Safety Of Screw Placement Research Articles

A Novel Pedicle Screw Placement Surgery Based on Integration of Surgical Guides and Augmented Reality.

Augmented reality is a new technology that, when applied to spinal surgery, offers the potential for efficient, safe, and accurate placement of pedicle screws. This study investigated whether augmented reality combined with a guide board improved the safety and accuracy of pedicle screw placement compared to traditional freehand screw placement. Four trainers were divided into augmented reality navigation and freehand groups. Each group consisted of a novice and an experienced spine surgeon. A total of 80 pedicle screws were implanted. First, the AR group reconstructed the three-dimensional (3D) model and planned the screw insertion route according to the computed tomography (CT) data of L2 lumbar vertebrae. Next, the Microsoft HoloLens 2 was used to identify the vertebral model, and the planned virtual path was superimposed on the real cone model. Then, the screw was placed according to the projected trajectory. Finally, Micron Tracker was used to measure the deviation of screws from the preoperatively planned trajectory, and pedicle screws were evaluated using the Gertzbein-Robbins scale. In the augmented reality group, the linear deviation of the experienced doctors and novices was 1.59 ± 0.39 and 1.73 ± 0.52 mm, respectively, and the deviation angle was 2.72 ± 0.61 and 2.87 ± 0.63 degrees, respectively. In the freehand group, the linear deviation of the experienced doctors and novices was 2.88 ± 0.58 and 5.25 ± 0.62 mm, respectively, and the deviation angle was 4.41 ± 1.18 and 7.15 ± 1.45 degrees, respectively. The screw placement accuracy rate was 97.5% in the augmented reality navigation group and 77.5% in the freehand group. Augmented reality navigation improves the accuracy and safety of pedicle screw implantation compared with the traditional freehand method and can assist inexperienced doctors in successfully completing the surgery.

Lumbar Pedicle Morphometry in a Sample of the Egyptian Population, Parameters and Measures to Safe Screw Placement

Lumbar Pedicle Morphometry in a Sample of the Egyptian Population, Parameters and Measures to Safe Screw Placement

Efficacy and safety of navigation robot-assisted versus conventional oblique lateral lumbar interbody fusion with internal fixation in the treatment of lumbar degenerative diseases: A retrospective study.

Effective internal fixation with pedicle screw is a key factor in the success of lumbar fusion with internal fixation. Whether navigation robots can improve the efficacy and safety of screw placement is controversial. Thirty-eight patients who underwent oblique lateral lumbar interbody fusion internal fixation from March 2022 to May 2023 were retrospectively analyzed, 16 cases in the navigational robot group and 22 cases in the fluoroscopy group. Using visual analog score (VAS) for the low back and lower limbs, Oswestry Disability Index to compare the clinical efficacy of the 2 groups; using perioperative indexes such as the duration of surgery, intraoperative blood loss, intraoperative fluoroscopy times, and postoperative hospital stay to compare the safety of the 2 groups; and using accuracy of pedicle screws (APS) and the facet joint violation (FJV) to compare the accuracy of the 2 groups. Postoperative follow-up at least 6 months, there was no statistically significant difference between the 2 groups in the baseline data (P > .05). The navigational robot group's VAS-back was significantly lower than the fluoroscopy group at 3 days postoperatively (P < .05). However, the differences between the 2 groups in VAS-back at 3 and 6 months postoperatively, and in VAS-leg and Oswestry Disability Index at 3 days, 3 months, and 6 months postoperatively were not significant (P > .05). Although duration of surgery in the navigational robot group was significantly longer than in the fluoroscopy group (P > .05), the intraoperative blood loss and the intraoperative fluoroscopy times were significantly lower than in the fluoroscopy group (P < .05). The difference in the PHS between the 2 groups was not significant (P > .05). The APS in the navigation robot group was significantly higher than in the fluoroscopy group, and the rate of FJV was significantly lower than in the fluoroscopy group (P < .05). Compared with the traditional fluoroscopic technique, navigation robot-assisted lumbar interbody fusion with internal fixation provides less postoperative low back pain in the short term, with less trauma, less bleeding, and lower radiation exposure, as well as better APS and lower FJV, resulting in better clinical efficacy and safety.

Modified Tap-drilling Technique for Mid-cervical Pedicle Screw Placement: A Case Series of 473 Consecutive Screws.

Retrospective cohort study. To report our modified tap-drilling technique for mid-cervical pedicle screw placement and to evaluate its safety and accuracy. Cervical pedicle screw fixation, which provides a strong stabilization, has been a major concern due to the potential risks to neurovascular structures despite its increasing use. Several insertion techniques have been described so far to improve the cervical pedicle screw placement accuracy. This study retrospectively reviewed patients who underwent mid-cervical (C3-C6) pedicle screw fixation between September 2005 and September 2020. Laminectomy, laminoforaminotomy, or notch-referred anatomic landmark methods were used to adjust the entry point and the direction of the screws. After the cortical bone was removed at the entry point with a diamond burr, the cancellous bone was slowly drilled with a hand drill starting from 8 to 10 millimeters in length. Then, all of the bone walls were checked with a ball-tip probe to determine if there was any breach. The procedure was repeated several times. After completing the drilling, the screw was inserted without tapping. The breach rate of pedicle screws was analyzed on postoperative computed tomography scans. A total of 473 mid-cervical pedicle screws were placed in 122 consecutive patients. No navigation or computer-assisted system was used, and the first 2 authors inserted all of the screws. All patients completed the surgery, and no evident intraoperative complications occurred. Postoperative CT scans were obtained for 405 screws. Although deviation was observed for 131 pedicle screws, a critical deviation was observed for only 25 pedicle screws. Cervical pedicle screw insertion is a risky but applicable technique. Checking all of the bone walls with a ball-tip probe before gradually advancing the hand drill in small amounts, as presented in this article, may lead to the safe and effective placement of cervical pedicle screws.

Antegrade posterior column screw fixation for acetabular fractures: It's time to standardize the surgical technique

Antegrade fixation of posterior column fractures of the acetabulum is challenging due to the narrow corridor and risk of screw misplacement. Although both antegrade and retrograde lag screws have been previously described for posterior column fracture fixation, the literature lacks a standardized technique for correct and safe screw placement, especially in an antegrade fashion. This technical note aims to optimize intraoperative images during posterior screw insertion using the antegrade technique, according to predetermined landmarks to save surgical time, decrease radiation exposition, and prevent surgical complications.

Anatomical study of the technique of the axis laminar screws and development of guide

PurposeTo develop a bidirectional slide guide to assist screw placement in the axial lamina and to preliminarily discuss the accuracy and feasibility of auxiliary screw placement.MethodsCT data from 40 randomly selected patients were imported into the software for modelling, and cross-pinning was used to simulate pinning. According to the different crossing methods of the upper and lower laminar screws, they are divided into two groups. In the software, the position of the needlepoint of each screw is accurately measured, and the needle point is kept unchanged to simulate the movable range of the screw tail under the condition that the body does not penetrate the cortical bone. The data were compared by grouping and gender. Finally, the guide was designed by combining the screw exit point and fine adjustment angle data of all patients with the centripetal principle of the slide rail.ResultsThe needle exit data L1/L2/L3/L4 were 6.44 ± 0.52 mm, 7.05 ± 0.48 mm, 3.55 ± 0.75 mm and 5.09 ± 0.74 mm, respectively, and the fine adjustment angle of the slide rail was 10.51° ± 0.87°. There was no significant difference between the two groups or between men and women (p > 0.05).ConclusionIn this experiment, using the data obtained from the simulation of screw insertion, a two-way slide guide was designed to assist the insertion of axial laminar screws. The guide locks the screw outlet point to position and guides the screw inlet point, which improves the accuracy and safety of screw placement.

Spinal navigation with preoperative computed tomography

Safe placement of posterior cervical-sacral pedicle screws, S2-Ala-iliac screws, iliac screws, transarticular screws C1/2, translaminar screws C2 or cervical lateral mass screws under the guidance of spinal navigation. All posterior spinal instrumentations with screws: instabilities and deformities of rheumatic, traumatic, neoplastic, infectious, iatrogenic or congenital origin; multilevel cervical spinal stenosis with degenerative instability or kyphosis of the affected spinal segment. There are no absolute contraindications for spinal navigation. Cervical spine: Prone position on agel mattress, rigid head fixation, e.g., with Mayfield tongs; if appropriate, closed reduction under lateral image intensification; thoracic + lumbar spine: prone position on acushioned frame; midline posterior surgical approach at the level of the segments to be instrumented; if necessary, open reduction; insertion of the cervical/upper thoracic screws under the guidance of spinal navigation; if necessary, posterior decompression; instrumentation longitudinal rods; if fusion is to be obtained, decortication of the posterior bone elements with ahigh-speed burr and onlay of cancellous bone or bone substitutes. In stable instrumentations, no postoperative immobilization with orthosis is necessary, removal of drains (if used) 2-3days postoperatively (postop), removal of the sutures 14days postop, clinical and x‑ray controls 3and 12months postop or in case of clinical or neurological deterioration. Numerous studies showed that the use of spinal navigation significantly reduces implant malplacement rates, complications, and revision surgery. Furthermore, intraoperative radiation exposure to the operation team can be reduced by up to 90%.

Thoracolumbar Spinal Stabilization with Three Dimensional-Printed Drill Guides and Pre-Contoured Polyaxial Bone Plates.

The aim of this study was to report new preoperative and intraoperative techniques performed for canine thoracic or lumbar spine kyphosis stabilization using three-dimensional-printed patient-specific drill guides, polyaxial titanium bone plates and drill stops, and to determine the accuracy of screw placement using these techniques. Retrospective study, five client-owned dogs. Three-dimensional-printed patient-specific drill guides and drill stops allowed safe drilling and screw placement in all of the cases, with (i) 84% of the screws graded as I (ideal placement) and 16% as IIa, IIIa or IIIb according to the modified Zdichavsky classification (partial penetration of medial pedicle wall, partial penetration of lateral pedicle wall and full penetration of lateral pedicle wall respectively), (ii) mean mediolateral deviation of ± 4.06 degrees (standard deviation: 8.21 degrees) compared to planned trajectories and (iii) variation in screw depth of ± 2.29mm (standard deviation: 3.07mm) compared to planned depth. We believe that the techniques presented here for thoracic spinal stabilization in dogs show promise; they allowed safe placement of screws along planned trajectories and depth; they also removed the need to use polymethylmethacrylate, while the use of titanium offers the possibility to repeat magnetic resonance imaging in these cases with chronic spinal conditions.

Sagittal imaging study of the lumbar spine with the short rod technique.

The short rod technique (SRT) is a novel method for lumbar pedicle screw placement to reduce surgical trauma and avoid damage to the facet joint and articular surface. The core concept is to change the entry point and angle of the screw on the vertebrae at both ends in the sagittal plane to shorten the length of the longitudinal rods. The purpose of this study is to determine the sagittal screw angle (SSA) and its safe Maximum (MAX) value on each lumbar vertebra for the SRT and to observe the shortening effect on the longitudinal rods. A total of 152 healthy adults were investigated by measuring the lumbar spine lateral view images. The SSA and MAX-SSA were measured with SRT as reference to the conventional placement technique method. The distance between the entry points of the proximal and distal vertebrae was measured to compare the changes in the length of the longitudinal rods using the two screw placement techniques. + SSA increased from L1 to L4, and -SSA increased from L2 to L5, in which the -SSA of L2, L3, and L4 were significantly greater than those of + SSA (P < 0.05). + MAX-SSA at L1-L4 was 23.26 ± 3.54°, 23.68 ± 3.37°, 24.12 ± 3.29°, and 24.26 ± 3.42°, respectively. -MAX-SSA at L2-L5 was 36.25 ± 3.26°, 38.26 ± 3.73°, 38.62 ± 3.63° and 37.33 ± 3.31°, respectively. Theoretical reductions by calculation for the 2-segment lumbar pedicles were: L1-2: 9mm, L2-3: 9.29mm, L3-4: 6.23mm, and L4-5: 7.08mm; And the 3-segment lumbar pedicles were: L1-3: 16.97mm, L2-4: 16.73mm, L3-5, and 18.24mm, respectively. The application of the SRT to lumbar pedicles is a safe screw placement method that can significantly shorten the length of the used longitudinal rods.

Augmented reality in minimally invasive spine surgery: early efficiency and complications of percutaneous pedicle screw instrumentation

Augmented reality (AR) employs an optical projection directly onto the user's retina, allowing complex image overlay on the natural visual field. In general, pedicle screw accuracy rates have improved with increasingly use of technology, with navigation-based instrumentation described as accurate in 89%-100% of cases. Emerging AR technology in spine surgery builds upon current spinal navigation to provide 3-dimensional imaging of the spine and powerfully reduce the impact of inherent ergonomic and efficiency difficulties. This publication describes the first known series of in vivo pedicle screws placed percutaneously using AR technology for MIS applications. After IRB approval, 3 senior surgeons at 2 institutions contributed cases from June, 2020 - March, 2022. 164 total MIS cases in which AR used for placement of percutaneous pedicle screw instrumentation with spinal navigation were identified prospectively. 155 (94.5%) were performed for degenerative pathology, 6 (3.6%) for tumor and 3 (1.8%) for spinal deformity. These cases amounted to a total of 606 pedicle screws; 590 (97.3%) were placed in the lumbar spine, with 16 (2.7%) thoracic screws placed. Patient demographics and surgical metrics including total posterior construct time (defined as time elapsed from preincision instrument registration to final screw placement), clinical complications and instrumentation revision rates were recorded in a secure and de-identified database. The AR system used features a wireless headset with transparent near-eye display which projects intra-operative 3D imaging directly onto the surgeon's retina. After patient positioning, 1 percuntaneous and 1 superficial reference marker are placed. Intra-operative CT data is processed to the headset and integrates into the surgeon's visual field creating a "see-through" 3D effect in addition to 2D standard navigation images. MIS pedicle screw placement is then carried out percutaneously through single line of sight using navigated instruments. Time elapsed from registration and percutaneous approach to final screw placement averaged 3 minutes and 54 seconds per screw. Analysis of the learning curve revealed similar surgical times in the early cases compared to the cases performed with more experience with the system. No instrumentation was revised for clinical or radiographic complication at final available follow-up ranging from 6-24 months. A total of 3 screws (0.49%) were replaced intra-operatively. No clinical effects via radiculopathy or neurologic deficit postoperatively were noted. This is the first report of the use of AR for placement of spinal pedicle screws using minimally invasive techniques. This series of 164 cases confirmed efficiency and safety of screw placement with the inherent advantages of AR technologies over legacy enabling technologies.

Imaging, post-processing and navigation: Surgical applications in pelvic fracture treatment

Technical advancements of the past decade have led to massive improvements regarding imaging and visualization in trauma care. Digital imaging technology has fundamentally changed most processes in fracture management. However, the digital revolution in trauma surgery has just begun.Optical tracking navigation is currently the gold standard for positioning of implants for advanced applications in trauma surgery. Digital technology may enable the surgeon to achieve the same level of safety even in non-navigated placement of screws: We developed a new planning tool to transcript a preoperative into a semi-transparent “fluoroscopic like” image that can be identified intraoperatively and used as a map for the safe placement of sacro-iliac screws based on the “vestibule concept”. In the future, development of artificial intelligence algorithms may provide features like automated segmentation of bone-fragments and other applications for a systematic fracture analysis to improve the standard of care in trauma surgery.Digital transformation has massive impact on diagnostics and surgical management of pelvic fractures. Improved visualization technology provides a better understanding of the surgical anatomy of the pelvis and may enable the surgeon to achieve greatest safety in percutaneous placement of screws even without using optical tracking navigation tools. The “para-axial fusion technique” is a useful tool to plan fluoroscopic views based on a 3D dataset prior to the surgery.

Effects of anode position on pedicle screw testing during lumbosacral spinal fusion surgery

SUMMARY OF BACKGROUND DATAPedicle screws are commonly placed with lumbar/lumbosacral fusions. Triggered electromyography (tEMG), which employs the application of electrical current between the screw and a complementary anode to determine thresholds of conduction, may be utilized to confirm the safe placement of such implants. While previous research has established clinical thresholds associated with safe screw placement, there is variability in clinical practice of anode placement which could lead to unreliable measurements. PURPOSETo determine the variance in pedicle screw stimulation thresholds when using four unique anode locations (ipsilateral/contralateral and paraspinal/gluteal relative to tested pedicle screws). STUDY DESIGNProspective cohort study. Tertiary medical center. PATIENT SAMPLETwenty patients undergoing lumbar/lumbosacral fusion with pedicle screws using tEMG OUTCOME MEASUREStEMG stimulation return values are used to assess varied anode locations and reproducibility based on anode placement. METHODSMeasurements were assessed across node placement in ipsilateral/contralateral and paraspinal/gluteal locations relative to the screw being assessed. R2 coefficients of correlation were determined, and variances were compared with F-tests. RESULTSA total of 94 lumbosacral pedicle screws from 20 patients were assessed. Repeatability was verified using two stimulations at each location for a subset of the screws with an R2 of 0.96. Comparisons between the four anode locations demonstrated R2 values ranging from 0.76 to 0.87. F-tests comparing thresholds between each anode site demonstrated all groups not to be statistically different. CONCLUSIONThe current study, a first-of-its-kind formal evaluation of anode location for pedicle screw tEMG testing, demonstrated very strong repeatability and strong correlation with different locations of anode placement. These results suggest that there is no need to change the side of the anode for testing of left versus right screws, further supporting that placing an anode electrode into gluteal muscle is sufficient and will avoid a sharp ground needle in the surgical field.

Can Robotic Spine Surgery Become the Standard of Care?

Concerns regarding traditional techniques led to the development of robotic systems to facilitate the safe and accurate placement of pedicle screws. The Mazor Spine Assist was the first robotic spine surgery (RSS) platform to receive US Food and Drug Administration approval in 2004. Since then, there has been a steady increase in the application of RSS with several additional iterations of the Mazor platform and other competing systems receiving approval. As the indications, potential benefits, and utilization of RSS continue to expand, the question naturally arises as to whether RSS will eventually become the standard of care for spine surgery. In this article, we review the available evidence and experience with RSS and discuss the potential for RSS to become the medical standard of care.

Percutaneous posterior lumbar interbody fusion using optical topographic navigation: Operative technique

Despite the availability of navigation systems in spine surgery for over two decades, uptake into routine clinical practice has been limited in large part due to disruption of workflow with associated increased operative time. Optical topographical navigation for spine surgery permits safe and accurate placement of pedicle screws without any exposure to intraoperative ionizing radiation and may in fact improve workflow owing to a rapid registration time. Here we describe a novel application of 7D navigation system in a minimally invasive approach for posterior lumbar inter-body fusion (PLIF) with percutaneous screw placement.To our knowledge, this is the first publishable paper discussing the application of optical topographic navigation in minimally invasive PLIF. In our experience this technique was efficient, reliable and requires systematic study to evaluate long-term outcomes and potential benefits and pitfalls.

Is the Use of Intraoperative 3D Navigation for Thoracolumbar Spine Surgery a Risk Factor for Post-Operative Infection?

Pedicle screw fixation is a technique used to provide rigid fixation in thoracolumbar spine surgery. Safe intraosseous placement of pedicle screws is necessary to provide optimal fixation as well as to avoid damage to adjacent anatomic structures. Despite the wide variety of techniques available, none thus far has been able to fully eliminate the risk of malpositioned screws. Intraoperative 3-dimensional navigation (I3DN) was developed to improve accuracy in the placement of pedicle screws. To our knowledge, no previous studies have investigated whether infection rates are higher with I3DN. A single-institution, retrospective study of patients age > 18 undergoing thoracolumbar fusion and instrumentation was carried out and use of I3DN was recorded. The I3DN group had a significantly greater rate of return to the operating room for culture-positive incision and drainage (17 (4.1%) vs. 1 (0.6%), p = 0.025). In multivariate analysis, the use of I3DM did not reach significance with an OR of 6.49 (0.84–50.02, p = 0.073). Post-operative infections are multifactorial and potential infection risks associated with I3DN need to be weighed against the safety benefits of improved accuracy of pedicle screw positioning.

Minimally Invasive Iliac Screw Insertion: Clinical Case Series and Technical Note

Objective: Iliac screw fixation has numerous indication and techniques. To describe the technique of minimally invasive screw insertion of the iliac screw by freehand and navigated iliac screw placement using intraoperative image guidance.Methods: Bilateral iliac screws were inserted in a total of seven patients. Five patients underwent navigation guided iliac screw placement and the freehand technique was used in 2 patients. Results: A total of 7 patients underwent minimally invasive iliac screw fixation in our series. The pathology in 4 of the cases was spondylodiscitis, among them 2 cases each at L5-S1 and L4-L5, one with the destruction of L5 vertebral body and the other with the destruction of both L4 and L5 vertebral bodies. Of the remaining cases, two cases had sacral insufficiency fracture and the last case was implant failure after L2-L5 oblique lumbar fusion. None of the cases required conversion to open procedure and none had wound or hardware related complications till the last follow-up. All patients had an uneventful post-operative period with improvement in pain scores and were mobilized on the 1st postoperative day. One 50-year-old female patient suffering from L5-S1 tubercular spondylodiscitis died due to underlying chronic kidney disease three months post-surgery. Conclusion: Minimal invasive iliac screw placement with or without navigation offers the same biomechanical stability as the open approach but without the need for extensive soft tissue exposure needed for a conventional/open procedure; thereby reducing exposure-related complications and enhancing post-operative recovery and early mobilization. Incorporating intra-operative 3D navigation provides real-time multi-planar images which help in easy planning and safe screw placement whilst reducing radiation exposure.

Aberrant Vertebral Artery and Screw Placement in Lateral Mass of C1 in Atlantoaxial Fixation

Aberrant vertebral arteries at C1 and C2 facet regions are rare. These vessels can pose challenges while inserting screws into the lateral mass. However, mobilization of these vessels is possible to obtain specific screw entry points. In normal bony anatomy, these aberrant vessels are tortuous and hence can be mobilized quickly. Multiple screw entry points are available for safe screw placement. Aberrant vessels at this region do not preclude the placement of screws in lateral mass.

Quantitative Analysis of Temporal Bone Density and Thickness for Robotic Ear Surgery.

Background and Objective: Quantitative assessment of bone density and thickness in computed-tomography images offers great potential for preoperative planning procedures in robotic ear surgery.Methods: We retrospectively analyzed computed-tomography scans of subjects undergoing cochlear implantation (N = 39). In addition, scans of Thiel-fixated ex-vivo specimens were analyzed (N = 15). To estimate bone mineral density, quantitative computed-tomography data were obtained using a calibration phantom. The temporal bone thickness and cortical bone density were systematically assessed at retroauricular positions using an automated algorithm referenced by an anatomy-based coordinate system. Two indices are proposed to include information of bone density and thickness for the preoperative assessment of safe screw positions (Screw Implantation Safety Index, SISI) and mass distribution (Column Density Index, CODI). Linear mixed-effects models were used to assess the effects of age, gender, ear side and position on bone thickness, cortical bone density and the distribution of the indices.Results: Age, gender, and ear side only had negligible effects on temporal bone thickness and cortical bone density. The average radiodensity of cortical bone was 1,511 Hounsfield units, corresponding to a bone mineral density of 1,145 mg HA/cm3. Temporal bone thickness and cortical bone density depend on the distance from Henle's spine in posterior direction. Moreover, safe screw placement locations can be identified by computation of the SISI distribution. A local maximum in mass distribution was observed posteriorly to the supramastoid crest.Conclusions: We provide quantitative information about temporal bone density and thickness for applications in robotic and computer-assisted ear surgery. The proposed preoperative indices (SISI and CODI) can be applied to patient-specific cases to identify optimal regions with respect to bone density and thickness for safe screw placement and effective implant positioning.

Lateral mass screw placement in the atlas: description of a novel surgical technique, radiographic parameters, and review of the literature.

Numerous techniques of C1 lateral mass screw placement have been described. We sought to delineate the radiographic angle of safety medially and laterally and describe a novel surgical technique of C1 lateral mass screw placement. We sought to (I) determine the angle of safety medially and laterally of the C1 lateral mass; (II) assess the size available of the lateral mass in the AP and coronal planes; (III) describe novel technique of insertion of a C1 lateral mass screw utilizing navigation and a novel start point. We retrospectively reviewed cervical computed tomography (CT) images of normal adults. Radiographic measurements were then obtained using these images including the angle (degrees) of safety medially and lateral of the C1 lateral mass bilaterally, as well as the length and width (mm) of the C1 lateral masses. A novel surgical technique was used by identifying the confluence of the medial aspect of the posterior arch and the lateral mass. This confluence is then marked out as the C1 screw start point. Under navigation guidance, lateral mass screws were placed with 0 degrees of medial-lateral angulation from posterior to anterior. Forty-five patients with a mean age of 52.6±25.6 years (33% female) were included. The mean medial and lateral angle of safety of the C1 lateral mass bilaterally was 23±3.8 degrees and 32±5 degrees, respectively. Average length and width of the lateral mass was 17.7 and 13.3 mm respectively. This study describes the radiographic window of safety medially and laterally for safe and reproducible placement of C1 lateral mass screws. Further, a novel technique using a medial start point and navigation guidance with 0 degrees of angulation in the coronal plane is described. Further research is required to assess outcomes of patients utilizing this method as well as biomechanical studies to assess this construct strength compared to others that are frequently used.

Mapping of Venous Sinus Anatomy and Occipital Bone Thickness for Safe Screw Placement in 100 Patients with 46,200 Standardized Measurements Using Computed Tomography Angiography.

Retrospective descriptive study. The aim of this study was to create topographical maps of occipital bone thickness and venous sinus (VS) presence to assess the risks of screw insertion in four commercially available occipital plates. Craniocervical junction instability and deformity are serious pathological conditions that require posterior fixation of the occipital bone to the cervical vertebrae. Insertion of occipital bone screws requires evaluation of both occipital bone thickness for effective internal fixation and intracranial VS presence for vascular injury prevention. Despite the surgical risks, there is a paucity of research on safe screw placement. We created a matrix of 231 standardized measurement points to analyze the occipital bone thickness and VS presence in cervical spine CT angiograms. These measurements were used to create topographical maps of occipital bone thickness and likelihood of VS presence, which we then compared to the screw hole configurations of four occipital plates. Hundred patients were assessed. Maximum occipital bone thickness of 13.9 ± 3.3 mm was midline in the occipital bone, 45 mm from the foramen magnum, around the external occipital protuberance (EOP). Regions with thicknesses >8 mm were 2 cm lateral to the EOP at the level of the superior nuchal line and 2.5 cm inferior to the EOP. The area with the highest VS presence rate was around the EOP and the superior nuchal line. The right transverse VS was more prominent in both sexes. There is a limited area of the occipital bone with thicknesses for enough screw purchase. Previous studies have shown 8 mm as the minimum screw length to reduce the risk of implant failure. In our analysis, only "T"-shaped plates had configurations with thicknesses >8 mm for each screw hole. For every screw hole in the analyzed occipital plates, there was a possibility of VS presence ranging from 8% to 33%.Level of Evidence: 5.