S 1 Pedicle Subtraction Osteotomy in Sagittal Balance Correction. A Feasibility Study on Human Cadaveric Specimens

World Neurosurg. 2019 Mar;123:e85-e102. doi: 10.1016/j.wneu.2018.11.052. Epub 2018 Nov 20.

Abstract

Background: A cadaveric feasibility study was carried out. Osteotomies to correct fixed sagittal imbalance are usually performed at L3/ L4.

Objective: To investigate the feasibility of S1 pedicle subtraction osteotomy to correct spinal deformity and spinopelvic parameters, achieving better results with more limited exposure. The data obtained will allow a fixation construct specific for this osteotomy to be designed.

Methods: S1 pedicle subtraction osteotomy was performed on 12 cadaveric specimens. Baseline and postprocedural computed tomography and biomechanical studies were performed. Data were analyzed with a fixation system SolidWorks model, and the redesigned fixation construct was described and analyzed with an ANSYS model.

Results: S1 pedicle subtraction osteotomy is technically feasible. The fixation can be achieved with L4, L5, and iliac screws connected with bars. The system can be reinforced with a polyetheretherketone cage placed anteriorly in the S1 body osteotomy site, a cross-connecting bar, a double iliac screw, or an anterior interbody cage placed at the L5-S1 disc. The fixation strength is improved by angulating the iliac rod channel 10°, adding a semi-sphere to the locking screw contact surface and 2 fins to its saddle. The redesigned construct showed suitable stress and deformation levels, achieving the expected biomechanical requirements.

Discussion: Compared with surgery on higher levels, S1 pedicle subtraction osteotomy allows greater correction with shorter fixation, because the osteotomy is performed at a more caudal level, modifying the spinopelvic parameters.

Conclusions: S1 pedicle subtraction osteotomy is technically feasible. Finite element analysis results indicate that it has appropriate biomechanical properties.

Keywords: Finite element analysis; S(1) pedicle subtraction osteotomy; Sagittal profile; Spinal balance; Spinopelvic alignment; Spinopelvic parameters.

MeSH terms

  • Aged
  • Biomechanical Phenomena
  • Computer-Aided Design
  • Feasibility Studies
  • Female
  • Finite Element Analysis
  • Humans
  • Internal Fixators
  • Male
  • Materials Testing
  • Middle Aged
  • Osteotomy / methods*
  • Prosthesis Design
  • Sacrum / surgery*
  • Spinal Curvatures / surgery*
  • Stress, Mechanical