Episode 29: Bone Age Explained: How Much Will Your Child Grow and How Tall Will They Be?

So let's begin with the most important distinction.

Chronological age is not the same as bone age.

Chronologic age is simply the time since a child was born.

If your child turned 12 last month, for example, the chronological age is 12.

Bone age describes how mature the skeleton appears on an x-ray compared with reference images from a child of different ages.

So, for example, a 12-year-old child might have a bone age of 10, 12, or 14.

That does not mean the child is really 10 or 14.

It means the bones show a pattern of maturation that most closely resembles the reference pattern assigned to the skeletal age.

Why do we care? Well, because children grow in length at specialized areas of cartilage near the ends of their long bones called their growth plates.

So as children mature, especially during puberty, those growth plates become progressively thinner and eventually fuse.

The bone age helps us estimate where a child is along that maturation pathway.

Now, Think of chronological age as the date printed on the calendar, so that child's birth date, and the bone age as the chapter that the skeleton appears to be reading.

Most children are reading roughly the same expected chapter, but some are a chapter or two behind or ahead.

Now, the difference may be normal or it may be a clue that deserves further evaluation.

The next question I get from parents is, how is the test performed? A traditional bone study is a simple x-ray of the left hand and wrist.

The left side is mainly used for standardization so that doctors are comparing the same view with the same reference material.

The test is very quick.

It involves a small amount of radiation.

The best known reading method in the United States is what's called the Grulich and Pyle method.

The clinician or the radiologist compares the child's x-ray with images in an atlas and chooses the image that most closely matches the maturity of the hand and the wrist bones.

Another approach is the Tanner Whitehouse method.

Instead of matching the whole hand to one Atlas image, it assigns maturity scores to individual bones and combines those scores.

It is more detailed and it can take longer.

Now, these days, computer-assisted and AI systems are also increasingly being used.

These tools may improve consistency and speed, but they do not eliminate every limitation.