New Treatment for Cartilage Defects in the Knee
Thanks to the increased use of arthroscopy of the knee, we now know that lesions to the joint cartilage are common. Arthroscopy is the use of a long, thin needle with a tiny TV camera on the end. It is inserted inside a joint and transmits a visual image on a computer screen.
High-impact sports that load the joints can lead to damage of the articular cartilage. This type of cartilage provides a smooth surface for joint motion.
Micro-trauma or injury can cause defects in the smooth surface. At first the cartilage loses volume and stiffness. This is called chondropenia. Chondropenia can progress to cartilage breakdown. This occurs when there are other soft tissue injuries to the ligaments or meniscus at the same time.
Without treatment, deterioration of the articular cartilage can lead to osteoarthritis (OA). There are several new treatment options for cartilage including repair or replacement.
Stem cells have been used to repair cartilage defects. The surgeon uses a small surgical awl (ice pick) to make tiny holes in the cartilage down to the bone. The procedure is called microfracture. It stimulates the bone marrow to form stem cells. Stem cells can then become cartilage or bone.
Microfracture works well when the lesion is small. But there are some concerns that the new cells aren't true articular cartilage. And the repair may not hold up over time. For this reason, scientists are looking for ways to replace, rather than repair, the damaged tissue.
Mosaicplasty is one method of cartilage replacement. Small plugs of cartilage and bone are harvested from the patient. These plugs are then transplanted to fill in the defect. Medium sized defects are treated with this method. The size depends on how much tissue can be taken safely from the donor site without causing donor site problems.
Large defects can be treated with autologous chondrocyte implantation (ACI). Normal, healthy cartilage cells are removed and taken to a lab where they are reproduced. When there are enough cells, they can be transplanted back into the damaged area.
ACI can be used in younger patients (ages 15 to 55) who are not obese. The lesion must be less than eight millimeters deep. Bone grafting may be needed for defects deeper than eight millimeters.
Studies show good-to-excellent results with ACI. Some long-term studies (up to 11 years after ACI) continue to show that results are maintained. Many athletes are able to return to their previous level of competitive play.
Current research efforts are centered on improving the chondrocyte cover. After an ACI is done, a thin layer of cells is placed over the transplanted tissue. But sometimes the tissue reproduces too many of the wrong kind of cells. This can cause problems.
The next step is to find a way to place a matrix (layer) of cells directly over the defect. The matrix method would eliminate the need for transplantation of healthy chondrocytes. The goal is to find the right kind of matrix material to fill in without overflowing the defect.
Timothy R. McAdams, MD, and Bert R. Mandelbaum, MD. Articular Cartilage Regeneration in the Knee. In Current Opinion in Orthopaedics. January 2008. Vol. 19. No. 1. Pp. 37-43.
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