Hypothesis:​ The distinctive anatomy of the cervicothoracic junction region requires careful study of the biomechanics of the region and the impact of surgical interventions to better inform healthy and disease states in addition to potential treatments.

The objective of this research is to gain an understanding of the biomechanical properties of the cervicothoracic junction of the human spine.

Specific Aim 1 developed a reproducible protocol that used a synthetic spine to evaluate the capabilities and limitation of a custom spine biomechanics simulator. The machine’s ability to accurately report positional data and apply a load in one physiological plain, a pure moment, was evaluated. The test machine was shown to accurate to within <0.25° and capable of applying a pure moment. A standard validation protocol was presented for biomechanical spine testing machines needed for transparency and accurate field-wide data interpretation and comparison.

Specific Aim 2 compared the mechanical properties of three posterior spinal fusion assemblies commonly used to cross the cervicothoracic junction. The assembly that consisted of 3.5 mm diameter rods only were significantly less stiff and had larger ranges of motion compared to the assemblies that incorporated a 5.5 mm rod in some capacity. This result suggests that a transition from cervical to thoracic instrumentation provides increased stability to an assembly.

Specific Aim 3 quantified the biomechanical properties of the cervicothoracic region with the use of a cadaveric model with the upper ribcage intact. A baseline was established for further study of the region.

Specific Aim 4 compared the biomechanical implications of caudal endpoint of a long posterior cervical fusion. The endpoints compared were the C7 and the T2 vertebrae. The difference in range of motion and stiffness values were compared. The fusion that was extended into the thoracic region produced reduced range of motion and marginally increased stiffness values.

This work provides vital information in the understanding of the upper spine, fusion instrumentation, and testing methods. The results can inform computational modeling of the spine, clinical decision making, instrumentation design and improve patient outcome.