Summary. Optimum position of pedicle screws can be determined preoperatively by CT based planning. We conducted a comparative study in order to analyse manually determined pedicle screw plans and those that were obtained automatically by a computer software and found an agreement in plans between both methods, yet an increase in fastening strengths was observed for automatically obtained plans. Hypothesys. Automatic planning of pedicle screw positions and sizing is not inferior to manual planning. Design. Prospective comparative study. Introduction. Preoperative planning in spinal deformity surgery starts by a proper selection of implant anchors throughout the instrumented spine, where pedicle screws provide the optimum choice for bone fixation. In the case of severe spinal deformities, dysplastic pedicles can limit screw usage, and therefore studying the anatomy of vertebrae from preoperative images can aid in achieving the safest screw position through optimal fastening strength. The purpose of this study is to compare manually and automatically obtained preoperative pedicle screw plans. Materials and Methods. CT scans of 17 deformed thoracic spines were studied by two experienced spine deformity surgeons, who placed 316 pedicle screws in 3D using a software positioning tool by aiming for the safest trajectory that permitted the largest possible screw sizes. The resulting manually obtained screw sizes, trajectory angles, entry points and normalised fastening strengths were compared to those obtained automatically by a dedicated computer software that, basing on vertebral anatomy and bone density in 3D, determined optimal screw sizes and trajectories. Results. Statistically significant differences were observed between manually and automatically obtained plans for screw sizes (p < 0.05) and trajectory angles (p < 0.001). However, for automatically obtained plans, screws were not smaller in diameter (p < 0.05) or shorter in length (p < 0.001), while screw normalised fastening strengths were higher (p < 0.001). Conclusions. In comparison to manual planning, automatically obtained plans did not result in smaller screw diameters or shorter screw lengths, which is in agreement with the definition of the pull-out strength, but in different screw trajectory angles, which is reflected by higher normalised fastening strengths. Captions. Fig. 1. Visual comparison among automatically obtained (green colour) and manually defined pedicle screw placement plans by two experienced spine surgeons (red and blue colour) for three different patients with adolescent idiopathic scoliosis, shown from top to bottom in a three-dimensional view, left sagittal, right sagittal and coronal view. Fig. 2. Histograms of differences between observers and (left column), between observer and automated method (middle column), and between observer and automated method (right column), shown from top to bottom for differences in pedicle screw pedicle screw diameter, sagittal inclination, and normalised fastening strength. For figures/tables, please contact authors directly.

We present an analysis of manual and computer-assisted preoperative pedicle screw placement planning. Preoperative planning of 256 pedicle screws was performed manually twice by two experienced spine surgeons (M1 and M2) and automatically once by a computer-assisted method (C) on three-dimensional computed tomography images of 17 patients with thoracic spinal deformities. Statistical analysis was performed to obtain the intraobserver and interobserver variability for the pedicle screw size (i.e. diameter and length) and insertion trajectory (i.e. pedicle crossing point, sagittal and axial inclination, and normalized screw fastening strength). In our previous study, we showed that the differences among both manual plannings (M1 and M2) and computer-assisted planning (C) are comparable to the differences between manual plannings, except for the pedicle screw inclination in the sagittal plane. In this study, however, we obtained also the intraobserver variability for both manual plannings (M1 and M2), which revealed that larger differences occurred again for the sagittal screw inclination, especially in the case of manual planning M2 with average differences of up to 18.3°. On the other hand, the interobserver variability analysis revealed that the intraobserver variability for each pedicle screw parameter was, in terms of magnitude, comparable to the interobserver variability among both manual and computer-assisted plannings. The results indicate that computer-assisted pedicle screw placement planning is not only more reproducible and faster than, but also as reliable as manual planning

Pedicle screw fixation is a technically demanding procedure with potential difficulties and reoperation rates are currently on the order of 11%. The most common intraoperative practice for position assessment of pedicle screws is biplanar fluoroscopic imaging that is limited to two- dimensions and is associated to low accuracies. We have previously introduced a full-dimensional position assessment framework based on registering intraoperative X-rays to preoperative volumetric images with sufficient accuracies. However, the framework requires a semi-manual process of pedicle screw segmentation and the intraoperative X-rays have to be taken from defined positions in space in order to avoid pedicle screws' head occlusion. This motivated us to develop advancements to the system to achieve higher levels of automation in the hope of higher clinical feasibility. In this study, we developed an automatic segmentation and X-ray adequacy assessment protocol. An artificial neural network was trained on a dataset that included a number of digitally reconstructed radiographs representing pedicle screw projections from different points of view. This model was able to segment the projection of any pedicle screw given an X-ray as its input with accuracy of 93% of the pixels. Once the pedicle screw was segmented, a number of descriptive geometric features were extracted from the isolated blob. These segmented images were manually labels as ‘adequate’ or ‘not adequate’ depending on the visibility of the screw axis. The extracted features along with their corresponding labels were used to train a decision tree model that could classify each X-ray based on its adequacy with accuracies on the order of 95%. In conclusion, we presented here a robust, fast and automated pedicle screw segmentation process, combined with an accurate and automatic algorithm for classifying views of pedicle screws as adequate or not. These tools represent a useful step towards full automation of our pedicle screw positioning assessment system

The accuracy of pedicle screw placement is essential for successful spinal reconstructive surgery. The authors of several previous studies have described the use of image-based navigational templates for pedicle screw placement. These are designed based on a pre-operative computed tomographic (CT) image that fits into a unique position on an individual's bone, and holes are carefully designed to guide the drill or the pedicle probe through a pre-planned trajectory. The current study was conducted to optimise navigational template design and establish its designing method for safe and accurate pedicle screw placement. Thin-section CT scans were obtained from 10 spine surgery patients including 7 patients with adolescent idiopathic scoliosis (AIS) and three with thoracic ossification of the posterior longitudinal ligament (OPLL). The CT image data were transferred to the commercially available image-processing software and were used to reconstruct a three-dimensional (3D) model of the bony structures and plan pedicle screw placement. These data were transferred to the 3D-CAD software for the design of the template. Care was taken in designing the template so that the best intraoperative handling would be achieved by choosing several round contact surfaces on the visualised posterior vertebral bony structure, such as transverse process, spinous process and lamina. These contact surfaces and holes to guide the drill or the pedicle probe were then connected by a curved pipe. STL format files for the bony models with planned pedicle screw holes and individual templates were prepared for rapid prototype fabrication of the physical models. The bony models were made using gypsum-based 3D printer and individual templates were fabricated by a selective laser melting machine using commercially pure titanium powder. Pedicle screw trajectory of the bony model, adaptation and stability of the template on the bony model, and screw hole orientation of the template were evaluated using physical models. Custom-made titanium templates with adequate adaptation and stability in addition to proper orientation of the screw holes were sterilised by autoclave and evaluated during surgery. During segmentation, reproducibility of transverse and spinous processes were inferior to the lamina and considered inadequate to select as contact surfaces. A template design with more bone contact area might enhance the stability of the template on the bone but it is susceptible to intervening soft tissue and geometric inaccuracy of the template. In the bony model evaluation, the stability and adaptation of the templates were sufficient with few small round contact surfaces on each lamina; thus, a large contact surface was not necessary. In clinical patients, proper fit for positioning the template was easily found manually during the operation and 141/142 screws were inserted accurately with 1 insignificant pedicle wall breach in AIS patient. This study provides a useful design concept for the development and introduction of custom-fit navigational template for placing pedicle screws easily and safely

Background. Accurate insertion of pedicle screws in scoliosis patients is a great challenge for surgeons due to the severe deformity of thoracic and lumbar spine. Meanwhile, mal-position of pedicle screw in scoliosis patients could lead to severe complications. Computer-assisted navigation technique may help improving the accuracy of screw placement and reducing complications. Thus, this meta-analysis of the published researches was conducted concentrating on accuracy of pedicle screw placement and postoperative assessment in scoliosis patients using computer-assisted navigation technique. Methods. PubMed, Cochrane and Web of Science databases search was executed. In vivo comparative studies that assessed accuracy and postoperative evaluation of pedicle screw placement in scoliosis patients with or without navigation techniques were involved and analysed. Results. One published randomised controlled trial (RCT) and seven retrospective comparative studies met the inclusion criteria. These studies included 321 patients with 3821 pedicle screws inserted. Accuracy of pedicle screw insertion was significantly increased with using of navigation system, while average surgery time was not significantly different with non-navigated surgery. And Correction rate for scoliosis in navigated surgery was not significantly different with non-navigated surgery. Conclusions. Navigation technique does indeed improve the accuracy of pedicle screw placement in scoliosis surgery, without prolong the surgery time or decrease the deformity correction effect

To introduce a new robot-assisted surgical system for spinal posterior fixation which called TiRobot, based on intraoperative three-dimensional images. TiRobot has three components: the planning and navigation system, optical tracking system and robotic arm system. By combining navigation and robot techniques, TiRobot can guide the screw trajectories for orthopedic surgeries. In this randomised controlled study approved by the Ethics Committee, 40 patients were involved and all has been fully informed and sign the informed consent. 17 patients were treated by free-hand fluoroscopy-guided surgery, and 23 patients were treated by robot-assisted spinal surgery. A total of 190 pedicle screws were implanted. The overall operation times were not different for both groups. None of the screws necessitated re-surgery for revised placement. In the robot-assisted group, assessment of pedicle screw accuracy showed that 102 of 102 screws (100%) were safely placed (<2 mm, category A+B). And mean deviation in entry point was 1.70 +/− 0.83mm, mean deviation in end point was 1.84 +/− 1.04mm. In the conventional freehand group, assessment of pedicle screw accuracy showed that 87 of 88 (98.9%) were safely placed (<2 mm, category A+B), 1 screw fall in category C, mean deviation in entry point was 3.73 +/− 2.28mm, mean deviation in end point was 4.11 +/− 2.31mm. This randomised controlled study verified that robot-assisted pedicle screw placement with real-time navigation is a more accuracy and safer method, and also revealed great clinical potential of robot-assisted surgery in the future

A retrospective descriptive preliminary study on early experience using all pedicle screw correction. Pedicle screw fixation enables enhanced correction of spinal deformities. However, the technique is still in early development in our clinic. Tends of the scoliosis patient to come in late ages make maximum correction failed. A total 16 patients are subjected to pedicle screw fixation for spinal deformities were analyzed descriptively as an early follow-up in the last two-year. 14 patients are girl and 2 are boys. The age range between 12 to 18 year. 8 are Kings type II and 8 are Kings type III, 212 screws were inserted between Th3 – L2 (14-18 screws per-patient), all concave pedicles were inserted with screws but in convex side every two or three pedicles were inserted. The position of screws was analyzed using the post-operative plain X ray film. Before surgery the mean deformity measurement are 52.56° (range, 42-72°, correction achieved was 18° (range 10-34%, it was correlated to 68% achievement (range, 53-80%). All patients are happy with their image improvement. In total 212 screws inserted, 28 screws are malpositions (13.2%), but no clinical complication recorded. In this early experience using all pedicle screw scoliosis surgery, all patients are happy with the results although the correction only 53-80(. More patients are needed to improve this achievement

Introduction. Radiostereometric Analysis (RSA) is an imaging method that is increasingly being utilized for monitoring fixation of orthopaedic implants in randomized clinical trials. Extensive RSA research has been conducted over the last 35+ years using standard clinical x-ray acquisition modalities that irradiate screen/film media or Computed Radiography (CR) plates. The precision of RSA can depend on a number of factors including modality image quality. Objective. This study assesses the precision of RSA with a novel Digital Radiography (DR) system compared to a CR imaging system using different imaging techniques. Additionally, the study assesses the precision of locating beads embedded in a modified spine pedicle screw. Methods. A modified titanium spinal pedicle screw 4.5 mm diameter, 35 mm length, marked with two 1.0 mm tantalum beads, one inside the head and one near the screw tip was inserted into a bovine tibia segment. Six additional 1.0 mm tantalum beads were inserted into the bone segment superiorly, distally and adjacent to the pedicle screw. The phantom was placed on a standard clinical diagnostic imaging bed above a custom RSA carbon fiber calibration cage (Halifax Biomedical Inc.). A pair of DR or CR imaging plates were placed below the calibration cage and irradiated 8 times at 100, 125 kV at 2.5 mAs. For DR additional test were performed at 150 kV, and again at 100 kV at 0.5 mAs. At the time of abstract submission CR results at these settings were not available. To determine precision, the standard deviation of 3D vector distances between beads was determined using RSA for each of the different imaging parameters. Results. Standard deviations of the inter-bead distances measured in the pedicle screw were 44.4 and 32.1 μm (N=8) respectively for the 100 and 125 kV settings at 2.5 mAs using the DR system, compared to 109.0, 55.8 μm for CR [Fig. 1]. The distances between the bone implanted beads provided standard deviations of 24.4 and 22.7 μm respectively for the 100 and 125 kV settings at 2.5 mAs using the DR system, compared to 33.1 and 33.0 μm with the CR system. Further increasing the photon energy to 150 kV with the DR system reduces the precision error to 22.4 μm in the pedicle screw and remains approximately the same at 21.0 μm in bone. Lowering the mAs while maintaining 100 kV increases the precision error in the pedicle screw (64 μm) and showed no significant difference in bone (24.4 μm). Conclusion. The current phantom design is basic in nature and does not account for any soft tissue scatter. However, initial results indicate a considerable reduction in precision error when using DR compared to CR imaging equipment for RSA analysis. Increasing the kV did not significantly influence the precision in measuring bead locations in bone. For embedded tantalum beads within a titanium pedicle screw, imaging at higher kV values with the described DR imaging system did allow more precise localization. This approach may be useful in assessing the in vivo position of spine or other titanium implants

Introduction. Pedicle screw fixation is considered gold standard as it provides stable and adequate fixation of all the three columns of spine. Mal-placement of screws in dorso-lumbar region, using fluoroscopic control only, varies from 15% to 30 %. The aim of this study was to determine whether accuracy of pedicle screw placement can be improved using CT based navigation technique. Material & methods. 15 patients with fracture of D12 in 4 patients, L1 in 6 patients, L2 in 4 patients, and L4 in 1 patient underwent pedicle screw fixation using CT based navigation. Each fracture was fixed with 4 pedicle screws, 2 each in one level above and one level below the fractured vertebrae. A total of 60 pedicle screws was inserted. A pre-operative 1mm slice planning CT scan was taken from two levels above to two levels below the fractured vertebrae. It was loaded into the workstation and pre-operative planning was made of screw trajectory and screw size i.e. thickness and length, according to the dimensions of the pedicle and vertebral body. Screws were then inserted using opto-electronic navigation system. Screw placement was analysed in all patients using post-operative CT scan and graded according to the Laine's system. Results. The average time for matching was 10.8 minutes and average time for screw insertion was 4.3 minutes (range 2-8 minutes). One screw in right sided pedicle of L2 perforated the lateral cortex (1.66%). There was no neuro-vascular complication. Conclusion. The incidence of a misplaced screw in the present study is only 1.66% which is much less than reported with conventional technique, reflecting enhanced accuracy with computer assisted navigation. Thus computer assisted navigation is a potent tool in the hands of a spine surgeon in improving the accuracy of pedicle screw placement

The use of cervical pedicle screws as anchors in posterior reconstruction surgery has not been widely accepted due to the neurological or vascular injury. We thus sought to investigate the accuracy of free-handed pedicle screw placement in the cervical and upper thoracic spine at the early stage of clinical application. Eight patients (five males and three females) were included in this study. Mean age was 63 years (31 to 78 years). There were three patients with rheumatoid arthritis, three with cervical fracture-dislocation, and two with spinal metastasis. Twenty-four pedicle screws (3.5 mm diameter: Vertex, Medtronic Sofamordanek) were placed into the pedicle from C2 to T2 level by free-handed technique2). Grade of breaching of pedicle cortex was divided into four groups (Grade 0–3). In addition, screw axis angle (SAA) were calculated from the horizontal and sagittal CT images and compared with pedicle transverse angle (PTA). Furthermore, perioperative complications were also examined. Our free-handed pedicle screw placement with carving technique is as follows: A longitudinal gutter was created at the lamina-lateral mass junction and then transverse gutter perpendicular to the longitudinal gutter was made at the lateral notch of lateral mass. The entry point of the pedicle screw was on the midline of lateral mass. Medial pedicle cortex through the ventral lamina was identified using the probes to create the hole within the pedicle. The hole was tapped and the screw was gently introduced into the pedicle to ensure the sagittal trajectory using fluoroscopy. In the transverse direction, 22 out of 24 screws (92%) were entirely contained within the pedicle (Grade 0). In contrast, only teo screws (8%) produced breaches less than half the screw diameter (Grade 1). In the sagittal direction, all screws were within the pedicle (Grade 0). Screw trajectories were not consistent with anatomical pedicle axis angle; the mean SAA were smaller than the mean PTA at all levels. The pedicle diameter ranged from 3.9 to 9.2 mm. The mean value gradually increased toward the caudal level. There were no neurological and vascular complications related to screw placement

We prospectively studied the use of intercostal EMG monitoring as an indicator of the accuracy of the placement of pedicle screws in the thoracic spine. We investigated 95 thoracic pedicles in 17 patients. Before insertion of the screw, the surgeon recorded his assessment of the integrity of the pedicle track. We then stimulated the track using a K-wire pedicle probe connected to a constant current stimulator. A compound muscle action potential (CMAP) was recorded from the appropriate intercostal or abdominal muscles. Postoperative CT was performed to establish the position of the screw. The stimulus intensity required to evoke a muscle response was correlated with the position of the screw on the CT scan. There were eight unrecognised breaches of the pedicle. Using 7.0 mA as a threshold, the sensitivity of EMG was 0.50 in detecting a breached pedicle and the specificity was 0.83. Thoracic pedicle screws were accurately placed in more than 90% of patients. EMG monitoring did not significantly improve the reliability of placement of the screw

Simulation is an effective adjunct to the traditional surgical curriculum, though access to these technologies is often limited and costly. The objectives of this work were to develop a freely accessible virtual pedicle screw simulator and to improve the clinical authenticity of the simulator through integration of low-cost motion tracking. The open-source medical imaging and visualisation software, 3D Slicer, was used as the development platform for the virtual simulation. 3D Slicer contains many features for quickly rendering and transforming 3D models of the bony spine anatomy from patient-specific CT scans. A step-wise pedicle screw insertion workflow module was developed which emulated typical pre-operative planning steps. This included taking anatomic measurements, identifying insertion landmarks, and choosing appropriate screw sizes. Monitoring of the surgeon's simulated tool was assessed with a low-cost motion tracking sensor in real-time. This allowed for the surgeon's physical motions to be tracked as they defined the virtual screw's insertion point and trajectory on the rendered anatomy. Screw insertion was evaluated based on bone density contact and cortical breaches. Initial surgeon feedback of the virtual simulator with integrated motion tracking was positive, with no noticeable lag and high accuracy between the real-world and virtual environments. The software yields high fidelity 3D visualisation of the complex geometry and the tracking enabled coordination of motion to small changes in both translational and angular positioning. Future work will evaluate the benefit of this simulation platform with use over the course of resident spine rotations to improve planning and surgical competency

Purpose. Radiostereometric Analysis (RSA) is a well developed imaging technique used to estimate implant fixation of orthopaedic implants in randomized clinical trials. The precision of RSA depends on a number of factors including image quality related to the individual modality properties. This study assesses the precision of RSA with a novel Digital Radiography (DR) system compared to a CR imaging system using different imaging techniques. Additionally, the study assesses the precision of locating beads embedded in a modified spine pedicle screw. Method. A modified titanium spinal pedicle screw 4.5 mm diameter, 35 mm length, marked with two 1.0 mm tantalum beads, one inside the head and one near the screw tip was inserted into a bovine tibia segment. Six additional 1.0 mm tantalum beads were inserted into the bone segment – superiorly, distally and adjacent to the pedicle screw. The phantom was placed on a standard clinical diagnostic imaging bed above a custom RSA carbon fiber calibration cage (Halifax Biomedical Inc.). A pair of DR or CR imaging plates were placed below the calibration cage and irradiated 15 times at 100, 125 kV at 2.5 mAs. To determine precision, the standard deviation of 3D vector distances between beads was determined using RSA for each of the different imaging parameters. Results. The precision error (PE), defined as the standard deviation of the 3D Bone Marker marker locations for CR is 35.5 m for 100kV at 0.5 mAs setting and 42.2, 39.4, and 26.7 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. However, for DR, the PE is 27.5 m for 100kV at 0.5 mAs setting and 25.7, 25.1, and 20.1 m for the 2.5 mAs at 100, 125, and 150 kV settings. The PE for Screw Marker 3D locations, for CR is 38.2 m for the 100kV at 0.5 mAs setting and 55.2, 47.3, and 37.1 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. However for DR, the PE is 40.3 m for 100kV at 0.5 mAs setting and 33.2, 24.9, and 17.0 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. The PE for all Bone Marker and Screw Marker 3D locations were significantly lower (P<0.05) for the DR technology than the CR technology except at the 100kV at 0.5 mAs exposure of the Screw Marker, P = 0.589. Conclusion. The PE decreases for increasing kV, especially in the case of screw markers where the error goes from 33 micron (100kV) to 17 micron (150 kV). Increasing the mAs reduces the error for the DR, but increases the error for CR. Increasing the kV did not significantly influence the precision in measuring bead locations in bone. For embedded tantalum beads within a titanium pedicle screw, imaging at higher kV values with the described DR imaging system did allow more precise localization. The current phantom design is basic in nature and does not account for any soft tissue scatter. However, initial results indicate a gain in precision when using DR compared to CR imaging equipment for RSA analysis

Minimally invasive (MIS) screw fixation for Hangman's fracture can decrease iatrogenic soft-tissue injury compared with conventional open approach, but increase the risk of instrumentation-related complications due to lack of anatomical landmarks. With the advantages, the intra-operative three-dimensional fluoroscopy-based navigation (ITFN) system seems to be an inherent partner for MIS techniques. The purpose of this study was to evaluate the accuracy and feasibility of MIS techniques incorporating with ITFN for treating Hangman's fracture. 20 patients with Hangman's fracture underwent C2-C3 pedicle screw fixation using ITFN. 6 patients used MIS technique, with the other 14 patients using conventional open technique. Preoperative visual analogue score (VAS) was 5.7±1.4 in CAOS-MIS group and 5.5±0.9 in CAOS-open group. Operative time, blood loss and postoperative neurovascular complications were recorded. The accuracy of screw positions was studied by postoperative CT scan. All patients were followed up for at least 6 months and the fusion status was ascertained by dynamic radiographs. The average operative time was 134.2±8.0 min in CAOS-MIS group and 139.3±25.8 min in CAOS-open group, and there was no significant difference between the two (p&gt;0.01). The blood loss was 66.7±25.8 ml in CAOS-MIS group and 250.0±141.4 ml in CAOS-open group. Statistical difference existed with CAOS-MIS group significant less than CAOS-open group (p&lt;0.01). A total of 80 screws were inserted. No screw-related neurovascular injury was observed. Post-operative CT scan revealed 83.3% (20/24) screws of grade 1 and 16.7% screws of grade 2 (4/24) in CAOS-MIS group, meanwhile 89.3% screws of grade 1 (50/56) and 10.7% screws of grade 2 (6/56) in CAOS-open group. There was no grade 3 screw detected. Fisher's exact test showed there was no statistical difference between these two groups (p&gt;0.01). There was no statistical difference in pre-operative VAS between these two groups (p&gt;0.01). Compared with the CAOS-open group (1.7±0.6), neck pain VAS at 6-month follow-up in CAOS-MIS group (0.3±0.5) was significantly lower (p&lt;0.01). Solid fusion was demonstrated in all the cases by dynamic radiographs. So it is feasible and safe for percutaneous minimally invasive C2-C3 pedicle screw fixation for Hangman's fracture using intra-operative three-dimensional fluoroscopy-based navigation, which can also decrease the incidence of post-operative neck pain

Aim:. To review the use of traction x-rays under anaesthesia in Late Onset Scoliosis to correlate traction x-ray flexibility and postoperative correction using posterior nonsegmental all pedicle screw constructs. Methods:. Prospective study. Preoperative anteroposterior, lateral and side bending x-rays were done and Cobb angles were measured. Intraoperatively, traction anteroposterior x-rays were taken under anaesthesia and Cobb angles were measured. All patients underwent nonsegmental posterior all pedicle screw construct correction using Biomet implants. Cobb angles greater than 60 degees were included in the study. Calculations were done including correction rate, traction flexibility and traction correction index. Results were entered onto an excel spreadsheet and analyzed using Statistica software. Results:. 16 patients were studied, 3 boys and 13 girls, average age 14, ranging from 8 to 17 years. Preoperative Cobb angles were mean 82 (60 to 105) degrees. Traction x-rays mean Cobb angle was 42 degrees with mean traction flexibility rate 49%. Mean correction rate was 65% and mean traction correction index 106. Preoperative Cobb angles correlated with traction flexibility with a p value of 0.01. Traction x-rays Cobb angle correlated with the traction correction index (p = 0.003), postoperative x-rays (p = 0.000) and also with correction rate (p = 0.024). There was no correlation between preoperative Cobb angle and correction rate. Conclusion:. Traction x-rays under anaesthesia in late onset scoliosis are a good predictor of postoperative correction with posterior nonsegmental all pedicle screw constructs in curves greater than 60 degrees

Pedicle screw (PS) insertion has been critised for its risk of serious injury to neurovascular structures. Although computed tomography (CT)-based navigation has been developed to avoid such complications, perforation remains an issue, even with the aid of additional guidance. We clarify screw perforation rate and direction in 359 consecutive patients treated using CT-based PS insertion and present important considerations for more accurate screw placement. The medical records of 359 consecutive patients who underwent PS insertion involving C2-L5 using a CT-based navigation system were reviewed. Postoperative CT images were analysed to evaluate the accuracy of screw placement. We investigated both rate and direction of screw perforation according to vertebral level. Of the 3413 PS that were inserted, 3.0% (104/3413) were judged as Grade 3 (more than 4mm) perforations. Allover perforation rates by vertebral level were shown in Table 1. The rate of these perforations was 5.0% for C2, 7.8% for C3–5, 3.9% for C6–7, 3.4% for T1–4, 3.5% for T5–8, 1.4% for T9–12, and 1.7% for L1–5. We also analysed the odds ratio (OR) for screw perforation in vertebrae accounting for the effects of age and disease. Multivariate analysis identified that PS insertions at C3–5 (OR 4.9, 95% CI 2.2–10.9; p<0.001) were significantly associated with Grade 3 screw perforation as compared with that of L1–5. Even with CT-based navigation, careful insertion of PS is needed in the middle cervical spine because of a significantly higher perforation rate as compared with the lumbar region. For figures and tables, please contact authors directly

Pedicle screws fixation to stabilise lumbar spinal fusion is the gold standard for posterior stabilisation. Pedicle screws are today positioned in free hand or under fluoroscopic guidance with an error from 20% up to 40–50%, which can determine the inefficacy of treatment or severe damages to close neurologic structures. Surgical navigation drastically increases screws placement accuracy. However its clinical application is limited due to cost reasons and troubles related to the presence of a localiser in the OR and the need to perform a registration procedure before surgery. An alternative image guided approach is the use of patient specific templates similar to the ones used for dental implants or knee prosthesis. Until now, the proposed solutions allow to guide the drill, and in some cases, as templates fit completely around vertebra, they require the complete removal of soft tissues on a large portion of the spine, so increasing intervention invasiveness. To reduce the soft tissue demolition, some authors proposed a fitting based on small “V shape” contact points, but these solutions can determine instability of the template and the reacting of wrong stable positions. In our solution, after spine CT acquisition, each vertebra is segmented using a modified version of ITK-SNAP software, on which the surgeon plans screws positioning and finally the template is designed around the chosen trajectories, using a tool which allows to insert cylinders (full or empty) in the segmented images. Each template, printed in ABS, contains two hollow cylinders, to guide the screws, and multiple contact points on the bone surface, for template stabilisation. We made an in-vitro evaluation on synthetic spine models (by Sawbones) to study different template designs. During this first step an ongoing redesign allowed to obtain an optimal template stability and an easy template positioning to minimise the intervention invasiveness. A first contact point, which fits on the sides of the spinous process, is used to simplify template alignment. The other 4 contact points, which consists of cylinders (diameter 5 mm), fit exactly on spine surface in correspondence to the vertebra's lamina and articular processes to stabilise the template in an unique position. Templates can be used to guide not only the drill, but also Kirschner wires, to guide cannulated screws. After the Kirschner wires insertion the template can be dismounted for its removal (the direction of the kirschner wires are not parallel). After the definitive template design an ex-vivo animal test on 2 porcine specimens has been conducted to evaluate template performance in presence of soft-tissue in place. The specimens have been scanned with CT, we realised a total of 14 templates and we performed the insertion of 28 Kirschner wires. We evaluated that after the soft tissue dissection and the bone exposure, the template can be easily positioned in the right unique position, with no additional tissue removal compared to the traditional approach, requiring just removal of the soft tissue under the small contact points using an electric cutter. The surgeon evaluated (and corrected) some wrong stable template positions when not all the contact points were in contact with the bone surface. The post-op evaluation was made with a CT scan that showed 1 cortical pedicle violation (3.5%) (grade II according to the FU classification)

Purpose

Bone morphogenic protein (BMP-2) is used in spinal arthrodesis to induce bone growth. Studies have demonstrated that it achieves similar fusion rates compared to iliac crest bone graft when used in instrumented fusions. Our study aims at evaluating the requirement for instrumentation in one and two-level spinal arthrodeses when BMP-2 is used in conjunction with local bone to achieve fusion.

The purpose of this study is to evaluate risk factors for distal construct failure (DCF) in posterior spinal instrumented fusion (PSIF) in adolescent idiopathic scoliosis (AIS). We observed an increased rate of DCF when the pedicle screw in the lowest instrumented vertebra (LIV) was not parallel to the superior endplate of the LIV, however this has not been well studied in the literature. We hypothesise a more inferiorly angled LIV screw predisposes to failure and aim to find the critical angle that predisposes to failure. A retrospective cohort study was performed on all patients who underwent PSIF for AIS at the Starship Hospital spine unit from 2010 to 2020. On a lateral radiograph, the angle between the superior endplate of the LIV was measured against its pedicle screw trajectory. Data on demographics, Cobb angle, Lenke classification, instrumentation density, rod protrusion from the most inferior screw, implants and reasons for revision were collected. Of 256 patients, 10.9% (28) required at least one revision. The rate of DCF was 4.6% of all cases (12 of 260) and 25.7% of revisions were due to DCF. The mean trajectory angle of DCF patients compared to all others was 13.3° (95%CI 9.2° to 17.4°) vs 7.6° (7° to 8.2°), p=0.0002. The critical angle established is 11°, p=0.0076. Lenke 5 and C curves, lower preoperative Cobb angle, titanium only rod constructs and one surgeon had higher failure rates than their counterparts. 9.6% of rods protruding less than 3mm from its distal screw disengaged. We conclude excessive inferior trajectory of the LIV screw increases the rate of DCF and a screw trajectory greater than 11° predisposes to failure. This is one factor that can be controlled by the surgeon intraoperatively and by avoiding malposition of the LIV screw, a quarter of revisions can potentially be eliminated

In orthopaedic spine surgery pedicle screw systems are used for stabilisation of the spine after injuries or disorders. With an percutaneous operation method surgeons are faced with huge challenges compared to an open surgery, but it's less traumatic and the patient benefits with a faster rehabilitation and less traumatic injuries. The screw positions and the required rod dimensions for the stabilising connection between the screws are hard to define without an open view on the operating field. Because of these facts a new smart device based system for rod shape determination was invented. Therefore, an application was developed, which integrates a localiser module to get the position data of the pedicle screws, with help of rigid bodies placed on top of the pedicle screws down-tubes. An algorithm was developed to choose the best fitting rod to connect the pedicle screws with help of calculating the rod length and the rod radius. The system was tested in a test scenario where four pedicle screws were drilled into a wooden plate. The positions of the screws were adjusted to fit a curved and a straight rod. In the test scenario the application chose always the rod correctly