Two very different operations for focal knee cartilage defects — and the right answer is almost always about your lesion size, your age, and your activity goals. LAOSS sports-medicine surgeons walk through the decision honestly: when microfracture is enough, when MACI is worth the two-stage commitment, and when neither is the right call.
We match the technique to your lesion, not the other way around.
Microfracture and MACI are both joint-preserving operations for focal articular cartilage defects in the knee — usually on the femur (top of the thigh bone) or the patella (kneecap). They share a goal (restore the smooth cartilage surface so the joint glides again) and a population (active patients with a defined cartilage hole, not widespread arthritis). They differ in almost everything else.
Microfracture is the older of the two. The surgeon arthroscopically cleans up the defect and then makes small holes in the underlying subchondral bone using an awl or drill. Those holes release marrow cells that form a clot in the defect. Over the following months, the clot remodels into fibrocartilage — a repair tissue that looks similar to native cartilage but is mechanically inferior. It's covered by insurance, done in one operation, and recovery runs about 6–9 months. The downside: fibrocartilage tends to wear down faster, and outcomes for many patients decline noticeably between years 2 and 5, especially for larger defects.
MACI (Matrix-Induced Autologous Chondrocyte Implantation) is a two-stage procedure. Stage one is an arthroscopic biopsy where your surgeon harvests a small piece of healthy cartilage from a non-weight-bearing area. That sample is shipped to a specialty lab, where your own chondrocytes are grown for about six weeks on a porcine collagen membrane. Stage two is a mini-arthrotomy — a small open incision — to implant the cell-seeded membrane into the prepared defect. The repair tissue that grows in is hyaline-like cartilage, far closer to your native cartilage in structure and durability. The trade-offs: two surgeries, a longer 9–12 month recovery, higher cost, and insurance pre-authorization. The upside is a more durable repair, especially for larger defects (roughly 2–10 cm²).
The honest answer to which is better is: it depends on the lesion. A 1 cm² defect in a 25-year-old usually does fine with microfracture. A 6 cm² defect in a 45-year-old who wants to keep running marathons is almost always better served by MACI. The 2–4 cm² range is where the conversation gets nuanced — and where having a surgeon who does both routinely matters most.
MACI is the modern, membrane-based evolution of ACI. This animation shows the two-stage workflow — biopsy, lab culture, then implantation — that distinguishes cell-based cartilage repair from marrow-stimulation techniques like microfracture.
Animations licensed from ViewMedica · Swarm Interactive
Microfracture works from the bottom up: by penetrating the subchondral bone, the surgeon releases pluripotent marrow cells that form a clot in the defect and remodel into fibrocartilage over 6–9 months. MACI works from the top down: your own chondrocytes are harvested, expanded for six weeks on a collagen membrane, and then implanted into the prepared defect — where they organize into hyaline-like cartilage that more closely matches your native joint surface. Hyaline cartilage is what was there before; fibrocartilage is the body's best attempt at a substitute.
Both microfracture and MACI start with the same diagnostic workup, because the decision is driven by what we actually see on imaging.
Your first visit includes a focused history (mechanism of injury, prior surgeries, what aggravates symptoms, your activity goals), a hands-on knee exam, and same-day X-ray to assess alignment, joint space, and any underlying bony causes. When a focal cartilage lesion is suspected, we order an MRI with cartilage-specific sequences — typically a 3T scan with high-resolution mapping that lets us measure the defect in two dimensions and assess the depth and the state of the underlying subchondral bone.
The MRI gives us the four variables that drive the decision: size (in cm²), depth (chondral only vs. osteochondral), location (femoral condyle, trochlea, patella, tibial plateau), and the rest of the joint (meniscus status, alignment, ligament integrity, any kissing lesion on the opposing surface). With those numbers in hand, the technique choice is usually straightforward — and we walk you through the reasoning, not just the recommendation.
Neither operation is universally better. The decision turns on the lesion itself, the rest of the joint, and what you want to be doing in five and ten years. Here's the framework LAOSS surgeons use — the same one we'll walk through with you at your visit.
Microfracture is the right starting point when the defect is small, the patient is younger, and a single straightforward operation is the priority.
MACI is worth the two-stage commitment when the defect is larger, the patient wants durable repair tissue, and a higher-demand activity life is on the table.
Cost is rarely the deciding factor for cartilage reconstruction — both procedures are typically covered when medical necessity is documented — but it does shape the timeline. Here's how the two compare in practice.
Microfracture is the lower-friction option financially and administratively, which is why it's still often the first cartilage operation a patient is offered.
MACI is more expensive on paper, but in our experience it's covered for the majority of medically appropriate patients — with paperwork the LAOSS team handles in-house.
Both procedures share the same baseline candidacy criteria. The split happens after that, on lesion size and durability priorities.
These rough profiles are how we think about candidacy in clinic — not a hard rule, but the pattern we see most often.
We'll give you a real answer the same day — including a candid read on whether either operation actually fits your case.
Both operations follow a protected-loading model — the repair has to mature before it can take full weight. MACI runs about three months longer end-to-end, but the phase structure is similar.
Early protection is non-negotiable for both procedures. The repair tissue (fibrocartilage clot for microfracture, cell-seeded membrane for MACI) is at its most fragile in the first six weeks.
Load increases on a schedule. MACI typically lags microfracture by 2–4 weeks at each milestone because the membrane takes longer to integrate.
Microfracture patients often clear for light running around month 4–5 and sport around 6–9. MACI patients clear for running closer to month 6 and sport at 9–12 — with a one-year MRI to confirm repair maturation.
Both operations are safe in experienced hands, but each has its own profile of risks and failure modes. These are part of every pre-op conversation at LAOSS.
Microfracture is technically straightforward, but its biology has real ceilings — especially for larger defects and higher-demand patients.
MACI's failure modes are more about logistics and the two-stage timeline than the biology itself, which is generally more favorable than fibrocartilage.
Cartilage reconstruction is one of the most technique-dependent operations in orthopedics — and the surgeons who do it well do both microfracture and MACI routinely, so the recommendation isn't biased by what they're comfortable performing. At LAOSS, our sports-medicine team matches the procedure to your MRI and your goals, not to a preferred technique.
5 stars. Got in same day for a soccer injury, X-ray right there in the office, had a plan before I left. Couldn't ask for more.
Book a visit with a cartilage reconstruction specialist at any of our eight Los Angeles–area offices. We'll review your MRI, measure the defect, and walk through microfracture vs MACI for your specific case.
