Chondrocyte Grafting

Since its first use in 1987, the use of autologous chondrocyte implantation (ACI) for cartilage repair has captured media attention and gained a place in the surgical toolbox. In this procedure cartilage cells, or chondrocytes, are harvested from a patient's own cartilage, multiplied in culture and grafted into the damaged site.

Cartilage and Chondrocytes

• Cartilage protects the ends of bones from rubbing together, but it can be damaged by joint injury or inflammatory diseases like arthritis. Chondrocytes are sparse within the cartilage, and they are often located far from nutrient-rich blood vessels. Because of this, cartilage, unlike bone or skin, is slow to heal and permanent damage can result in the absence of surgical intervention. ACI works by increasing the number of chondrocytes available to make cartilage at the damage site.

Procedure

• ACI requires two separate surgical procedures. During the first surgery, chondrocytes are harvested in a cartilage plug from a donor site, usually the top of the knee joint. The cells are then extracted and grown in special nutrient medium. After about two weeks, the second surgery is performed. The damaged cartilage is thoroughly removed, leaving a hole in the surrounding healthy cartilage. A small section of periosteum, the thin membrane that covers all long bones, is harvested and used to cover the empty hole. The chondrocytes are injected into the hole and the surgical site is closed.

Indications

• According to a recent review, ACI has now been used on over 15,000 patients. Originally the procedure was performed for patients with damaged knee cartilage; it is now used for damage to the ankle joint as well. Because of the need for healthy cartilage surrounding the hole, ACI is not currently indicated for patients with very large damage sites or systemic cartilage damage like that seen in severe arthritis. At the same time, relatively small damage sites can be repaired using autologous cartilage plugs directly, without the need for isolating and culturing the chondrocytes or a second surgical procedure. ACI is therefore indicated in a relatively narrow range of patients, with the best results seen in patients with injury-caused defects between about 3 mm and 10 mm in diameter.

Outcomes

• Numerous studies have demonstrated the efficacy of ACI. In a study where half of the patients received ACI and half received mosaicplasty, in which several cartilage plugs are harvested and directly transplanted into the injury site, the ACI patients had significantly better outcomes. In the patient population where it has been used, a success rate of about 80 to 90 percent has been reported, as defined by reduced pain and increased function. A 2002 study of 61 patients indicated that in successful cases the resulting cartilage can remain stable for at least 10 years. In cases where the repaired joint was subsequently probed arthroscopically, the cartilage in the defect had the same appearance and consistency as the original cartilage.

Advantages and Disadvantages

• As described in the previous sections, ACI has the a high success rate in patients with narrowly defined cartilage defects. In these patients, the regenerated cartilage is durable and structurally similar to the original cartilage. The main disadvantages of ACI are the need for two surgical procedures, the technically demanding surgical technique, and its high cost. Another drawback is the limited patient population for which the technique is applicable.

Scaffold-Assisted ACI

• Some new techniques are available in which the chondrocytes are grafted into the joint in a gel-like scaffold, with the intention of providing a more even distribution of cells, allowing use of the ACI technique in a wider variety of circumstances, and negating the need for a periosteum flap transplant. Although followup studies show that this is as safe and effective as free implantation of the chondrocytes, there is no data to date suggesting that the use of the scaffold improves clinical outcomes.