Effect of the Pedicle and Posterior Arch on Vertebral Body Strength Predictions in Finite Element Modeling

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Abstract

Study Design.

A finite element study to predict the contribution of the pedicles and the posterior arch to vertebral body strength.

Objective.

To determine the effect of the pedicle and posterior arch on strain distributions occurring within the vertebral body under axial compressive loading.

Summary of Background Data.

Posterior vertebral body fracture can arise from high-impact or normal loading in bones compromised by osteoporosis or neoplasm and can result in spinal canal encroachment. Anatomically, the pedicles and posterior arch have a potential role as a structural buttress to the posterior vertebral body wall. However, most finite element models used to investigate vertebral body strength have neglected these structures.

Methods.

Three 3-dimensional finite element models were developed of L1, incorporating anatomic curvature, with varying degrees of posterior element inclusion (no pedicle, pedicle, and pedicle and posterior arch). Three cases were analyzed with each model: 25% dehydrated disc, normal healthy disc, and uniform pressure loading. Outcome variables were the maximum von Mises strains and the displacement of the posterior wall into the spinal canal.

Results.

Inclusion of the posterior arch resulted in substantial decreases in maximum strain and posterior wall displacement under all loading configurations using transversely isotropic trabecular bone properties. No changes in maximum strains or displacements were recorded in the pedicle model, compared with that observed in the no-pedicle baseline case.

Conclusions.

The pedicle functions as a structural buttress, providing support to the posterior wall of the vertebral body when constrained through the posterior arch. To yield more accurate vertebral body strength predictions from finite element modeling, the posterior arch should be included.

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