Quantitative anatomy of C7 vertebra in Southern Chinese for insertion of lateral mass screws and pedicle screws

Abstract

Study Design: Retrospective study.Purpose: To analyze the quantitative anatomy of C7 vertebra for insertion of lateral mass screws and pedicle screws in Southern Chinesepatients.Overview of Literature: C7 lateral mass is smaller when compared to other subaxial cervical levels, which limits the length of lateralmass screws that can be used. Some studies have suggested pedicle screws for better fixation. But, this option is limited by thenarrow pedicle width.Methods: We have obtained computed tomography (CT) cervical spine data in 0.625 mm slices from our radiology department. Thepatients were adults. CTs were from May to August, 2015. The lateral mass screw length was measured using Margerl's techniqueand pedicle width and pedicle screw trajectory were determined in three-dimensional reformated images.Results: CT scans of cervical spines of 94 patients were obtained and 188 lateral masses and pedicles of C7 vertebrae were measured.The mean lateral mass screw length was 13.2 mm (standard deviation [SD] 1.6 mm), mean outer pedicle width was 5.9 mm (SD 1.0 mm)and mean pedicle screw trajectory was 29.4 degrees (SD 3.6 degrees). Most (91.0%) of the pedicles had an outer diameter =4.5 mm.Conclusions: The mean lateral mass screw length was longer when compared with other similar studies, while the mean outerpedicle width was narrower. Nearly 10% of the pedicles were unable to accommodate 3.5 mm screws. These findings favor the useof lateral mass screws to provide a safe and stable fixation for C7 vertebrae in Southern Chinese patients, while the final choice offixation method should only be confirmed after careful preoperative planning with CT scan.