Meghan Vaccaro ran to defend against her soccer opponent as she'd done hundreds of times before.

But the girls collided. The opponent slammed into the side of Vaccaro's right knee. 

"I felt something pop," she said. "I knew right away it was bad." 

What began as an innocuous play left Vaccaro, then 16, with a torn anterior cruciate ligament (ACL). It launched her into surgery and grueling rehabilitation in hopes of returning to the game she fell in love with as a 5-year-old. 

Her injury highlights the challenges female athletes face and the importance of following direction during physical therapy after an injury. At the same time, sports medicine specialists note, there are preventive exercises females can take to reduce their chance of ACL injuries. 

The ACL is one of the four key ligaments that help stabilize the knee joint, connecting the thighbone (femur) to the shinbone (tibia). Injuring the ACL can be crushing to an athlete, and it's more prone to happen to young females. 

Female athletes are four to six times more at risk of sustaining a noncontact ACL injury compared to males, according to the National Institutes of Health. 

The road to recovery isn't easy, and it wasn't for Vaccaro, who lives in Waxhaw, North Carolina, and sustained her injury in the first club soccer match of the season in September 2016. Her surgery, which also included repair to her lateral collateral ligament (LCL), was performed by Dr. Marcus Cook, an orthopedist at Novant Health. She recovered under the guidance of Dr. Eric Warren of Novant Health Waxhaw Family & Sports Medicine. 

Vaccaro's world of fast-paced games and practices dissolved into rest, rehab and watching. "Sitting on the bench was rough," she said. "It felt weird seeing the team play and not being out there." She missed the club season in the fall and her school season (Cuthbertson High) in the spring of 2017.  

Vaccaro's new friends became weights, exercise machines and Dr. Anthony Q. Walker, a physical therapist at Novant Health Waxhaw Family & Sports Medicine. Therapy sessions were three or four times each week.  

That lasted about nine months. “We spent a lot of time together working," Vaccaro said. "He became a friendly face."  

Walker said recovering from ACL surgery can be a tough process for young athletes.

"It's taking a big part of their life — playing and practicing — out from under them," he said. "There is a fear there. So the key is establishing trust and developing confidence. It's a very tight relationship. I call it a partnership between the patient, the parents and the physician."  

Nearly 80 percent of all ACL injuries — unlike Vaccaro's — aren't caused by contact, according to NIH studies. They're prevalent in sports with plenty of cutting and pivoting, including soccer, volleyball, handball and basketball.  

Athletes ages 15-25 are at the greatest risk of ACL injury, according to NIH research, more so females. Warren said there are three key factors:  

1.  Females have a wider pelvis. Because of the angle difference, more force is transferred to a female’s ligament when the knee twists, which increases the possibility of an ACL injury.  

2. Less muscle strength. Before puberty, boys and girls have the same risk for an ACL rupture.

"The problem with puberty is that boys get a testosterone surge and they develop more muscle mass, and women do not get that," Warren said. "They end up with less muscle strength in their quadriceps (thigh) and hip abductors.  

3. Looser ligaments. "With the estrogen and progesterone (female hormone) changes, girls' ligaments get looser, so they naturally have more relaxed ligaments," Warren said. "Those looser ligaments are why women in general are more flexible than men. And it will help them later to give birth, as it helps the pelvis expand."  

Warren, who has had eight knee surgeries (and twice torn his ACL), suggests that female athletes engage in a “pre-hab” regimen well before their season begins. 

"In some ways it's analogous to hydration, you can't really catch up on your fluids the day of the game," Warren said. "It's the day before. Same with building muscle. This is a two- or three-months in advance sort of thing. It takes 8-12 weeks to really build muscle."  

It’s important to strengthen the front and back of your leg, your body’s core and both sides of your body equally. Common drills that help soccer athletes include a Nordic hamstring curl, body squat and jump squat. 

Warren said several studies have shown that strength-building is beneficial. "That's going to pay you dividends later," he said.  “Mom and Dad need to have an awareness that this could help keep you injury-free during the season." 

Vaccaro, a midfielder, plowed through rehab and was cleared to play in July 2017. She played the club season and her senior year in high school.  

"Meghan was very compliant," Walker said. "She did what we asked her to do. The surgeon plays a key part. The rehab is critical. But also, the determination has to be there."   

Vaccaro, now 18, said she's pain-free and continues to work out. This month, she began classes at UNC Wilmington.  

One of her early spare-time activities — she played in an indoor soccer match.  

You don’t have to be a professional athlete to get world-class care for your sports-related needs. Download our guide on common sports-related injuries.