Recently, Dr. Constance R. Chu, the Albert Ferguson associate professor of orthopaedic 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 only 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’s 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.
As knees bear our weight, an injury like this is going to influence the range of our movement. An ACL tear hampers the normal joint functions as it affects the normal muscle action and strength across it. The joint then becomes unstable and weak. If the torn ligament is located in a very severe state then the individual may not even be in a position to move the knee. Sometimes the affected part may even get numb in addition to knee pain.
On another note…
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 of the impact. ‘ We saw an expanding zone of death, ” Dr. Chu said. By the end of her group’s planned observation period, four days of the impact, cartilage cells well far from the original injury site were still dying.
A Few Other Things
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 during 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 among men and women in their 20s and 30s who fall on the ski slopes, for instance.
An early and mass death of certain of their cartilage cells may help to explain why, Dr. Chu says. If the results of her cow study can be extrapolated to human knees, then it is possible that ripping an A.C.L. does not damage just the A.C.L. The trauma from the incident affects the knee’s cartilage cells, too. These cells make up the tissue that coats the confines of the knee bones. The bones rub on each other without this coating. Pain and disability can follow.
Unfortunately, the damage caused to the cartilage cells is invisible, Dr. Chu says. The dead or dying cells do not show up on a typical M.R.I. Scan. ‘ The surface ” of the cartilage ‘looks fine, ” she says. The knee, in fact, after the A.C.L. Reconstruction surgery, seems to have fully recovered. People return to full activity, including soccer games or skiing, ‘without realizing that their cartilage is weaker now, ” and more prone to re-injury and disintegration, resulting in arthritis.
Dr. Chu and many other researchers all over the country are trying to develop methods to identify which people will develop arthritis after a knee injury and why. ‘ Many labs are interested in this question, ” she said. But for the moment, no one’s had much success.