An anatomically based functional upper cervical spinal unit tested under low quasi-static loading for use in an omnidirectional surrogate neck

Safety devices designed to prevent spinal cord and traumatic brain injuries are often evaluated using anthropometric test devices (ATDs). However, commonly used ATD necks lack biomechanical fidelity under multiplane loading, particularly during low-speed head impacts and axial loading. This study aimed to develop an anatomically-accurate upper cervical spine (UCS) surrogate that exhibits biofidelic kinematic responses under quasi-static flexion-extension, lateral bending, and axial torsion-a preliminary step toward a full neck surrogate capable of simulating complex multiplane loading. CT scans of a healthy 31-year-old male were used to generate vertebral geometry. Based on similarity to cadaveric ligament properties, woven cotton was selected as a ligament surrogate material. Anatomical landmarks were used to define ligament attachment points, and an adjustable attachment system enabled in-situ tensioning. The resulting UCS model was evaluated against post-mortem human subject data under quasi-static loading, assessing neutral zone (NZ), range of motion (ROM), repeatability, and helical axis of motion (HAM) using the CORA method. ROM and NZ values across all joints and degrees of freedom were within one standard deviation of literature values. The model demonstrated excellent repeatability (CORA:0.87-0.97), good biofidelity in flexion-extension (CORA:0.69-0.75; C0-C1 unloading:0.47), good-to-excellent in lateral bending (CORA:0.75-0.94), and fair-to-good in axial rotation (CORA:0.44-0.65). The mean HAM location aligned with cadaveric data in axial rotation and was slightly anterior during flexion-extension. Overall, the UCS model exhibited strong repeatability and biofidelity, supporting its potential as a preliminary component of a full cervical spine surrogate for future multiplane biomechanical research.