What a decade of data actually shows

The most common concern patients bring to a MACI consultation is not about the operation itself — it is about what comes after. Will the improvement hold, or will the knee gradually slip back to where it started?

Two of the strongest studies now available give a direct answer. A 2024 systematic review by Wang et al. followed 168 patients across 188 treated defects for a minimum of ten years. The prospective Australian registry (Ebert 2024, 204 patients enrolled) tracked outcomes across the same timeframe. Both tell a consistent story: patient-reported outcome measures — including KOOS, IKDC, and Lysholm scores — rise substantially in the first one to two years after MACI and then hold. There is no statistically significant decline from year two through year ten. The pattern is a plateau, not a slow decay.

That plateau has a real-world correlate. At the ten-year mark in the registry cohort, 92% of patients reported satisfaction with their pain relief, and 76% were satisfied with their capacity to participate in sport and physical activity. These are not marginal gains preserved only under clinical conditions — they represent a decade of lived experience for people who had complex, full-thickness focal defects where simpler treatment options were unlikely to be durable.

For patients weighing a two-stage procedure against less involved alternatives, this durability is the central piece of evidence. The data suggest MACI does not merely provide short-term relief; in appropriately selected patients, it consistently maintains that improvement across a clinically meaningful horizon.

How MACI compares to microfracture at five years

Registry data is persuasive, but head-to-head trial evidence carries more weight when comparing two techniques — confounding by patient selection, defect size, and surgeon choice is largely removed. The SUMMIT Phase 3 RCT provides exactly that benchmark for MACI versus microfracture.

In SUMMIT (144 patients, mean lesion size 4.8 cm²), MACI was statistically superior to microfracture across all five KOOS domains at two years — pain, symptoms, activities of daily living, sport and recreation, and quality of life. Crucially, that superiority did not narrow at the five-year follow-up; the between-group advantage held. Sustained RCT-level superiority to five years is uncommon in the cartilage literature, and SUMMIT remains one of the few trials to demonstrate it.

Defect size sharpens the picture further. For lesions measuring 3 cm² or more, both KOOS pain and KOOS function favoured MACI at two and five years. This is consistent with a broader principle: MACI is indicated for full-thickness defects of roughly 2–10 cm², a range where marrow-stimulation techniques tend to underperform. Microfracture produces fibrocartilage — a structurally inferior repair tissue — and evidence shows this begins to break down within two to three years. The procedure also carries a risk of subchondral bone plate disruption, which can compromise the biological environment for any subsequent repair attempt.

Microfracture retains a historical role for very small defects in selected patients, but it is not a modern first-line option for the lesion sizes that typically present for MACI assessment.

Graft survival and the risk of needing further surgery

Structural graft survival — whether the implant itself remains intact — is the bedrock question beneath everything else. By Kaplan-Meier analysis, MACI achieves a graft survival rate of 97.2% at 9.5 years, free from revision for any reason (SAGE 2024).

Survival of the graft is not the same as freedom from any further surgery. The 2024 systematic review by Wang et al. (168 patients, 188 defects, 10–17 years' follow-up) puts the all-cause reoperation rate at 9.0% — low, but not zero. Over the same follow-up window, 7.4% of patients progressed to total knee arthroplasty.

That figure deserves context before it is read as a failure rate. Patients who reach MACI assessment typically carry ICRS grade 3–4 full-thickness defects of 2–10 cm² — lesions where simpler options were already unlikely to hold. Against that background, 92% of patients with complex focal damage avoided knee replacement across more than a decade. For joint preservation, that is the meaningful benchmark.

MRI data runs parallel to the clinical picture. MOCART scores — which grade the quality and completeness of repair tissue fill on imaging — show good defect coverage in the early postoperative period and remain stable at later time points, corroborating the durability already visible in the patient-reported outcomes. The structural and functional signals point in the same direction.

Why the tissue biology doesn't tell the whole story

Around 73% of MACI grafts produce fibrocartilage rather than true hyaline cartilage when examined histologically — a finding that sounds alarming until the functional data is placed alongside it. Hyaline cartilage is the native articular tissue; fibrocartilage is structurally coarser and biomechanically less resilient. The gap between those two facts is wide: 82% of patients achieve return to sport after MACI, a rate that histological classification alone would not predict.

The explanation lies in how cartilage repair is measured clinically. Patient-reported outcome measures — KOOS, IKDC, Lysholm — are the established benchmark precisely because joint function and pain relief are what patients live with. A graft that is fibrocartilage on biopsy but delivers stable, pain-free movement is, by that standard, a successful graft. MRI MOCART scoring reinforces the point from a different angle: it grades defect fill and structural integration rather than tissue lineage, and its stable trajectory over time reflects a repair that remains mechanically coherent even where the cartilage type is fibrous. Histology captures what the tissue is; PROMs capture what it does — and in the long-term MACI data, what it does holds up well.

Which patients tend to do best

Several factors consistently emerge from long-term registry and trial data as predictors of stronger MACI outcomes:

Age under 45. Younger patients show more durable improvement across KOOS and IKDC measures at 10 years. Older patients — particularly those with early focal OA rather than purely traumatic defects — still achieve meaningful pain relief and joint preservation, but the magnitude and reliability of benefit are generally lower.

Fewer prior knee surgeries. Previous marrow-stimulation procedures such as microfracture are associated with reduced outcomes, largely because the subchondral bone plate may have been disrupted in ways that affect graft integration. This is a planning consideration rather than an absolute barrier to treatment.

Lower BMI. Higher body weight increases mechanical load on the repair and is associated with greater revision risk in long-term data.

Limb alignment. Where the mechanical axis is abnormal — tending to overload the repaired compartment — MACI may be combined with a corrective osteotomy (HTO or DFO) to shift load away from the graft. Without that correction, even a technically sound implant faces unfavourable mechanical conditions.

The OA boundary. MACI is designed for deep, full-thickness focal damage — the kind that ICRS grading classifies as grade 3 or 4. Patients with diffuse or advanced osteoarthritis, where cartilage loss is widespread rather than focal, sit outside this scope; for them, the appropriate pathway shifts toward joint replacement rather than focal repair.

Getting an assessment at the London Cartilage Clinic

Deciding whether MACI is appropriate requires a structured clinical assessment rather than a review of population data alone. The relevant variables — defect size and ICRS grade, limb alignment, number of prior procedures, age, and BMI — interact in ways that population averages cannot resolve for an individual patient. A specialist with experience across the full range of cartilage restoration options is best placed to weigh those factors together and, where MACI is not the right fit, to identify which alternative — AMIC, OATS, osteochondral allograft, or a staged approach — is more likely to be durable.

For patients in London exploring these options, Professor Paul Y. F. Lee and the team at the London Cartilage Clinic on Harley Street offer that kind of specialist cartilage assessment. An initial consultation at londoncartilage.com is a practical starting point for anyone who wants a clearer picture of their own situation.

1. [1] Minimum 10-Year Outcomes of Matrix-Induced Autologous Chondrocyte Implantation in the Knee. (2024). https://doi.org/10.1177/03635465231205309 https://doi.org/10.1177/03635465231205309
2. [2] Comparison of MACI vs AMIC and Arthroscopic Minced Cartilage — 2-Year Follow-Up. (2025). https://doi.org/10.3390/jcm14072194 https://doi.org/10.3390/jcm14072194
3. [3] Favorable Short-Term Outcomes of MACI for Osteochondral Lesions of the Talus: A Systematic Review. (2025). https://doi.org/10.1016/j.arthro.2025.07.045 https://doi.org/10.1016/j.arthro.2025.07.045