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PurposeDespite proven biomechanical superiority and resultant superior clinical outcomes, pedicle instrumentation in cervical spine is not widely practiced due to technical difficulties, steep learning curve, and possible potential catastrophic complications due to screw misplacement. This study was undertaken with the purpose to evaluate the feasibility, accuracy, and complications of cervical pedicle screw instrumentation solely using O-arm-based 3D navigation technology.MethodsProspectively maintained data from a single-surgeon case series were retrospectively analyzed. All the patients had undergone cervical pedicle instrumentation under O-arm 3D navigation. Screw placement accuracy was analyzed and compared among different vertebral levels and also between different patient groups.ResultsA total of 241 cervical pedicle screws were inserted in 44 patients. Out of the 241 screws, 197 (81.74%) were inserted at the level of C3–C6 vertebrae with nearly equal distribution among the 4 vertebrae, followed by 32 (13.28%) and 12 (4.98%) screws at C2 and C7 vertebrae, respectively. After the analysis of screw placement as per Gertzbein classification, the overall breach rates were found to be 7.05% (17 screws) with 52.94% (10 screws) Grade I, 47.06% (7 screws) Grade II, and nil Grade III screw breaches.ConclusionThe use of O-arm-based intra-operative 3D scans for navigation can make cervical pedicle screw placement reliable. High accuracy and better intra-operative control can increase surgeon’s confidence in using cervical pedicle instrumentation on more regular basis.Graphical abstractThese slides can be retrieved under Electronic Supplementary Material.

Study design: Clinical trial for cervical screw insertion by using individualized 3-dimensional (3D) printing screw insertion templates device. Objective: The objective of this study is to evaluate the safety and accuracy of the individualized 3D printing screw insertion template in the cervical spine. Materials and methods: Ten patients who underwent posterior cervical fusion surgery with cervical pedicle screws, laminar screws or lateral mass screws between December 2014 and December 2015 were involved in this study. The patients were examined by CT scan before operation. The individualized 3D printing templates were made with photosensitive resin by a 3D printing system to ensure the screw shafts entered the vertebral body without breaking the pedicle or lamina cortex. The templates were sterilized by a plasma sterilizer and used during the operation. The accuracy and the safety of the templates were evaluated by CT scans at the screw insertion levels after operation. Results: The accuracy of this patient-specific template technique was demonstrated. Only one screw axis greatly deviated from the planned track and breached the cortex of the pedicle because the template was split by rough handling and then we inserted the screws under the fluoroscopy. The remaining screws were inserted in the track as preoperative design and the screw axis deviated by less than 2 mm. Vascular or neurologic complications or injuries did not happen. And no infection, broken nails, fracture of bone structure, or screw pullout occurred. Conclusion: This study verified the safety and the accuracy of the individualized 3D printing screw insertion templates in the cervical spine as a kind of intraoperative screw navigation. This individualized 3D printing screw insertion template was user-friendly, moderate cost, and enabled a radiation-free cervical screw insertion.

Purpose Due to better primary stability and repositioning options, pedicle screws are increasingly used during posterior stabilization of the cervical spine. However, the serious risks generally associated with the insertion of screws in the cervical spine remain. The purpose of this study is to examine the accuracy of pedicle screw insertion with the use of 3D fluoroscopy navigation systems, also accounting for various spine levels. Methods Data of 64 patients were collected during and after screw implantation (axial and subaxial) in the cervical spine. 207 screws were implanted from C1 to C7 and analyzed for placement accuracy according to postoperative CT scans and following the modified Gertzbein and Robbins classification. Results The accuracy of most of the inserted screws was assessed as grade 2 according to the modified Gertzbein and Robbins classification. 93.9 % of the screws implanted at C1 or C2, and 78.51 % of the screws implanted at levels C3–C7 showed placement accuracy grade 2 or better, indicating pedicle wall perforation of <2 mm. Overall, seven complications were observed. In three cases, the vertebral artery was affected, leading to one fatality. Surgical revision was necessary once because of Magerl screw misplacement and three times due to impaired wound healing. No radicular symptoms resulted from screw malposition. Conclusion Axial and subaxial screws can be inserted with a high grade of accuracy using 3D fluoroscopy-based navigation systems. Nevertheless, while this useful innovation helps to minimize the risks of misplacement, the surgery is still a challenge, as arising complications remain severe.

Introduction Pedicle screw stabilization, the standard technique in the thoracic and lumbar spine, is increasingly used in the cervical spine. Initial studies on the use of anterior pedicle screws (ATPS) in the cervical spine have been recently published. ATPS use has theoretical advantages over posterior stabilization. We have already established a 3D-fluoroscopy navigation setup in a study of artificial bones. The aim of the current study was to evaluate the positioning quality/accuracy of ATPS introduced to human specimens. Methods 36 cannulated screws (3.5 mm) were implanted anteriorly into the C3–C7 segments of four spines (unfixed, frozen, cadaveric specimens) using a 3D-fluoroscopy navigation system. Placement accuracy was evaluated using a recently published classification on postoperative CT scans. Grade 1 is perfect position with pedicle wall perforation <1 mm, grade 2 is perforation <2 mm, etc., and finally grade 5 is cortical perforation of >4 mm and/or transverse foramen entry. Results 36 anterior pedicle screws were inserted into four human cervical spine specimens. Of these, seven screws were introduced to C3, five to C4 and eight each to C5, C6, and C7. Classified with the modified G&R, 21 of 36 (58.3%) were grade 1. Ten screws (27.8%) were grade 2. Grade 4 was assessed for two screws and grade 5 for three. Customary “good” positioning, combining grades 1 and 2, was thus found in 86.1%. Five screws (13.9%) did not meet this criterion (grade ≥3). Conclusions With 86.1% of good positioning (grade 2 or better), a 3D-fluoroscopy navigation of ATPS screws into human c-spine specimens achieved a satisfying results. These are at least comparable to results presented in the literature for posteriorly introduced subaxial pedicle screws.

Purpose The technique of pedicle screw stabilization is finding increasing popularity for use in the cervical spine. Implementing anterior transpedicular screws (ATPS) in cervical spine offers theoretical advantages compared to posterior stabilization. The goal of the current study was the development of a new setting for navigated insertion of ATPS, combining the advantage of reduced invasiveness of an anterior approach with the technical advantages of navigation. Methods 20 screws were implanted in levels C3 to C6 of four cervical spine models (SAWBONES ® Cervical Vertebrae with Anterior Ligament) with the use of 3D fluoroscopy navigation system [Arcadis Orbic 3D, Siemens and VectorVision fluoro 3D trauma software (BrainLAB)]. The accuracy of inserted screws was analyzed according to postoperative CT scans and following the modified Gertzbein and Robbins classification. Results 20 anterior pedicle screws were placed in four human cervical spine models. Of these, eight screws were placed in C3, two screws in C4, six screws in C5, and four screws in C6. 16 of 20 screws (80 %) reached a grade 1 level of accuracy according to the modified Gertzbein and Robbins Classification. Three screws (15 %) were grade 2, and one screw (5 %) was grade 3. Grade 4 and 5 positions were not evident. Summing grades 1 and 2 together as “good” positions, 95 % of the screws achieved this level. Only a single screw did not fulfill these criteria. Conclusion The setting introduced in this study for navigated insertion of ATPS into cervical spine bone models is well implemented and shows excellent results, with an accuracy of 95 % (Gertzbein and Robbins grade 2 or better). Thus, this preliminary study represents a prelude to larger studies with larger case numbers on human specimens.

Pedicle screw fixation is a spinal fusion technique that involves the implantation of screws into vertebral pedicles to restrict movement between those vertebrae. The objective of this research is to measure pedicle screw placement accuracy using a novel automated measurement system that directly compares the implanted screw location to the planned target in all three anatomical views. Preoperative CT scans were used to plan the screw trajectories in 122 patients across four surgical centers. Postoperative scans were fused to the preoperative plan to quantify placement accuracy using an automated measurement algorithm. The mean medial–lateral and superior–inferior deviations in the pedicle region for 500 screws were 1.75 ± 1.36 mm and 1.52 ± 1.26 mm, respectively. These deviations were measured using an automated system and were statistically different from manually determined values. The uncertainty associated with the fusion of preoperative to postoperative images was also quantified to better understand the screw-to-plan accuracy results. This study uses a novel automated measurement system to quantify screw placement accuracy as it relates directly to the planned target location, instead of analyzing for breaches of the pedicle, to quantify the validity of using of a robotic-guidance system for accurate pedicle screw placement.

Cannulation process intervenes before implantation of pedicle screw and depends on the surgeon’s experience. A reliable experimental protocol has been developed for the characterization of the slipping behavior of the surgical tool on the cortical shell simulated by synthetic materials. Three types of synthetic foam samples with three different densities were tested using an MTS Acumen 3 A/T electrodynamic device with a tri-axis 3 kN Kistler load cell mounted on a surgical tool, moving at a constant rotational speed of 10° mm −1 and performing a three-step cannulation test. Cannulation angle varied between 10° and 30°. Synthetic samples were scanned after each tests, and cannulation coefficient associated to each perforation section was computed. Reproducibility tests resulted in an ICC for Sawbone samples of 0.979 ( p  < 0.001) and of 0.909 ( p  < 0.001) for Creaplast and Sawbone samples. Cannulation coefficient and maximum force in Z -axis are found the best descriptors of the perforation. Angular threshold for perforation prediction was found to be 17.5° with an area under the curve of the Receiver Operating Characteristic of 89.5%. This protocol characterizes the cannulation process before pedicle screw insertion and identifies the perforation tool angle until which the surgical tool slips on the cortical shell depending on bone quality. Graphical Abstract

PurposeTo determine if the novel 3D Machine-Vision Image Guided Surgery (MvIGS) (FLASH™) system can reduce intraoperative radiation exposure, while improving surgical outcomes when compared to 2D fluoroscopic navigation.MethodsClinical and radiographic records of 128 patients (≤ 18 years of age) who underwent posterior spinal fusion (PSF), utilising either MvIGS or 2D fluoroscopy, for severe idiopathic scoliosis were retrospectively reviewed. Operative time was analysed using the cumulative sum (CUSUM) method to evaluate the learning curve for MvIGS.ResultsBetween 2017 and 2021, 64 patients underwent PSF using pedicle screws with 2D fluoroscopy and another 64 with the MvIGS. Age, gender, BMI, and scoliosis aetiology were comparable between the two groups. The CUSUM method estimated that the MvIGS learning curve with respect to operative time was 9 cases. This curve consisted of 2 phases: Phase 1 comprises the first 9 cases and Phase 2 the remaining 55 cases. Compared to 2D fluoroscopy, MvIGS reduced intraoperative fluoroscopy time, radiation exposure, estimated blood loss and length of stay by 53%, 62% 44%, and 21% respectively. Scoliosis curve correction was 4% higher in the MvIGS group, without any increase in operative time.ConclusionMvIGS for screw insertion in PSF contributed to a significant reduction in intraoperative radiation exposure and fluoroscopy time, as well as blood loss and length of stay. The real-time feedback and ability to visualize the pedicle in 3D with MvIGS enabled greater curve correction without increasing the operative time.

Nonlinear micro finite element (µFE) models have become the gold-standard for accurate numerical modeling of bone-screw systems. However, the detailed representation of bone microstructure, along with the inclusion of nonlinear material and contact, and pre-damage due to pre-drilling and screw-insertion, constitute significant computational demands and restrict model sizes. The goal of this study was to evaluate the agreement of screw pull-out predictions of computationally efficient, materially nonlinear µFE models with experimental measurements, taking both contact interface and pre-damage into account in a simplified way. Screw pull-out force was experimentally measured in ten porcine radius biopsies, and specimen-specific, voxel-based µFE models were created mimicking the experimental setup. µFE models with three levels of modeling details were compared: Fully bonded interface without pre-damage (FB), simplified contact interface without pre-damage (TED-M), and simplified contact interface with pre-damage (TED-M + P). In the TED-M + P models, the influence of pre-damage parameters (damage zone radial thickness and amount of damage) was assessed and optimal parameters were identified. The results revealed that pre-damage parameters highly impact the pull-out force predictions, and that the optimal parameters are ambiguous and dependent on the chosen bone material properties. Although all µFE models demonstrated high correlations with experimental data ( R 2 > 0.85), they differed in their 1:1 correspondence. The FB and TED-M models overestimated maximum force predictions (mean absolute percentage error (MAPE) > 52%), while the TED-M + P model with optimized pre-damage parameters improved the predictions (MAPE <17%). In conclusion, screw pull-out forces predicted with computationally efficient, materially nonlinear µFE models showed strong correlations with experimental measurements. To achieve quantitatively accurate results, precise coordination of contact modeling, pre-damage representation, and material properties is essential.

Background The implantation of screws is a standard procedure in musculoskeletal surgery. Heat can induce thermal osteonecrosis, damage the bone and lead to secondary problems like implant loosening and secondary fractures. The aim of this study was to investigate whether screw insertion generates temperatures that can cause osteonecrosis. Methods We measured the temperature of twenty human femur diaphysis in a total of 120 measurements, while screws of different material (stainless steel and titanium alloy) and different design (locking and cortex screw) were inserted in three different screwing modes (manual vs. machine screwing at full and reduced rotational speed) with 6 thermocouples (3 cis and 3 trans cortex). Each was placed at a depth of 2 mm with a distance of 1.5 mm from the outer surface of the screw. Results The screw design (cortical > locking), the site of measurement (trans-cortex > cis-cortex) and the type of screw insertion (hand insertion > machine insertion) have an influence on the increase in bone temperature. The screw material (steel > titanium), the site of measurement (trans-cortex > cis-cortex) and the type of screw insertion (machine insertion > hand insertion) have an influence on the time needed to cool below critical temperature values. The combination of the two parameters (maximum temperature and cooling time), which is particularly critical for osteonecrosis, is found only at the trans-cortex. Conclusion Inserting a screw hast the potential to increase the temperature of the surrounding bone tissue above critical values and therefore can induce osteonecrosis. The trans-cortex is the critical area for the development of temperatures above the osteonecrosis threshold, making effective cooling by irrigation difficult. It would be conceivable to cool the borehole with cold saline solution before inserting the screw or to cool the screw in cold saline solution. If possible, insertion by hand should be considered.