Knees can ache for many reasons, including runner’s knee. Runners with weak thigh muscles may have kneecaps that move sideways and rub abnormally against the thigh bone, causing pain.
Furthermore, “The knee is vulnerable,” Carpenter says, “because of all your weight and your pivoting, and it’s often hit in contact or twisted. That is still far and away the most commonly injured joint.”
If people play team sports such as football and soccer, trauma to the knee can damage ligaments, for example, when the knee is struck during a block or tackle, Carpenter says. If the knee is struck from the outside, the medial collateral ligament inside the knee can be stretched -- and if the force is significant -- it can be injured or torn.
In contrast, non-contact injuries usually result from twisting the knee or deceleration. A “sudden plant and cut in one direction” or an awkward landing from a jump can damage the knee, Carpenter says. “Those are more typically injuries to the anterior cruciate ligament (ACL),” he says. “If someone comes in and no one hit them, they just turned sharply, the knee went ‘pop’ and swelled up, the majority of time, that’s an injury to the anterior cruciate ligament.”
Women are more at risk for ACL tears, but according to Doperak, doctors aren’t sure of the reasons. “There are a lot of theories, but no one really knows exactly why. Some people think it has to do with hormones, or the way [women] land when they jump, or anatomy.”
Strengthening the knee with targeted exercises and having good balance will help prevent ligament tears, according to Doperak, who is also a team physician for the University of Pittsburgh and Carnegie Mellon University. Bracing the knee might also help prevent injuries, Carpenter says.
Entire textbooks have been written about the extensive range of knee injuries, Doperak says. The bottom line: “You should be concerned about your knee injury if there’s knee swelling,” she says. “That would suggest that there’s something going on within the joint, like a ligament tear or a meniscal tear, or perhaps some sort of cartilage injury. You should probably see your doctor about that.”