Evaluation of the Accuracy of Free-hand C1 and C2 Screw Placement

Abstract

Objective Posterior atlantoaxial fixation is an effective treatment for various pathologies. The anatomies of the atlas and axis are highly complex, and thus, freehand placement of C1, 2 instrumentation is technically challenging. The objective of this study was to evaluate the accuracy and safety of C1, 2 screw placement without fluoroscopic or any other guidance method by a 2-year spine surgeon. Methods A retrospective analysis of radiologic data was performed on all patients that underwent C1 or C2 instrumentation from April 2019 to January 2020; all procedures were performed by a 2-year spine surgeon. Computed tomography was used to assess cortical breaches of screw placement at C1 or C2. Severities of breaches were quantified using percentages screw diameter beyond cortical edges (0=cortical touch, 1≤25%; II=26-50%; III=51-75%; IV=76-100%). Results The surgeon placed 16 C1 screws and 20 C2 screws in 10 consecutively treated patients. For C1 screws, there were 4 breaches (25%), of which 3 were medial (18%) and 1 was anterior (7%), and for C2 screws, there were 3 total breaches (15%), of which 2 were anterior (10%) and 1 was medial (5%). Breaches were classified as grade I in 3 cases (42.8%), grade III in 1 case (14.4%), and grade IV in 3 cases (42.8%). No clinical sequelae were attributed to these breaches. Conclusion Although 25% of C1 screws and 15% of C2 screws placed using a freehand technique without guidance may be achieved accurately and safely. Preoperative morphometric evaluation and controlled exposure to this unique anatomy are essential to improve screw placement. Key Words: Accuracy of screws; Free hand technique; Malposition; Posterior atlantoaxial fixation; VA injury