Soccer here in the U.S. and Britain suffered a setback in late August: David Beckham sprained his knee and is probably out for the season. The injury comes on the heels of an ankle sprain in the other leg one month earlier. Are the two connected? Here's a look at whether blowing out one joint leads to injury in a second.
The data are scant, says UCLA orthopedic surgeon Dr. David McAllister, because studies looking at the effect of one injury on the risk of hurting some other part of an athlete's body are hard to do. "We would need to identify a lot of people who sequentially got the same two injuries," he says.
Some data exist on whether athletes are more likely to reinjure a previously hurt knee ligament or damage the healthy one instead. One 1998 study of 714 athletes who'd had surgery to repair the anterior cruciate ligament (ACL) of one knee tallied how many tore their previously injured ACL again or hurt their healthy ACL instead. The half who had thinner ligaments were far more likely to damage the ACL in the healthy leg than the half who had thicker ligaments, and most of the thin ACLs belonged to women.
But in a 2007 study of 235 patients, risk of injuring either knee was the same, about 3%, two years after ACL repair.
The best data come from baseball, which is an easier sport than most to study because pitchers tend to injure the same kinds of joints. Players who hurt their elbows are more likely to have shoulder injuries, says orthopedic researcher Brady Tripp of Florida International University in Miami. A 2007 study by Dr. William Grana and colleagues at the University of Arizona Health Sciences Center in Tucson found that of 84 Chicago White Sox pitchers, 27 had elbow ligament injuries, and 60% of the pitchers later had shoulder injuries.
It "is an incredible number. That's two and a half to three times what you'd expect [for shoulder injuries] in an unoperated population," Grana says. "The pitchers try to externally rotate their shoulder to get the velocity they've lost from their elbow surgery." The same study found that of the 60% who had shoulder injuries, half had to have shoulder surgery later on. (Oddly, right-handed pitchers suffered more injuries than left-handed ones. "Right-handed pitchers have to throw harder than left-handed pitchers," Grana says. Lefties can get away with 88 mph on a ball, but righties need to throw above 90 mph for the same effect on batters.)
McAllister says that even though data are lacking, common sense dictates that one injury could lead to a second one, because an injury can alter the way an athlete moves. An injury that causes discomfort for an athlete who normally plants his foot and turns to the right, for example, might make him want to plant his foot and turn to the left.
Because the new pattern is one the athlete's body isn't used to, it could have unintended consequences in other joints.
Soreness in a joint can also cause unstable motion, which could lead to damage as well. Injuries, especially to the ankle, affect a person's sense of where the joint is in time and space.
And, says Dr. Gerald Finerman, director of UCLA's orthopaedic sports medicine program, subsequent injuries can also occur because of the downtime that injured athletes experience. Finely tuned professional and collegiate athletes lose their fitness edge if they take a few weeks off to let an injury recover.
That's why when football players sprain their ankles, UCLA has them put on a buoyancy vest and run in a swimming pool without putting any pressure on their sore ankle. "It's important to not only rehabilitate the specific site you're concerned about, but the athlete's entire fitness," Finerman says.
A person's body type can lead to certain injuries, which then, predictably, lead to certain other injuries, says sports medicine director Dr. Joel Brenner of the Children's Hospital of the King's Daughters in Norfolk, Va. People whose leg joints and muscles are a little out of whack -- people who have bow legs, for example -- are prone to an injury called iliotibial band syndrome (ITBS), which pains the knees. The knee pain can then lead to shin splints or stress fractures, Brenner says.
Making sure the first injury is fully recovered is key to preventing additional injuries, the doctors say. "Waiting for the pain to go away is not enough to be considered cured," Brenner says. Finerman says recovering joints should have the same range of motion as the healthy joints, and the limb should be worked until it regains its full strength. In addition, tests exist that determine whether an injury is fully recovered, Finerman says, although the tests aren't often used. "Coaches don't say, 'Run this at the same time as you ran it before you were injured,' " he says.
The doctors say there's no way to tell for sure, in the case of one athlete, if the first injury led to a second -- unless the player returned to the sport still obviously injured. Beckham speculated in media reports that maybe he went back too soon. But McAllister guesses that the golden boy of soccer just had some bad luck. And so did his fans.