Orthopedic Biomaterials in the Clinical Reconstruction of Osteoporotic Atlantoaxial Injuries: A Review

Background: Aging of the population increases the incidence of osteoporosis with atlantoaxial instability. Poor bone microarchitecture causes high rates of screw loosening, implant failure, and revision surgery, which remains a critical challenge for upper cervical surgery. Traditional atlantoaxial fixation is less effective in those with low bone mineral density, while thoracolumbar screw augmentation techniques are limited by the complex craniocervical anatomy. Methods: This review systematically summarizes the mainstream screw optimization strategies from a bioengineering perspective, including low-modulus alloy substrate modification, bionic threaded structural design, bioactive surface coatings, expandable screws, and cement-augmented cannulated screws. We compare the biomechanical anchorage performance, osteogenic capacity, and clinical complications of each technique. Results: Low-elastic-modulus titanium alloys reduce stress shielding; gradient multi-thread, bicortical, and CBT trajectory designs significantly improve anti-pullout stability; HA, tantalum, and composite extracellular matrix coatings promote osseointegration; and expandable screws and fenestrated cement screws can achieve reliable reinforcement. However, a narrow atlantoaxial space restricts the application of cement augmentation and expandable implants, and long-term, large-sample clinical evidence for the efficacy of novel screws is insufficient. Conclusion: Patient-specific porous degradable screws, which combine 3D-printed biomaterials, gradient alloys, and sustained-release bioactive coatings, represent a promising future research direction. This review provides theoretical support for the development of atlantoaxial internal fixation devices targeting elderly osteoporotic patients.