MACI — Matrix-Induced Autologous Chondrocyte Implantation

Matrix-induced autologous chondrocyte implantation (MACI) is a third-generation autologous chondrocyte implantation (ACI) technique that uses tissue-engineered cartilage cells loaded onto a biocompatible porcine type I/III collagen bilayer scaffold for treatment of symptomatic full-thickness articular cartilage defects in the knee. It evolved from first-generation ACI (Brittberg, 1994) and second-generation membrane-cover ACI to overcome cell leakage, periosteal hypertrophy and uneven cell distribution.

Indications include symptomatic, full-thickness ICRS (International Cartilage Repair Society) grade 3 or 4 articular cartilage defects of the knee, 2–10 cm², in skeletally mature patients (≥ 18 years), with intact menisci, stable ligaments and well-aligned limb (corrected at concomitant osteotomy if needed). MACI is FDA-approved (2016) for trochlea, condyles, and patella; commonly performed in athletes and active patients for whom microfracture would yield inferior fibrocartilage repair.

Procedure is two-staged: Stage 1 (arthroscopy) — biopsy of 200–300 mg of healthy cartilage from a non-weight-bearing area (intercondylar notch, superior trochlea); cells are isolated, expanded in GMP-certified facility, and seeded onto a 14.5-cm² porcine collagen I/III bilayer membrane over 4–6 weeks. Stage 2 (mini-arthrotomy) — defect is debrided to subchondral bone (preserving subchondral plate to avoid mosaicplasty-style chondral overgrowth), MACI membrane trimmed to defect template, fixed with fibrin glue (Tisseel), with optional sutures at edges. Rehabilitation involves protected partial weight-bearing 6 weeks, progressive ROM, full return to recreational sport at 12–18 months.