3D printing enabled biomechanical evaluation of a novel expandable wedge spacer for atlantoaxial reduction

Atlantoaxial subluxation (AAS) is a severe instability of the craniovertebral junction that may cause progressive spinal cord compression and neurological impairment. Achieving complete reduction remains challenging when anterior inclination deformity of the atlas limits posterior traction. This study introduces a novel titanium alloy expandable wedge-shaped spacer designed to correct the anterior inclination of the atlantoaxial joint (AAJ) and facilitate controlled distraction and reduction. The implant integrates a two-stage expansion mechanism that enables sequential anterior elevation and fixation stability. To overcome the scarcity of cadaveric specimens, a patient-specific 3D-printed C1–C2 model was reconstructed from clinical CT data to replicate pathological morphology, simulate ligament behavior, and provide a reproducible biomechanical testing platform. Static and fatigue compression tests, performed according to ASTM F2077 and ISO 23089-2, demonstrated superior load-bearing strength (6725 ± 123 N) and long-term durability over 5 million cycles at 1650 N, with an expansion torque of only 52.56 ± 7.54 N·mm. Reduction experiments using the 3D-printed platform showed that the spacer decreased the required traction force by approximately 70% and redirected the reduction trajectory toward the physiological axis. The integration of medical imaging and high-resolution 3D printing enabled precise replication of patient-specific anatomy and standardized mechanical evaluation that is otherwise unachievable with cadaveric models. This study highlights how 3D printing enables patient-specific modeling, quantitative validation, and iterative optimization of implant design—illustrating its critical role in bridging preclinical testing and clinical translation for complex spinal applications.