• Vicente Vanaclocha, Amparo Vanaclocha-Saiz, Marlon Rivera-Paz, Carlos Atienza-Vicente, José María Ortiz-Criado, Vicente Belloch, José Manuel Santabárbara-Gómez, Amelia Gómez, and Leyre Vanaclocha.
• Hospital General Universitario de Valencia, Valencia, Spain. Electronic address: vvanaclo@hotmail.com.
• World Neurosurg. 2019 Mar 1; 123: e85-e102.

BackgroundA cadaveric feasibility study was carried out. Osteotomies to correct fixed sagittal imbalance are usually performed at L3/ L4.ObjectiveTo 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.MethodsS1 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.ResultsS1 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.DiscussionCompared 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.ConclusionsS1 pedicle subtraction osteotomy is technically feasible. Finite element analysis results indicate that it has appropriate biomechanical properties.Copyright © 2018 Elsevier Inc. All rights reserved.

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