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Long-Term Results of Autologous Chondrocyte Implantation of the Knee

The authors of this study provide us with some long-term information about the results of autologous chondrocyte implantation (ACI) for large lesions in high-demand patients (athletes). Autologous chondrocyte implantation refers to using the patient's own cartilage to repair the problem.

This study follows a long line of other studies that have led to the current standard of care for hyaline or articular cartilage injuries of the knee. The affected cartilage covers the ends of bones. It is made up of cartilage cells called chondrocytes. Damage to this structure can cause holes called defects or lesions. Continued daily use of the joint puts pressure on the damaged area leading to pain, swelling, and sometimes locking or catching of the knee.

When these symptoms result in loss of function, the surgeon can perform a debridement or microfracture procedure. Debridement removes any loose fragments and smoothes the cartilage surface of the joint. Microfracture is the drilling of tiny holes through the cartilage to the joint surface. This technique stimulates bleeding and sets up a healing response.

A third treatment option for first-line care of cartilage injuries is an osteochondral autograft transplantation. This involves harvesting a layer of cartilage and bone from a healthy area of the same patient's joint and transferring it to fill in the hole. Any of these first-line treatment approaches work well for inactive or low-demand patients with a small lesion. But for active patients with large defects, a different procedure might work better. That's the autologous chondrocyte implantation (ACI).

To perform an ACI, the surgeon first removes healthy cartilage cells from the patient and sends them to a special lab where they grow more of the same type of cells. When there are enough cells to fill the hole, the surgeon performs the second part of the procedure. The hole is prepped for the new cells, which are then placed in and around the defect. The implanted area is then covered over with a patch of periosteum, the outer layer of bone (also harvested from the patient). The patch fits over the repaired defect like a manhole cover.

The surgeon doesn't just repair the defect. It's also important to take a look at the patient's alignment and correct any problems that contributed to the cartilage damage in the first place. Many times, the cartilage wears down through all its layers because the bones forming the knee joint are angled unevenly. The surgeon can correct this by performing a procedure called an osteotomy. A wedge of bone is placed along the side of increased pressure in order to shift the point of weight-bearing contact over toward the other side of the joint. This helps even out the weight-bearing surface of the knee.

Although autologous chondrocyte implantation has good results, it is not the first treatment of choice for this type of cartilage damage. As mentioned, it is reserved for patients with large defects and who are very active. There are some potential problems with this treatment method. Removing cartilage cells and periosteum needed for the implantation always leaves the donor site at risk for subsequent problems. And the implanted chondrocytes don't always fill in with good, solid cartilage. Sometimes, the new growth is just a fibrous type of cartilage.

So, how well does it hold up with everyday function and under the pressure of sports participation? Is it possible to predict who will have a good (or poor) result? How often is another operation necessary due to failure of the ACI? These are the questions the authors tried to answer with this study. They followed 137 patients who had ACI of the knee and reported on results measured by symptom improvement and function.

Everyone was treated by the same surgeon and followed the same postoperative rehab protocol. They wore a hinged knee brace for two weeks after the procedure. The brace kept the knee straight and the patient was not to put any weight on the leg. Knee movement (bending and straightening) was accomplished using a continuous passive motion machine. Weight-bearing was added after six weeks with gradual progression from partial- to full-weight bearing by the end of 12 weeks.

The patients filled out several different surveys answering questions that could help evaluate the results in five areas: pain, symptoms, daily activities, sports function, and quality of life (related to knee function). They found a significant improvement in all areas. The implant was durable and 83 per cent of the patients said they would have the same surgery again if they had to do it all over. A small number of patients ended up with some arthritic (degenerative) changes in the joint but they still were better off than before surgery. Two factors that are linked with an increased risk of failure with this procedure included increasing age and worker's compensation status.

Having only one surgeon involved in the study offers a unique advantage in research. Consistent care and follow-up was possible, reducing the chances that different surgical techniques or rehab efforts would affect the overall results. The authors believe that autologous chondrocyte implantation (ACI) should be considered for large or irregular full-thickness cartilage lesions. This type of implantation works well, no matter which part of the knee joint has been affected. It should still be used after the standard first-line treatment has failed. Properly selected patients can expect the good results to last for many years as shown by this study. Patients older than 40 are less likely to have chondrocytes with active growth factors and more likely to have fewer new, healthy cartilage cells form.

Allison G. McNickle, MS, et al. Outcome of Autologous Chndrocyte Implantation in a Diverse Patient Population. In The American Journal of Sports Medicine. July 2009. Vol. 37. No. 7. Pp. 1344-1350.


*Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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