Theoretical Modeling and Experimental Validation of In Vivo Mechanics for Subjects Having Variable Cervical Spine Conditions

The objective of this study was to use the state-of-art 3D-to-2D registration technologies including fluoroscopic, CT and MRI methods to analyze 2D and 3D in vivo kinematics of the whole cervical spine under variable conditions; and use inverse dynamic model based on Kane’s dynamics to predict their 2D and 3D in vivo interactive contact and muscular forces. Totally, forty patients (ten having normal cervical spines, ten having degenerative cervical spines, ten having anterior cervical decompression and fusion (ACDF), and ten having cervical artificial disc replacement (CADR)) were enrolled into 2D study and three patients (one having normal cervical spines, one having degenerative cervical spines, one having ACDF) were involved into 3D study. All of the patients had their symptoms, if any, at the C5-C6 level. Error analysis was performed on an entire cadaveric cervical spine. Two major mathematical models were derived using the principles governing Kane’s dynamics. At the adjacent levels, both 2D and 3D study showed the ACDF group had relatively larger kinematic and kinetic data compared to the normal group, the degenerative group had relatively smaller kinematic and kinetic data. At the same time, 2D study demonstrated that the CADR group had similar kinematic and kinetic data compared to the normal group. Cadaveric error analysis demonstrated that the 3D-to-2D registration method and the inverse dynamic method had high accuracy and can be used in the cervical spine field.