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Matrix-Associated Chondrocyte Transplantation (MACT)

Matrix-associated chondrocyte transplantation (MACT) is a modern regenerative procedure used to repair cartilage defects in the knee using the patient's own cartilage cells.

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Matrix-associated chondrocyte transplantation (MACT) is a modern regenerative procedure used to repair cartilage defects in the knee using the patient's own cartilage cells.

What is matrix-associated chondrocyte transplantation?

Matrix-associated chondrocyte transplantation (abbreviated MACT or MACI) is a biological procedure in regenerative medicine used to treat cartilage defects, primarily in the knee joint. The patient's own cartilage cells (chondrocytes) are harvested, multiplied outside the body on a biodegradable carrier matrix, and then implanted into the cartilage defect. The technique represents an advancement of the classic autologous chondrocyte transplantation (ACT).

Indications

MACT is primarily used for larger, well-defined cartilage defects caused by trauma, sports injuries, or degenerative changes. Typical indications include:

Focal cartilage defects of the knee joint (e.g., on the femoral condyle or patella)
Cartilage defects grade III and IV according to the ICRS classification (International Cartilage Repair Society)
Osteochondral lesions (combined cartilage and bone damage)
Failed previous cartilage repair procedures (e.g., microfracture surgery)

The procedure is generally suitable for patients between 15 and 55 years of age, as the regenerative capacity of chondrocytes may be reduced in older patients.

Procedure Overview

Step 1: Cartilage cell harvest

In an initial minimally invasive procedure (arthroscopy), a small sample of healthy cartilage tissue is taken from a low-load-bearing area of the knee joint. This biopsy contains living chondrocytes that are then sent to a specialized laboratory.

Step 2: Cell culture and matrix seeding

In the laboratory, the harvested chondrocytes are multiplied (cultured) over several weeks. They are then seeded onto a biodegradable carrier matrix, typically composed of collagen type I/III or synthetic biopolymers. This matrix serves as a scaffold that holds the cells in place and supports their integration into the surrounding tissue.

Step 3: Implantation

In a second surgical procedure, the chondrocyte-seeded matrix is placed into the prepared cartilage defect. This can be performed arthroscopically (minimally invasive) or via open surgery. The matrix is secured with fibrin glue or sutures and gradually integrates into the surrounding cartilage tissue during healing.

Difference from classic autologous chondrocyte transplantation (ACT)

In classic autologous chondrocyte transplantation (ACT), the cells are injected as a cell suspension beneath a periosteal flap. MACT uses a carrier matrix instead, offering several advantages:

More uniform distribution of cells within the defect
Greater mechanical stability during the healing phase
Reduced risk of hypertrophy (excessive tissue overgrowth)
Possibility of minimally invasive implantation

Aftercare and Rehabilitation

Post-operative rehabilitation is critical to the success of the treatment. In the first weeks after surgery, partial weight-bearing of the operated joint is required to protect the integrating cells. A typical rehabilitation protocol includes:

0–6 weeks: Non-weight-bearing or partial weight-bearing, passive range-of-motion exercises
6–12 weeks: Gradual increase in loading, physiotherapy
3–6 months: Muscle strengthening and coordination training
6–12 months: Return to sports activities possible

The newly formed cartilage tissue can take up to two years to fully mature and become load-bearing.

Outcomes and Prognosis

Clinical studies show that MACT can lead to significant improvements in pain relief and joint function in suitable patients. Long-term studies demonstrate good to excellent outcomes in the majority of patients over a period of 5 to 10 years. MACT is considered a promising alternative to joint replacement (endoprosthesis) for younger patients with focal cartilage defects.

Risks and Side Effects

As with any surgical procedure, general risks such as infection, thrombosis, and bleeding exist. Specific risks of MACT include:

Insufficient integration of the transplanted cells
Graft failure (cell death)
Graft hypertrophy (less common than with classic ACT)
Joint stiffness or arthrofibrosis

References

Brittberg M. et al. - Treatment of Deep Cartilage Defects in the Knee with Autologous Chondrocyte Transplantation. New England Journal of Medicine, 1994; 331(14): 889–895.
Kon E. et al. - Matrix-assisted autologous chondrocyte transplantation for the repair of cartilage defects of the knee. American Journal of Sports Medicine, 2011; 39(12): 2558–2565.
Saris D. et al. - Matrix-Applied Characterized Autologous Cultured Chondrocytes Versus Microfracture. American Journal of Sports Medicine, 2014; 42(6): 1384–1394.

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