab schedule look like week by week, and what activity limits apply? How many MACI procedures has the surgeon's team performed, and how do they define success?
Find a doctor
Find a Doctor Haute MD does not currently list an orthopedic knee or cartilage specialist. Use Find a Doctor to browse member physicians, and confirm board certification and fellowship training in sports medicine or cartilage surgery with any surgeon you consult. Haute MD is an editorial directory; inclusion is not a ranking or a guarantee of outcomes.
Sources
FDA, MACI (autologous cultured chondrocytes on porcine collagen membrane) product page, STN BL 125603 (https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/maci-autologous-cultured-chondrocytes-porcine-collagen-membrane). FDA, MACI Package Insert, Highlights and Full Prescribing Information, revised 8/2024 (https://www.fda.gov/media/101914/download). FDA, Supplement Approval Letter BL 125603/576, August 23, 2024, adding arthroscopic delivery (https://www.fda.gov/media/181301/download). FDA Purple Book, MACI BLA 125603, original approval date December 13, 2016 (https://purplebooksearch.fda.gov/index.cfm?blaNo=125603&event=productdetails). Label and approval documents checked October 16, 2026. This information is general education, not medical advice, and does not create a doctor–patient relationship. Whether MACI or any cartilage procedure is appropriate depends on an evaluation by a qualified orthopedic surgeon.
Frequently Asked Questions
Is MACI FDA-approved?
Yes. MACI is licensed by the FDA as a biologic (BLA 125603, Vericel Corporation), with original approval on December 13, 2016. It is indicated for symptomatic, full-thickness cartilage defects of the knee in adults.
Is MACI the same as ACI?
MACI is a form of autologous chondrocyte implantation (ACI): the patient's own cartilage cells are grown and implanted. In MACI the cells are delivered on a resorbable porcine collagen membrane.
Can MACI be used in the hip, ankle, or shoulder?
The FDA label says effectiveness in joints other than the knee has not been established. Its approved indication is the knee.
Can MACI be done arthroscopically?
Since an August 2024 label update, yes, for lesions up to 4 cm² that are reachable arthroscopically. Larger or less accessible defects are implanted through an open incision.
How long between the biopsy and the implant?
The label says about 6 weeks on average, and the cells can be stored until the patient and surgeon agree on a surgery date.
Is MACI an option for arthritis?
Severe knee osteoarthritis (Kellgren-Lawrence grade 3 or 4) is a contraindication on the label. MACI is labeled for focal cartilage defects, not widespread joint wear.
Does Haute MD list prices or insurance coverage for MACI?
No. Costs and coverage vary by insurer and case. Ask the surgeon's office and your insurer directly.
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