The autogenous cartilage implantation procedure (ACI) is utilized for those patients who have a small localized area of arthritis on the end of their femur (thigh bone). FDA approval was obtained for this procedure in September 1997. Its use in the patella, tibial plateau, and other joints is still considered experimental, but has been proven to be useful for specific lesions in some centers.


ACI is not indicated for those patients who have advanced arthritis or arthritis on both sides of the joint (femur and tibia or femur and patella). It is proven to be effective for the treatment of small localized articular cartilage lesions (2 - 10 cm²), which are due to osteochondritis dissecans, traumatic injuries (such as a joint injury after an anterior cruciate ligament tear), or those with small localized areas of arthritis for which no specific cause can be determined. In addition, it is important that the selected patient not have any malalignment of their lower extremity (such as a varus (or bow-legged), or valgus (knock- kneed) knee), or any ligamentous instability. In these patients, any instability and/or malalignment of the extremity must be addressed prior to attempts at ACI. In general, the x-rays for patients who are candidates for an ACI procedure show no or minimal osteophytes (bone spurs) on their x-rays. The average age range for a patient who may be a candidate for an ACI is 15 - 55 years. Patients older than 55 are generally found to have thinner cartilage present in their remaining cartilage outside the area of the lesion and are generally felt not to benefit from this procedure.

Patients who have local areas of arthritis in their knees are generally found to have pain localized to the joint line with some possible intra-articular crepitation (crunching) associated due to the cartilage defect. It is important that all other sources of potential pathology in the joint which could be contributing to this joint line pain are ruled out. The ACI procedure involves an extensive period of rehabilitation and cost, and it is important to make sure that we are selecting patients for the surgery who would truly benefit from it.


Once a patient has been found to be a potential candidate for an ACI procedure, the next step in the work-up is to visually inspect the knee to see if in fact they have a localized area of arthritis. This is performed through the use of an arthroscopy in which the articular cartilage of the joint can be visualized and palpated with an instrument. If there is an area of arthritis which extends down to bone or has significant damage to it, the patient is a candidate for an ACI if all of the above criteria have been met. Once this has been judged to be present, it is necessary to obtain a biopsy of normal articular cartilage so that these cells can be grown and multiplied in the lab for purposes of reimplantation at a future date. This cartilage is usually taken from the superior medial trochlear groove (upper portion of the femur articular cartilage) or the intercondylar notch of the femur (which is most often utilized in those patients who are concurrently undergoing an anterior cruciate ligament reconstruction).

Once the patient has been properly rehabilitated from their arthroscopic or other concurrent surgery, they are ready for reimplantation of their cartilage cells. The usual minimal time for reimplantation to occur is 3 - 4 weeks. In the stages between the actual arthroscopy and evaluation of the articular cartilage and the implantation of the cartilage cells, it is important that the patient receive proper counseling as to the necessary steps in rehabilitation after surgery and to the absolute need for their compliance to increase their chances of a successful result. Noncompliance on the part of the patient could result in significant patellofemoral dysfunction after surgery, disruption of the implant, or development of joint stiffness after surgery.

The ACI procedure needs to be performed with an open knee incision. The incision is approximately 10 inches long and through the process of making this incision the kneecap must be elevated and displaced laterally (towards the outside of the knee) to gain access to the articular cartilage defect. Once the cartilage defect has been defined, the areas of abnormal cartilage are removed with the use of a curette or knife and the supporting bone structure of the cartilage defect base is freshened up to remove all scar tissue. Once this defect has been well defined, methylene blue dye is placed around the sides of the sides of the defect, and then a sterile piece of surgical glove paper is placed over the defect and the imprint from the dye is used as a template for the next stage of the procedure.

The next stage of the procedure involves taking a piece of periosteum from either the tibia or the femur. The periosteum is a covering over the bone and is analogous to the bark on a tree. It is very thin and removing it from the bone is very meticulous. Once the piece of periosteum has been harvested, the tourniquet can be let down on the knee and all bleeding is stopped with the use of a coagulator. It is especially important to stop all the bleeding in the base of the cartilage defect, as the hemosiderin (iron) in blood has been found to be toxic to the growing chondrocytes. Once all the bleeding in the prepared defect area has been stopped, the periosteum is microsutured to the edge of the remaining articular cartilage. This portion of the procedure is very tedious and involves microsuturing techniques. Both the periosteal flap and the articular cartilage are very fine. The suturing technique is analogous to sewing tissue paper to a hard boiled egg. It is important to make sure that the sutures are placed correctly on the first attempt, as holes in the periosteum or cartilage could result in leakage of some of the cells out from under the graft. Once the periosteal flap has been sutured to the articular cartilage, it is important to test the integrity of this suture repair to make sure that there is no leakage of fluid from it. We do this by injecting sterile saline into the defect and verifying that there is no leakage. Once a watertight seal has been obtained, a fibrin glue, which can be prepared either from a patient's own donated blood or from commercially available product, is placed around the edges of the microsutured periosteum to serve as an additional backup to the suture repair. A small area is left unsutured at the top of the periosteum for purposes of injecting the cells.

At this point in time, the cells are obtained from their vial which has been shipped via overnight express from the preparing laboratory. These are obtained in a small syringe and are then injected under the periosteal flap. The final suturing of the periosteum at the top of the defect is performed, followed by further use of fibrin glue. At this point, attention is turned towards closure of the knee joint.


Immediately after surgery, the patient is placed into a knee immobilizer to give stability to the knee and is maintained on a nonweight bearing status using crutches for approximately 4 weeks. This period of nonweight bearing can be variable depending upon the location and size of the lesion. The use of a continuous passive motion (CPM) machine is utilized in the initial 6 weeks after surgery for 2 purposes. The purpose of the machine is to actually move the knee joint such that it does not become stiff and it does this by not having to have the patient fire their own muscles which could negatively affect the suture repair. It is important that the joint not become stiff after surgery and a CPM is very valuable in preventing this stiffness. In addition, it has been shown in animal studies that the use of a CPM machine provides nourishment to damaged cartilage and we believe that this assists the implanted cartilage cells in obtaining nutrition.

We have developed a specific rehabilitation program at the University of Minnesota for the treatment of ACI patients. In this protocol, patients are allowed weight bearing based to tolerance at approximately 4 weeks after surgery and then are advanced along the protocol according to their level of pain. They are allowed to wean themselves off of crutches once they can walk without a limp and then slowly increase their activities. The total time of rehabilitation after an ACI lasts for approximately 1 year.

It is important to realize that an ACI procedure is different than any other procedure currently being performed in orthopaedic surgery. At 3 months after surgery, it has been found that the healing cartilage cells are soft as a marshmallow when probed arthroscopically and therefore it is important not to perform any strenuous activities at this time so that the graft does not pop off. It is generally felt that most activities are safe at approximately 1 year after surgery. This has been confirmed by stiffness evaluations of the cartilage at which point it is felt to be close to normal.

ACI has been found to be an excellent procedure in patients with a localized area of arthritis or areas of osteochondritis dissecans on their femoral condyles. In a 5 year clinical follow up in the United States, approximately 80% of patients have been found to have good or excellent results with this procedure. ACI is a procedure which requires strict attention to detail and precision on the part of the surgeon in order to obtain maximum benefit. However, in addition to obtaining good cells and good operative technique, it is important that the patient be compliant in their postoperative rehabilitation and follow their protocol to maximize their chance of obtaining a good result.

Injection of cells under periosteal flap
ACI region 6 months after surgery
Articular cartilage defect