Abstract
Pedicle subtraction osteotomy (PSO) is an invasive surgical technique allowing the restoration of a well-balanced sagittal profile, however, the risks of pseudarthrosis and instrumentation breakage are still high. Literature studied primary stability and posterior instrumentation loads, neglecting the load shared by the anterior column, which is fundamental to promote fusion early after surgery. The study aimed at quantifying the load-sharing occurring after PSO procedure across the ventral spinal structures and the posterior instrumentation, as affected by simple bilateral fixation alone, with interbody cages adjacent to PSO level and supplementary accessory rods. Lumbar spine segments were loaded in vitro under flexion–extension, lateral bending, and torsion using an established spine tester. Digital image correlation (DIC) and strain-gauge (SG) analyses measured, respectively, the full-field strain distribution on the ventral surface of the spine and the local strain on posterior primary rods. Ventral strains considerably decreased following PSO and instrumentation, confirming the effectiveness of posterior load-sharing. Supplemental accessory rods considerably reduced the posterior rod strains only with interbody cages, but the ventral strains were unaffected: this indicates that the load transfer across the osteotomy could be promoted, thus explaining the higher fusion rate with decreased rod fracture risk reported in clinical literature.
Highlights
Pedicle subtraction osteotomy (PSO) is an invasive surgical technique allowing the restoration of a well-balanced sagittal profile, the risks of pseudarthrosis and instrumentation breakage are still high
The range of motion (RoM) was consistent for all intact specimens with higher values in flexion–extension and lateral bending compared to torsion (Table 2, Supplementary Table 1)
Following PSO and bilateral instrumentation (“PSO-2”), the RoM approached the error of measurement (0.1°) without relevant differences compared to cages implantation (“PSO-2 + Cages”) and addition of supplementary rods (“PSO-4 + Cages”) both in flexion/extension and lateral bending, while torsional values were relatively higher
Summary
Pedicle subtraction osteotomy (PSO) is an invasive surgical technique allowing the restoration of a well-balanced sagittal profile, the risks of pseudarthrosis and instrumentation breakage are still high. Grade 2 (moderate degeneration) are not able to fully appreciate this process In this context, an experimental approach based on Digital Image Correlation (DIC) could offer the potential to measure the superficial full-field strain distribution on hard and soft-tissue, both on the treated vertebral body (VB), the adjacent intervertebral disc (IVD), as well as the ligamentous structures. An experimental approach based on Digital Image Correlation (DIC) could offer the potential to measure the superficial full-field strain distribution on hard and soft-tissue, both on the treated vertebral body (VB), the adjacent intervertebral disc (IVD), as well as the ligamentous structures The potential of such an approach has been recently demonstrated for intact porcine[24,25] and human[26,27] poly-segmental spine specimens
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