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 spina l segment was used to compute loads in various structures in response to clinically relevant loading modes. Objective. To predict biomechani cal parameters, including intradisc pressure, tension in ligaments, an d forces across facets that are not practical to quantify with an expe rimental approach. Summary of Background Data. Finite element models o f the cervical spine in their present form, because of inherent assump tions and simplifications, are not entirely satisfactory for studying the biomechanics of the intact, injured, and stabilized cervical spina l segment. Methods. A three-dimensional finite element model of a C5-C 6 motion segment was developed from serial computed tomographic scans of a ligamentous cervical spinal segment. This model included nonlinea r ligament definition, fully composite intervertebral disc, fluid nucl eus, and Luschka's joints. The model-based displacement predictions we re in agreement with the experimental data. This model was used to pre dict load sharing and other related parameters in spinal elements in r esponse to various loading modalities. Results. In axial compression, 88% of the applied load passed through the disc. The interspinal ligam ent experienced the most strain (29.5%) in flexion, and the capsular l igaments 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 increa sed with the increase in axial compression (up to 800 N). Conclusion. The results provide new insight into the role of various elements in t ransmitting loads. The model represents significant and essential adva ncement in compression with previous finite element models, making it possible for such models to be used in investigating a broad spectrum of clinically relevant issues.