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

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

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

Pedicle screws allow for biomechanically secure fixation of the spine. However if they are misplaced they may effect the strength of the fixation, damage nerve roots or compromise the spinal cord. For these reasons image guidance systems have been developed to help with the accuracy of screw placement. The accuracy of pedicle screw placement outside the lumbar spine is not well published. To determine the accuracy of pedicle screw placement using CT scanning post operatively. Cortex perforations were graded in 2mm steps. Prospective observational study. Plain x-rays are inaccurate for determining screw placement and therefore high definition CT scanning was used. The screw positioning on the post-operative CT scans was independently determined by a research registrar who was not present at the time of surgery. Screw position and clinical sequelae of any malposition. Thirty patients (13 F:17 M) with segmental instability. Twelve were for metastatic disease, seven for trauma, seven for spondylolisthesis, three for atlanto-axial instability and one for a vertebral haemangioma. All patients were operated on by the senior author. One hundred and seventy six pedicle screws were inserted in the thirty patients over the 20 month study period. Six screws violated the lateral cortex of the pedicle but none perforated the medial cortex. There were no adverse neurological sequelae. The findings from this study will serve as a good comparison with future studies on pedicle screw placement, which may claim to improve accuracy and safety by the use of image guidance systems, electrical impedance or malleable endoscopes

Using post-operative CT analysis the clinical accuracy of computer-assisted fluoroscopy for the placement of thoracic (n=69) and lumbosacral (n=271) pedicle screws was assessed. All screws were placed using the Fluoro-Nav™ system (Medtronic Sofamor Danek, Memphis, TN, USA). Screw position was completely intrapedicular in 86.5%. There were no clinically significant screw misplacements. Pedicle breaches with a potential for neurological injury (> 2 mm; medial) was 0.6%. The overall pedicle screw misplacement rate in this study is less than or comparable to reported misplacement rates using other techniques. The use of computer-assisted fluoroscopy may improve the safety of pedicle screw placement. The purpose of this prospective study is to evaluate the clinical accuracy of computer-assisted fluoroscopy for the placement of thoracic (T) and lumbosacral (LS) pedicle screws. The overall thoracic and lumbar pedicle screw misplacement rate in this study is less than or comparable to reported misplacement rates using other techniques. The use of computer-assisted fluoroscopy may improve the safety of pedicle screw placement. Postoperative computed tomographs (CT) of three hundred and forty pedicle screws were independently reviewed. All screws were placed using the Fluoro-Nav™ system (Medtronic Sofamor Danek, Memphis, TN, USA). The relative position of the screw to the pedicle was assessed and graded as follows – A- completely in; B – < 2mm breach; C – 2–4mm breach; D – > 4–6mm breach. If an osseous breach occurred, the direction of the breach was further classified. Overall screw position was graded A in 86.5% (294/340) of screws (91.1 % (24/271) -lumbosacral and 68.1.0% (47/69)-thoracic). Forty-six pedicle breaches occurred (24 medial; 22 lateral). Thirty-five percent (16/46) of breaches were unavoidable secondary to a pedicle screw that was larger than the size of pedicle (thoracic-13). Pedicle breaches were Grade B in 11.8%, Grade C in 1.5% and Grade D in 0.3% of screws. There were no clinically significant screw misplacements. Pedicle breaches with a potential for neurological (> 2 mm; medial) or vascular injury was 0.6% and 0% respectively. FluoroNav™ appears to be a safe and practical adjunct for the placement of thoracic and lumbosacral pedicle screws. Funding: Medtronic-Sofamor Danek – research support

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

Background: Misplaced pedicle screws are associated with significant complications during posterior spinal instrumentation. Purpose: The purpose of this study is to evaluate the efficacy of triggered electromyographic stimulation in predicting the appropriate placement of pedicle screws. Study Design: Prospective clinical trial. Patient Sample: Fifteen consecutive patients (3 males; 12 females). Outcome Measures: Not applicable. Materials and Methods: All patients underwent posterior thoracolumbar spine fusion. Surgery was performed for spondylolisthesis, spinal stenosis, degenerative scoliosis and fractures. All patients received continuous electromyographic monitoring during surgery. During insertion of pedicle screws the integrity of the medial pedicle cortex was tested by stimulating each screw head with a monopolar pedicle probe stimulator and recording the compound muscle action potentials. A threshold of 7 mA and below was considered indicative of pedicle breach. Intraoperative screw placement was verified with the use of image intensifier. Finally, all patients following surgery underwent plain radiographs and CT scan of the operated region to evaluate the position of the pedicle screws. Results: One hundred and fourteen pedicle screws were inserted from T7 to S1 in all patients. There were no myogenic responses at the threshold tested. No screw had to be repositioned intraoperatively. There were no new neurologic deficits recorded following surgery. Review of the radiographs and CT scans obtained following surgery revealed no medial pedicle cortex breach. There were two screws that violated the lateral pedicle cortex, without any subsequent complications for the patients. Conclusions: Our study suggests that the absence of myogenic responses following stimulation at a threshold of 7 mA and below during pedicle screw placement, is a strong indicator that no medial pedicle cortex breach has occurred

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

To evaluate the clinical accuracy of computer-assisted fluoroscopy for the placement of percutaneous lumbosacral (LS) pedicle screws. A prospective computed tomographic (CT) analysis was performed in forty consecutive patients. Three independent observers were utilised. Postoperative CT scans of one hundred and fifty-nine titanium pedicle screws (n = 6(L3); thirty-eight(L4); sixty-five(l5) and fifty(S1)) were reviewed. All screws were percutaneously placed using the two-dimensional FluoroNavTM system. The relative position of the screw to the pedicle was graded as follows: I-completely in; II – < 2mm breach; III - = 2–4mm breach; IV – > 4mm breach. The direction of the breach was further classified as well as its trajectory. Correlation between observers was near perfect. The three observers rated 74.2%, 78.6%, and 78.0% of screws were completely contained within the pedicle. The data from the observer with the most significant pedicle breaches is as follows: thirty-five (22%) pedicle breaches (grade II -n=30; III - n=4; IV - n=1/n= 11 medial; n=19 lateral; 5 superior). Only one clinically significant breach occurred medially (grade III) at L5. This required screw revision (performed with a minimal access technique) with complete resolution of acute post-op L5 radiculopathy. The in-vivo percutaneous pedicle breach rate in this study was higher than that reported for similar open navigational techniques. The majority (85.7%) of breaches were minor (< 2mm) and over half (54.3%) were lateral with no potential for clinical squealae. This high lateral breach rate is due to a modified lateral starting point required for the percutaneous technique. However, there is concern that this technique resulted in one clinically significant medial breach and highlights the increased risk associated with percutatneous pedicle screw placement. The findings of this study suggest that improved screw placement accuracy for minimal access instrumented fusions is required

Introduction. A new triggered electromyography test for detection of stimulus diffusion to intercostal muscles of the contralateral side during thoracic pedicle screw placement was evaluated. Experimental research was carried out in order to determine if, using this test, neural contact at different aspects of the spinal cord and nerve roots could be discriminated. Methods. Nine industrial pigs (60–75 kg) had 108 pedicle screws placed bilaterally in the thoracic spine (T8–T13). Neural structures were stimulated under direct vision at different anatomic locations from T9 to T12. Recording electrodes were placed over the right and left intercostal muscles. Increasing intensity of the stimulus was applied until muscle response was detected at the contralateral side (diffusion phenomenon). After this first experiment, the thoracic spine was instrumented. Screws were placed in the pedicle in two different positions, the anatomic intrapedicular location and with purposeful contact with the neural elements. Results. Response thresholds to direct stimulation of nerve root at different points were significantly lower than those obtained by stimulation of the dorsal aspect of the spinal cord (0.44±0.22 mA vs 1.38±0.71 mA). However, a 24-fold stimulation intensity (6.50±0.29 mA) was necessary to obtain diffusion of the EMG response to the opposite left side if the right nerve root was stimulated. Only a 2-fold increment (3.17±0.93 mA) was able to elicit diffusion of EMG responses to the contralateral side when stimulation was applied to the dorsal aspect of the spinal cord. Contralateral EMG responses after high increases of stimulation thresholds indicated nerve root contact. Diffusion phenomenon after low threshold increments reflected medullar contact. Electromyography recordings after triggered stimulation of the screws showed that only screws in contact with the spinal cord had significantly lower responses (2.72±1.48 mA). Conclusion. Stimulus-triggered EMG could only discriminate screws with violation of the medial pedicle wall if they were contact with neural tissues. Recording EMG-potentials at the contralateral paraspinal muscles (stimulus diffusion phenomenon) proved to be a reliable method to discriminate which of the neural structures was at risk

The aim of this study was to assess the accuracy of pedicle screw placement using NAVITRAK, a system of Computer Assisted Orthopaedic Surgery and conventional fluoroscopic technique. Twelve porcine lumbar spines were scanned pre-operatively by computer tomography for 3-D reconstruction ( 1 mm slice thickness, 1mm increment and 2.5 mm pitch ). Computer randomisation divided the specimens between surgeons of different experience, and the two pedicles of each vertebral level between the two surgical techniques. Stainless steel screws (6.5 spongiosa) were inserted. Post-operatively, fluoroscopic- and CT imaging were blindly assessed for accuracy by two independent observers, and compared to macroscopic dissection of the spinal segments. Of 168 pedicles in 12 porcine specimens, 166 received a pedicle screw. Two pedicle screw placements were abandoned. Sixyty-one screws (73%) were placed satisfactorily with the CAOS system, 56 (67.5%) in the conventional group. In 26 pedicles the screws were placed unsatisfactorily (12 pedicles (46.2%) with the NAVITRAK system and 14 pedicles (53.8%) with the conventional technique. The NAVITRAK system in combination with stainless steel screws showed a difference of 5.5% in misplacement in favour for the computer assisted technique

Between 11/2005, and 9/2006 a first series of patients has undergone transpedicular instrumentation with 3D robotic assistance in the lumbar spine at our Orthopaedic Department. This technology must not be confused with standard spine navigation and will be presented in detail. 16 patients (12m, 4f, avg. age 55 yrs.) were randomly selected from our clientele for lumbar fusion or dynamic stabilization via transpedicular instrumentation. After informed consent they obtained thin slice CT scans of the operating field prior to surgery. The Mazor computer system then imported the scans, allowing 3-D planning of screw placement. A fixation device was then attached to the patient and the system was calibrated in connection with a standard fluoro-scope. On the device a robotic device with a working arm was mounted. Automatic matching algorithms then moved the robot, pointing its arm towards the designated pedicle screw portals. The screws could then be placed through the working arm, either cannulated (ICON) via K-wires, or solid (XIA) via standard awls. Percutaneous MIS insertion was also feasible. Instrumentation was then set forth after removal of the robot as usual. The CT accuracy of screw placement in all robot-assisted patients was scored according to Mattes et al. postoperatively. 1 patient had to be instrumented manually for reasons unrelated to the system. In 2 early obese patients the system denied robotic access due to insufficient imaging, thus enforcing standard manual technique. In the remaining patients a total of 58 screws had to be placed. No clinical complication related to the Mazor system occurred. A total of 6 screws could not be placed by the system due to steep lumbosacral angles. Additional time of surgery could be reduced to 40 minutes per case during the series. None of the robotic screws was misplaced in the final CT. 1 of the 6 non-robotic screws was misplaced at the S1 level and needed replacement due to apparent nerve contact without palsy. The robotic screws reached an average Mattes score of 1.5 which can be considered superior to sole fluoroscopic techniques (2.5). Additional decompression did not impede the system which does not rely on surface matching. On the basis of the clinical application, additional features were developed, e.g. robot mounting wedges for hyperlordosis, and oblique fluoro view acquisition. The planning software also avoids “supercharging” of the pedicle due to screw oversize. In one case this inevitably would have happened in conventional technique. This is the first report worldwide about the beginning of robotic assisted pedicle screw placement in Europe in daily routine. The Mazor System now has proven its usefulness and potential. Additional most recent data will be available at time of presentation as the system is further evolving and under continuous use

The aim of this study was to assess the accuracy of pedicle screw placement comparing Computer Assisted Orthopaedic Surgery equipment with conventional fluoroscopic technique. Twelve porcine cervical spines were scanned pre-operatively by computer tomography for 3D reconstruction (1 mm slice thickness, 1mm increment and 1 mm pitch). Computerised randomisation divided the specimens between surgeons of different experience, and the two pedicles of each vertebral level between the two surgical techniques. Stainless steel screws (6.5 diameter, spongiosa) were inserted. Post-operatively, fluoroscopic imaging was used for accuracy assessment by two independent observers, and findings were compared to macroscopic dissection of the spinal segments. Of 96 pedicles in 12 porcine specimens, 78 received a pedicle screw, 18 screw placements were abandoned, 38 (39.6%) were satisfactorily placed (19 in each, p> 0.05). 40 screws were misplaced, 18 (45%) with the NAVITRAK system vs. 22 (55%) with the conventional technique. These single factor results (all non-significant), were corroborated using a linear logistic regression model. Some heterogeneity in performance was detected between surgeons, independently of the type of technique used. Computer assisted surgery is an aiming device and is not advantageous over conventional methods in spines with high bone density

Pedicle screw fixation is an effective and reliable method for achieving stabilization in lumbar degenerative disease. The procedure carries a risk of violating the spinal and neural canal which can lead to nerve injury. This audit examines the accuracy of screw placement using intra-operative image guidance.

Retrospective audit of patients undergoing lumbar pedicle screw fixation using image guidance systems over an 18-month period. Case records were reviewed to identify complications related to screw placement and post-operative CT scans reviewed to study the accuracy of screw position.

Of the 98 pedicle screws placed in 25 patients, pedicle violation occurred in 4 screw placements (4.1%). Medial or inferior breach of the pedicle cortex was seen in 2 screws (2%). Nerve root injury as a consequence of this violation was seen in one patient resulting in irreversible partial nerve root dysfunction. Mean set up time for the guidance system was 42 minutes. The mean operative time was 192 minutes.

Violation of either the medial or inferior pedicle cortex during placement of fixation screws is a rare, but potentially serious complication bearing lasting consequences. Image-guided placement can be helpful and possibly improve accuracy; particularly in patients with distorted spinal anatomy.

Introduction: We have assessed the clinical observation that the angle of the contralateral lamina matches the angle required from the sagittal plane for the placement of pedicle screws in the subaxial cervical spine. Method: 54 axial CT scans were examined. All subjects were scanned for the exclusion of fracture between December 2003 and December 2004. The digitised images were analysed on the Philips PACS system using SECTRA software. 168 individual vertebrae were assessed between C3 and C7. The following were measured; the angle of the pedicle relative to the sagittal plane, the smallest internal and external diameter, the angle of the lamina and the distance from the lateral mass to the anterior vertebral body (LMAVB) in the line of the pedicle. Reproducibility was assessed in a subset of 10 individuals with paired measures using the FDA approved formula for CV%. Results: Angular measures had a CV% of 3.9%. The re-measurement error for distance was 0.5mm. 336 pedicles were assessed in 25 females and 29 males. Average age was 48.2 years (range 17–85). Our morphologic data from live subjects was comparable to previous cadaveric data. Mean pedicle external diameter was 4.9mm at C3 and 6.6mm at C7. Females were marginally smaller than males. Left and right did not significantly differ. In no case was the pedicle narrower than 3.2mm. Mean pedicle angle was 130 deg at C3 and 140 deg at C7. The laminar angle correlated well at C3,4,5 (R2> 0.7) and was within 1 deg of pedicle angle. At C6,7 it was within 11 deg. In all cases a line parallel to the lamina provided a safe corridor of 3mm for a pedicle implant. Conclusions: The contralateral lamina provides a reliable intraoperative guide to the angle from the sagittal plane for subaxial cervical pedicle instrumentation in adults

Computer assisted surgery is becoming more prevalent in spinal surgery with most published literature suggesting an improvement in accuracy and reduction in radiation exposure. This has been particularly highlighted in scoliosis surgery with regard to the placement of pedicle screws. Anecdotally this has been challenged with concerns with regard to the steep learning curve using this equipment and the high cost of purchasing said systems. The more traditional technique utilises the surgeon's knowledge of anatomic landmarks and tactile palpation added with fluoroscopy to place pedicle screws. We retrospectively looked at 161 scoliosis corrections performed using this technique over three years by 3 main surgeons at the same centre (Frenchay). With an average of 10 levels per procedure and over 2000 pedicle screws inserted. We reviewed the radiation time exposure and dose of radiation given during each case. Our results compared favourably to published data using computer and robot assisted surgery with an average exposure time of 80 seconds and a mean dose of 144 mGy using a standard C-arm guided fluoroscopy. Our study suggests that armed with good surgical knowledge and technique it is possible to obtained low levels of radiation exposure of benefit to both patient and the operating team

Introduction. The use of thoracic pedicle screws for the treatment of adolescent idiopathic scoliosis (AIS) has gained widespread popularity. Many techniques has been described to increase the accuracy of free hand placement; however the placement of pedicle screws in the deformed spine poses unique challenges because of possible neurologic and vascular complications. We are describing a universal way of insertion of pedicle thoracic screws which has been applied in many pathologies including the deformed spine. Methods. Our technique includes exposure of the superior facet of the corresponding body to identify its lateral border border which together with the superior border of the TP denotes our entry point which is just lateral to this crossing, we make a short entry with a straight Lenke probe then continue the track with a strong ball probe to go safely through the cancellous bone of the body. This is retrospective review of radiographs and clinical notes of all the patients who underwent posterior thoracic instrumentation by pedicle screws using the same single technique by one surgeon between June 2008 and December 2009; 1653 screws in 167 consecutive patients (119 females and 48 males). There were 139 deformities, 130 scoliosis (AIS 80, Congenital 31, Neuromuscular 10 and Degenerative 9), 19 kyphosis and 18 other diagnoses (fractures 14, revision 3 and tumour 1). Results. The recorded complications for all the patients were: 1 patient had pain due to nerve impingement, 1 parasthesia and 1 CSF leak intraoperatively. There were no revision of any of the screws, no vascular complications. Conclusion. Thoracic pedicle screws can be inserted with a universal point of entry using the same technique in all the levels of the dorsal spine. This technique seems to be simple and safe. Ethics approval: None. Interest Statement: None

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).

In the last few decades pedicle screw placement has brought in a genuine scientific revolution in the surgical care of spinal disorders. The technique has dramatically improved the outcomes of spinal reconstruction requiring spinal fusion. Short segment surgical treatments based on the use of pedicle screws for the treatment of neoplastic, developmental, congenital, traumatic and degenerative conditions have been proved to be practical, safe and effective. The reported incidence of nerve root damage after the use of pedicle screws ranges from 2% to 32%. The utilization of computerized image-guided technology in lumbosacral spinal fusion surgery offers increased accuracy of pedicle screw placement. We decided to review our x-rays of pedicle screw placement, and to assess the percentage misplacement of pedicle screws inserted without computer assistance. This is a retrospective study and our results are compared with those in the literature. 80 Post operative radiographs of patients operated on for trauma and degenerative conditions of the thoracolumbar spine were studied. Initially these were looked at independently by 2 orthopaedic spinal surgeons and a radiologist, and subsequently all x-rays were reviewed together to see where consensus could be reached where there was any disagreement. The percentage of misplaced screws inserted under fluoroscopy was obtained, and compared to the percentage of misplaced screws inserted under image guidance reported in the literature. Our study shows that there is no significant difference between the 2 techniques

Introduction. Pedicle screw fixation commonly uses a manual probe technique for preparation and insertion of the screw. However, the accuracy of obtaining a centrally located path using the probe is often dependent on the experience of the surgeon and may lead to increased complications. Fluoroscopy and navigation assistance improves accuracy but may expose the patient and surgeon to excessive radiation. DSG measures electrical conductivity at the tip and provides the surgeon with real-time audio and visual feedback based on differences in tissue density between cortical and cancellous bone and soft tissue. The authors investigated the effectiveness of DSG for training residents on safe placement of pedicle screws. Methods. 15 male cadaveric thoracolumbar spine specimens were fresh-frozen at the time of expiration. Residents were assigned 3 specimens each and randomised by pedicle side and order of technique for pedicle screw placement (free-hand versus DSG). Fluoroscopy and other navigation assistance were not used for pedicle preparation. All specimens were imaged using CT following insertion of all pedicle screws. The accuracy was assessed by a senior radiologist and graded as within (≤ 2mm breach) or outside (> 2mm breach) the pedicle. Results. 15 specimens were dissected in standard fashion to expose the thoracolumbar spine (T7-L5). 5 residents were randomised and assigned 3 specimens each to prepare bilateral pedicles from T8 to L5 (60 pedicles per resident) using either PediGuard or free-hand technique. A total of 249 pedicle screws were placed. Post-procedure CT scans demonstrated 214 (85.9%) screws within the pedicle. Breach rate for the DSG group was 8.2% and 19.7% for the non-DSG group, with an overall reduction of 58% (p=0.025). Conclusion. The use of Dynamic Surgical Guidance decreased the pedicle screw placement learning curve in residents, while improving breach rate by 58%. This study demonstrates that DSG has the potential for resident education and refinement in operative technique