Why Is Cam Morphology Increasing in Teens and Young Adults?

New study suggests it may be an adaptation to protect the growth plate from stress

 Innovations in Pediatrics - Spring 2017

 Raymond Liu, MD

The hip impingement disorder known as cam morphology is an increasing problem in teenagers and young adults, especially those who are athletes. It’s characterized by a bony extension that forms at the junction of the head and neck of the femur, which prevents smooth rotation inside the hip joint.

“Cam morphology is increasing tremendously in terms of how much it’s being treated in medicine,” says Raymond W. Liu, MD, a pediatric orthopaedic surgeon at University Hospitals Rainbow Babies & Children’s Hospital and Assistant Professor of Pediatrics and Associate Professor of Orthopaedics, Case Western Reserve University School of Medicine. “The use of hip arthroscopy is up, in part, because of it. But no one understands quite where it comes from.”

Dr. Liu’s team’s theory is that the extra bone formation characteristic of cam morphology is an adaptation to provide stability to the capital femoral growth plate, which is most vulnerable to injury around the time the bone is almost done growing.

“Around late adolescence and early adulthood, the body is trying to protect itself,” he says. “If you happen to be someone who does a tremendous amount of athletics, like year-round sports, by not giving the growth plate any break, your body is forced into the position where it has to grow extra bone. The alternative would be for the growth plate to lose stability. So in an attempt to prevent the resultant condition of slipped capital femoral epiphysis (SCFE), the body stabilizes the bone short-term at the long-term cost of cam morphology.”

Some researchers have addressed this hypothesis by studying x-rays taken at a single point in time, looking for the growth plate extension. Dr. Liu and his colleagues, however, have gone one better – studying more than 500 x-rays from children and teens taken a year apart over five years.

They’ve found that there is indeed an extension at the edge of the capital femoral growth plate that corresponds to a parameter of cam morphology. This alteration in the top of the femur (capital femoral epiphysis) occurred immediately before the growth plate closed. The group published its findings in the Journal of Bone and Joint Surgery.

“When you become mature, the bony edge of the growth plate becomes very sharp and extends out. We call that cupping because it looks like the edge of a cup. When you get to that point in your development when your growth plate is weakest, your growth plate cups, we think in order to provide stability. We saw that in general in all the growth plates that we studied. We think that cam morphology is excessive local cupping in one region in particular in the area that has the most stress, and it ends up creating this negative outcome of cam morphology.”

Dr. Liu and his research group have also compared radiographs of patients who developed SCFE and those who didn’t. They’ve found that those who developed SCFE had less epiphyseal extension in the top of the femur, when compared with healthy controls.

“We wondered if they would have less bone in this area, which turned out to be true,” he says. “This result fits with our overall concept of how stability around the growth plate affects these conditions.”

Dr. Liu and his team will next be collaborating with other research centers to replicate these findings by reviewing MRI scans. Ultimately, he says, he hopes this research points toward a solution to a growing problem.

“Cam deformity is in 15 to 20 percent of young males in some studies,” he says. “Most are not going to have symptoms, but that’s a huge number. It’s associated with future arthritis of the hip, so it can have a large impact. By better understanding this pervasive condition, we can hopefully contribute towards improving this issue in the future.”

For more information on this research, email Peds.Innovations@UHhospitals.org.