Musculoskeletal Report—December 12, 2008
Mosaicplasty, the process of inserting several plugs of osteochondral tissue to repair focal cartilage defects, may soon be the method of choice for orthopaedic surgeons, but stem cell-based cartilage repair is also moving stealthily down the pike according to Riley J. Williams III, MD, director of the Institute for Cartilage Repair at Hospital for Special Surgery in New York City. Dr. Williams discussed innovations in articular cartilage repair at a symposium sponsored by Hospital for Special Surgery.1
"The best candidates for mosaicplasty are individuals, regardless of age, with focal symptomatic lesions around 2 to 3 cm2 in size," Dr. Williams told MSKreport.com. "We like to do these in high-demand individuals such as basketball players, runners, and patients who play other contact sports because it is a hyaluronic repair-based strategy, so we are not worried about new cartilage, just healing." Dr. Williams is also the Head Team Physician for the New Jersey Nets professional basketball team, the New York Red Bulls professional soccer team, and the Iona College Department of Athletics.
One advantage of mosaicplasty is that inserting a collection of small osteochondral cylinders side by side enables the surgeon to maintain the radius of curvature of the articular surface. The surgeon transfers cells from a non-weight bearing part of the knee to the damaged area. The spongy element of the graft fuses with the spongy bed at the recipient site, and fibrocartilage that forms between the grafts helps integrate the transplant with the adjacent cartilage.
Bigger lesions are likely to require autologous chondrocyte implantation (ACI), according to Dr. Williams. "ACI has more morbidity, is a bigger operation and technically more demanding," he said. "You go in with a scope, get cells, grow them and put them back."
Another new option in cartilage repair is osteochondral allograft transplantation. This method is similar to mosaicplasty, but there may be a dearth of available donors and there is also a theoretical disease risk, Dr. Williams said.
Many questions need answers before mosaicplasty hits prime time, Dr. Williams said. For one, detection is still lacking as surgeons do not yet have the imaging technology to detect the small lesions before surgery.
Now, "we go in to repair a meniscal tear, see a lesion for the first time, so doing microfracture repair is much easier, but if we could see the lesion beforehand we could do a mosaicplasty that may have better durability in high-demand knees," Dr. Williams said.
During microfracture repair, a tiny 'pick' spikes holes into the base of the damaged cartilage area to promote bleeding. This allows the patient's bone marrow cells to come to the surface of the damaged tissue. As a result, the cells then change into fibrocartilage cells and heal the defect.
While microfracture is minimally invasive and quick, the defect may not always be fully repaired, and there is a risk of it breaking down again. As a result, surgeons continue to pursue new methods of repairing cartilage injuries.
Some orthopaedic surgeons are less convinced about the potential benefits of mosaicplasty, including Russell F. Warren, MD, the surgeon-in-chief emeritus at Hospital for Special Surgery and the team physician for the New York Giants football team. "The numbers are pretty similar to microfracture repair except for the return to play," he said. Some studies comparing the two procedures have found similar clinical benefits, but patients undergoing mosaicplasty show greater increases in activity rating scales.
In 20 years, "we will be seeing more stem-cell based repair that is combined with matrix scaffolding to be implanted arthroscopically," Dr. Williams predicted. "We will aspirate cells from the hip, knee or ankle, set them on a scaffold and place them in the hip, knees or ankles."
There are currently many types of scaffolds available including hyaluronic-acid and collagen-based scaffolds or combinations of the two that seem to be working. "The cells like the 3-D matrix," he said.
A new multi-center clinical trial at Hospital for Special Surgery is looking at NeoCart®, a protein matrix which holds the patient's own cells. First, a small piece of the patient's healthy cartilage is taken and then the cells are grown in a laboratory. These cells are put into the new matrix to create a piece of new cartilage which is then, through a tiny incision, implanted into the patient's joint over the damaged area. The hope is that the new cartilage will repair the damage and integrate seamlessly with the surrounding cartilage.
Read the full story at mskreport.com.
1. Presented at: Hospital for Special Surgery 2nd Annual Articular Cartilage Repair Symposium; December 5-6 2008; New York, N.Y