Khamis-Roche vs Bone Age X-Ray: Which Is Better?

Two approaches, one question

Will my child be tall? It is one of the most common questions parents ask pediatricians. Two evidence-based methods dominate the field of height prediction: the Khamis-Roche formula, which uses simple measurements and parent heights, and bone age assessment via X-ray, which examines skeletal maturation. Both have strengths, both have limitations, and understanding the difference can help you interpret your child's predicted adult height more realistically.

How the Khamis-Roche method works

Published in 1994 by Houtkooper J. Khamis and Alex F. Roche, this method predicts adult stature using the child's current height, current weight, and the heights of both biological parents. It was developed using data from the Fels Longitudinal Study, one of the longest-running growth studies in the world, which followed participants from birth through adulthood.

The formula applies age- and sex-specific regression coefficients to the input values. It does not require any medical imaging, blood tests, or clinic visits -- just a tape measure, a scale, and knowledge of parental heights. The method is validated for children aged 4 to 17.5 years.

How bone age X-ray works

Bone age assessment uses an X-ray of the left hand and wrist to evaluate skeletal maturity. The most common reference systems are the Greulich-Pyle atlas, which compares the X-ray to a series of standard images, and the Tanner-Whitehouse method, which scores individual bones numerically.

Once the bone age is determined, the Bayley-Pinneau tables or similar methods use the ratio of current height to predicted percentage of mature height to estimate final adult stature. If a child's bone age is younger than their chronological age, they likely have more growth potential remaining. If bone age is advanced, they may reach adult height sooner but with a lower final value.

Accuracy comparison

Surprisingly, the Khamis-Roche method often performs as well as or better than bone age in population studies. In the original validation, the median absolute error was 2.2 cm for both boys and girls. Bone age methods, while clinically valuable, introduce additional sources of variability: inter-reader disagreement on bone maturity, the quality of the X-ray image, and the reference tables used.

A 2016 review in the Journal of Pediatric Endocrinology and Metabolism found that bone age predictions had median errors of 3 to 5 cm depending on the method, with the Greulich-Pyle atlas showing slightly better performance than TW3 in most populations. Importantly, bone age shines in clinical scenarios where growth is disordered -- conditions like precocious puberty, growth hormone deficiency, or constitutional delay -- where Khamis-Roche assumptions about normal growth patterns may not hold.

Pros and cons

When to use each method

For healthy children following a normal growth trajectory, the Khamis-Roche method is an excellent first-line tool. It is free, instant, requires no radiation, and has comparable accuracy to bone age in typical populations. Use it to get a reasonable estimate without a medical visit.

Bone age X-ray is more appropriate when there is clinical suspicion of a growth disorder, when the child is growing significantly faster or slower than expected, when puberty appears unusually early or late, or when a medical decision (such as growth hormone therapy) depends on the height prediction. In these cases, the additional information about skeletal maturity justifies the cost and radiation exposure.

In many pediatric endocrinology clinics, both methods are used together. The Khamis-Roche gives a baseline prediction assuming normal development, while the bone age provides a maturity-corrected estimate. Comparing the two can reveal whether a child's growth pattern is typical or warrants further investigation.

Key takeaways