Spinopelvic sagittal balance: what does the radiologist need to know?

Sagittal balance describes the optimal alignment of the spine in the sagittal plane, resulting from the interaction between the spine and lower limbs, via the pelvis. Understanding sagittal balance has gained importance, especially in the last decade, because sagittal imbalance correlates directly with disability and pain. Diseases that alter that balance cause sagittal malalignment and may trigger compensatory mechanisms. Certain radiographic parameters have been shown to be clinically relevant and to correlate with clinical scores in the evaluation of spinopelvic alignment. This article aims to provide a comprehensive review of the literature on the spinopelvic parameters that are most relevant in clinical practice, as well as to describe compensatory mechanisms of the pelvis and lower limbs.

Keywords:
Spine; Pelvis; Radiography; Lordosis/diagnostic imaging; Kyphosis/diagnostic imaging; Spinal curvatures/diagnostic imaging; Postural balance

Authorship

Leonor Garbin Savarese Correspondence: Dra. Leonor Garbin Savarese. Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo, Divisão de Radiologia. Avenida Bandeirantes, 3900, Vila Monte Alegre. Ribeirão Preto, SP, Brazil, 14048-900. Email: leonorgs@usp.br / leonorsavarese@hotmail.com.

Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (HCFMRP-USP), Ribeirão Preto, SP, Brazil.Universidade de São Paulo (HCFMRP-USP)BrazilRibeirão Preto, SP, BrazilHospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (HCFMRP-USP), Ribeirão Preto, SP, Brazil.

https://orcid.org/0000-0002-1372-9162

Rafael Menezes-Reis

https://orcid.org/0000-0002-8496-5939

Gustavo Perazzoli Bonugli

https://orcid.org/0000-0003-2740-3371

Carlos Fernando Pereira da Silva Herrero

https://orcid.org/0000-0002-3387-4797

Helton Luiz Aparecido Defino

https://orcid.org/0000-0003-4274-0130

Marcello Henrique Nogueira-Barbosa

https://orcid.org/0000-0002-7436-5315

Correspondence: Dra. Leonor Garbin Savarese. Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo, Divisão de Radiologia. Avenida Bandeirantes, 3900, Vila Monte Alegre. Ribeirão Preto, SP, Brazil, 14048-900. Email: leonorgs@usp.br / leonorsavarese@hotmail.com.

SCIMAGO INSTITUTIONS RANKINGS

Figures

Figures (12)

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Figure 1
Panoramic X-ray acquired in the sagittal plane (on the left) and patient positioning for its acquisition (on the right).

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Figure 2
Schematic representation of the pelvic tilt (PT), which is the angle formed by a vertical line originating from the midpoint of the femoral head and a line running from the midpoint of the femoral head to the midpoint of the upper endplate of S1.

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Figure 3
Schematic representation of the sacral slope (SS) angle, which is the angle between the upper endplate of S1 and a horizontal line.

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Figure 4
Schematic representation of the pelvic incidence (PI), which is the angle between a line perpendicular to the upper endplate of S1 and a line connecting the midpoint of that endplate with the midpoint of the femoral head.

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Figure 5
Schematic representation of pelvic retroversion. By bringing the upper endplate of S1 closer to the axis of the femoral heads and increasing the sacrofemoral distance, this mechanism compensates for the anterior shift in the center of gravity. Adapted from Barrey et al.⁽⁹9 Barrey C, Roussouly P, Le Huec JC, et al. Compensatory mechanisms contributing to keep the sagittal balance of the spine. Eur Spine J. 2013;22 Suppl 6:S834-41.⁾. SS, sacral slope; PT, pelvic tilt.

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Figure 6
A: Schematic representation of the thoracic kyphosis (TK) angle, which is the measurement of the Cobb angle between the lower endplate of T12 and the upper endplate of T4. B: Schematic representation of the lumbar lordosis (LL) angle, which is the measurement of the Cobb angle between the upper endplate of S1 and the upper endplate of L1.

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Figure 7
Schematic representation of the sagittal vertical axis (SVA), which is the horizontal distance between the C7 plumbline and the posterior edge of the upper endplate of S1.

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Figure 8
Schematic representation of the T1 pelvic angle (TPA), which is the angle between the line running from the midpoint of the vertebral body of T1 to the geometric midpoint of the femoral heads and the line running from the geometric midpoint of the femoral heads to the midpoint of the upper endplate of S1.

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Figure 9
Schematic representation of the global tilt (GT), which is the angle between the line running from the midpoint of the vertebral body of C7 to the midpoint of the upper endplate of S1 and the line running from the midpoint of the upper endplate of S1 to the geometric midpoint of the femoral heads.

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Figure 10
Schematic representation of spinopelvic angle (SPA), which is the angle between the line running from the midpoint of C7 to the midpoint of the upper endplate of S1 and the line running from the midpoint of the upper endplate of S1 to the geometric midpoint of the femoral heads.

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Figure 11
Schematic representation of spinosacral angle (SSA), which is the angle formed by the line that runs from the midpoint of C7 to the midpoint of the upper endplate of S1 and the surface of that same endplate.

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Figure 12
Postural types according to the Roussouly classification.

Figure 1 Panoramic X-ray acquired in the sagittal plane (on the left) and patient positioning for its acquisition (on the right).

Figure 2 Schematic representation of the pelvic tilt (PT), which is the angle formed by a vertical line originating from the midpoint of the femoral head and a line running from the midpoint of the femoral head to the midpoint of the upper endplate of S1.

Figure 3 Schematic representation of the sacral slope (SS) angle, which is the angle between the upper endplate of S1 and a horizontal line.

Figure 4 Schematic representation of the pelvic incidence (PI), which is the angle between a line perpendicular to the upper endplate of S1 and a line connecting the midpoint of that endplate with the midpoint of the femoral head.

Figure 5 Schematic representation of pelvic retroversion. By bringing the upper endplate of S1 closer to the axis of the femoral heads and increasing the sacrofemoral distance, this mechanism compensates for the anterior shift in the center of gravity. Adapted from Barrey et al.⁽⁹9 Barrey C, Roussouly P, Le Huec JC, et al. Compensatory mechanisms contributing to keep the sagittal balance of the spine. Eur Spine J. 2013;22 Suppl 6:S834-41.⁾. SS, sacral slope; PT, pelvic tilt.

Figure 6 A: Schematic representation of the thoracic kyphosis (TK) angle, which is the measurement of the Cobb angle between the lower endplate of T12 and the upper endplate of T4. B: Schematic representation of the lumbar lordosis (LL) angle, which is the measurement of the Cobb angle between the upper endplate of S1 and the upper endplate of L1.

Figure 7 Schematic representation of the sagittal vertical axis (SVA), which is the horizontal distance between the C7 plumbline and the posterior edge of the upper endplate of S1.

Figure 8 Schematic representation of the T1 pelvic angle (TPA), which is the angle between the line running from the midpoint of the vertebral body of T1 to the geometric midpoint of the femoral heads and the line running from the geometric midpoint of the femoral heads to the midpoint of the upper endplate of S1.

Figure 9 Schematic representation of the global tilt (GT), which is the angle between the line running from the midpoint of the vertebral body of C7 to the midpoint of the upper endplate of S1 and the line running from the midpoint of the upper endplate of S1 to the geometric midpoint of the femoral heads.

Figure 10 Schematic representation of spinopelvic angle (SPA), which is the angle between the line running from the midpoint of C7 to the midpoint of the upper endplate of S1 and the line running from the midpoint of the upper endplate of S1 to the geometric midpoint of the femoral heads.

Figure 11 Schematic representation of spinosacral angle (SSA), which is the angle formed by the line that runs from the midpoint of C7 to the midpoint of the upper endplate of S1 and the surface of that same endplate.

Figure 12 Postural types according to the Roussouly classification.

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