Scientific American—February 17, 2015
If you look very carefully at the C-curved squiggle taking shape on a 3-D printer, you just might spot the future of knee repair. Layer by layer, the machine's tiny needle squirts out a bead of white polymer, matching a virtual blueprint of a meniscus—the semicircular band of tough, fibrous cartilage that serves as the knee's shock absorber.
Every year an estimated 5.5 million people in the U.S. visit orthopedic surgeons for a knee problem. About a million undergo outpatient knee surgery, and that figure does not include another 700,000 annually who have reached the end of the line with one or both of their own knees and wind up with artificial replacements.
Tendons, the flexible ropes of fibrous tissue that connect muscles to bone, and ligaments, the slightly stretchy bands that link bone to bone, are less well nourished by blood vessels than are most other tissues. As for cartilage—such as the super smooth white material on the end of bones (think chicken legs) that helps joints glide—most of it has no blood supply. "So cartilage has virtually no capacity to heal," says Scott Rodeo, an orthopedic surgeon and researcher at the Sports Medicine and Shoulder Service at Hospital for Special Surgery in New York City and a team physician for the New York Giants.
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