Cartilage Injury in the Knee: Assessment and Treatment Options

Aaron J. Krych, MD; Daniel B. F. Saris, MD, PhD; Michael J. Stuart, MD; Brittney Hacken, MD


J Am Acad Orthop Surg. 2020;28(22):914-922. 

In This Article

Matrix-induced Autologous Chondrocyte Implantation

Matrix-induced autologous cultured chondrocytes implantation (MACI) was approved by the FDA in 2017 in the United States and is currently the only FDA-approved cell-based cartilage treatment option. MACI has evolved from the excellent long-term track record of ACI but fulfills the need for a more efficient technique. Previously, first-generation ACI used an autologous periosteal membrane, with the second generation using a bioabsorbable collage membrane sewn into place, under which cultured chondrocytes were injected (Figure 6). MACI uses a membrane that acts as a cell carrier to more evenly distribute the cells with a density of 500,000 to 1,000,000 cells per cm2 and is easier to implant.[34,35]

Figure 6.

Photographs of the autologous chondrocyte implantation with a collagen membrane sewn in place with injection of autologous cultured chondrocytes under the membrane.

MACI is typically used in patients with an articular cartilage lesion greater than 2 cm2 in size who have failed nonsurgical treatment. It has the advantage of being a form-fitting membrane that can fit into a variety of different size and shape lesions.

MACI is a two-stage procedure, with the first stage involving cartilage biopsy that is then sent to a laboratory for culturing of the chondrocytes on a collagen membrane. The biopsy most typically is harvested from either the intercondylar notch, the proximal aspect of the medial or lateral femoral condyle, or from the rim of the lesion. During the second stage of the procedure, the defect is débrided to stable edges with vertical walls. Any remaining cartilage is curetted down to the level of the calcified cartilage to create a contained defect. The graft is then prepared to the same size and shape. This can be performed using preshaped cutting tools or can be performed free hand.[34,36] During implantation, fibrin glue is applied within the defect bed, and the membrane is then gently compressed down against the defect. After securing the membrane, an additional thin even layer of fibrin glue is applied over the membrane and allowed to cure. The final result should be a stable membrane that evenly fills the defect (Figure 7).

Figure 7.

Photographs showing the matrix-induced autologous cultured chondrocytes implantation. A, Demonstrates a >2 cm2 trochlear lesion after it has been cleared of fibrous tissue and stable walls now surround the defect. B, A size- and shape-matched graft has been secured with fibrin glue. C, Second look procedure demonstrates the graft has nicely filled in the defect with stable rims.

The results after MACI have been promising and demonstrate notable clinical improvement when compared with microfracture in randomized prospective studies at the 5-year follow-up.[35] Studies have shown an estimated 9% to 10% revision surgery rate in MACI/ACI patients with symptomatic overgrowth of the cartilage is a potential source of revision surgery.[34,35] The fact that MACI requires two stages and being expensive are the greatest limitations to this procedure.[37]