Arthroscopic Debridement and Marrow Stimulation
Using the familiar arthroscopic approach (typically under local anesthetic), surgeons locate the damaged chondral tissue and trim away or stabilize the area. The prevents the damaged tissue from flaking off, which is often responsible for swelling, joint line irritation, and pain. This "clean up" is called a chondroplasty. When the injury is less than 1 cm (3/8 inch) in diameter, in certain circumstances, it has a lower probablity of progressing.
For lesions that chondroplasty alone will have a poor probability of helping, the body can be stimulated to produce repair tissue. This repair tissue develops from cells which migrate to the area through small holes made in the bone by abrasion, drilling, or more recently, using a small pick to create microfractures. This can be thought of as repairing "potholes" in a road. It may not last as long as a normal road, but it is often successful in eliminating symptoms in many patients. Studies suggest this repaired cartilage is fibrocartilage-like (scar cartilage), which is less resistant to wear than normal joint articular (hyaline) cartilage. In the future, a variety of means (for example, local growth factors, pulsed electrical current, or gene regulation) may be used to enhance marrow stimulation cartilage to a more hyaline-like quality.
This technique is analogous to a hair plug transfer. The surgeon removes a small plug of the patient's own cartilage along with an attached underlying bone plug. This is obtained from an area of the knee, which does not participate in high loading. The typical site of harvest is at the margin of the knee. If the area of harvest is involved with damage, then this technique may not be possible or an alternative site in the notch may be utilized. This bone and cartilage (hence the term: osteo (bone), chondral (cartilage)) local graft is then transferred to the defect where a receiving hole (socket) has been prepared. Obviously, there is a limit to the amount of tissue available for "harvesting" and thus, the size of the lesions treated with this technique are usually between 1-2 cm in diameter.
Autologous Chondrocyte Implantation (ACI)
This was one of the pioneering techniques in cartilage restoration. The technique was perfected in Sweden over 15 years ago and ACI, or its variants, have gained acceptance at cartilage centers across the world. While "next generation" cell therapy technologies are being evaluated in Europe, ACI is currently the only FDA-approved cultured chondrocyte treatment in the US. The technique is performed in two stages. The first stage may be performed when initially assessing the joint arthroscopically and an appropriate lesion is noted (ACI is typically used for a cartilage lesion greater than 2 cm2). A small amount of the patient's own articular cartilage is harvested and through cell culturing techniques, the cell number is increased from a few hundred thousand to over 10 million cells. These prepared cells are then reimplanted in the knee under a water tight collagen membrane placed over the defect. The cells then gradually form hyaline-like cartilage to resurface areas of prior cartilage loss.
For large defects of cartilage loss (and those with bone loss), surgeons can implant a freshly donated cadaver cartilage and bone plug (similar to osteochondral autograft plug technique, but without the size limitations) or shell (larger section of "shell" as the name implies) that may allow restoration of joint function. The tissue is maintained viable with cooled nutrient storage or other means while the donor is tested for possible disease transmission. Issues remain regarding availability and size matching the recipient.