Routine insertion of the lateral mass screw via the posterior arch for C1 fixation: feasibility and related complications.

BACKGROUND CONTEXT: To our knowledge, there is no clinical study analyzing the feasibility and complications of the routine insertion of the lateral mass screw via the posterior arch for C1 fixation in a live surgical setting.

PURPOSE: To evaluate the feasibility of routine insertion of the lateral mass screw via the posterior arch and related complications.

STUDY DESIGN: Prospective clinical-radiological analysis.

PATIENT SAMPLE: Fifty-two consecutive patients with 102 C1 lateral mass screws inserted via the posterior arch.

OUTCOME MEASURES: Cortical perforation, vertebral artery injuries, and visual analog scale score of occipital neuralgia recorded on a prospective database.

METHODS: All consecutive patients in whom lateral mass screw placement via the posterior arch was attempted as the first choice whenever C1 posterior fixation was necessary were enrolled. Prospective database, clinical records, questionnaires regarding occipital neuralgia, pre- and postoperative computed tomography (CT) angiograms, and follow-up radiographs and CT scans were analyzed. This study was supported by a $9,000 academic research grant by the first author's hospital. The last author receives royalties for a posterior cervical fixation system, which is not the topic of this study and is not used or mentioned in this article.

RESULTS: One hundred two screws were attempted in 52 consecutive patients by a single surgeon. The height of 43 posterior arches (42%) was smaller than 4 mm on preoperative CT angiography. Lateral mass screws could be inserted via the posterior arch in all cases including eight with nine ponticuli posticus and seven with seven persistent first intersegmental arteries, but the posterior arch was perforated cranially by 7, caudally by 30, and craniocaudally (partially) by 3 screws and vertically split by 14 screws. Among the last 28 screws for which the authors' overdrilling technique was used, only one vertical split occurred, whereas among the first 74 screws without overdrilling, 13 vertical splits occurred. None of them led to screw loosening or nonunion. There were no vertebral artery injuries. Among the 19 patients with preoperative occipital neuralgia, 12 had complete resolution and seven had alleviation at the last follow-up. Among the 33 patients without preoperative neuralgia, seven developed new neuralgia postoperatively. Three of them underwent C2 root transection and the other four underwent C2 root dissection for intraarticular fusion of the facet joints. Of the seven, five had complete resolution and two had mild discomfort at the last follow-up.

CONCLUSIONS: Routine insertion of the lateral mass screw via the C1 posterior arch was feasible in even those with a small posterior arch, ponticulus posticus, or persistent first intersegmental artery. Although cortical perforation or vertical splitting of the posterior arch was often inevitable, it did not lead to significant weakening of the fixation or nonunion. Vertical split could be minimized by overdrilling the posterior arch. Vertebral artery injury was preventable by mobilization before screw insertion. Occipital neuralgia was not uncommon but thought to be unrelated to screw placement in most cases.