Percutaneous placement of pedicle screws is a well-established technique, however, no studies have compared percutaneous and open placement of screws in the thoracic spine. The aim of this cadaveric study was to compare the accuracy and safety of these techniques at the thoracic spinal level. A total of 288 screws were inserted in 16 (eight cadavers, 144 screws in percutaneous and eight cadavers, 144 screws in open). Pedicle perforations and fractures were documented subsequent to wide laminectomy followed by skeletalisation of the vertebrae. The perforations were classified as grade 0: no perforation, grade 1: < 2 mm perforation, grade 2: 2 mm to 4 mm perforation and grade 3: > 4 mm perforation. In the percutaneous group, the perforation rate was 11.1% with 15 (10.4%) grade 1 and one (0.7%) grade 2 perforations. In the open group, the perforation rate was 8.3% (12 screws) and all were grade 1. This difference was not significant (p = 0.45). There were 19 (13.2%) pedicle fractures in the percutaneous group and 21 (14.6%) in the open group (p = 0.73). In summary, the safety of percutaneous fluoroscopy-guided pedicle screw placement in the thoracic spine between T4 and T12 is similar to that of the conventional open technique. Cite this article: Bone Joint J 2015;97-B:1555–61

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.

To determine if there is a safe osseous corridor for trans-sacroiliac screw fixation of U-type sacral fractures using fluoroscopic landmarks.

We reviewed the sacral anatomy of patients who underwent Computed Tomography (CT) investigations between October and December 2009. Agfa-IPMAX Version 5.2 software was used to determine if there was a trans-sacroiliac osseous corridor in the S1 and S2 vertebrae from one ilium to the other.

76 patients were in the study, 38 male and 38 female. Exclusion criteria were patients under 18 years old; patients with degenerate lumbar spine and lumbo-sacral junction; CT imaging slices greater than 2.5mm.

We measured various parameters including the dimensions of the S1 and S2 mid-sagittal vertebral body; cross-sectional areas of the S1 and S2 corridor; location of the centre of the S1 and S2 corridor.

The mean cross-sectional area for S1 and S2 corridors in males and females are 21mm² and 15mm² respectively. The mean cross-sectional area for the S2 corridor in males and females were 15mm² and 11mm² respectively. The centre of the S1 and S2 corridor is located in the centre of both S1 and S2 vertebrae.

Two-thirds of males and females have a complete osseous corridor to pass a trans-sacroiliac S1 screw. The S2 corridor was present in all males but only in 87% of females. Before placement of trans-sacroiliac screws, the surgeon should review the CT sacral anatomy to determine if the trans-sacroiliac osseous corridor is present.

Ethics Approval: None – Audit Interest Statement: None

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.

Aims. The aim of this study was to assess the accuracy of pedicle screw placement, as well as intraoperative factors, radiation exposure, and complication rates in adult patients with degenerative disorders of the thoracic and lumbar spines who have undergone robotic-navigated spinal surgery using a contemporary system. Methods. The authors reviewed the prospectively collected data on 196 adult patients who had pedicle screws implanted with robot-navigated assistance (RNA) using the Mazor X Stealth system between June 2019 and March 2022. Pedicle screws were implanted by one experienced spinal surgeon after completion of a learning period. The accuracy of pedicle screw placement was determined using intraoperative 3D fluoroscopy. Results. A total of 1,123 pedicle screws were implanted: 1,001 screws (89%) were placed robotically, 63 (6%) were converted from robotic placement to a freehand technique, and 59 (5%) were planned to be implanted freehand. Of the robotically placed screws, 942 screws (94%) were determined to be Gertzbein and Robbins grade A with median deviation of 0.8 mm (interquartile range 0.4 to 1.6). Skive events were noted with 20 pedicle screws (1.8%). No adverse clinical sequelae were noted in the 90-day follow-up. The mean fluoroscopic exposure per screw was 4.9 seconds (SD 3.8). Conclusion. RNA is highly accurate and reliable, with a low rate of abandonment once mastered. No adverse clinical sequelae occurred after implanting a large series of pedicle screws using the latest generation of RNA. Understanding of patient-specific anatomical features and the real-time intraoperative identification of risk factors for suboptimal screw placement have the potential to improve accuracy further. Cite this article: Bone Joint J 2023;105-B(5):543–550

Aims. Minimally invasive transforaminal lumbar interbody fusion (MITLIF) has been well validated in overweight and obese patients who are consequently subject to a higher radiation exposure. This prospective multicentre study aimed to investigate the efficacy of a novel lumbar localisation system for MITLIF in overweight patients. Patients and Methods. The initial study group consisted of 175 patients. After excluding 49 patients for various reasons, 126 patients were divided into two groups. Those in Group A were treated using the localisation system while those in Group B were treated by conventional means. The primary outcomes were the effective radiation dosage to the surgeon and the exposure time. Results. There were 62 patients in Group A and 64 in Group B. The mean effective dosage was 0.0217 mSv (standard deviation (. sd. ) 0.0079) in Group A and 0.0383 mSv (. sd. 0.0104) in Group B (p <  0.001). The mean fluoroscopy exposure time was 26.42 seconds (. sd. 5.91) in Group A and 40.67 seconds (. sd. 8.18) in Group B (p < 0.001). The operating time was 175.56 minutes (. sd. 32.23) and 206.08 minutes (. sd. 30.15) (p < 0.001), respectively. The mean pre-operative localisation time was 4.73 minutes (. sd. 0.84) in Group A and 7.03 minutes (. sd. 1.51) in Group B (p < 0.001). The mean screw placement time was 47.37 minutes (. sd. 10.43) in Group A and 67.86 minutes (. sd. 14.15) in Group B (p < 0.001). The pedicle screw violation rate was 0.35% (one out of 283) in Group A and 2.79% (eight out of 287) in Group B (p = 0.020). Conclusion. The study shows that the localisation system can effectively reduce radiation exposure, exposure time, operating time, pre-operative localisation time, and screw placement time in overweight patients undergoing MITLIF. Cite this article: Bone Joint J 2017;99-B:944–50

We undertook a retrospective study investigating the accuracy and safety of percutaneous pedicle screws placed under fluoroscopic guidance in the lumbosacral junction and lumbar spine. The CT scans of patients were chosen from two centres: European patients from University Medical Center Hamburg-Eppendorf, Germany, and Asian patients from the University of Malaya, Malaysia. Screw perforations were classified into grades 0, 1, 2 and 3. A total of 880 percutaneous pedicle screws from 203 patients were analysed: 614 screws from 144 European patients and 266 screws from 59 Asian patients. The mean age of the patients was 58.8 years (16 to 91) and there were 103 men and 100 women. The total rate of perforation was 9.9% (87 screws) with 7.4% grade 1, 2.0% grade 2 and 0.5% grade 3 perforations. The rate of perforation in Europeans was 10.4% and in Asians was 8.6%, with no significant difference between the two (p = 0.42). The rate of perforation was the highest in S1 (19.4%) followed by L5 (14.9%). The accuracy and safety of percutaneous pedicle screw placement are comparable to those cited in the literature for the open method of pedicle screw placement. Greater caution must be taken during the insertion of L5 and S1 percutaneous pedicle screws owing to their more angulated pedicles, the anatomical variations in their vertebral bodies and the morphology of the spinal canal at this location. Cite this article: Bone Joint J 2015; 97-B:1111–17

INTRODUCTION. The correct placement of pedicle screws is a major part of spine fusion and it requires experienced trained spinal surgeons. In the era of European Working Time Directive (EWTD), surgical trainees have less opportunity to acquire skills. Josh Kauffman (Author of The First 20 Hours) examined the K. Anders-Ericsson study that 10,000 hours is required to be an expert. He suggests you can be good at anything in 20 hours following 5 methods. This study was done to show the use of accelerated learning in trainees to achieve competency and confidence on the insertion of pedicle screws. METHODS. Data was collected using 3 experienced spine surgeons, 8 trainees and 1 novice (control) on the cadaveric insertion of pedicle screws over a 4 day didactic lecture in the cadaver lab. Each candidate had 2 cadavers and 156 screw placements over 4 hour shifts. Data was collected for time of pedicle screw insertion for each level on the left and right side. A pre-course and post-course questionnaire (Likert scale) was conducted. RESULTS. There were 8 candidates (surgeons) involved. 1 spinal SpR, 6 spine fellows and 1 junior consultant. A physiotherapist was the control novice. The surgeons and the control got significantly faster over time. The control made significantly more errors than the surgeons. Surgeons were significantly faster by the end (p value < 0.05). The control got faster over time and by the end, was no longer significantly slower than the surgeon when they first started. CONCLUSION. Pedicle screw insertion can cause significant morbidity, which includes paralysis. As a trainee, this is not an easy skill to acquire or practice. This focused pedicle screw course shows that a junior spinal surgeon can achieve improved competency and confidence in 20 hours but furthermore a complete novice can learn to insert pedicle screws and reach a level of competence almost at the level of the trainee in 20 hours as well

Pedicle screws as the principal anchors of instrumentation in correction of scoliosis as described by Suk 15 years ago have now gained a wide acceptance among deformity surgeons. Pedicles in the concavity of the major as well as compensatory curves are often dysplastic making screw placement occasionally problematic. In cases of dural ectasia with dystrophic pedicles, the transpedicular screw anchorage is sometimes impossible. In 2009 Gardner et al. presented a case of NF-1 with a troublesome cervico-thoracic kyphosis where they created distal anchors by means of laminar screw fixation. In the presentation of this case, the idea is further developed. Case. A 14 year old girl without any obvious syndromic feature underwent surgery for a 70 degree thoracic scoliosis. A preoperatively MRI showed a dural ectasia. A preoperative low dose–CT revealed dystrophic pedicles from Th4 to L4, making transpedicular screw placement problematical. The operation was performed with the aid of an O-arm. At all levels from Th2 – L2 laminar screw fixation was used. Postoperatively, low-dose CT showed excellent screw positioning with the exceptiuon of one proximal screw which compromised a foramem but, without any symptoms. The postoperative course was quite uneventful and the patient was discharged at day 5days postoperatively. The correction rate was 70%. Conclusion. In cases of scoliosis with severe dystrophic pedicles, the use of laminar screws is a good alternative to problematic transpedicular screw placement

Introduction. We prospectively examined the effect of pedicle screw placement at a young age (<5 years) for early-onset spinal deformity on the growth and development of pedicles and the spinal canal. Methods. Patients with early-onset deformity who received pedicle screw placement before the age of 5 years and had preoperative and final follow-up axial imaging were included. To increase sample size, patients who had the same criteria but with no preoperative axial images were also included. Anteroposterior and transverse diameters of the canal and pedicle length were measured on axial images cutting through the middle of the pedicle (figures 1 and 2). Results. 13 patients (five male, eight female) met inclusion criteria. Average age at surgery was 46·6 months (29–60), and average follow-up 49·8 months (24–82). 77 instrumented and 32 non-instrumented levels were studied. The table summarises measurements. In the nine patients without preoperative axial imaging, pedicle lengths and canal diameters seemed to accord with previously published normative morphological data for this age group. Conclusions. Animal studies have shown the potential slowing of pedicle and canal growth in immature spines with pedicle screws. This is the first study to examine the behaviour of instrumented immature human vertebrae prospectively. Early application of pedicle screws does not seem to cause adverse effects on pedicle and canal growth in young patients. This discordance between human and animal studies may have three explanations: (1) although the neurocentral cartilage is still visible it may not be physiologically active in this age group; (2) a single screw across may not exert sufficient compression; (3) or the canal may have means of remodelling that is yet not known

Study design. Retrospective study. Objectives. To optimise the radiation doses and image quality for the cone-beam O-arm surgical imaging system in spinal surgery. Summary of Background. Neurovascular compromise has been reported following screw misplacement during thoracic pedicle screw insertion. The use of O-arm with or without navigation system during spinal surgery has been shown to lower the rate of screw misplacement. The main drawback of such imaging surgical systems is the high radiation exposure. Methods. Chest phantom and cadaveric pig spine were examined on the O-arm with different scan settings: two were recommended by the O-arm manufacturer (120 kV/320 mAs, and 120 kV/128 mAs), and three low-dose settings (80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs). The radiation doses were estimated by Monte Carlo calculations. Objective evaluation of image quality included interobserver agreement in the measurement of pedicular width in chest phantom and assessment of screw placement in cadaveric pig spine. Results. The effective dose/cm for 120 kV/320 mAs-scan was 13, 26, and 69 times higher than those delivered with 80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs-scans, respectively. Images with 60 kV/40 mAs were unreliable. Images with 80 kV/80 mAs were considered reliable with good interobserver agreement when measuring the pedicular width (random error 0.38 mm and intraclass correlation coefficient 0.979) and almost perfect agreement when evaluating the screw placement (κ-value 0.86). Conclusions. The radiation doses of the O-arm system can be reduced 5–13 times without negative impact on image quality with regard to information required for spinal surgery

Aims

To report the development of the technique for minimally invasive lumbar decompression using robotic-assisted navigation.

To determine whether neurophysiological electrical pedicle testing (EPT) is a useful aid in the detection of malpostioned pedicle screw tracts. EPT data from 246 screws in 32 spinal operations on 32 patients over a 5 year period (2009–2014) were recorded and analysed. In addition to physical palpation, a ball-tipped electrode delivered stimuli and the output was recorded by evoked electromyogram (EMG). When breach threshold values were recorded, the surgeon rechecked the tract for breaches and responded appropriately. In addition, standard motor evoked potential (MEP) and sensory evoked potential(SEP) spinal cord monitoring was performed. There were 24(9.8%) pedicle breaches by tract testing and 8(3.3%) by screw testing. In 11 instances in 7 patients where the tract testing showed a breach, the tract was redirected and subsequent screw testing showed adequate integrity of the pedicle. The total time for tract and screw testing was 25 seconds. There were no associated changes in MEP or SEP monitoring with any of the recorded pedicle breaches and none of the patients had any post-operative neurological deficit. EPT for the pedicle screw and tract is a safe, simple, practical and reliable technique which improves the accuracy of screw placement. Further studies would be required to confirm (and possibly revise) the threshold levels and to demonstrate whether EPT reduces the risk of misplaced screws or post-operative neurological deficit

Aims

The aim of this study was to investigate the impact of the level of upper instrumented vertebra (UIV) in frail patients undergoing surgery for adult spine deformity (ASD).

Different methods of lateral mass(LM) screw placement in the cervical spine have been described. In the axial plane, 30 degrees is the recommended angle to avoid neurovascular injury. The estimation of this angle remains arbitrary and operator dependant. To assess how accurately the lateral trajectory angle (LTA) for cervical LM screws is achieved by visual estimation amongst experienced spinal surgeons. A sawbone model of cervical spine with simulated lordosis was used. Five spinal consultants and five senior spinal fellows were asked to insert 1.6 mm K wires into lateral masses of C3 to C6 bilaterally to simulate screws. The LTA in transverse plane was measured using a customised protractor. Basic statistical analyses of all the data were obtained. Using all the angles derived, a virtual screw trajectory was drawn in the lateral plane, on a normal axial Computerised Tomography scan of cervical spine of an anonymous patient using PACS system. The overall mean LTA for the group was 25.15 degrees, that of the fellows 24.4 and consultants 26.2 degrees. Mean deviation from 30 degrees for fellows was 5.2 and 6.4 degrees for consultants. Overall standard deviation was 4.78, for fellows and consultants it was 3.3 and 5.8 respectively. Two episodes of vertebral artery injury occurred at 15 and 16 degrees with simulated angles on CT. A moderate variability in visual estimation of the trajectory angle exists even amongst experienced surgeons during insertion of cervical LM screws. An anatomical landmark would be useful to improve the reliability of the procedure

To describe a modification of the existing technique for C2 translaminar screw fixation that can be used for salvage in difficult cases. Bilateral crossing C2 laminar screws have recently become popular as an alternative technique for C2 fixation. This technique is particularly useful in patients with anomalous anatomy, as a salvage technique where other modes of fixation have failed or as a primary procedure. However, reported disadvantages of this technique include breach of the dorsal lamina and spinal canal, early hardware failure and difficulty in bone graft placement due to the position of the polyaxial screw heads. To address some of these issues, a modified technique is described. In this technique, the upper part of the spinous process of C2 is removed and the entry point of the screw is in the base of this removed spinous process. From October 2008 to March 2009, 6 patients underwent insertion of unilateral translaminar screws using our technique. The indications were: basilar invagination(three cases), C1/C2 fracture (two cases), tumour (one case). Age varied from 22 to 81 years (mean 48 years). All patients had post-operative x-ray and CT scan to assess position of the screws. Mean follow-up was 6 months. The screw position was satisfactory in all patients. There were no intraoperative or early postoperative complications. Our modification enables placement of bone graft on the C2 lamina and is also less likely to cause inadvertent cortical breach. Because of these advantages, it is especially suitable for patients with advanced rheumatoid arthritis with destruction of the lateral masses of C2 or as part of a hybrid construct in patients with unilateral high riding vertebral artery. This technique is not suitable for bilateral translaminar screw placement

Introduction. Recently published results suggest insertion of shorter screws in L5/S1 stand-alone anterior interbody fusion, fearing S1 nerve root violation. However, insertion of shorter screws led to screw fixation failure and new onset of S1 body fractures. Material and Methods. Retrospective review of patients with L5/S1 stand-alone anterior interbody fusion, focussing on screw length, radiological outcomes (especially metal work failure, screw fixation and S1 body fractures) and new onset of S1 nerve root irritation. Results. 38 patients were included (mean age 46.2±13.3 years, 21 females, 17 males). Fusion of the L5/S1 segment was performed in between 2003-2010; postoperative follow-up ranged from 2-24 months. 15 patients had multilevel surgery (7 multiple segmental fusion, 8 hybrid procedures). Screw length ranged from 20-30 mm. No patient had new postoperative S1 nerve root irritation. Interestingly, 2 patients out of the hybrid group had a new onset of L5 radiculopathy, concordant to the level of disc-replacement. Follow-up x-ray review showed no fracture of S1 body fractures in all patients. No evidence of screw loosening, migration or metal work failure was reported. Conclusion. In our opinion, this review showed that insertion of longer screws for stand-alone anterior interbody fusion in L5/S1 is safe. Longer screws offer better stabilization and seem to minimize risks like S1 body fractures. Short and long-term follow-ups were satisfactory regarding screw placement, migration and positioning of implants in all patients

Purpose. Posterior lumbar fusion using minimally invasive surgical (MIS) techniques are reported to minimise postoperative pain, soft tissue damage and length of hospital stay when compared to the traditional open procedure. Methods. This is a review of patients who underwent MIS for posterolateral lumbar fusion in a single practice over a 2-year period. Results. Twenty-eight patients underwent this procedure. The median age was 57 (range 34-80). Male:female ratio was 1:1. The most common symptom was radicular pain (n=26). Two patients had back pain without radicular symptoms. Primary degenerative spondylolisthesis was seen in 22 patients and post-laminectomy spondylolisthesis in 3 patients. Transforaminal interbody fusion (TLIF) with pedicle screw fixation was the commonest procedure (20) while the rest had pedicle screw fixation and inter-transverse fusion. Along with fusion, nerve root decompression alone was performed in 19, while 5 had decompression of the central spinal canal. Intra-operative navigation was used to assist screw placement in 5 patients. The typical hospital stay was 3 days. All but two patients were mobilised the same or the following day. Twenty-one patients with radiculopathy (80%) reported improvement in VAS at 6-months. One patient suffered irreversible nerve root injury (L5). Significant pedicle breach without nerve injury by a screw was seen in one patient. Conclusion. Minimally invasive TLIF and pedicle screw fixation lumbar degenerative condition is a safe procedure with complications comparable to traditional open techniques. Minimal muscle dissection and soft tissue damage allows for earlier ambulation and reduced hospital stay. The procedure however required longer operative time and increased exposure to intra-operative x-rays

Background. Minimally invasive surgery is an alternative therapeutic option for treating unstable spinal pathologies to reduce approach-related morbidity inherent to conventional open surgery. Objective. To compare the safety and therapeutic efficacy of percutaneous fixation to that of open posterior spinal stabilisation for instabilities of the thoraolumbar spine. Study Design. Comparison study of prospective historical cohort versus retrospective historical control at a tertiary care centre. Methods. Patients who underwent open or percutaneous posterior fixation for thoracic-lumbar instabilities secondary to metastasis, infection and acute trauma were included. Minimally access non traumatic instrumentation system (MANTIS) was used for percutaneous stabilisation. Outcome Measures. The differences in surgery-related parameters including operative time, blood loss, radiation exposure time, analgesia requirement, screw related problems and length of hospitalisation between the groups were analyzed. Results. There were a total of 50 patients with 25 in each group. There were no significant differences concerning age, sex, ASA, pathology causing instability, level and number of segments stabilised between the groups. There were significant differences between the MANTIS and open group in terms of blood loss (492 versus 925 ml, p<0.0001), post-op analgesia requirement (33 versus 45 mg/day of morphine, p<0.0004) and length of hospital stay for trauma sub-group of patients (6.2 versus 9.6 days, p< 0.0008). Average operative time of the MANTIS group was 190.2 minutes, not significantly longer to that of the conventional open group (183.84 minutes, p>0.05) Open group patients had less radiation exposure (average of 0.6 minutes) compared to MANTIS cohort (3.1 minutes). There were 2 patients with screw misplacements comprising one from each group that needing revision. Conclusion. Percutaneous spinal stabilisation using mini-invasive system is a good surgical therapeutic choice in thoracic-lumbar instabilities. It has the advantage of less trauma, quick recovery and shortened hospital stay with accuracy of screw placement as similar to those reported for other techniques. Indications and limitations of this technique must be carefully identified. Interest Statement. There was no commercial support or funding of any sort

Study design. Literature review of the best available evidence on the accuracy of computer assisted pedicle screw insertion. Background. Pedicle screw misplacement rates with the conventional insertion technique and adequate postoperative CT examination have ranged from 5 to 29 % in the cervical spine, from 3 to 58 % in the thoracic spine, and from 6 to 41% in the lumbosacral region. Despite these relatively high perforation rates, the incidence of reported screw-related complications has remained low. Interestingly, the highest rates of neurovascular injuries have been reported from the lumbosacral spine in up to 17% of the patients. Gertzbein and Robbins introduced a 4-mm “safe zone” in the thoracolumbar spine for medial encroachment, consisting of 2-mm of epidural and 2-mm of subarachnoid space. Later, several authors have found the safety margins to be significantly smaller, suggesting that the “safe zone” thresholds of Gertzbein and Robbins do not apply to the thoracic spine, and seem to be too high even for the lumbar spine. The midthoracic and midcervical spine, as well as the thoracolumbar junction set the highest demands for accuracy in pedicle screw insertion, with no room for either translational or rotational error at e.g. T5 level. Computer assisted pedicle screw insertion (navigation) was introduced in the early 90's to increase the accuracy and safety of pedicle screw insertion. Material. PubMed literature search revealed two randomized controlled trials (RCT) comparing the in vivo accuracy of conventional and computer assisted pedicle screw insertion techniques. Three meta-analyses have assessed the published reports on the accuracy of pedicle screw insertion with or without computer assistance, one additional meta-analysis concentrated on the functional outcome of computer assisted pedicle screw insertion. Results. The RCTs by Laine et al and Rajasekaran et al achieved significantly higher screw placement accuracy with computer assistance than with the conventional techniquebased on anatomical landmarks. In a degenerative patient population, Laine et al reported a misplacement rate of 4.6% with computer assistance compared to 13.4% with the conventional technique. In addition to this quantitative difference, a qualitative difference in the misplaced screws was noticed: in the conventional group, 28 out of 37 misplaced screws were either inferior or medial, whereas in the computer assisted group, 1 out of 10 misplaced screws was situated in these ”danger zones”. In deformity surgery, Rajasekaran et al reported a 2% pedicle screw misplacement rate with a computer assisted technique compared to 23% with the conventional technique. Interestingly, in their study, the average screw insertion time in the computer assisted group was significantly shorter than with the conventional technique. The three meta-analyses, assessing up to 37 337 pedicle screws, reported significantly higher accuracy in the placement of pedicle screws with computerassistance compared with the conventional methods. The superiority of the computer assisted technique was even more obvious with abnormal surgical anatomy. CT-based and 3D-fluoroscopy-based navigation methods provided better accuracy compared to 2Dfluoroscopy-based navigation. No statistically significant benefit with computer assistance in the incidence of neuro-vascular complications, or in functional outcome was demonstrated. Conclusion. High pedicle screw misplacement rates have been reported with the conventional technique based on anatomical landmarks and intraoperative fluoroscopy. The concept of ”safe zone” is hypothetical, and underestimates the true risks of misplaced pedicle screws. Computer assistance significantly improves the accuracy and safety of pedicle screw insertion. It will, however, be difficult to correlate this increased accuracy to improved patient outcomes