Biomechanical Modeling of a Direct Vertebral Translation Instrumentation System: Preliminary Results

2010

INTRODUCTION

For severe spine deformities, instrumentation remains an effective option. Biomechanical models have been proposed to simulate the instrumentation and improve the preoperative planning. The modeling of the nonstructural curves remains a challenging difficulty because of the different patient-specific spontaneous corrections.

OBJECTIVE

To improve our biomechanical model in order to better simulate and predict the spontaneous nonstructural curve correction.

MATERIALS and METHODS

The spine geometry was reconstructed using calibrated radiographs. Vertebrae were modeled as rigid bodies and the intervertebral structures as flexible elements. Structural and nonstructural curves were identified using bending radiographs and modeled differently. Using an optimization procedure, compensation forces and boundary conditions were applied to produce the nonstructural curve correction based on the following assumptions: the structural deformation is due to anatomical changes; the nonstructural deformation is due to the gravity and forces from muscles and ligaments to adopt a specific posture. This approach was tested on 3 surgical cases.

RESULTS

The simulations agreed well with the surgeries with an average difference of 5° (max 7°) on non instrumented proximal thoracic, main thoracic and thoraco-lumbar/lumbar segments. The proposed modeling technique allowed an average improvement of 9° of the Cobb angles of the non-instrumented segments.

CONCLUSION

The developed model allowed better representation of the nonstructural curves' biomechanical behavior and improved the prediction of spinal instrumentation outcome.

SIGNIFICANCE

The developed model provides an effective approach to address the difficult issue of modeling, simulating, and predicting the response of the nonstructural curves to spinal instrumentation.