Joseph Schooling's Olympic gold-medal win and his journey to get there has sparked off a discussion about bone age among readers and parents.
His parents had taken him for a bone-age assessment when he was 11 years old.
This was to gauge how tall he would eventually be and to see if that augured well for a competitive sports career.
However, the usual requests for bone-age assessment that I see in my clinic are typically over concerns of height growth and precocious puberty.
The commonest scenario is a worried parent with a 12-year-old who appears much shorter than his peers.
Oftentimes, when a bone-age assessment is done on such a child, the age of his bones is more than two years younger than the child's actual age. This is called constitutional growth and pubertal delay (CGPD) and is a normal variant among children.
Such children appear short in their younger years as they have a delayed maturation and will have an extra two or more years to grow after their peers have stopped growing.
Sometimes, their height eventually exceed those of their other classmates.
A bone-age test is an X- ray assessment of the degree of maturation of a child's bones.
As a person grows from birth through childhood and puberty, and completes growth as a young adult, skeletal bones change in size and shape.
The bone age of a child is the average age at which children reach this stage of bone maturation.
A child's current height and bone age can thus be used to predict his adult height.
However, children do not mature at exactly the same time.
Just as there is wide variation in the normal population for when tooth eruption or menstruation occur, the bone age of a healthy child may be a year or two ahead, or delayed, compared to actual age.
For most people, their bone age is similar to their biological or chronological age and may differ by only a few months.
For others, their bone age could be a few years older or younger.
The assessment involves a single X-ray of the left hand, fingers and wrist. The bones in the X-ray are compared to a standard atlas of bone development.
Different small bones in the wrist start appearing as the child gets older and the shapes of various bones change.
Growth plates (gaps between bones) get narrower with age. A growth plate is a hyaline cartilage plate at each end of a long bone.
These are found in children and adolescents. In adults who have stopped growing, the plate is fused and replaced by a line.
Typically, paediatric endocrinologists order bone-age X-rays to evaluate children for advanced or delayed growth and physical maturation.
A worried father once brought his 12-year-old daughter to see me.
His burning question was how much taller she would be and whether there was something that could be done. At that age, she was already as tall as him, standing at 1.75m.
He was worried that it would be difficult for her to find a husband taller than her.
Her bone age was found to be already at 15 years. Her case is one of familial tall stature, because she has relatives who are tall.
Based on her bone age, which showed that she would have only another year or so to grow and at a very slow rate, I could reassure her father that her growth was almost done.
Then there are children who go into earlier puberty than average.
They will have a bone age that is more than two years ahead of their actual age. Because they experience pubertal growth spurts, they appear taller than many of their peers. However, as they complete puberty and their bones fuse, they stop growing taller while their friends continue doing so. This results in a shorter stature as an adult.
I have a very young patient who went into precocious puberty due to a condition resulting in excess sex steroid production.
This caused his bones to advance in age. His bone age was 13 years old when he was only five.
His predicted height was only 1.4m, which is very short for a boy.
He has been started on hormone treatment for his disease that will reduce the excess sex steroid production.
In some situations of precocious puberty, it is sometimes recommended that puberty be blocked with medications to "buy" time for the child to grow taller.
Girls who have not gone into puberty by age 13, and boys by age 14, are said to have delayed puberty and will be referred for further assessment.
A bone-age assessment in this case will determine if the bones are, in fact, younger than the patient's chronological age. If so, this is often due to constitutional growth and pubertal delay and all that needs is "masterly inactivity". That is, to do nothing and observe when puberty comes about.
There is a possibility that puberty does not happen and it could be due to missing messengers (hormones called LH/FSH) for puberty to start. Then, we need to give hormone treatment to initiate puberty.
Most parents get a little worried about the variant between their child's actual age and bone age, especially when the difference is more than two years.
I always tell the parents that it is important to know that advanced or delayed bone age does not always indicate disease.
Take, for example, a boy whose bone age is delayed by three years.
While he may be shorter than his peers now, it also means that he will continue to grow for three years after his peers have stopped.
Hence, bone age has to be considered in the context of broader considerations such as delayed or advanced puberty, tall or short stature and chronic illness, in order to draw meaningful conclusions.
•Dr Ho is an associate consultant in the division of paediatric endocrinology at the National University Hospital. She completed her paediatric endocrinology fellowship training at the Royal Children's Hospital in Melbourne, Australia. She sees all paediatric endocrine conditions but has special interests in bone health and growth in children, and late effects in children who have survived cancer.