Double Major Scoliosis: S-Shaped and Sigmoid Curves, and Why Two Structural Curves Change the Plan

By Dr. Justin Dick, DC · Clear Life Scoliosis and Chiropractic Center, Charlotte, NC · Published October 14, 2026

A double major scoliosis has two structural curves, usually a thoracic curve and a thoracolumbar or lumbar curve bending in opposite directions. On an X-ray the spine forms an S. "Sigmoid scoliosis" describes the same S-shaped pattern. The defining word is structural: both curves are fixed, rotated deformities, not one real curve with a flexible compensation below or above it.

I am Dr. Justin Dick, and at Clear Life Scoliosis and Chiropractic Center in Charlotte, NC, the double major pattern is the one I see underestimated most often, because two opposite curves can make the trunk look balanced in the mirror. This post explains how the pattern is identified and why it changes treatment.

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Structural Versus Compensatory

Almost every scoliosis has more than one bend. A single structural thoracic curve usually has a smaller lumbar bend below it that keeps the head over the pelvis. That lower bend is compensatory: it is flexible and corrects on side-bending films. In a true double major, both curves are structural. They have rotation, they resist correction on bending films, and both need to be addressed.

The Lenke classification makes this distinction formally. It sorts adolescent idiopathic curves into six types according to which of three regions, proximal thoracic, main thoracic, and thoracolumbar or lumbar, contain structural curves, using standing films and supine side-bending views. The double and triple patterns are separate types from the single thoracic and single thoracolumbar patterns. Our Lenke classification page covers the system, and my posts on thoracic scoliosis and thoracolumbar scoliosis cover each curve on its own.

Why Double Major Curves Get Missed

This section is clinical observation, not trial data. When two curves of similar size bend in opposite directions, the shoulders and pelvis can end up nearly level and the trunk centered over the pelvis. The usual visual clues of a single curve, a trunk shift or one high shoulder, may be subtle. What remains is rotation: a thoracic rib prominence on one side and a lumbar prominence on the other during the forward bend test. A screener who looks only at shoulder and hip height can miss it. This is one reason the forward bend test and a scoliometer reading at both levels matter. My post on spinal rotation explains why rotation is the more reliable sign.

How Double Curves Behave

Each curve carries its own progression risk. In Weinstein and Ponseti's 40-year follow-up, thoracic curves were most likely to progress after maturity when they measured 50° to 75°, and lumbar curve progression related to rotation, Cobb angle, direction, and the position of L5 relative to the pelvis. A double major exposes the patient to both sets of risk factors. During growth, Lonstein and Carlson found that curve pattern was one of the factors related to progression, alongside magnitude, Risser sign, age, and menarche.

The rib cage is affected through the thoracic curve. Assi and colleagues' 3D study of 200 adolescents with idiopathic scoliosis found that rib cage deformity did not always follow the axial rotation of the spine, and that patients with severe hypokyphosis had reduced rib cage volume. In a double major, the thoracic component determines most of that effect.

Why Two Structural Curves Change the Plan

Correcting one curve affects the other. If treatment straightens the thoracic curve without addressing the lumbar curve, the lumbar curve has to absorb the change, and the trunk can shift. Bracing and scoliosis-specific exercise for a double major must be designed for both curves. A brace built for a single thoracic pattern is not the same device as one built for a double curve, and exercises that correct one curve can load the other in the wrong direction if they are not curve-specific. That is why the curve type, not a generic program, drives the plan at our office.

How Dr. Justin Dick Evaluates S-Shaped Curves at Clear Life

At our Charlotte office, a suspected double curve gets standing PA and lateral films, measurement of both curves and their rotation, angle of trunk rotation at both levels, and, when the structural question affects treatment, side-bending assessment. Bracing through ScoliBrace is designed from the individual curve pattern, and rehabilitation through the CLEAR protocol is curve-specific.

Comparison

Research and Evidence

Evidence tiering: the classification rests on the Lenke reliability study. Natural history data come from Weinstein and Ponseti and from Lonstein and Carlson, both older cohorts that did not report double major curves as a separate outcome group in their abstracts. The observation that balanced double curves are easier to miss is my clinical reasoning, not a tested finding. The 3D rib cage data come from a cross-sectional study.

My published cases do not include a double major curve. The closest is the cervical mechanics study, A Retrospective Cross-Sectional Analysis of Abnormal Cervical Mechanics in Patients With Scoliosis (Cureus, 2025, PMID 41018459), which included 37 patients across curve types and found cervical hypolordosis throughout, a reminder that curve pattern does not stop at the thoracolumbar spine.

References

1. Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am. 2001;83(8):1169-81. PMID 11507125
2. Weinstein SL, Ponseti IV. Curve progression in idiopathic scoliosis. J Bone Joint Surg Am. 1983;65(4):447-55. PMID 6833318
3. Lonstein JE, Carlson JM. The prediction of curve progression in untreated idiopathic scoliosis during growth. J Bone Joint Surg Am. 1984;66(7):1061-71. PMID 6480635
4. Assi A, Karam M, Skalli W, et al. A novel classification of 3D rib cage deformity in subjects with adolescent idiopathic scoliosis. Clin Spine Surg. 2021;34(9):331-341. doi:10.1097/BSD.0000000000001139
5. Bunnell WP. An objective criterion for scoliosis screening. J Bone Joint Surg Am. 1984;66(9):1381-7. PMID 6501335
6. Dick JM. A retrospective cross-sectional analysis of abnormal cervical mechanics in patients with scoliosis. Cureus. 2025;17(8):e91098. doi:10.7759/cureus.91098

Frequently Asked Questions

Service Area

Clear Life Scoliosis and Chiropractic Center sees patients from Charlotte NC, Huntersville NC, Ballantyne NC, Matthews NC, Concord NC, Mooresville NC, Rock Hill SC, Fort Mill SC. Families from across the Charlotte region and the South Carolina border communities come to the Rachel Freeman Way office for radiographic scoliosis evaluation with Dr. Justin Dick.

Related Pages

• Lenke Classification
• Scoliosis Curve Patterns
• Spinal Rotation in Scoliosis
• Postural vs Structural Scoliosis
• Rib Prominence and Scoliosis
• When Scoliosis Progresses the Most
• ScoliBrace in Charlotte
• CLEAR Scoliosis Protocol
• Free Scoliosis Screening Tool
• Dr. Justin Dick Research

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If your child has been told the spine curves in two directions, the key question is whether both curves are structural. Dr. Justin Dick answers that at our Charlotte office before any treatment plan is set.

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