O-arm navigation vs. freehand screw placement in adolescent idiopathic scoliosis: A comparative analysis of screw size and reoperation rates

Objective: Pedicle screw fixation is the gold standard for surgical correction of adolescent idiopathic scoliosis (AIS). Prior to the adoption of intraoperative O-arm navigation, surgeons relied on freehand pedicle screw insertion. While freehand insertion demonstrates acceptable safety, comparative data on screw size selection between techniques remain limited. Screw size selection, screw size variability, and complication rates between O-arm navigation and freehand pedicle screw techniques in AIS surgery were compared.Methods: This was a retrospective comparative cohort study of AIS patients treated with either freehand or navigated pedicle screw insertion by a single senior surgeon. Two cohorts of consecutive AIS patients were analyzed: freehand (n=137; February 2014-November 2018) and navigated (n=137; September 2018-August 2024). Data were extracted from a prospectively maintained surgical registry. Measured outcomes included: (1) screw diameter distribution per vertebral level; (2) pedicles deemed too small to cannulate; (3) intra- and intervertebral screw size variability; (4) intraoperative cerebrospinal fluid (CSF) leak rates; and (5) reoperation for symptomatic screws. Screwdiameter distributions were analyzed by region and vertebral level. Variability in screw size was evaluated within vertebrae and between adjacent vertebrae. Rates of non-cannulatable pedicles, CSF leaks, and symptomatic screw reoperations were compared using chi-square and t-tests.Results: Operative time was longer in the navigated cohort (312 ± 54 minutes) compared to the freehand cohort (279 ± 48 minutes, P <.001). Navigation resulted in a broader range of screw diameters. Screws sized 4.0-4.5 mm were used in 49.6% of navigated cases vs. 0.4%of freehand cases (P < .0001), while screws ≥7.0 mm were used in 1.5% vs. 0%, respectively (P = .003). Use of 5.0 mm screws was similar(18.0% vs. 13.7%, P=.16), while screws sized 5.5-6.5mm were more common in freehand cases (85.9% vs. 30.8%, P < .0001). Intravertebralscrew size differences ≥1.5 mm were seen in 3.6% of navigated vertebrae vs. 0.2% in freehand (P < .0001), and intervertebral (adjacentlevel) differences occurred in 6.9% vs. 0% (P < .0001). Pedicles too small to cannulate were identified in 5.0% of navigated cases vs. 1.9%freehand (P < .0001), with greater right-sided prevalence in both cohorts. Intraoperative CSF leaks occurred in 2.7% of navigated casesvs. 0.7% freehand (P=.397). Symptomatic screw-related reoperations were infrequent in both cohorts (1.5% navigation vs. 3.6% freehand,P=.44).Conclusion: Navigation was associated with broader screw size utilization, greater intra- and intervertebral screw diameter variability,and improved identification of pedicles too small to safely instrument. Although complication and reoperation rates were low in bothgroups, there was a non-significant trend toward fewer symptomatic screw-related reoperations in the navigated cohort. These findingssuggest that navigation enhances intraoperative matching of screw size to pedicle anatomy.Level of Evidence: Level IV, Therapeutic Study.Cite this article as: Ramanathan R, Luck C, Dede O, Ward T. O-arm navigation vs. freehand screw