Some people with idiopathic scoliosis see their curves continue to worsen into adulthood; others see their curves hold steady once they reach skeletal maturity. As a general rule:

Scoliosis curves measuring 30 degrees or less at skeletal maturity tend to stop progressing (or progress very slowly) and require no treatment.
Curves measuring 50 degrees or more at skeletal maturity tend to worsen about 1 degree per year throughout adulthood, and in these cases surgery will usually be recommended to avoid severe spinal deformity.

The reason for this discrepancy in curve progression is not known, but the historical data are helpful when clinicians make determinations about whether observation, bracing, or surgery might be best for a patient who is at or near skeletal maturity.

See Bracing Treatment for Idiopathic Scoliosis

Risser Sign Estimates Skeletal Maturity

Determining skeletal maturity is not an exact science. While many methods exist for estimating how much skeletal growth remains, the Risser sign is most commonly used for adolescent idiopathic scoliosis patients.

The Risser classification method makes use of the fact that as a person’s skeleton matures during adolescence, bone starts to form on the outer part of the iliac crest (upper edge of the pelvis) and calcifies inward along the ridge. After this bone formation along the iliac crest is complete, the new bone growth fuses to the hip bone and this fusion is believed to correspond with full skeletal maturity.

With this information in mind, doctors are able to view an x-ray (typically the same x-ray of the back taken for the Cobb angle measurement) and determine a Risser sign number based on the following:

Stage 0. No bone growth on the iliac crest.
Stage 1. Bone growth covers less than 25% of the iliac crest.
Stage 2. Bone growth covers 25% to 50% of the iliac crest.
Stage 3. Bone growth covers 50% to 75% of the iliac crest.
Stage 4. Bone growth covers 75% to 100% of the iliac crest.
Stage 5. Bone growth completely covers and is fused to the iliac crest.

Risser stage 0 or 1 could indicate years of skeletal growth still to go and a major growth spurt in the future, whereas Risser stage 4 or 5 could indicate little or no growth remains.

Other Methods for Estimating Skeletal Maturity

Some doctors might take other factors into consideration when estimating skeletal maturity, such as:

Tanner scale. This method requires measuring and observing several areas of the body to estimate the progression of sexual maturity.
Peak height velocity. By tracking a child’s growth into and through adolescence, a period of peak height velocity (PHV) can be found. PHV is usually a telling reference point for where an adolescent might be in terms of physical development and amount of skeletal growth remaining.

Using the Tanner scale or PHV is more time-consuming and often not realistic in the clinical setting for a scoliosis patient. Therefore, the Risser sign remains the most commonly used method for estimating skeletal growth in adolescent scoliosis patients.

Dr. Ali Baaj is the Chief of Spine Surgery at Banner Health and the Associate Professor of Neurological & Orthopedic Surgery at the University of Arizona. He specializes in complex and minimally invasive spine surgery for adults and children.