Porcine spine finite element model: a complementary tool to experimental scoliosis fusionless instrumentation

Developing fusionless devices to treat pediatric scoliosis necessitates lengthy and expensive animal trials. The objective was to develop and validate a porcine spine numerical model as an alternative platform to assess fusionless devices. A parametric finite element model (FEM) of an osseoligamentous porcine spine and rib cage, including the epiphyseal growth plates, was developed. A follower-type load replicated physiological and gravitational loads. Vertebral growth and its modulation were programmed based on the Hueter-Volkmann principle, stipulating growth reduction/promotion due to increased compressive/tensile stresses. Scoliosis induction via a posterior tether and 5-level rib tethering, was simulated over 10 weeks along with its subsequent correction via a contralateral anterior custom tether (20 weeks). Scoliosis induction was also simulated using two experimentally tested compression-based fusionless implants (hemi- and rigid staples) over 12- and 8-weeks growth, respectively. Resulting simulated Cobb and sagittal angles, apical vertebral wedging, and left/right height alterations were compared to reported studies. Simulated induced Cobb and vertebral wedging were 48.4A degrees and 7.6A degrees and corrected to 21A degrees and 5.4A degrees, respectively, with the contralateral anterior tether. Apical rotation (15.6A degrees) was corrected to 7.4A degrees. With the hemi- and rigid staples, Cobb angle was 11.2A degrees and 11.8A degrees, respectively, with 3.7A degrees and 2.0A degrees vertebral wedging. Sagittal plane was within the published range. Convex/concave-side vertebral height difference was 3.1 mm with the induction posterior tether and reduced to 2.3 with the contralateral anterior tether, with 1.4 and 0.8 for the hemi- and rigid staples. The FEM represented growth-restraining effects and growth modulation with Cobb and vertebral wedging within 0.6A degrees and 1.9A degrees of experimental animal results, while it was within 5A degrees for the two simulated staples. Ultimately, the model would serve as a time- and cost-effective tool to assess the biomechanics and long-term effect of compression-based fusionless devices prior to animal trials, assisting the transfer towards treating scoliosis in the growing spine.