O2128: Segmental Trans-endplate Pedicle Screws do not Induce Spinal Deformity in Pigs

Background: Growth modulation is an effective method for limb deformity correction and is increasingly being applied to spinal deformities. Anterior spinal growth modulation offers a means for gradual correction of spinal deformities while avoiding the need for spinal fusion. However, reliable techniques for performing anterior growth modulation via a posterior approach remain underdeveloped. We hypothesized that unilateral trans-endplate screws — referred to as spinal epiphysiodesis trajectory (SET) screws — could induce partial anterior spinal growth arrest and thus promote scoliotic deformity in a porcine model.

Methods: A pilot study was conducted using four male piglets (two experimental, two control) at 8 weeks of age. Unilateral posterior spinal instrumentation was performed at 4 levels in the lower thoracic spine. The experimental group received trans-endplate SET screws (Fig 1A) and the control group received pedicle screws (Fig 1B). Radiographs, Magnetic Resonance Imaging and Computed Tomography were used to evaluate coronal and sagittal vertebral wedging, disc and facet degeneration, physeal bar presence, and endplate irregularities.

Results: Three months postoperatively, no significant differences in coronal or sagittal curve magnitudes were observed between the SET and pedicle screw groups. Neither screw type induced coronal or sagittal segmental vertebral wedging (Figure 1C,D). Neither SET screws nor pedicle screws limited vertical growth, with mean vertebral height gains of 40%, 27%, and 27% in the SET group, pedicle screw group, and adjacent uninstrumented segments, respectively. No significant changes in disc or facet health were observed, as assessed by the Pfirrmann and Fujiwara classifications. No physeal bars were detected, though one experimental specimen exhibited endplate irregularities.

Conclusion: In this porcine pilot study, SET screws, as applied, did not induce scoliotic or kyphotic deformity. Further research is needed to explore the mechanisms and timing of spinal growth modulation, which are crucial for achieving effective deformity correction.