S1 Pedicle Subtraction Osteotomy in Sagittal Balance Correction. A Feasibility Study on Human Cadaveric Specimens

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.