Matrix-induced autologous chondrocyte implantation (MACI) can be used to restore knee cartilage in cases of medium to large defects. MACI is a two-stage procedure.

In the first stage, arthroscopy is performed to evaluate the size and location of the defect. If the surgeon determines that MACI is appropriate, a sample of cartilage is taken from a non-weight-bearing part of the knee. This sample tissue then is sent to a lab, where cells are removed and expanded over 4 to 6 weeks through a special procedure.

The second stage involves implanting the expanded cells back into the area of the defect. This can be performed within 4 to 6 weeks, or the cells can remain frozen for up to two years if implantation is delayed. The surgeon may implant the expanded cells through an open incision or arthroscopy, depending on the size and location of the defect being treated.

At the time of re-implantation, the new material, called the MACI membrane, is trimmed to the desired size and shape, and secured to the bone with a special glue. Sutures might also be used to attach the material to the stable surrounding rim of cartilage.

Rehabilitation

Post-operative rehabilitation starts with immediate motion. A special machine is used for 6 to 8 hours a day for the first 6 weeks to move the patient toward a 90-degree knee bend. Depending on the type of defect, the patient may remain toe-touch weight-bearing for 6 weeks and then progress towards weight-bearing as tolerated, or may be full weight-bearing with full extension as tolerated immediately after surgery. Running and strenuous sports activity is not allowed for 9 to 12 months.

Outcome

Five-year outcomes reveal success rates of 90 percent or greater. Longer-term (10 to 20 years) outcomes have reported success rates of 70 to 75 percent.