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 evolution of operative technology has allowed correction of complex spinal deformities. Neurological deficits following spinal instrumentation is a devastating complication and the risk is especially high in those with complex sagittal and coronal plane deformities. Prior to intraoperative evoked potential monitoring, spinal cord function was tested using the Stagnara Wake up test, typically performed after instrumentation once the desired correction has been achieved. This test is limited as it does not reflect the timeframe in which the problem occurred and it may be dangerous to some patients. Intraoperative neuromonitoring allows timely feedback of the effect of instrumentation and curve correction on the spinal cord. Pedicle screws that are malpositioned can result in poor fixation or neuronal injury. Evoked EMG monitoring can aid in accurate placement. A positive EMG response can alert the surgeon to a potential pedicle breech and allow them to reassess the placement of their hardware intraoperatively. The stimulation threshold is affected by the amount of surrounding bone acting as an insulator to electrical conduction and is variable in different regions of the spine. In the non-deformed, lumbar spine stimulation thresholds have been established. Such guidelines have not been well-developed for the thoracic spine, or for severely scoliotic spines. Thus our primary objective was to compare the stimulation threshold of the apical pedicle on the concave side to the stimulation threshold of the pedicles at the upper and lower instrumented levels. Intraoperative EMG stimulation thresholds were done at 192 apical pedicles on the concave side of the deformity and then compared to those thresholds found at 169 terminal level pedicles. Only pedicles for which a stimulation threshold was found were reported and excluded those where a breech was suspected. The lowest stimulation required for an EMG response was documented to a maximum stimulation of 20 mA. The mean threshold at the apex was 16.62 milliamps (mA) compared to 18.25mA at the terminal levels. This was compared with the t-test and showed a statistically significant difference (p<0.05). In this study we report only the thresholds for the concave side, the pedicle that is most likely to be reduced in size. The threshold for stimulation is reduced compared to those seen at the highest and lowest instrumented level. Most of the apexes are located in the mid-thoracic spine with the highest instrumented levels being in the high thoracic spine and the lowest levels being in the lumbar spine. This study provides preliminary evidence that the apical, concave pedicle has a lower threshold than the end pedicles and one cannot rely on established thresholds from different areas of the spine. The surgeon should be cognisant of these differences when instrumenting at the apical level. Ongoing work is examining the convex apex threshold as well as the relationship between the effect of age and a diagnosis other than adolescent idiopathic scoliosis

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.

Inserting screws into the vertebral pedicles is a challenging step in spinal fusion and scoliosis surgeries. Errors in placement can lead to neurological complications. The more experienced the surgeon, the better the accuracy of the screw placement. A physical training system would provide residents with the feel of performing pedicle cannulation before operating on a patient. The proposed system consists of realistic bone models mimicking the geometry and material properties of typical patients, coupled with a force feedback probe. The purpose of the present study was to determine the forces encountered during pedicle probing to aid in the development of this training system. We performed two separate investigations: [1] 15 participants (9 expert surgeons, 3 fellows and 3 residents) were asked to press a standard pedicle awl three times onto a mechanical scale, blinded to the force, demonstrating what force they would apply during safe pedicle cannulation and during unsafe cortical breach; [2] three experienced surgeons used a standard pedicle awl fitted with a one-degree of freedom load cell to probe selected thoracolumbar vertebrae of eight cadaveric specimens to measure the forces required during pedicle cannulation and deliberate breaching. A total of 42 pedicles were tested. Both studies had wide variations in the results, but were in general agreement. Cannulation (safe) forces averaged approximately 90 N (20 lb) whereas breach (unsafe) forces averaged approximately 135–155 N (30–35 lb). The lowest average forces in the cadaveric study were for pedicle cannulation, averaging 86 N (range, 23–125 N), significantly lower (p<0.001) than for anterior breach (135 N; range, 80–195 N); medial breach (149 N; range, 98–186 N) and lateral breach (157 N; range, 114–228 N). There were no significant differences between the breach forces (p>0.1). Cannulation forces were on average 59% of the breach forces (range, 19–84%) or conversely, breach forces were 70% higher than cannulation forces. To our knowledge, these axial force data are the first available for pedicle cannulation and breaching. A large range of forces was measured, as is experienced clinically. Additional testing is planned with a six-degree-of-freedom load cell to determine all of the forces and moments involved in cannulation and breaching, throughout the thoracolumbar spine. These results will inform the development of a realistic bone model as well as a breach prediction algorithm for a physical training system for spine surgery

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

Pedicle screw systems are now the commonest method of achieving posterior spinal fixation. Surgical planning in spinal surgery may include measuring pedicle size to guide screw size on WEBPACS. We performed a study to determine whether measuring pedicle size on CT is accurate and reproducible using the WEBPACS ruler tool. A human cadaveric spine along with 5 geometrical shapes were scanned using a multislice spiral CT scanner with 1mm cuts. The objects and the pedicle diameters for lumbar and thoracic vertebrae in the axial plane were measured independently using the WEBPACS ruler tool by 2 observers (to the nearest 0.1mm). The geometrical shapes and pedicle size on the skeleton were then measured using Vernier callipers by an independent third observer. All measurements were repeated a week later. The WEBPACS ruler on a CT scan is accurate to within 0.5-0.6mm of the true size of an object. The error for pedicle measurements is marginally higher (0.6-1.0mm) and this may reflect the fact that they are ill defined geometric shapes. Measuring pedicle size on CT for surgical planning may have implications for small pedicles when sizing them up for a good screw

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

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

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

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

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

In posterior fixation for deformity correction and spinal fusion, there is increasing discussion around auxiliary rods secured to the pedicle screws, sharing the loads, and reducing stresses in the primary rods. Dual-rod, multiaxial screws (DRMAS) provide two rod mounting points on a single screw shaft to allow unique constructs and load-sharing at specific vertebrae. These implants provide surgical flexibility to add auxiliary rods across a pedicle subtraction osteotomy (PSO) or over multiple vertebral levels where higher bending loads are anticipated in primary rods. Other options include fixed-angle devices as multiple rod connectors (MRC) and variable-angle dominoes (VAD) with a single-axis rotation in the connection. The objective in this simulation study was to assess rod bending in adult spinal instrumentation across an osteotomy using constructs with DRMAS, MRC, or VAD multi-rod connections. The study was performed using computer biomechanical models of two adult patients having undergone posterior instrumented spinal fusion for deformity. The models were patient-specific, incorporating the biomechanics of the spine, have been calibrated to assess deformity correction and intra- and postoperative loads across the instrumented spine. One traditional bilateral-rod construct was used as a control for six multi-rod configurations. Spinal fixation scenarios from T10 through S1 with the PSO at L4 were simulated on each patient-specific model. The multi-rod configurations were bilateral and unilateral DRMAS at L2 through S1 (B-DRMAS and U-DRMAS), bilateral DRMAS at L3 and L5 (Hybrid), bilateral MRC over L3-L5, bilateral and unilateral VAD over L3-L5 (B-VAD and U-VAD). Postoperative gravity plus 8-Nm flexion and extension loads were simulated and bending moments in the rods were computed and compared. In the simulated control for each case (#1 & #2), average rod bending moments (of the right and left rods) at the PSO level were 6.7Nm & 5.5Nm, respectively, in upright position, 8.8Nm & 7.3Nm in 8-Nm flexion, and 4.6Nm & 3.7Nm in 8-Nm extension. When the primary rods of the multi-rod constructs were normalized to this control, the bending moments in the primary rods of Case #1 & #2 were respectively 57% & 58% (B-DRMAS), 54% & 62% (B-VAD), 60% & 61% (MRC), 72% & 69% (Hybrid), 81% & 70% (U-DRMAS), and 81% & 73% (U-VAD). Overall, the reduction in primary rod bending moments ranged from 19–46% for standing loads. Under simulated 8-Nm functional moments, the primary rod moments were reduced by 18–46% in flexion and 17–48% in extension. More rods and stiffer connections produced the largest reductions for the primary rods, but auxiliary rods had bending moments that varied from 49% lower to 13% higher than the primary ones. Additional rods through DRMAS, MRC, and VAD connections noticeably reduced the bending loads in the primary rods compared with a standard bilateral-rod construct. Yet, bending loads in the auxiliary rods were higher or lower than those in the primary rods depending on the 3D spinal deformity and stiffness of the auxiliary rod connections. Additional studies and patient-specific analyses are needed to optimize instrumentation parameters that may improve load-sharing in these constructs

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

Introduction. Pedicle subtraction osteotomy is a powerful technique for correcting sagittal imbalance in ankylosing spondylitis. There has been significant perioperative morbidity associated with this technique in the peer review literature. We present the Royal National Orthopaedic Hospital experience with a single surgeon retrospective study that was conducted to evaluate the outcomes in patients who underwent lumbar pedicle subtraction osteotomy for the correction of thoracolumbar kyphotic deformity in ankylosing spondylitis. Method. Twenty seven patients underwent a lumbar pedicle subtraction osteotomy and adjacent level posterior instrumentation between 1995 and 2010. There were 18 males and 9 females in the study. Events during the peri-operative course and post-operative complications were recorded. The radiological outcome and patient satisfaction were analysed with mean follow-up of one and a half years. Results. The mean operative time was three and half hours and the mean blood loss was 2290mls. Final follow-up radiograph showed an increase in lumbar lordosis angle from 17 degrees to 45 degrees. The sagittal imbalance improved by 85mm with the operation. Complications included loosening in two patients, one transient neurologic deficit and one infective non-union occurred overall. There were no mortalities from the surgery. Two patients developed junctional kyphosis and required a repeat operation. There was an improvement in the Oswestry Disability Score from a mean of 29 to 16 after the surgey. All (100%) of the patients were satisfied with the results of the procedure and would recommend the surgey to others. Conclusion. The study shows that pedicle subtraction extension osteotomy is effective for the correction of kyphotic deformity in ankylosing spondylitis

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

Introduction. Pedicle Subtraction osteotomy (PRO) in correction of severe spinal deformities is well established. Prospective analysis of its efficacy in complex spinal deformities is sparse in literature. Aims and objectives. To assess the role of PRO in correction of uniplanar and multiplanar spinal deformity and to assess the role of revision PRO in failed corrections. Material and methods. 50 patients were operated between 1996-2007 and followed up for 2 years (2-6). 27 had uniplanar kyphosis (60-128 degrees) and kyphoscoliosis was seen in 10. Failed corrections were seen in 11 uniplanar and 2 multiplanar deformities. The average pre-operative kyphosis and sagittal balance was 78.7 degrees and 22 mm (7-30) respectively. Scoliotic deformity ranged from 97-138 (average 108 degrees) and the coronal imbalance from 10-55 (average 24mm). Deformity distribution was upper dorsal 5, mid dorsal 22, dorso-lumbar 18 and lumbar 5. A single posterior approach sufficed in 47 cases while 3 required an anterior approach for reconstruction. 13 patients had pre-operative neurological deficit (bedridden 10, ambulatory 3). The average surgical time required was 300 minutes and blood loss was 800cc. The anterior defect reconstructed averaged 16.5mm (5-28). Results. Pulmonary complications occurred in 8 (21%), (embolism 1, pneumonia 2, hypoxia 5). Wound infection required debridement in 3 (8%). Failed corrections were seen in 10 (3 out of 37 in our series, 8%) due to failure of construct 2, severe disease 2, infection (active 2, quiescent 4). Neurological deterioration occurred in 1(2%), medial pedicle wall perforation. 12 patients regained ambulation (independent 7, support 5). Post-operative kyphosis and sagittal balance was 36.5 (10-108) and 10mm (5-20) respectively. Average correction was: sagittal 46.4%, coronal 37.5% and revisions 58%. The correction of kyphosis and sagittal balance was statistically comparable between primary and revision cases (p >0.05). Conclusions. PRO offers an excellent single stage decompression and controlled correction of kyphosis

Fracture neck of femur with delayed presentation in young patients can be a surgical challenge. Such scenarios are rare in the developed world but not uncommon in developing countries. To present the medium term results of open reduction and internal fixation accompanied by Quadratus Femoris muscle pedicle grafting in young patients who presented with a delay after sustaining a fracture neck of femur, 42 patients with fracture neck of femur with delayed presentation were treated with open reduction and internal fixation and supplemented with Quadratus Femoris muscle pedicle graft. A posterior approach was used in all cases. The patients were advised not to bear weight until there was clinical and radiological union. Functional recovery was assessed by gait and ability to squat on the floor. The age of the patients, predominantly male, ranged from 24 yrs to 50 yrs. Radiological union occurred on average at 6 months. Thirty-six patients proceeded to union; six patients had non-union and needed revision surgery. Complications included varus union in 9 cases; shortening greater than 2 cms occurred in 6 cases. Quadratus Femoris muscle pedicle grafting described by Meyer in the 1970s is useful in treating fracture neck of femur. Open reduction and internal fixation of the fracture neck of femur when supplemented with Quadratus Femoris muscle pedicle graft fixation promoted the union of fracture and preserved the head the femur

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

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)