Ex vivo biomechanical comparison of pedicle screw and rod constructs with and without interbody fusion devices for equine cervical vertebral stabilization.

Objective: To determine the biomechanical properties of pedicle screw and rod (PSR) constructs alone and with an interbody fusion device (PSRIFD) for equine ventral cervical vertebral stabilization.

Study Design: Cadaveric ex vivo biomechanical analysis.

Sample Population: A total of 14 (n = 14) adult equine cervical vertebral columns.

Methods: Cervical vertebral columns were stabilized by PSR alone (n = 6) or PSRIFD (n = 5). Three columns were left unaltered as controls. Non-destructive biomechanical testing showed the kinematic range of motion (ROM), compliance, and neutral zone of each spinal unit in the three main kinematic directions (flexion-extension, lateral bending and axial rotation). Destructive testing was performed to identify mode of failure and stiffness in flexion. Non-destructive and destructive biomechanical data were compared by ANOVA between experimental groups.

Results: In flexion-extension, PSR and PSRIFD had significantly lower ROM, compliance and neutral zone than controls (all p < .05). ROM, compliance and neutral zone were not different between PSR and PSRIFD groups. In axial rotation, the neutral zone of PSR was lower than PSRIFD (p = .013) and both were lower than controls (p < .0001 and p < .02, respectively). Stiffness and moment failure between PSR and PSRIFD groups were not different. All constructs failed through articular process joint dislocation, though the PSRIFD group also had ventral IFD migration.

Conclusion: PSR and PSRIFD groups have similar biomechanical properties and modes of failure, though PSRIFD had higher catastrophic injury potential.

Clinical Significance: These findings support that PSR constructs provide comparable biomechanical stability to PSRIFD, reducing time and potential complications associated with IFD placement.