Search

Background Context: Lateral mass screw fixation is the standard for posterior subaxial cervical fixation. Several freehand surgical techniques for placing lateral mass screws have been described which rely on anatomical landmarks and surgeon mastery of the technique to safely place screws. The accuracy of these freehand techniques is inherently variable and can be influenced by a surgeon's level of clinical experience. A novel technique was developed that utilizes the plane of the facet joint to create lateral mass screw pilot holes parallel with the joint line to improve the safety and accuracy of lateral mass screw placement regardless of experience., Purpose: To assess the safety and accuracy of lateral mass screw placement using a novel lateral mass drill guide instrument (LM Guide), compared to standard freehand technique., Study Design: Randomized cadaveric study utilizing multiple surgeon evaluators to compare the safety and accuracy of guided cervical lateral mass placement compared to traditional freehand techniques., Materials and Methods: Lateral mass screws were placed from C3 to C7 in 20 cadaver specimens by 8 spine surgeons of varying levels of clinical experience (4 attendings, 4 fellows). Screws were placed bilaterally using standard anatomic landmarks ("freehand") randomly allocated on one side and using the LM Guide on the other. Cadaveric specimens were imaged with high-resolution CT to assess screw placement. Zone grading for safety was conducted based on screw tip position and clinical severity of screw breach was based on proximity to surrounding neurovascular anatomy. Screws were graded as safe, at-risk, or critical, with at-risk and critical screws considered malpositioned. To assess the accuracy of screw trajectory placed using the LM Guide compared to freehand, sagittal screw angle was measured and compared to an "ideal" screw path parallel to the facet joint line. Freehand and LM Guide groups were compared using Pearson's chi-square correlation., Results: Screw placement using the LM guide yielded a significantly lower rate of screw malpositioning, with 7 of 91 (7.7%) compared with 18 of 99 (18.2%) screws placed in the At-Risk or Critical Zones, p<.05. Of the 91 screws inserted using the LM Guide, 84 (92.3%) were in the Safe Zone, 7 (7.7%) were At-Risk, and 0 were in Critical zones. There was no incidence of neural or transverse foramen breaches with the LM Guide. In comparison, for the 99 screws inserted freehand, 81 (81.8%) were Safe, 14 (14.1%) were At-Risk, and 4 (4.1%) were in Critical zones. The 4 Critical zone freehand screw breaches included 1 neural foramen breach, 2 transverse foramen breaches, and 1 facet breach. The LM Guide also resulted in higher accuracy of screw trajectory, as indicated by a significant reduction in sagittal screw angle compared with freehand, p<.01. Notably, in the less-experienced surgeon cohort, the LM Guide significantly reduced the sagittal screw angle and resulted in no critical screw breaches compared to 3 critical breaches with freehand technique suggesting there might be a benefit in decreasing the learning curve associated with lateral mass screw placement., Conclusions: Lateral mass screw placement with a novel LM Guide that uses the facet joint to control screw trajectory improved the accuracy and reproducibility of screw placement with a significant reduction in screw breach rate and sagittal screw angle compared to freehand techniques regardless of surgeon experience level., Clinical Significance: The inherent variability of freehand lateral mass screw placement can increase the risk of clinical complications associated with screw malpositioning. The technique presented in this cadaveric study may be a viable alternative to standard freehand technique that can improve the overall safety of lateral mass screw placement., Competing Interests: Declaration of Competing Interest One or more of the authors declare financial or professional relationships on ICMJE-TSJ disclosure forms., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Background Context: Due to the underlying pathology and altered biomechanics, traumatic cervical fractures have been reported in patients with ankylosing spondylitis (AS), diffuse idiopathic skeletal hyperostosis (DISH), ossification of the posterior longitudinal ligament (OPLL), and combination of DISH and OPLL. However, incidence of a fracture-dislocation through a solid multilevel anterior cervical discectomy and fusion (ACDF) construct with no associated underlying pathology of AS, DISH, or OPLL but severe osteopenia has not, to the best knowledge of the authors, been reported in the medical literature., Purpose: To report the development of an unstable cervical spine fracture that occurred through a previous multilevel anterior cervical fusion and the challenges associated with the diagnosis and surgical management of these uncommon lesions., Study Design/setting: A case report and review of the literature., Methods: A case report entailing the clinical history, operative management, and postoperative course of a 72-year-old male patient with no known AS, DISH, or OPLL who suffered a cervical spine fracture-dislocation, secondary to a motor vehicle accident, through a previous solid three-level ACDF that was performed 20 years earlier., Results: The patient underwent emergent reduction and realignment of the cervical fracture-dislocation, eventual posterior spinal fusion and stabilization with rigid segmental internal fixation, and application of external halo immobilization. At recent follow-up, he has radiographic evidence of fusion and maintenance of sagittal alignment without loss of reduction., Conclusions: Multilevel cervical fusion constructs are susceptible to traumatic injuries. Many of the same challenges in the management of the previously fused ACDF patient, who sustains a fracture-dislocation, are similar to those found in the patient with mass-inflammatory conditions or metabolic disorders, such as AS, DISH, or OPLL. In many cases, this includes severe osteopenia, long unstable fusion segments, and difficulties associated with prolonged halo vest immobilization. As a result, preoperative surgical planning should take into consideration the difficulties in achieving fracture reduction, decompression, and proper stabilization.