Golfer Tiger Woods won the U.S. Open earlier this week while grimacing with pain due to a knee injury. On Wednesday, he announced that that he’d be out for the season because he needs surgery to repair a torn anterior cruciate ligament (ACL). So what exactly is an ACL tear, and did Woods make it worse by playing with the injury?
ACLs are fibrous bands of tissue that connect the upper and lower leg bones in a crisscross shape in the middle of the knee joint. They give the knee stability.
ACL tears, which can occur if the joint is bent backward or twisted when the foot is planted firmly on the ground, are “probably the most common season-ending injury in sports,” says Sherwin Ho, MD, an associate professor of surgery at the University of Chicago and a team orthopedist for the Chicago Blackhawks.
ACL tears are not common injuries in golfers. “Golf is not one of those types of activity that will cause an ACL injury unless you’re just awful,” says Dr. Ho. But Woods injured his a year ago while running. He had surgery in April to clear out damaged cartilage, and he also happens to have double stress fractures in the shinbone of the same leg.
An ACL injury would pose no problems for the average weekend warrior, says Dr. Ho, who is also a spokesperson for the American Academy of Orthopaedic Surgeons. “The majority of people will do fine with an isolated ACL tear and a normal, pedestrian, human golf circuit.”
Woods, however, played 91 holes over five days to win the U.S. Open.
Surgery to repair a damaged ACL is not as easy as stitching the torn pieces together. The procedure, called an ACL reconstruction, involves rebuilding the ligament “by taking tissue either from elsewhere in the knee or from a tissue bank and making a brand new ligament for them,” says Dr. Ho. “That is a very reliable, dependable surgery.”
But it’s not always necessary to surgically repair the damage. If you have a torn ACL but don’t have any pain or swelling, you may be able to avoid surgery. For example, a recreational skier with an ACL injury who avoids moguls and jumps might not need surgery. But if you’re a 20-year-old extreme skier, then “no, he’s got to have his ACL fixed,” says Dr. Ho.
If you have other knee injuries, such as a torn meniscus (a pad of cartilage that prevents the bones from rubbing together), you probably do need surgery, says Dr. Ho. The longer you play sports, the worse the damage in those cases. “They’re going to lose more of their cushiony tissue and it will lead to early arthritis,” he says. “With an ACL tear, it’s not as clear cut. You can function fine without an ACL.”
In Woods’s case, “it was his knee that made the decision for him,” says Dr. Ho. He had the option of having his knee repaired all at once, but he chose to have the cartilage repaired first and the ligament reconstruction at a later date.
After a ligament is repaired, there is a risk of developing arthritis earlier than normal, but that depends on the amount of damage to the cartilage. When the knee is destabilized by an injury, its more likely that the end of the bones will rub together and wear away the cushiony pads that protect them.
“If you look at the chicken bone, that white glistening stuff [is cartilage]. When that’s gone, you’re bone on bone, and that is essentially arthritis,” says Dr. Ho. “The risk is very high if the damage to the cartilage in the knee is greater than 50%.”
Grade 2 cartilage damage indicates that the surface of the cartilage is broken, and over time this can worsen and become grade 3 damage.
If Woods has grade 2 or mild grade 3 damage, it probably won’t affect his career too much, according to Dr. Ho. “If he manages it correctly, he can have a long, full career before he develops arthritis,” he says.
When Is it OK to play through the pain?
What about knee injuries among average, non-superstar athletes? Dr. Ho says the risk of further injury can depend on your symptoms and how often they recur.
“If every time you go out running it swells or hurts, you need to see a physician,” he says. “And if the pain on a scale of 1 to 10 is more than 5, that’s a good reason to see a doctor.”
If, like Tiger, you have an unstable knee that gives out on a regular basis, you also need to see a doctor. “Those situations are the ones we worry about—that they are doing further damage to the knee,” says Dr. Ho.
Dr. Ho also notes that the amount of stress on your knee can vary. Woods injured his left knee, which is particularly important because he’s a right-handed golfer.
“He might have gotten by a little longer if it was his right knee, but the left knee is the one you torque and load up, and so that’s why it’s harder—you can’ t make the weight shift,” he says.
Dr. Ho marvels that Tiger was able to play as long as he did. (See pictures of athletes playing through the pain on SI.com.)
“It’s so hard to force yourself to load up and take a full swing and end up on that painful left knee. He could hold it right through the swing and then collapse in pain,” he says. “Mentally, the guy’s tougher than anybody out there.”