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Tratado de Cirurgia da Coluna Vertebral
SECTION 1 • Basic Concepts
Chapter8

The Spine in the Sagittal Plane

Authors:Marcelo Italo Risso Neto•Paulo Tadeu Maia Cavali
Vancouver: Risso Neto MI, Cavali PTM📖 Pages: 95-112
Full reading of this chapter is available exclusively in the printed edition of the Treatise.
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Sec. 1Basic Concepts
Cap. 8Clinical Chapter
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Chapter Summary

• Context: Sagittal balance results from the functional integration of pelvic morphology, regional spinal curvatures, antigravity musculature, and lower extremity compensatory mechanisms (hip extension, knee flexion, ankle pelvic rotation). In upright posture, the human body strives to maintain its center of mass over the narrow polygon of support with minimal muscular work and energy expenditure, a concept synthesized by Jean Dubousset as the "cone of economy." When spinal malalignment shifts the trunk outside this physiological zone, muscular fatigue, chronic pain, functional disability, and compensatory recruitment escalate. Sagittal evaluation cannot rely on a single radiographic parameter because of substantial interindividual anatomical variation and age-related physiological changes. This chapter presents sagittal alignment as the structural congruence between the spine and pelvis, analyzing fixed anatomical and dynamic positional parameters, regional lordosis distribution, cervical balance, compensatory reserves, and global proportionality models (Roussouly, SRS-Schwab, and GAP score). Mastering these concepts is essential for evaluating spinal deformity, functional impairment, and mechanical failure risk in reconstructive spine surgery.
• Chapter Objective: To present the anatomical and biomechanical foundations of sagittal balance and organize the primary radiographic parameters used in spinopelvic assessment. The reader should be able to distinguish fixed anatomical from dynamic positional parameters; recognize spinal and lower extremity compensatory mechanisms; understand the classification models of Roussouly, SRS-Schwab, and Global Alignment and Proportion (GAP); and apply personalized spinopelvic analysis (including regional lumbar distribution, global balance, and cervical alignment) to surgical planning and deformity correction.
• The Cone of Economy and Spinopelvic HarmonyHuman bipedalism relies on harmonious alternating sagittal curves: cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacral kyphosis. The "cone of economy" defines the narrow spatial cylinder within which a person can stand erect with minimal muscular effort. Loss of sagittal alignment displaces the gravity line, forcing compensatory energy-consuming muscular contractions. The pelvis serves as the mechanical base of the spine, linking the mobile axial column to the lower extremities.
• Pelvic Parameters: PI, PT, and SSPelvic incidence (PI) is a fundamental, fixed morphological anatomical parameter after skeletal maturity that dictates the spatial capacity and orientation of the pelvic base. PI is geometrically related to two dynamic, positional parameters: Pelvic Tilt (PT, representing pelvic retroversion) and Sacral Slope (SS, representing horizontal sacral orientation), defined by the fundamental equation: PI = PT + SS. Patients with a high PI require greater lumbar lordosis and sacral slope to maintain balance, whereas patients with a low PI require flatter lordosis and lower sacral slope. Normal pelvic tilt is generally <20°; an elevated PT indicates active compensatory pelvic retroversion to maintain an upright trunk.
• Spinal and Global Alignment ParametersThe sagittal vertical axis (SVA, horizontal offset from the C7 plumb line to the posterosuperior corner of S1, normal <4–5 cm) reflects global trunk offset. However, SVA alone can be masked by pelvic retroversion and knee flexion. Angular global parameters such as the T1 Pelvic Angle (TPA, line from femoral heads to center of T1 and S1, normal <14°–15°) and Full Balance Integrated (FBI) index integrate trunk tilt and pelvic compensation into a single measurement that cannot be hidden by compensatory posturing. Lumbar lordosis (LL) is divided into upper lordosis (L1–L4) and lower lordosis (L4–S1), with lower lordosis normally providing approximately two-thirds (60–70%) of total lordosis.
• Classification Models: Roussouly, SRS-Schwab, and GAPThe Roussouly classification stratifies normal sagittal lordosis into four morphological types based on sacral slope and the lordosis apex/inflection point (with an added anteverted Type 3+ and degenerative variations), guiding restoration to the patient's constitutional baseline. The SRS-Schwab adult spinal deformity classification utilizes PI–LL mismatch (<10° normal, 10°–20° moderate, >20° severe), Pelvic Tilt (PT <20°, 20°–30°, >30°), and SVA (<4 cm, 4–9.5 cm, >9.5 cm) to grade deformity severity. The Global Alignment and Proportion (GAP) score evaluates proportionality (relative pelvic version, relative lumbar lordosis, lordosis distribution index, relative spinopelvic alignment, age) to predict mechanical hardware complications (proximal junctional kyphosis [PJK], rod breakage, and revision surgery).
• Cervical Alignment and Compensatory ReservesThe cervical spine adapts secondarily to maintain horizontal gaze. Cervical lordosis (CL), T1 slope (T1S), and C2–C7 SVA are interconnected: an increased thoracic kyphosis or positive global sagittal balance forces an increase in T1 slope and compensatory cervical hyperlordosis. When compensatory capacity is exhausted, progressive cervical kyphosis and inability to maintain horizontal gaze ensue.
• Clinical Application: In clinical practice, full-length standing 36-inch radiographs (EOS or stitched whole-spine radiographs including femoral heads and knees) are mandatory. Evaluation begins by calculating constitutional Pelvic Incidence (PI). Determine target lumbar lordosis using validated formulas (such as LL = PI ± 9° or age-adjusted targets) and ensure that 60–70% of the reconstructed lordosis is placed across L4–S1. Check PT to identify hidden pelvic retroversion. In elderly patients, overcorrecting to youthful alignment standards increases proximal junctional failure (PJK/PJF); age-adjusted alignment targets (higher PT and SVA thresholds) should be utilized. When planning osteotomies (PCO/Smith-Petersen, PSO, or VCR), pre-calculate the required angular correction and reconstruct apex position according to the patient's Roussouly type to achieve harmonious, proportional balance and prevent mechanical construct failure.
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Keywords

Preferred DeCS/MeSH Descriptors:
SpinePelvisPostural BalanceLordosisKyphosisRadiographySpinal CurvaturesSurgical Procedures, Operative
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Why this chapter matters

A patient may appear balanced on a standard radiograph while standing in exhausting compensation—retroverting the pelvis, hyperlordosing the cervical spine, and flexing the knees. This chapter provides the tools to look beneath the surface: assessing fixed pelvic morphology, anatomical lordosis distribution, compensatory reserve, and the energy cost of posture. Understanding sagittal balance prevents reliance on isolated metrics, refines realignment targets, and reduces catastrophic mechanical complications (pseudarthrosis, PJK, and hardware failure).

“Sagittal balance is not a single rigid number, but the harmonious congruence between pelvic morphology, regional curve distribution, global alignment, and compensatory reserve. Pelvic incidence, PT, SS, regional lordosis distribution, cervical parameters, and global angular measurements must be evaluated collectively. Reconstructive spine surgery should aim for proportional, energy-efficient balance tailored to the patient's age, constitutional anatomy, and functional demands, avoiding both undercorrection and rigid overcorrection.”
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Chapter Highlights

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Card 1 — Core Concept
Pelvic Incidence Dictates Lordosis

Pelvic incidence (PI) is a fixed anatomical parameter that determines the required lumbar lordosis (LL) and sacral slope (SS). PI = PT + SS. Patients with high PI require substantial, steeply inclined lordosis; patients with low PI require a flatter, shorter lordosis.

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Card 2 — Clinical Decision
Distribute Two-Thirds of Lordosis at L4–S1

Regardless of total lordosis magnitude, 60% to 70% of normal lumbar lordosis is located between L4 and S1. Reconstructing lordosis predominantly in the upper lumbar spine (L1–L3) creates an unphysiological flat lower spine, increasing shear stress, PJK risk, and implant failure.

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Card 3 — Key Pearl / Warning
Age-Adjust Alignment Targets

Never apply youthful alignment metrics (SVA < 4 cm, PT < 15°) indiscriminately to elderly deformity patients. Forcing rigid youthful alignment in elderly individuals leads to catastrophic proximal junctional kyphosis (PJK/PJF). Tailor correction targets to age and compensatory capacity.

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How to Cite this Chapter (Vancouver Format)

Official bibliographic indexing and citation guidelines
📖 Pages: 95-112Vancouver Style
Authors (Vancouver):Risso Neto MI, Cavali PTM

Risso Neto MI, Cavali PTM. Coluna vertebral no plano sagital. In: Pudles E, Defino H, Risso M, editors. Tratado de Cirurgia da Coluna Vertebral (Treatise of Spine Surgery). 1st ed. Rio de Janeiro: Dilivros Editora; 2026. p. 95-112.

ISBN: 978-85-8053-292-0 • 1.ª Edição • Dilivros Editora
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Bibliographic References

1. Dubousset J. Three-dimensional analysis of the scoliotic deformity. The pediatric spine: principles and practice. New York: Raven Press; 1994.
2. Le Huec JC, Aunoble S, Pellet N, Sibilla F, Saddiki R, Roussouly P. Importance de l’analyse de l’équilibre sagittal en pathologie rachidienne – rôle de la balance spino-pelvienne dans les maladies dégénératives du rachis. Maîtrise Orthopédique. 2009;184.
3. Le Huec JC, Thompson W, Mohsinaly Y, Barrey C, Faundez A. Sagittal balance of the spine. European Spine Journal. 2019;28(9):1889-905.
4. Rothman-Simeone. The spine. 2 ed. Philadelphia: Saunders; 2006.
5. Dufour M, Pillu M. Biomécanique Fonctionelle. 1 ed. Paris: Masson; 2006. p. 438-439.
6. Konz RJ, Fatone S, Stine RL, Ganju A, Gard SA, Ondra SL. A kinematic model to assess motion during walking. Spine (Phila Pa 1976). 2006;31(24).
7. Saha D, Gard S, Fatone S. The effect of trunk flexion on able-bodied gait. Gait Posture. 2008;27(4):653-60.
8. Vialle R, Levassor N, Rillardon L, Templier A, Skalli W, Guigui P. Radiographic analysis of the sagittal alignment and balance of the spine in asymptomatic subjects. J Bone Joint Surg Am. 2005;87(2):260-7.
9. Henneman SA, Antoneli PHL, Oliveira GC. Incidência pélvica: um parâmetro fundamental para definição do equilíbrio sagital da coluna vertebral. Coluna/Columna. 2012;11(2):139-56.
10. Roussouly P, Gollogly S, Berthonnaud E, Dimnet J. Classification of the normal variation in the sagittal alignment of the human lumbar spine and pelvis in the standing position. Spine. 2006;30(3):346-53.
11. Roussouly P, Gollogly S, Noseda O, Berthonnaud E, Dimnet J. The vertical projection of the sum of the ground reactive forces of a standing patient is not the same as the C7 plumb line: a radiographic study of the sagittal alignment of 153 asymptomatic volunteers. Spine (Phila Pa 1976). 2006;31(11).
12. Lafage V, Schwab F, Patel A, Hawkinson N, Farcy JP. Pelvic tilt and truncal inclination: two key radiographic parameters in the setting of adults with spinal deformity. Spine (Phila Pa 1976). 2009;34(17).
13. Hills J, Lenke LG, Sardar ZM, Le Huec JC, Bourret S, Hasegawa K, et al. The T4-L1-hip axis: defining a normal sagittal spinal alignment. Spine (Phila Pa 1976). 2022;47(19):1399-406.
14. Legaye J, Duval-Beaupère G, Hecquet J, Marty C. Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves. European Spine Journal. 1998;7(2):99-103.
15. Schwab F, Patel A, Ungar B, Farcy JP, Lafage V. Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery. Spine (Phila Pa 1976). 2010;35(25):2224-31.
16. Labelle H, Roussouly P, Berthonnaud E, Dimnet J, O’Brien M. The importance of spino-pelvic balance in L5-S1 developmental spondylolisthesis: a review of pertinent radiologic measurements. Spine (Phila Pa 1976). 2005;30(6 Suppl).
17. Berthonnaud E, Dimnet J, Roussouly P, Labelle H. Analysis of the sagittal balance of the spine and pelvis using shape and orientation parameters. J Spinal Disord Tech. 2005;18(1):40-7.
18. Roussouly P, Gollogly S, Berthonnaud E, Dimnet J. Classification of the normal variation in the sagittal alignment of the human lumbar spine and pelvis in the standing position. Spine. 2006;30(3):346-53.
19. Offierski CM, MacNab I. Hip-spine syndrome. Spine. 1983;8(3):316-21.
20. Buckland AJ, Vigdorchik J, Schwab FJ, Errico TJ, Lafage R, Ames C, et al. Acetabular anteversion changes due to spinal deformity correction: bridging the gap between hip and spine surgeons. J Bone Joint Surg Am. 2015;97(23):1913-20.
21. Schwab FJ, Blondel B, Bess S, Hostin R, Shaffrey CI, Smith JS, et al. Radiographical spinopelvic parameters and disability in the setting of adult spinal deformity: a prospective multicenter analysis. Spine. 2013;38(13).
22. Esposito CI, Carroll KM, Sculco PK, Padgett DE, Jerabek SA, Mayman DJ. Total hip arthroplasty patients Wwth fixed spinopelvic alignment are at higher risk of hip dislocation. J Arthroplasty. 2018;33(5):1449-54.
23. Roussouly P, Pinheiro-Franco JL. Sagittal parameters of the spine: biomechanical approach. Eur Spine J Off Publ Eur Spine Soc Eur Spinal Deform Soc Eur Sect Cerv Spine Res Soc. 2011;20(Suppl 5):578-85.
24. Lima MC, Risso Neto MI, Cavali PTM, Gehhlen SHJ, Rosa AF, Mistro Neto S, et al. Relação entre alinhamento sagital cervical e padrão de curva na escoliose idiopática. Coluna/Columna. 2024;24(1).
25. Laouissat F, Sebaaly A, Gehrchen M, Roussouly P. Classification of normal sagittal spine alignment: refounding the Roussouly classification. Eur Spine J. 2018;27(8):2002-11.
26. Lafage R, Schwab F, Glassman S, Bess S, Harris B, Sheer J, et al. Age-adjusted alignment goals have the potential to reduce PJK. Spine (Phila Pa 1976). 2017;42(17):1275-82.
27. Glassman SD, Bridwell K, Dimar JR, Horton W, Berven S, Schwab F. The impact of positive sagittal balance in adult spinal deformity. Spine. 2005;30(18):2024-9.
28. Lafage V, Schwab F, Skalli W, Hawkinson N, Gagey PM, Ondra S, et al. Standing balance and sagittal plane spinal deformity: analysis of spinopelvic and gravity line parameters. Spine. 2008;33(16):1572-8.
29. Le Huec JC, Hasegawa K. Normative values for spinopelvic parameters. Eur Spine J. 2016;25(11):3630-7.
30. Yilgor C, Sogunmez N, Boissiere L, Yavuz Y, Obeid I, Kleinstück F, et al. Global Alignment and Proportion (GAP) Score: development and validation of a new method of analyzing spinopelvic alignment to predict mechanical complications after adult spinal deformity surgery. J Bone Joint Surg Am. 2017;99(19):1661-72.
Episode 01 – The Spine in the Sagittal Plane
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Treatise in Debate

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Episode 01 – The Spine in the Sagittal Plane

Scientific debate on spinopelvic balance, contemporary classifications, and surgical planning