The visible scars on former Philadelphia Flyer Keith Primeau's face serve as a testament to the relentlessly physical contact sport he has so loved his whole life. But it was the invisible scars - the numerous concussions - that ended his 15-year hockey career.

"I feel the last one pushed me over the cliff, but they all certainly had a cumulative effect," said Primeau, who joined a panel discussion on youth sports injuries sponsored by Virtua Health last month at the Skate Zone in Voorhees. The 6-foot-5, 220-pound center retired from the National Hockey League officially in September 2006, almost a year after what would be the final blow - a severe hit in a game against the Montreal Canadiens.

Yet "it's only in the past six months that I'm starting to feel like myself," he says.

Like many athletes, Primeau, of Voorhees, was reluctant to bow out despite dangerous symptoms including dizziness, double vision, memory loss and lethargy. "I don't know if it was bravado or stupidity. I know I made mistakes and wrong decisions," he said.

For a professional hockey player, injuries would seem to come with the job. But as the number of children participating in sports continues to climb, so do injuries, medical experts say, from less severe muscle strains to broken bones and the most serious injury: head trauma. The Centers for Disease Control and Prevention estimate that 300,000 sports-related concussions occur annually in the United States.

Seth Keller, a Virtua neurologist and former high school athletic trainer, says proper equipment, condition, preparation, and simply playing by the rules can prevent many injuries. Still, they will occur, particularly in contact sports. The danger lies in failing to closely monitor athletes after an injury, Keller said. Returning to competition too soon could risk life-altering impairment.

Greg Palmer knows firsthand what it's like to get back in the game too soon. The 16-year-old sophomore from Haddon Heights sustained a concussion in a soccer game last fall. Knocked unconscious for approximately 15 minutes, Palmer is told he dove for the ball and received a knee to his temple from an opposing player. He was out of school for a week and warned by his doctor: no sports for three weeks. That was fine - until wrestling season began.

Soccer was just a "stay in shape" sport, Palmer said. "I probably lied about being fully recovered." Telling his parents and coaches he was good to go, Palmer returned to wrestling on Christmas Eve. He competed for about three weeks, until Jan. 11, when he was taken out of a match after a temporary bout of amnesia.

"I was in the middle of a match, and I didn't know where I was," he said. He hadn't told his coaches or parents that he was still dizzy and still getting headaches.

Initially after the soccer injury, his father, Greg Sr., noticed his son was quiet and lethargic. But now, he says he sees his son's energy level returning emotionally and physically and is eager to see his son return to competition. Socially, the younger Palmer says he hasn't missed a beat, despite being mostly home-schooled since January. Upon returning to school three weeks ago, he started light conditioning with the school's athletic trainer, Tim O'Donnell.

"We're basically relying on what he tells us," O'Donnell said.

Palmer said he's been symptom-free for about six weeks. However, toward the end of April, he scored poorly on an ImPACT test, a computerized assessment of neurocognitive function used for about 15 years by professional sports teams and, more recently, by high school athletic departments to measure how the brain has recovered from an injury. He's scheduled to be retested in about a week.

Rest and patience - often the keys to rehabilitation - are in short supply these days. In 18 years of practice, Mark Schwartz, an orthopedic surgeon who specializes in sports medicine at Virtua Health in Voorhees, says the stress he has noticed on athletes lately is year-round. "There is no down time for a lot of these kids, no rest period," he said.

Yet sometimes even with proper care, it's a matter of susceptibility. One of Schwartz's patients, 18-year-old Kristen McAfee, did all the right things after she tore a ligament in her left knee during soccer practice just before her junior year at Moorestown High School. Despite her conscientious adherence to physical therapy after her first knee injury, McAfee tore her the same ligament in her right knee during a soccer game at the beginning of her senior year.

She remembers feeling that all-too-familiar "snap." "As soon as I went down I thought, 'Oh no, not again,' " she said.

Recovered from her injuries, McAfee is headed to the University of Maryland to play Division I soccer in the fall. Now playing lacrosse for Moorestown, she frequents the school's training room, performing a regimen of strength and conditioning exercises. "You can't get lazy," she says, "even after you're OKd to play again."

Whether Palmer or McAfee continues to play sports will be up to their bodies, say their physicians.

Decades have passed since Primeau's first body check at age 7 in Ontario, and now he has four young children, two of whom play ice hockey. His advice to budding athletes and their parents is to listen to their doctors, coaches and athletic trainers. Parents should be observant; kids should be up-front. Take it from one who has been there, Primeau says. "It's OK to say you don't feel well."