Recently, Dr. Constance R. Chu, the Albert Ferguson associate professor of orthopedic surgery at the University of Pittsburgh and director of the Cartilage Restoration Center there, confirmed a theory, and found herself troubled by the results. It turned out that if you dropped a heavy weight onto parts of a cow’s knee joint from various heights, the joint was hurt. (While the parts of the joint were damaged, the cow itself was uninjured by the experiment; the knees came from a local abattoir.) When the weight hit the joint’s surface cartilage with great speed and force, the bone and cartilage fractured. No surprise there. But it is what happened in Dr. Chu’s experiment when the impact was more subtle — closer to, for instance, the perturbations inside a human knee when a ligament is torn — that concerned her. She found that with lighter impact, the various parts of the knee appeared, visually at least, to be fine.
But when Dr. Chu and her colleagues examined the cartilage cells just below the placid surface, they found carnage. “Many of the cells within the impact zone” — the area that had been directly thwacked by the weight — “were dead,” she said. They died instantly. More insidiously, other cartilage cells, those outside the injury site, began to die in the hours and days after the impact. “We saw an expanding zone of death,” Dr. Chu said. By the end of her group’s planned observation period, four days after the impact, cartilage cells well away from the original injury site were still dying.
The results are fascinating, in a gruesome sort of way. But why should escalating damage to cows’ cartilage matter to the average active human? Well, Dr. Chu says, this study, which was just published in the December issue of The American Journal of Sports Medicine, in conjunction with other researchers’ findings, may help to explain why, she said, “I’m seeing so many patients in their 20s and 30s with knee arthritis after joint injury.”
Human knees (as well as bovine ones) are remarkable instruments, able to bear large loads and pivot in multiple directions. But they also damage easily, as evidenced by the approximately 175,000 anterior-cruciate-ligament-reconstruction operations performed in the United States every year, a number that, by all estimates, has risen steeply in the past decade or so. (No agency tracks the procedures.) Many of these operations are being done now on teenagers, who rip an A.C.L. during a soccer or basketball game. (A.C.L. operations were relatively uncommon in young people before youth sports grew so popular.) Others are in men and women in their 20s and 30s who fall on the ski slopes, for instance. Read more…
