Anatomical basis for a new method of atlas osteosynthesis in unstable C1 vertebra fractures

BACKGROUND: Surgical treatment for unstable atlas fractures is still controversial. Harm's atlantoaxial fusion or more extensive occipitospondylodesis reduces quality of life and functional status. Biomechanical rationales for anterior and posterior C1 osteosynthesis are based on small sample, and the role of ligamentous complex in C1-C2 segment remains understudied. OBJECTIVE: To evaluate the effectiveness of a new method of surgical treatment for unstable fractures of the first cervical vertebra. MATERIAL AND METHODS: Biomechanical analysis enrolled 10 anatomical specimens. Various injuries of the atlas ring and ligament complex were simulated. The role of apical and cruciate ligaments as additional stabilizers of craniovertebral junction was assessed. Morphometric parameters and anatomical relationships were presented using new surgical method for unstable C1 vertebral fractures and Harm's atlantoaxial fusion as a comparative treatment model. RESULTS: Instability was observed in all cases of ligamentous complex injury. Rotation angle in atlantoaxial segment remained stable. New surgical method for C1 vertebral injury reduces anterior atlantodental interval to 2.37±0.27 mm, distance between articular surfaces of C1-C2 vertebrae to 3.51±0.46 mm and Redlund-Johnell index to 36.61±1.22 mm without block rotation in atlantoaxial joint. CONCLUSION: Original surgical method for unstable C1 fractures is effective when patient selection principles are followed. Preoperative planning and assessment of integrity of craniovertebral ligaments are essential to avoid tactical errors when choosing surgical intervention.