MACI (Matrix-Induced Autologous Chondrocyte Implantation)

Overview

MACI is a two-stage cartilage repair that uses a patient's own cartilage cells, grown on a collagen membrane, to resurface a full-thickness knee defect. Dr. Raffo uses it for larger, contained chondral lesions in patients who want a durable, biologic repair. It requires an initial biopsy, several weeks of cell culture, then a second surgery to implant the graft.

How Dr. Raffo Performs This Procedure

The first stage is a brief arthroscopic procedure to harvest a small cartilage biopsy from a non-weight-bearing area of the knee. The biopsy is sent to the manufacturer, where chondrocytes are isolated and cultured onto a porcine collagen membrane over roughly 4 to 6 weeks. The second stage is the implantation itself: the defect is prepared through a small arthrotomy, sized precisely, and the cultured membrane is trimmed to match and secured in place, typically with fibrin glue. If the knee also needs a concomitant procedure — a tibial tubercle osteotomy for patellar maltracking, for example — it is generally performed at the same time as implantation.

Who Is This For?

MACI is FDA-indicated for "the repair of symptomatic, single or multiple full-thickness cartilage defects of the knee with or without bone involvement in adults" (FDA — MACI product page). The indication is not restricted to one part of the knee — a large US real-world series notes that "MACI has approval for any lesion within the knee joint," which is why patellar and trochlear defects are commonly treated on-label alongside femoral condyle lesions (Milliron/Flanigan, Cartilage 2025). Good candidates typically have a defect at or above roughly 3 cm² — the size threshold enrolled in the pivotal trial — since that is where MACI has demonstrated a clear advantage over microfracture (Saris et al. 2014). MACI is not the right choice when there is substantial bone loss requiring restoration of the osteochondral unit, or in a knee with underlying osteoarthritis, neither of which the MACI label is built to address.

Recovery & Rehabilitation

Recovery from MACI has two distinct phases relative to the two surgeries. After the biopsy, recovery is brief since it is a minor arthroscopic procedure. After implantation, the timeline is longer and protects the developing graft.

• 0–6 weeks post-implantation: Protected, limited weight-bearing with a brace, and range-of-motion exercises are introduced early.
• 6–12 weeks: Progressive weight-bearing and strengthening as the graft matures.
• 3–6 months: Return to low-impact activity and conditioning for most patients.
• 9–13 months: Assessment for return to higher-demand sport; outcomes continue to improve through the first 2 years before typically plateauing, with little further change from 2 to 10 years (Ebert et al. 2024).

Biologics Used