Biomechanical advantages of supplemental accessory and satellite rods with and without interbody cages implantation for the stabilization of pedicle subtraction osteotomy
To investigate the effect of anterior interbody cages, accessory and satellite rods usage on primary stability and rod strains for PSO stabilization.
Seven human cadaveric spine segments (T12-S1) underwent PSO at L4 with posterior fixation from L2 to S1. In vitro flexibility tests were performed under pure moments in flexion/extension (FE), lateral bending (LB) and axial rotation (AR) to determine the range of motion, while measuring the strains on the primary rods with strain gauge rosettes. Six constructs with 2, 3 and 4 rods, with and without interbody cages implantation adjacent to the PSO site, were compared.
All constructs had comparable effects in reducing spine kinematics compared to the intact condition (− 94% in FE and LB; − 80% in AR). Supplementation of 2 rods with lateral accessory rods (4 rods) was the most effective strategy in minimizing primary rod strains, particularly when coupled to cages (p ≤ 0.005; − 50% in FE, − 42% in AR and − 11% in LB); even without cages, the strains were significantly reduced (p ≤ 0.009; − 26%, − 37%, − 9%). The addition of a central satellite rod with laminar hooks (3 rods) effectively reduced rod strains in FE (p ≤ 0.005; − 30%) only in combination with cages.
The study supports the current clinical practice providing a strong biomechanical rationale to recommend 4-rod constructs based on accessory rods combined with cages adjacent to PSO site. Although weaker, the usage of accessory rods without cages and of a central satellite rod with hooks in combination with interbody spacers may also be justified.
KeywordsPedicle subtraction osteotomy Primary stability Revision Rod breakage Implant failure Accessory rods Satellite rod In vitro study Strain gauge Spine Biomechanics
This study was funded by the Scoliosis Research Society through a New Investigator Grant. The authors gratefully acknowledge DePuy Synthes (Raynham, MA, USA), Medtronic Sofamor Danek (Minneapolis, MN, USA) and NuVasive (San Diego, CA, USA) for providing the implants and surgical tools. The authors gratefully acknowledge Gloria Casaroli Ph.D., Maria Luisa Ruspi, Lisa Flachmüller and Theodor Di Pauli von Treuheim for their assistance during specimens’ preparation. Tito Bassani Ph.D. is gratefully acknowledged for comments regarding statistical analysis.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest related to the content of the current study.
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