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Freehand technique for C2 pedicle and pars screw placement: is it safe?
Prachya Punyarat1, Jacob M Buchowski2, Benjamin T Klawson2
1Division of Neurosurgery, Department of Surgery, Faculty of Medicine, Thammasat University, 95 Phahonyothin Rd, Klongluang, Pathumthani, 12120, Thailand.
Background Context:
During placement of C2 pedicle and pars screws, intraoperative fluoroscopy is used so that neurovascular complications can be avoided, and screws can be placed in the proper position. However, this method is time consuming and increases radiation exposure. Furthermore, it does not guarantee a completely safe and accurate screw placement.
Purpose:
The objective of this study was to evaluate the safety of the C2 pedicle and pars screw placement without fluoroscopic or other guidance methods.
Study Design:
This is a retrospective comparative study.
Patient Sample:
One hundred ninety-eight patients who underwent placement of C2 pedicle or pars screws without any intraoperative radiographic guidance were included in the study.
Outcome Measures:
Medical records and postoperative computed tomography (CT) scans were evaluated.
Materials And Methods:
Clinical data were reviewed for intraoperative and postoperative complications. The accuracy of screw placement was evaluated with postop CT scans using a previously published cortical-breach grading system (described by the location and the percentage of the screw diameter over the cortical edge [0=none, Grade I≤25% of the screw diameter, Grade II=26%-50%, Grade III=51%-75%, and Grade IV=76%-100%]).
Results:
A total of 148 pedicle screws and 219 pars screws were inserted by two experienced surgeons. There were no cases of cerebral spinal fluid leakage and no neurovascular complications during screw placement. Postoperative CT scans were available for 76 patients, which included 52 pedicle screws and 87 pars screws. For cases with C2 pedicle screws, there were 12 breaches (23%); these included 10 screws with a Grade I breach (19%), 1 screw with a Grade II breach (2%), and 1 screw with a Grade IV breach (2%). Lateral breaches occurred in seven screws (13%), inferior breaches occurred in three screws (6%), and superior breaches occurred in two screws (4%). For cases with C2 pars screws, there were 10 breaches (11%); these included 6 screws with a Grade I breach (7%), 2 screws with a Grade II breach (2%), and 2 screws with a Grade IV breach (2%). Medial breaches were found in four (5%), lateral breaches in two (2%), inferior breaches in two (2%), and superior breaches in two (2%). Two of the cases with superior breaches (one for pedicle and one for pars) experienced occipital neuralgia months after surgery. There was no statistically significant difference in the incidence of overall and high-grade breaches between the groups (p=.07 and 1.0, respectively).
Conclusions:
Although even in experienced hands up to 23% of C2 pedicle screws and 11% of C2 pars screws placed using a freehand technique without guidance may be malpositioned, a clear majority of malpositioned screws demonstrated a low-grade breach, and only 2 of 198 patients (1%) experienced complications related to screw placement.
