Prediction of load sharing among spinal components of a C5-C6 motion segment using the finite element approach.

STUDY

DESIGN

A finite element model of the ligamentous cervical spinal segment was used to compute loads in various structures in response to clinically relevant loading modes.

OBJECTIVE

To predict biomechanical parameters, including intradisc pressure, tension in ligaments, and forces across facets that are not practical to quantify with an experimental approach.

SUMMARY OF BACKGROUND DATA: Finite element models of the cervical spine in their present form, because of inherent assumptions and simplifications, are not entirely satisfactory for studying the biomechanics of the intact, injured, and stabilized cervical spinal segment.

METHODS

A three-dimensional finite element model of a C5-C6 motion segment was developed from serial computed tomographic scans of a ligamentous cervical spinal segment. This model included nonlinear ligament definition, fully composite intervertebral disc, fluid nucleus, and Luschka's joints. The model-based displacement predictions were in agreement with the experimental data. This model was used to predict load sharing and other related parameters in spinal elements in response to various loading modalities.

RESULTS

In axial compression, 88% of the applied load passed through the disc. The interspinal ligament experienced the most strain (29.5%) in flexion, and the capsular ligaments were strained the most (15.5%) in axial rotation. The maximum intradisc pressure was 0.24 MPa in the flexion with axial compression mode (1.8 Nm + 73.6 N). The anterior and posterior disc bulges increased with the increase in axial compression (up to 800 N).

CONCLUSIONS

The results provide new insight into the role of various elements in transmitting loads. The model represents significant and essential advancement in comparison with previous finite element models, making it possible for such models to be used in investigating a broad spectrum of clinically relevant issues.