Stent Screw-Assisted Internal Fixation (SAIF) of Severe Lytic Spinal Metastases: A Comparative Finite Element Analysis of the SAIF Technique

World Neurosurg. 2019 Aug;128:e370-e377. doi: 10.1016/j.wneu.2019.04.154. Epub 2019 Apr 25.


Objective: A new stent-screw-assisted internal fixation (SAIF) minimally invasive cement-augmentation technique has been introduced to treat patients with extreme osteolytic lesions of the vertebral body. The aim of the current finite element study, employing a spine model with an extreme osteolytic defect, was to assess the effect of the SAIF technique in reducing strains in the vertebral body in comparison with a standard surgical short posterior fixation.

Methods: Different finite element models of a L1-S1 spine were developed, representing an intact condition (reference configuration), an extreme osteolysis condition, and its treatment, respectively with stand-alone SAIF, SAIF and posterior fixation, and with stand-alone posterior fixation. Each model was loaded to reproduce standing and upper body bending. Principal strains were calculated on the superior endplate, anterior and posterior cortical walls. A paired Wilcoxon test with a 0.05 significance level was performed to statistically analyze the results.

Results: Median strains on the bony structures increased in the osteolysis model compared with the intact model, and the SAIF technique was effective in reducing such strains under both standing and flexion conditions. Additional posterior fixation, combined with the SAIF technique, produced minimal further reduction of the median strains on the bony structures. Stand-alone posterior fixation only shielded the osteolytic vertebra avoiding excessive displacements but failed in restoring the axial stiffness to values typical of the intact vertebra.

Conclusions: The new SAIF technique resulted effective in restoring the load-bearing capacity of the extensively osteolytic vertebra; additional posterior fixation provided only further minor advantages.

Keywords: Extreme osteolysis (EO); Finite element model (FEM); Screw stent−assisted internal fixation (SAIF); Spinal metastases; Spine biomechanics.

Publication types

  • Comparative Study

MeSH terms

  • Biomechanical Phenomena
  • Bone Cements / therapeutic use*
  • Bone Screws*
  • Finite Element Analysis
  • Fracture Fixation / methods*
  • Humans
  • Lumbar Vertebrae
  • Osteolysis / etiology
  • Osteolysis / surgery*
  • Spinal Fractures / etiology
  • Spinal Fractures / surgery*
  • Spinal Neoplasms / complications
  • Spinal Neoplasms / secondary*
  • Spinal Neoplasms / surgery*
  • Stents*
  • Weight-Bearing


  • Bone Cements