European Spine Journal

, Volume 27, Issue 9, pp 2262–2271 | Cite as

The influence of spinal fusion length on proximal junction biomechanics: a parametric computational study

  • Dominika Ignasiak
  • Tobias Peteler
  • Tamás F. Fekete
  • Daniel Haschtmann
  • Stephen J. Ferguson
Original Article



Proximal junctional kyphosis and failure are frequent complications in adult spinal deformity surgery with long fusion constructs. The aim of this study was to assess the biomechanics of the proximal segment for fusions of various lengths.


A previously established musculoskeletal model of thoracolumbar spine was used to simulate full-range flexion task for fusions (modeled by introduction of rigid constraints) with lower instrumented vertebrae at L5 or S1 and upper instrumented vertebrae (UIV) at any level above, up to T2. Inverse dynamics simulations with force-dependent kinematics were performed for gradually increasing spinal flexion in order to predict global and segmental range of flexion, maximum passive moment, segmental compression and shear forces, which were compared to the uninstrumented case.


For long fusions, with the UIV at T11 or higher, the model predicted an increase in segmental flexion (by 33–860%, or 1.6°–4.7°) and passive moment (by 39–1370%, or 13–31 Nm) at the proximal junction—generally increasing with fusion length. While the maximum shear force was 57–239% (135–283 N) higher for the proximal junction at the upper thorax (UIV at T6 or above), the compression forces were reduced by up to 44% (375 N).


The length of the instrumentation has an important effect on the proximal segment biomechanics. Despite the limitations of the current model, musculoskeletal modeling appears to be a promising and versatile method to support planning of spinal instrumentation surgeries in the future.

Graphical abstract

These slides can be retrieved under Electronic Supplementary Material.


Spinal fusion Proximal junctional failure Biomechanics Musculoskeletal model Thoracolumbar spine 



This study has been supported by a research grant from Mäxi Foundation, Switzerland.

Compliance with ethical standards

Conflict of interest

S. J. Ferguson received research project support from DePuy Johnson & Johnson. D. Ignasiak, T. Peteler, T. F. Fekete and Daniel Haschtmann declare that they have no conflict of interest.

Supplementary material

586_2018_5700_MOESM1_ESM.docx (528 kb)
Supplementary material 1 (DOCX 528 kb)
586_2018_5700_MOESM2_ESM.pptx (8.4 mb)
Supplementary material 2 (PPTX 8586 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Institute for Biomechanics, ETH ZurichZurichSwitzerland
  2. 2.Schulthess ClinicZurichSwitzerland

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