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Defining the Role of the Lower Limbs in Compensating for Sagittal Malalignment

Lafage, Renaud, MS; Liabaud, Barthelemy, MD; Diebo, Bassel G., MD; Oren, Jonathan H., MD; Vira, Shaleen, MD; Pesenti, Sébastien, MD∗,‡; Protopsaltis, Themistocles S., MD; Errico, Thomas J., MD; Schwab, Frank J., MD; Lafage, Virginie, PhD

doi: 10.1097/BRS.0000000000002157
BIOMECHANICS
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Study Design. Retrospective review.

Objective. To investigate the role of lower limbs compensation with progressive sagittal malalignment.

Summary of Background Data. Although lower limb compensatory mechanisms are established response to progressive sagittal malalignment, their specific role and potential impact on surgical planning has not been evaluated.

Methods. Single center retrospective review of full body x-rays was performed in patients of age >20 years. Parameters were measured with dedicated software. Population was stratified by 50 mm intervals of sagittal vertical axis (SVA) and one-way ANOVA was performed to compare P.shift (P.shift = anteroposterior translation of the pelvis vs. the feet) across SVA groups. Anteroposterior offset of each vertebra in relation to a vertical line extended from the distal tibial metaphysis (TM) was investigated. Linear regression was performed to predict pelvic tilt (PT) using Knee angle (KA) and P.shift, whereas controlling for pelvic incidence minus lumbar lordosis mismatch (PI-LL) and SVA.

Results. A total of 2124 patient visits were included (PI = 55.1 ± 14.1°, PT=21.0 ± 11°, PI-LL=6.3 ± 17.3°, SVA = 29 ± 51 mm). With progressively increased SVA, P.shift decreased from 30 to −100 mm (all P < 0.005). Analysis of vertebral offset from the distal tibial metaphysis revealed that T9 was aligned with the TM line across all SVA groups. Prediction of PT based on PI-LL and SVA yielded R2=0.76 (P < 0.001). Subsequent addition of KA and P.shift as independent parameters using hierarchical multiple regression led to significant improvement in R2, demonstrating the independent role of lower limbs parameters in PT prediction. KA and P.shift had a positive standardized coefficient (all P < 0.05).

Conclusion. Lower limb compensatory mechanisms increase with progressive sagittal malalignment. Anteroposterior translation of pelvis allows the T9 vertebra to remain in line with the ankle (“conus of economy”). Lower limb compensatory mechanisms are positive predictors of PT and thus do not require additional consideration in surgical realignment planning.

Level of Evidence: 3

Hospital for Special Surgery, New York, NY

NYU Hospital for Joint Diseases, New York, NY

Aix-Marseille University, French National Centre for Scientific Research, Institute Movement Science, Marseille, France.

Address correspondence and reprint requests to Virginie Lafage, PhD, Hospital for Special Surgery, 525 E 71st St., Belaire 4E, New York, NY 10021; E-mail: virginie.lafage@gmail.com.

Received 30 November, 2016

Revised 13 February, 2017

Accepted 23 February, 2017

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

Relevant financial activities outside the submitted work: board membership, consultancy, payment for lecture, grants, royalties, and stocks.

Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.