Scoliosis is defined as an abnormal, three-dimensional lateral curvature and rotation of the spine. This condition most frequently manifests as Adolescent Idiopathic Scoliosis (AIS), which accounts for approximately 80% of cases and develops in children between the ages of 10 and 18. The exact cause of AIS remains unknown (idiopathic), but the condition is fundamentally linked to a person’s growth and development. Curve progression is heavily influenced by the speed and duration of bone growth, meaning the risk of the curve worsening is not uniform across a patient’s lifetime. The question of when scoliosis stops progressing is therefore directly tied to the cessation of skeletal growth, not a specific chronological age.
Skeletal Maturity and the End of High-Risk Progression
The period of highest risk for scoliosis curve progression occurs during the adolescent growth spurt, a time of rapid skeletal elongation. Progression rates during this phase can be rapid, with some curves increasing by 10 to 20 degrees per year. This rapid worsening is closely associated with peak height velocity (PHV), which is the point when an adolescent is growing fastest.
Once the skeleton reaches full maturity, the rapid, puberty-driven progression of scoliosis largely stops. Skeletal maturity refers to the complete fusion of the growth plates, indicating that the long bones and vertebrae have finished growing. This growth cessation typically occurs in the late teenage years, often between 14 and 16 for females and 16 and 18 for males, though this timing can vary widely among individuals.
For most individuals with AIS, the spine stabilizes once the rapid growth phase is complete. Since the spine’s growth plates are no longer actively creating new bone, the mechanical force driving the rotational and lateral changes in the spine is removed. Chronological age is less important than biological or bone age when predicting this stabilization point, so medical professionals rely on specific clinical and radiographic markers to determine when this high-risk period has ended.
Clinical Markers Used to Determine Stabilization
Medical professionals use specific radiographic signs to precisely determine an adolescent’s skeletal maturity and their remaining growth potential. The most common method involves evaluating the Risser sign, a grading system that tracks the ossification, or bone formation, of the iliac apophysis, which is the growth plate on the top of the hip bone. This apophysis ossifies in a predictable sequence that correlates with the growth plates in the spine.
The Risser scale ranges from 0 to 5, where a Risser 0 indicates a highly immature skeleton with significant growth remaining, corresponding to the beginning of the growth spurt. As the iliac crest ossifies, the Risser grade increases, and the risk of progression decreases. A patient reaching Risser 5 signifies complete fusion of the iliac apophysis to the ilium, which is the definitive indicator of skeletal maturity and the end of the high-risk progression period.
Other markers are used, especially during the earliest phases of growth when the Risser sign is still at 0. For example, the status of the triradiate cartilage, a growth plate in the hip socket, can be monitored; its closure occurs during the peak growth period. Clinicians also assess the patient’s growth history, looking for the timing of peak height velocity, as this precedes the final stages of skeletal maturity.
Curve Magnitude and Long-Term Stability
Reaching skeletal maturity does not guarantee absolute stability for every scoliotic curve; the final size of the curve is a major determinant of its long-term behavior. The severity of the curve is quantified using the Cobb angle, which is a measurement taken on an X-ray to determine the degree of the lateral spinal deviation. This angle is a factor in predicting whether the curve will remain stable or continue to worsen slowly in adulthood.
Curves that measure less than 30 to 40 degrees at the time of skeletal maturity (Risser 5) are generally considered stable and have a low probability of progressing further. For these smaller curves, the forces of gravity and normal spinal wear are typically insufficient to cause significant changes over a patient’s lifespan. However, larger curves present a greater mechanical challenge to the spine’s long-term stability.
Curves that exceed 50 degrees at the time the patient completes growth have a notably higher risk of slow, continued progression throughout adulthood. The sheer magnitude of the curvature creates greater biomechanical instability, placing uneven stress on the vertebral discs and joints. This increased mechanical load, combined with degenerative changes, means that a curve over this threshold may never truly stop progressing entirely.
Progression Risk After Skeletal Maturity
While the rapid progression associated with adolescence ceases once skeletal maturity is achieved, a slow, subtle progression can still occur in adulthood. This late-stage progression is distinct from the growth-driven worsening seen in teenagers and is primarily influenced by degenerative changes in the spine. Patients with larger curves (over 50 degrees) are particularly susceptible to this slow progression.
The typical rate of this adult progression is modest, often reported to be between 0.5 to 1 degree per year. Factors contributing to this gradual change include the natural aging process, such as disc degeneration and the loss of disc height. Osteoporosis and changes in spinal balance, like the loss of the normal curvature in the lower back, can also introduce instability that drives the curve to progress slowly over decades.
For individuals with significant curves, scoliosis requires long-term monitoring, even after skeletal maturity. While the risk of progression in adulthood is lower than during the growth spurt, it remains a lifelong consideration for those whose final curve magnitude was substantial.