Melanie Boeyer stopped growing in seventh grade. She is 28 years old, 5 feet, 2 inches tall and can fit into the clothes she wore at age 12.

“People always said, ‘Don’t worry, Mel. You’re going to be taller,’ and I was like, ‘One day, I am going to be taller, yay,’’’ Boeyer said. “It never came.”

Now, Boeyer is a doctoral student at MU. She is among a group of researchers who analyzed radiographs of more than 1,000 children born between 1935 and 1995. They found that bones matured as much as six months earlier in boys and as much as nine months earlier in girls over those six decades. The study was published online in August and will be printed in Clinical Orthopaedics and Related Research this November. It was funded by the National Institutes of Health.

The research doesn’t just have implications for those marks you put on the kitchen wall as your child grows. It also has implications for scoliosis and leg-length discrepancy treatments, among others, because doctors use standards based on children born in the beginning of the last century to analyze how much growth a child has left.

It usually goes something like this: Parents bring a child to a clinic with growth delay, scoliosis or leg-length discrepancy. The physician orders an X-ray. By analyzing the X-ray of the left wrist and comparing it to the standards, the physician can estimate how much growth is left. If a child has a mild spinal curve and 5 percent of growth left, it probably won’t get much worse. So there might be nothing to worry about.

Except for one thing: The standards that physicians currently use are based on white children born almost a century ago.

Old bones, new findings

The data came from around 500 miles away as part of the Fels Longitudinal Study, which started in 1929 in Yellow Springs, Ohio. The researchers wanted to understand what makes people different. So they recruited pregnant women in the community and had them bring their newborns in for measurements of height and weight and X-rays. These became the basis for a couple of studies, including the one senior author Dana Duren’s team conducted.

Analyzing the data, the researchers found that, gradually, over the 60-year period, the epiphysis began to fuse earlier and earlier. And that was true for both boys and girls.

The research takes a close look at the process called epiphyseal fusion, which explains, for example, how the length of the average person’s legs increases ninefold between infancy and age 20.

Many bones in your skeleton are long bones, which have three distinct sections. The middle part, shaft, is called the diaphysis; the flared ends are the metaphysis; and the end cap of the bone is epiphysis. This last part is where the growth takes place. The names originate from Greek, where phusis means growth.

Until the skeleton becomes mature, the epiphysis is separated from the bone. The gap in between is called a growth plate. Although it appears on X-rays as if there were nothing in between, the growth plate consists of cartilage that is less dense and, therefore, doesn’t show up. Gradually, the growth plate mineralizes, and so the epiphysis fuses with the rest of the bone. Thus, epiphyseal fusion.

“Think of this as a land mass, and we have this little island out here, then we start building bridges between this island and the mainland,” Duren said. Once the cartilage growth plate is replaced with bone, the epiphysis is no longer an island but is part of the mainland.

Once the epiphysis is fused, the bone can’t grow anymore. So, the researchers looked at radiographs of hands and wrists of children to determine how much time it took for them to go from a cartilage growth plate to a solid bone.

“We are probably underestimating (children’s) bone age,” said Sumit Gupta, a pediatric orthopaedic surgeon at MU Health Care. “So we think they will grow for another two years, but they might not. They will probably grow for at least six months less in boys, on average.”

The researchers aren’t sure why bones are gradually maturing earlier. One of the culprits may be hormones in modern diets.

“If you use growth hormone in your beef, then guess what? You are eating growth hormone and your body is being exposed to more growth hormone than it is used to making,” Duren said. “So that’s going to change your physiology a little bit.”

Boeyer said the research should change expectations.

“So maybe seeing that 12-year-old in clinic, previously you would have said, ‘Oh, that’s fine; they are going to be totally OK,’” she said. “Now you need to say, ‘Oh, my. We should check, because it’s happening faster.’”

Although Boeyer got excited about skeletal maturity when she was an undergraduate, it was only while working with Duren that she realized she is part of this group of people who just grew faster. “I am just another average kid who did it earlier,” she said.

The earlier fusion mostly should not be cause for alarm, the researchers said. All of the children in the study were healthy and didn’t experience any harmful effects. Doctors and parents should simply be aware that kids are developing a little earlier, including their skeletons.

“When you were 12 or when you were 14, whatever milestones you were reaching then — expect your kid today to be doing them a bit earlier,” Boeyer said. “That’s just a new normal.”

Supervising editor is Katherine Reed

  • I am a first-year graduate student at the University of Missouri

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