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. 2025 Mar;15(2):1295-1305.
doi: 10.1177/21925682241235611. Epub 2024 Feb 28.

Characteristics of Spinal Morphology According to the "Current" and "Theoretical" Roussouly Classification Systems in a Diverse, Asymptomatic Cohort: Multi-Ethnic Alignment Normative Study (MEANS)

Yong Shen  1 , Zeeshan M Sardar  1 , Matan Malka  1 , Prerana Katiyar  1 , Gabriella Greisberg  1 , Fthimnir Hassan  1 , Justin L Reyes  1 , Jean-Charles Le Huec  2 , Stephane Bourret  2 , Kazuhiro Hasegawa  3 , Hee Kit Wong  4 , Gabriel Liu  4 , Hwee Weng Dennis Hey  4 , Hend Riahi  5 , Michael Kelly  6 , Joseph M Lombardi  1 , Lawrence G Lenke  1 ; Multi-Ethnic Alignment Normative Study Group
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Characteristics of Spinal Morphology According to the "Current" and "Theoretical" Roussouly Classification Systems in a Diverse, Asymptomatic Cohort: Multi-Ethnic Alignment Normative Study (MEANS)

Yong Shen et al. Global Spine J. 2025 Mar.

Abstract

Study design: Cross-sectional cohort study.

Objective: To classify spinal morphology using the "current" and "theoretical" Roussouly systems and assess sagittal alignment in an asymptomatic cohort.

Methods: 467 asymptomatic volunteers were recruited from 5 countries. Radiographic parameters were measured via the EOS imaging system. "Current" and "theoretical" Roussouly classification was assigned with sagittal whole spine imaging using sacral slope (SS), pelvic incidence (PI), and the lumbar apex. One-way analysis of variance (ANOVA) was performed to compare subject characteristics across Roussouly types, followed by post hoc Bonferroni correction.

Results: Volunteers were categorized into 4 groups (Types 1-4) and 1 subgroup (Type 3 AP) using the "current" and "theoretical" Roussouly systems. The mean PI in "current" Roussouly groups was 40.8° (Type 1), 43.6° (Type 2), 52.4° (Type 3), 62.4° (Type 4), and 43.7° (Type 3AP). The mean PI in "theoretical" Roussouly groups was 36.5° (Type 1), 39.1°(Type 2), 52.5° (Type 3), 67.3° (Type 4), and 51.0° (Type 3AP). The difference in PI between "current" and "theoretical" Roussouly types was significant for Type 1 (P = .02), Type 2 (P < .001), Type 4 (P < .001), and Type 3AP (P < .001). 34.7% of subjects had a "current" Roussouly type different from the "theoretical" type. Type 3 theoretical shape had the most frequent mismatch, constituting 61.1% of the mismatched subjects. 51.5% of mismatched Type 3 become "current" Type 4.

Conclusion: The distribution of Roussouly types differs depending on whether the "current" or "theoretical" classification are employed. A sizeable proportion of volunteers exhibited current and theoretical type mismatch, highlighting the need to interpret sagittal alignment cautiously when utilizing the Roussouly system.

Keywords: adult spinal deformity; multi-ethnic normative alignment study; pelvic incidence; radiographic parameters; roussouly classification; sagittal alignment.

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Conflict of interest statement

Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
A French volunteer with a current-theoretical type mismatch. SS = 28.12 deg, PI = 60.4 deg, lumbar apex = L4, and inflection point = T12. This volunteer is current Type 2 but theoretical Type 4.
See this image and copyright information in PMC

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