"There are probably some subtle genetic differences, disorders in soft tissue, in collagen makeup, but the number one genetic indicator is going to be the X chromosome," Karas said. The female is XX, and the male is XY, so the extra X is likely a factor.
Another reason ACL injuries are on the rise is because of better diagnostic techniques and a greater understanding of the knee ligaments.
Lohnes searched through records to see if football players from the 1930s and 1940s who had torn their ACLs developed arthritis later in life. "What I found out was that it was almost never diagnosed as an ACL tear because at that time, we didn't have (magnetic resonance imaging) scans (or) arthroscopic surgery. They didn't have a good way to look inside the knee without cutting it open."
Arthroscopy's emergence in the 1980s changed diagnostics. It allowed orthopedists to use fiber optics to get a detailed assessment of the knee, Karas said. With arthroscopy and MRI, surgeons are able to look at the knee in its native condition. This allowed orthopedists to see the ruptured ACL, in turn showing them precisely what needed to be fixed.
Of the about 175,000 ACL injuries every year, more than 70 percent are sports-related. Of that 70 percent, the majority result from no direct physical contact between athletes. "Any type of cutting activity or pivoting activity and also, now we're starting to implicate landing activity as primary factors causing ACL tears," Karas said.
As athletes have gotten bigger, stronger and faster over the past 25 years, Karas dispelled the notion that that is why ACL injuries are so prevalent. "It's not an issue that we're getting too strong for our bodies," he said. "It's a fluid system that allows increases in growth, speed and performance."
In addition to physical damage, an ACL injury can cause mental anguish as well. "I'm a big believer in God and that he does things for a reason. For a moment, I was just like, 'OK God, what am I supposed to do?'" said Tucker once she realized she'd be sidelined for six to nine months.
Losing a player to long-term injury is something UNC women's basketball coach Sylvia Hatchell has dealt with.
Marion Jones broke her foot while playing for Hatchell in the mid-1990s, and Jessica Gaspar tore her ACL in the Tar Heels' march to the Sweet 16 in 1998.
When Tucker went down, Hatchell said she was 75 percent sure it was the ACL. "I've seen it quite a bit. I've been doing this 27 years," she said.
Reconstructing the Damage
ACL injuries are nearly impossible to predict, and previous knee injuries have little, if any, effect on an ACL's health. But it is possible to protect against them through strength and conditioning.
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The American Academy of Orthopaedic Surgeons suggests year-round training, incorporating hamstring and quadriceps exercises as a part of the workout and practicing landing with the knee bent rather than straight.
A torn ACL cannot heal on its own due to poor blood supply, resulting in chronic knee instability. An ACL tear does not always require surgery. Sometimes a knee brace, with strengthening exercises, will suffice. But to return to high-intensity activities, such as basketball or soccer, surgery is a must.
Nearly 175,000 ACL reconstructions are performed every year in the United States. They are the sixth most performed orthopedic surgery per year, with an estimated annual cost of more than $2 billion, according to another article in Sports Medicine and Arthroscopy Review.
"It used to be they'd try to go and repair it, like sew it back together. They found that that didn't really work. It would just fall apart," said Lohnes, who has taken part in nearly 700 ACL surgeries.
Orthopedic surgeons had to find a way to build a new ACL. They discovered that using graft tissue from another source would be the best course of action.
Surgeons use three grafts to reconstruct the ACL: the patella tendon, allografts and the hamstring.
"The graft choices have allowed us to have more options in taking care of a wider spectrum of patients," said Karas.
With the patella graft, surgeons remove a piece of the patella tendon from the middle one-third of the surface area, harvest it and it becomes a graft ligament that replaces the old ACL.
However, there are some disadvantages to this surgery. "When you take out a piece of the patella tendon, you can pretty much be assured of the development of some patella tendinitis," Karas said. And the risk of patella fracture increases, he said.
A second graft surgeons use is allografts -- or cadaver or donor tissue.
Allografts offer a faster surgical time because there is no need to treat the tendon and there is no onset of tendinitis because the tissue is not taken out of the patient's body, Karas said.
But there are disadvantages of allografts. Because the tissue comes from a cadaver, there is a risk of disease transmission, and the healing time is slower than that of the patella graft, Karas said.
The third surgery is grafting the hamstring. It is a soft tissue graft, and tendinitis won't affect it, Karas said. This surgery is particularly good for someone who kneels a lot, like a wrestler.
However, there are disadvantages with the hamstring graft as well. The qualities of the graft might be softer or spongier, causing slowed rehab in the early stages because it is weaker than the patella graft, Karas said.
If placed correctly, all three grafts provide adequate strength and are unlikely to fail, he said. Surgeons generally wait to operate a few weeks following the ACL rupture to allow swelling to go down and range of motion to return.
Tucker had surgery at UNC Hospitals on Jan. 26, 20 days after her injury. Her surgeons chose the patella tendon graft to reconstruct her ACL because it was the surgeon's preference, said Dana Gelin, who works in sports information in the Department of Athletics.
Returning to Form
After surgery, patients enter physical rehabilitation for about six months.
The most important thing for a patient to do is to quickly regain full extension of the leg -- sticking it straight out and bending it 90 degrees, said Mark Davis, a physical therapist in UNC's Department of Sports Medicine.
"The day after surgery, we'll be working on getting the knee straight, walking and partial weight bearing on that leg," he said.
The next step is to restore normal range of motion. Once patients can bend their knees 90 degrees, they'll move to light weights and try to move as quickly as they can in a functional sense, Davis said. Patients must strengthen their hamstrings and quadriceps because they provide so much support and stability to the knee and the ACL.
After four to five months of rehab, athletes are cleared to play sports at the intensity they did prior to their injury, but they may still experience some pain in the knee for an additional six months.
Perhaps the biggest obstacle for an athlete recovering from an ACL injury is what Lohnes calls "gun shyness."
During recovery, patients are learning how to guard and protect their injured leg. Patients are told they are ready to play, but when the time comes, they simply can't.
"Now they are favoring the injured leg, even though there is no reason to. So we have to spend a lot of time reeducating people in terms of relearning moves that they used to do without thinking about it," Lohnes said.
Tucker is on the road to recovery. She has done weight training and strengthening exercises and some running. Tucker said she is not worried about the long-term effects of her injury, which include tendinitis and reinjuring her knee.
As athletes will continue to suffer ACL injuries, researchers will continue to investigate why.
Hatchell offers her own explanation. "They're just a freak accident."
The Sports Editor can be reached at sports.unc.edu.