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The importance of intervertebral disc material model on the prediction of mechanical function of the cervical spine

simulation model

Goal of the Study?

In this disc simulation model article from the BMC Musculoskeletal Disorders open access journal 1 the authors created detailed nonlinear 3D finite element models of the C2-C3 Functional Spine Unit.  The simulation models were tested, verified and then used to predict various biomechanical injuries such as tissue swelling and degeneration.

 

Why are they doing this study?

Spine simulation models, if constructed accurately, can be a very efficient tool to predict the impact of various biomechanical spine loading strains and stresses.  They must mimic as closely as possible real-world conditions.  Also, the range that the models are effective must be established.  Building an accurate simulation model that operates over a wide range of variables is the ultimate goal but it takes many incremental improvements to reach this stage.  This study represents one of these attempts at improving current spine simulation models.

 

What was done?

Three  3D Finite Element (FE) fibre-reinforced C2-C3 functional spinal disc models were developed with Linear Elastic (LE), Hyperelastic (HE) and biphasic Intervertebral Disc (IVD) behaviours. These three models were tested through two different loading modes; cyclic compression and sagittal bending, both flexion and extension.  Measurements included deformed disc height, disc fluid pressure, range of motion and stresses.  The three models were first validated with previous experimental models for compression, flexion and extension loading conditions and then compared to each other with the goal of finding the most robust model.

What did they find?

The two single-phase models; LE and HE failed to accurately describe the long-term intervertebral disc height decrease under cyclic compression loading when compared to other experimental data.  They were both a little closer under extension loads. All three models were accurate in predicting stresses during the flexion loading trials.  Overall the biphasic IVD model was the most robust.  It gave the best results in flexion and compression but was limited in extension loading.  Since this was only a partition spine model, C2-C3 there were issues with the inability to predict load sharing.  Given the inability to accurately predict load sharing the authors believe that a full spine model must be developed.

 

Why do these findings matter?

Cervical injuries and fractures are common in many contact-oriented activities and can be life-altering, as they can cause a permanent loss of neural functions.  Since it is impossible to test these conditions on people, simulation models must be developed.  These mechanical models must be robust and mimic as closely as possible real-world conditions.  The better these models are, the better we are able to test and understand various treatment alternatives.

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