Blog Topic What is Bone Age? Why does it matter for treatment of scoliosis? 5-9-2021
What is bone age?
Bone age is a method to determine the skeletal maturation level of a growing person. The younger the bone age, the more growth is ahead of them.
Why not just use someone’s chronologic age?
The chronologic age of a growing individual, which is calculated from their birth date to now, does not accurately estimate the maturation of their bones. We all know people who are “early bloomers” and “late bloomers”, those young men who started shaving in 7th grade vs. those who kept growing until they started college. There is wide variation in bony maturation and growth when we look at someone’s chronologic age.
Why does bone age matter?
We can get much more precise when we look at the actual bones, and their growth plates, to get a better idea of someone’s future growth. Remember, the more growth a person with scoliosis has remaining the greater the likelihood the scoliosis will worsen, and faster growth (during the pubertal growth phase) usually means faster progression (worsening). So better knowing how much growth is in the future helps plan treatment more precisely.
How do you tell how old are someone’s bones?
Radiographs/x-rays are used. Many different parts of the body have been used for determination of bone age, from the calcaneus (heel bone) to the olecranon (elbow) to the humerus (shoulder) and the hand. Classically, spine surgeons have use the Risser sign, which grades the iliac crest (hips) growth plates. Since this part of the body is seen on spine radiographs/x-rays it doesn’t require any additional imaging. See below image, the iliac crests are at the blue arrows.
Where does someone look for the Risser sign?
The iliac bones (above, blue arrows), and there are two of them, one on the left and one on the right side of the pelvis. The sit on each side of the sacrum and look like Mickey Mouse ears.
How is the Risser sign determined?
The Risser sign is from 0 to 5 (see below). The iliac apophysis (a growth center for the iliac crest) is a thin strip of bone that forms on top of the iliac crests. If there is no bone visualized on the plain radiographs/x-rays then it is called a Risser 0. The strip of bone keeps growing back to cover the entire iliac crest (Risser 4), and then fuses to the iliac crest (Risser 5). Once the Risser 5 stage is reached the patient has completed skeletal growth.
0 Bony iliac apophysis not yet visible
1 Initial (<25%) ossification of the iliac apophysis
2 From 25% to 50% ossification of the iliac apophysis
3 From 50% to 75% ossification of the iliac apophysis
4 More than 75% ossification of the iliac apophysis
5 Iliac apophysis fuses to the iliac crest
Below is an example of a Risser 1-2 sign. See the very small amount of bone on the outside part of the iliac crest (on the right side just below the “300” on the radiograph/x-ray).
The below graph demonstrates the velocity of growth, with year “zero” being the time of peak growth velocity. As you look to the right, after menarche occurs, then Risser sign 1 occurs, almost a full year after peak growth velocity. This is a weakness of the Risser sign, it doesn’t identify the peak growth velocity, as it only occurs after it has happened.
To deal with this the Sanders grade was developed by Dr. Jim Sanders, the Chair of Orthopaedics at the University of North Carolina.Next blog post a better way to estimate skeletal age will be presented: The Sander grading system.