Biomechanical in vitro comparison between anterior column realignment and pedicle subtraction osteotomy for severe sagittal imbalance correction

  • Luigi La BarberaEmail author
  • Hans-Joachim Wilke
  • Christian Liebsch
  • Tomaso Villa
  • Andrea Luca
  • Fabio Galbusera
  • Marco Brayda-Bruno
Original Article



To investigate the biomechanical effects of anterior column realignment (ACR) and pedicle subtraction osteotomy (PSO) on local lordosis correction, primary stability and rod strains.


Seven cadaveric spine segments (T12–S1) underwent ACR at L1–L2. A stand-alone hyperlordotic cage was initially tested and then supplemented with posterior bilateral fixation. The same specimens already underwent a PSO at L4 stabilized by two rods, a supplemental central rod (three rods) and accessory rods (four rods) with and without adjacent interbody cages (La Barbera in Eur Spine J 27(9):2357–2366, 2018). In vitro flexibility tests were performed under pure moments in flexion/extension (FE), lateral bending (LB) and axial rotation (AR) to determine the range of motion (RoM), while measuring the rod strains with strain gauge rosettes.


Local lordosis correction with ACR (24.7° ± 3.7°) and PSO (25.1° ± 3.9°) was similar. Bilateral fixation significantly reduced the RoM (FE: 31%, LB: 2%, AR: 18%), providing a stability consistent with PSO constructs (p > 0.05); however, it demonstrates significantly higher rod strains compared to PSO constructs with lateral accessory rods and interbody cages in FE and AR (p < 0.05), while being comparable in FE or slightly higher in AR compared to PSO constructs with two and three rods.


Bilateral posterior fixation is highly recommended following ACR to provide adequate primary stability. However, primary rod strains in ACR were found comparable or higher than weak PSO construct associated with frequent rod failure; therefore, caution is recommended.

Graphic abstract

These slides can be retrieved under Electronic Supplementary Material.


Anterior column release Pedicle subtraction osteotomy Primary stability Revision surgery Rod breakage In vitro study Strain gauge Spine Biomechanics 



The study was funded by the Scoliosis Research Society through a New Investigator Grant awarded to the first author. The implants and surgical tools for specimens’ preparation and instrumentation were provided by DePuy Synthes (Raynham, MA, USA), Medtronic Sofamor Danek (Minneapolis, MN, USA) and NuVasive (San Diego, CA, USA). The authors gratefully acknowledge Gloria Casaroli Ph.D., Maria Luisa Ruspi, Lisa Flachmüller and Theodor Di Pauli von Treuheim for their assistance during specimens’ preparation.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest related to the content of the current study.

Supplementary material

586_2019_6087_MOESM1_ESM.pptx (6.1 mb)
Supplementary file1 (PPTX 6255 kb)
586_2019_6087_MOESM2_ESM.tif (156 kb)
Supplementary Material – Figure 1 Range of motion (RoM) and neutral zone (NZ) on the intact condition and following ACR with a standalone hyperlordotic ACR-Cage and with bilateral instrumentation with 2 rods (ACR-Cage+2) in flexion-extension (FE). Statistically significant differences compared to ACR-Cage condition are denoted with “a”. (TIFF 155 kb)
586_2019_6087_MOESM3_ESM.tif (155 kb)
Supplementary Material – Figure 2 Range of motion (RoM) and neutral zone (NZ) on the intact condition and following ACR with a standalone hyperlordotic ACR-Cage and with bilateral instrumentation with 2 rods (ACR-Cage+2) in lateral bending (LB). Statistically significant differences compared to ACR-Cage condition are denoted with “a”. (TIFF 154 kb)
586_2019_6087_MOESM4_ESM.tif (156 kb)
Supplementary Material – Figure 3 Range of motion (RoM) and neutral zone (NZ) on the intact condition and following ACR with a standalone hyperlordotic ACR-Cage and with bilateral instrumentation with 2 rods (ACR-Cage+2) in axial rotation (AR). Statistically significant differences compared to ACR-Cage condition are denoted with “a”. (TIFF 155 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”Politecnico di MilanoMilanItaly
  2. 2.Institute of Orthopaedic Research and Biomechanics, Trauma Research Centre UlmUniversity of UlmUlmGermany
  3. 3.IRCCS Istituto Ortopedico GaleazziMilanItaly

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