Teflon Knees: New replacements for torn and worn-out cartilage include freeze-dried collagen

It seems as though modern humans and their knees aren't particularly well adapted to each other. We pound them down jogging on pavement, and we rip them up chasing inflated balls around a court or a field or zipping down snowy mountains on fiberglass planks. If we manage to escape this kind of trauma somehow, we just wear them out by living so long.

With all the practice repairing knees, orthopedic surgeons have made incredible progress over the past 25 years in learning new ways to reconstruct and replace knees. Ligament tears that once ended athletic careers now earn a lenient sentence of outpatient arthroscopic surgery and six months of rehab.

While the progress is appreciated, there is hardly a middle-aged athlete alive who doesn't wish more could be done, especially with the most nettlesome of knee problems: torn or worn-down cartilage. (Full disclosure: I have sampled heavily from the buffet of knee surgeries--a pair of ligament replacements, a pair of meniscus trimmings and an attempted cartilage repair job. The cartilage repair surgery was the hardest to recover from and sapped the most from a once-respectable vertical leap.)

A series of three recent papers in the Journal of Biomedical Materials Research outline an approach that could make one type of cartilage repair more successful. The paper's authors, researchers from Massachusetts Institute of Technology and Cambridge University in the U.K., describe a way to create a layered scaffolding of materials very similar to those already in bone and cartilage that can be placed in a torn section of cartilage to entice new cartilage to grow there.

Lorna Gibson, a professor of Materials Science and Engineering at MIT and one of the leaders of the research, says the teams' scaffolding improves on other similar approaches because it closely mimics the bone and cartilage interface in the human body.

The researchers' work is directed at a type of smooth cartilage that covers the ends of bones like Teflon, allowing hinged joints to glide open and closed easily. It's called articular cartilage, and it is strange stuff. Myron Spector, a Harvard Medical School professor and director of tissue engineering at VA Boston Healthcare System, describes articular cartilage cells as being "imprisoned in their own matrix."

The cells are thick with a tough, fibrous protein called collagen. They are unserviced by blood vessels or nerve cells. When there's a tear, there is no bleeding, no clotting, and no place for cells to migrate to and regrow. In fact, the fluid that lubricates the joint, called synovial fluid, is designed specifically to prevent clots, because scar tissue would gum up joints.

Spector says his work on cartilage can be more frustrating than his work on central nervous system problems. "You'd expect cartilage to be a no-brainer," he says, intending the pun. "But it's tough. It gets disheartening."