Scolliosis Under 40 Degrees

Scoliosis under 40 degrees

Objectives:

Understand the period of rapid curve progression and its relationship to maturity.
Have a basic understanding of the evidence for scoliosis bracing.
Understand the basic theory of various categories of scoliosis bracing.
Know the long term consequences of scoliosis under 40 degrees.

Idiopathic scoliosis under 40 degrees is generally regarded as benign, with no long-term health consequences. However, even scoliosis over 40 degrees was likely under this size at some time. Additionally, the evidence that scoliosis under 40 degrees is clinically different than scoliosis of 50 or 60 degrees is scant.

Duval-Beaupere found that scoliosis, whether idiopathic or neuromuscular, underwent a distinct change in behavior with rapid progression during the adolescent growth spurt. Idiopathic scoliosis typically appears in the preadolescent period. Smaller curves usually presents during a routine examination or school screening while larger curves are often noticed by the patient or parents. During the adolescent growth spurt, typically occurring ages 10-14 for girls and 12-16 for boys but with a wide standard deviation, curves can increase up to two degrees per month. This rapid change in curve behavior has been termed the curve acceleration phase (CAP). This rapid change in curve behavior is closely related to curve magnitude, curve pattern, and maturity.

Currently, the only method with the potential to retard or prevent scoliosis progression is with bracing. Several types of braces exist. The first brace used was the Milwaukee brace initially developed by Blount for use as a postoperative orthosis. This brace uses a stable pelvic girdle and uprights with straps attached at various locations to apply three-point pressure across the ribs, flank, and pelvis. Under-arm orthosis such as the Wilmington and Boston use similar principles with some variances. The Boston brace uses pelvic tilt to decrease lumbar lordosis, unlock the lumbar facets, and thereby provide further lumbar correction. Night only braces such as the Charleston and Providence aim to hold the spine in maximum correction during the night when growth is the most rapid. The Spine-Cor uses flexible straps attached to a pelvic piece for dynamic curve correction during activities. Various protocols require differing amounts of time in and out of the brace.

The major evidence for scoliosis bracing comes from a multicenter study published in 1995 which compared bracing to electrical stimulation and observation. Using an endpoint of 6 degrees progression, at five years, bracing had a success rate of 77% while observation and electrical stimulation had a success rate of only 37%. Unfortunately, their study only included thoracic and thoracolumbar curves, and picked a clinically meaningless endpoint of 6 degrees. It is impossible to determine what proportion of the 40% success from bracing meant these patients did not require surgery because of bracing. A recent meta-analysis could find no difference in the incidence of surgery for those undergoing bracing compared to those observed. Knowing which patients benefit from bracing must await the results of a current randomized, controlled study (BrAIST).

While the Risser sign was formerly the maturity measurement most used to identify the risk of curve progression, it occurs too late in the growth spurt to be highly useful. The rapid growth spurt is clinically recognized by the peak height velocity (PHV). Surgery is unlikely in patients with curves less than 30 degrees at their PHV but highly likely in those with curves more than 30 degrees at their PHV. Because the PHV is very difficult to identify without ready access to serial accurate height measurements, attempts have been made to identify this period of curve progression by other methods. Skeletal maturity using either the hand or the elbow is tightly related to the adolescent growth spurt. Skeletal maturity using the hand has been shown to correlate highly with the risk of curve progression.

In terms of curve patterns, thoracic curves and double major curves of 20 degrees at the start of the growth spurt or 30 degrees at the most rapid growth have the greatest risk of progressing to more than 50 degrees. Double thoracic, thoracolumbar, and double major with predominant lumbar curves still progress during this phase but are less likely to have large curves.

Overall, curves less than 30 degrees at maturity have little risk of progressing in adulthood. Curves at most risk of progression are those of 50-55 degrees in the thoracic spine or 35 degrees or more in the lumbar or thoracolumbar spine. Pulmonary changes rarely occur in curves less than 60 degrees thoracic. However, even patients with larger curves, despite their disfigurement, have little increased risk of cardiopulmonary failure if they are non-smokers. While there are strong opinions that thoracolumbar and lumbar curves may result in significant adult symptoms, longitudinal studies are lacking.

Key Points:

Scoliosis progression is tightly related to curve pattern, curve magnitude, and skeletal maturity.
The evidence that bracing prevents curves from reaching a surgical range is weak.
Curves less than 30 degrees at maturity are unlikely to progress.
Curve of >50-55 degrees thoracic and >35 degrees thoracolumbar or lumbar are at greatest risk of progression during adulthood.
Even larger curves seem to cause little physiological harm in non-smokers.

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