Autologous chondrocyte implantation (ACI) is a relatively new, state-of-the-art procedure used to treat full-thickness cartilage defects in knee joints. This surgical procedure replaces damaged cartilage in the knee joint with healthy cartilage cells. To carry out this procedure, small samples of normal cartilage with the cells (chondrocytes) that produce the cartilage are removed from the damaged joint. The chondrocytes are cultured in special laboratories to increase the number of cells and harvested for implantation into the areas of cartilage damage. The aim of this procedure is to restore normal cartilage to the ends of bones and thereby restore normal joint function.
ACI is most useful for younger patients who have single defects larger than 2 cm in diameter. It has the advantage of using the patient’s own cells, so there is no danger of a patient rejecting the tissue. It does have the disadvantage of being a two-stage procedure that requires an open incision. It also takes several weeks to complete.
The ACI procedure is usually performed in two stages, with two separate surgeries. New cartilage cells are grown and then implanted in the cartilage defect. The first procedure is performed arthroscopically in less than 30 minutes. In this step, healthy cartilage tissue is removed from a non-weight bearing area of the bone using arthroscopy. The tissue, which contains healthy cartilage cells or chondrocytes, is then cultured and harvested in the laboratory. The harvesting of chondrocytes from the culture takes three to five weeks. ACI is then carried out to implant the newly grown cells. The cartilage defect is prepared. A layer of bone-lining tissue, called periosteum, is sewn over the area. This cover is sealed with fibrin glue. The newly grown cells are then injected into the defect under the periosteal cover.
After surgery, the joint surface must be protected while the cartilage heals. Following implantation there is a period of restricted weight-bearing for up to eight weeks. The patient may need to use crutches to move around for the first few weeks after surgery. Physical therapy emphasizing range of motion of the knee and strengthening activities is prescribed. During the first weeks after surgery, patients may begin continuous passive motion therapy. A continuous passive motion machine constantly moves the joint through a controlled range of motion. As healing progresses, therapy will focus on strengthening the joint and the muscles that support it.
Return to light sports activities is typically allowed at approximately six months, with return to full sports activities between nine and twelve months following the procedure, based on the recovery. The overall success rate of ACI is approximately 85% in allowing patients to return to pain-free activities.