Accuracy of Pedicle Screw Placement and Four Other Clinical Outcomes of Robotic Guidance Technique versus Computer-Assisted Navigation in Thoracolumbar Surgery: A Meta-Analysis

BACKGROUND

Robotic guidance (RG) pedicle screw placement has been increasingly used to improve the rate of insertion accuracy. However, the superiority of the RG technique over computer-assisted navigation (CAN) remains debatable.

OBJECTIVE

To determine whether the Mazor RG technique is superior to CAN in terms of the rate of insertion accuracy and 4 other clinical indices, namely, intraoperative time, blood loss, complications and revision surgery caused by malposition.

METHODS

A search of PubMed, Embase, Cochrane, Web of Science, CNKI, and WanFang was conducted. We mainly aimed to evaluate the accuracy of pedicle screw placement between the Mazor RG and CAN techniques. The secondary objectives were intraoperative time, blood loss, complications, and revision surgery caused by malposition. The meta-analysis was conducted using the RevMan 5.3 and Stata 15.1 software.

RESULTS

A randomized controlled trial and 5 comparative cohort studies consisting of 529 patients and 4081 pedicle screws were included in this meta-analysis. The RG technique has a significantly higher accuracy than CAN in terms of optimal (odds ratio [OR], 2.26; 95% confidence interval [CI], 1.85-2.76; P < 0.01) and clinically acceptable (OR, 1.69; 95% CI, 1.22-2.34; P = 0.002) pedicle screw insertions. Furthermore, the RG technique showed significantly less blood loss (mean difference, -42.49; 95% CI, -78.38 to -6.61; P = 0.02) than did the CAN technique but has equivalent intraoperative time (mean difference, 0.75; 95% CI, -5.89 to 7.40; P = 0.82), complications (OR, 0.65; 95% CI, 0.32-1.33, P = 0.24), and revision surgery caused by malposition (OR, 0.46; 95% CI, 0.15-1.43, P = 0.18).

CONCLUSIONS

The Mazor RG technique is superior to CAN concerning the accuracy of pedicle screw placement. Thus, the Mazor RG technique is accurate and safe in clinical application.

Accuracy of pedicle screw placement by fluoroscopy, a three-dimensional printed model, local electrical conductivity measurement device, and intraoperative computed tomography navigation in scoliosis patients

INTRODUCTION

There are several assisted methods for the accurate placement of pedicle screw (PS), including fluoroscopy, a three-dimensional (3D) printed model, a local electrical conductivity measurement device (LECMD), and intraoperative computed tomography (CT) navigation.

OBJECTIVES

This study aimed to investigate the accuracy of PS placement and clinical results using different assisted methods.

METHODS

This study included 553 pedicle screws in 31 patients. We divided patients into the fluoroscopy (F) group (n = 79), 3D printed model and fluoroscopy (3D + F) group (n = 150), LECMD, 3D printed model, and fluoroscopy (LECMD + 3D + F) group (n = 171), and the intraoperative CT navigation (N) group (n = 153). We evaluated the operative time, intraoperative bleeding, number of fusion vertebrae, correction rate of the main curve, apical vertebral translation, grade of PS perforation (Grade 0: no perforation; Grade 1: < 2 mm; Grade 2: 2‒4 mm; Grade 3: > 4 mm), and accuracy of PS placement.

RESULTS

The N group had a significantly longer operative time. There were no significant differences in the clinical results excluding the operative time. The accuracy of PS placement was 93.7%, 91.3%, 93.6%, and 93.5% in the F, 3D + F, LECMD + 3D + F, and N groups, respectively. The Grade 2 perforation rate was 2.5%, 0%, 0.6%, and 0.7% in the F, 3D + F, LECMD + 3D + F, and N groups, respectively.

CONCLUSIONS

There were no significant differences in the accuracy of PS placement and clinical results excluding the operative time. The 3D printed model, LECMD, or intraoperative CT navigation would be useful to prevent Grade 2 perforation.

Surgical treatment of high-grade spondylolisthesis: Technique and results

Background

Surgical management of high-grade spondylolisthesis is not only challenging but also controversial, from in situ fusion to complete reduction. We report our results of a safe three-stage spinal procedure in a single surgical session with seven patients diagnosed high-grade spondylolisthesis.

Hypothesis

Posterior fixation combined with interbody fusion is effective on reduction, ossification and clinical outcomes in high-grade spondylolisthesis.

Patients and methods

This study is a retrospective review of patients who underwent surgery between 2016 and 2018. The surgical method involved specific installation for deformity reduction, pedicle screw fixation, correction of lumbosacral kyphosis with a specific distraction maneuver, wide decompression, gradual reduction of the deformity, and sometimes maintenance of the reduction with interbody fusion. Patients were checked out at 2, 6 and 12 months and yearly after the procedure. Clinical, radiological, Visual Analogic Scale (VAS) and Oswestry Disability Index (ODI) outcomes measures were collected.

Results

Seven patients with high-grade spondylolisthesis at L5-S1 (2 patients grade II, 4 patients grade IV and 1 patient grade V), with a median age of 37 years [17; 72] were included. Median follow-up was 24 months [12; 25 months]. All patients have a fused joint at 6 months except one. Median lumbosacral angle (LSA) improved from 76°[59; 85] to 94°[76; 104]. Meyerding grade of 2 cases was stable after surgery, 3 cases with loss of two ranks and 2 cases with loss of one rank. The radiological parameters showed statistically significant difference (p = 0.036) postoperatively. There was not deep infection. Medians VAS and ODI showed improved pain and disability scores.

Conclusion

This procedure allows correct reduction rate of high-grade spondylolisthesis with good clinic-radiologic outcomes. Though surgically demanding, it was safe and reproducible.

Level of evidence

IV, retrospective.

Personalized Three-Dimensional Printing Pedicle Screw Guide Innovation for the Surgical Management of Patients with Adolescent Idiopathic Scoliosis

OBJECTIVE

To assess the safety and efficacy of patient-specific three-dimensional (3D) rapid-prototype printing technology for pedicle screw insertion in patients with adolescent idiopathic scoliosis (AIS).

METHODS

The 3D pedicle screw guides were produced after selecting the fixation points for all individual levels to be used intraoperatively. Preoperative computed tomography images recreated 3D bone models of each vertebra specific to each patient. Safe pedicle trajectories were determined in all 3 planes on these models. 3D printed guides were modeled according to these trajectories and manufactured with a biocompatible material. Postoperatively, all screws were evaluated and scored with computed tomography as class 1 (accurate), class 2 (inaccurate), or class 3 (deviated). The mean angle between the inserted pedicle screw and the intended trajectory, and the mean distance between the central longitudinal axis of a screw and pedicle were also measured.

RESULTS

A total of 134 screws were inserted. On the concave and convex sides, the mean medial malposition was 0.5 ± 0.8 and 0.4 ± 0.6 mm, the mean lateral malposition was 1.4 ± 2.3 and 0.8 ± 1.3 mm, angle between the inserted pedicle screw and the intended trajectory was 4.2 ± 4.6 and 4.3° ± 6.0°, and distance between the central longitudinal axis of a screw and pedicle was 1.5 ± 2.1 and 0.9 ± 1.2 mm, respectively. A total of 117 screws were regarded as class 1, 14 as class 2, and 3 as class 3. Of all screws inserted, 92.5% achieved positional accuracy. There were no screw-related complications.

CONCLUSIONS

This is one of the initial reports to note the novel design and implementation of patient-specific 3D pedicle screw guides for adolescent idiopathic scoliosis surgery. Our pilot study shows that the use of these low-cost personalized 3D guides is completely safe and effective in both convex and concave sides of the curves.

Treatment of Thoracolumbar Spinal Fracture Accompanied by Diffuse Idiopathic Skeletal Hyperostosis Using Transdiscal Screws for Diffuse Idiopathic Skeletal Hyperostosis: Preliminary Results

STUDY DESIGN

This retrospective case series enrolled 13 patients who underwent posterior fixation with both transdiscal screws for diffuse idiopathic skeletal hyperostosis (TSDs) and pedicle screws (PSs) to treat spinal injury accompanied by diffuse idiopathic skeletal hyperostosis (DISH).

PURPOSE

To describe the usefulness, feasibility, and biomechanics of TSD.

OVERVIEW OF LITERATURE

Vertebral bodies accompanied by DISH generally have lower bone mineral density than normal vertebral bodies because of the stress shielding effect. This phenomenon tends to makes screw fixation challenging. To our knowledge, solutions for this issue have not previously been reported.

METHODS

Patients were assessed using the data on surgical time, estimated intraoperative blood loss, mean number of stabilized intervertebral segments, number of screws used, perioperative complications, union rate, and the three-level EuroQol five-dimensional questionnaire (EQ5D-3L) score at the final follow-up. The Hounsfield unit (HU) values of the screw trajectory area, and the actual intraoperative screw insertion torque of TSDs and PSs were also analyzed and compared.

RESULTS

The surgical time and estimated intraoperative blood loss were 165.9±45.5 minutes and 71.0±53.4 mL, respectively. The mean number of stabilized intervertebral segments was 4.6±1.0. The number of screws used was 4.9±1.3 for TSDs and 3.0±1.4 for PSs. One death occurred after surgery. The union rate and EQ5D-3L scores were 100% and 0.608±0.128, respectively. The HU value and actual intraoperative screw insertion torque of TSDs were significantly better than those of PSs (p<0.001, p=0.033).

CONCLUSIONS

We were able to achieve stable surgical outcomes using the combination of TSDs and PSs. The HU value and actual intraoperative screw insertion torque were significantly higher for TSDs than for PSs. Based on these results, when treating thoracolumbar spinal fractures accompanied by DISH in elderly populations, the TSD could be a stronger anchor than the PS.

Comparison of Navigated versus Fluoroscopic-Guided Pedicle Screw Placement Accuracy and Complication Rate

OBJECTIVES

Accurate placement of the pedicle screw is requisite for any successful spinal instrumentation procedure. Screw insertion can be achieved using free-hand and fluoroscopic- or navigation-guided techniques. We sought to assess the variation in accuracy between fluoroscopic- and navigation-guided techniques, which are both used in Sheffield Teaching Hospitals National Health Service Trust, a tertiary spine referral center.

METHODS

Using a retrospective study design, we assessed all the pedicle screws placed between 2013 and 2018. Radiographic and clinical assessment of all cases was performed.

RESULTS

We studied 176 spinal instrumented cases, with a total of 831 screws implanted, out of which 296 (35.6%) were navigated and 535 (64.4%) were fluoroscopic guided. Pathology treated included spinal stenosis, spondylolisthesis, tumors, and trauma. Suboptimal screw position was identified in 2.03% (n = 6) of the navigation-guided series and 4.11% (n = 22) of the fluoroscopic-guided series with an overall screw misplacement rate of 3.4%. Evaluating surgeons' individual accuracy rates revealed that suboptimal screw placement registered a higher variation for the fluoroscopy-guided technique, and the misplacement rate was higher for surgeons with a lower volume of cases.

CONCLUSIONS

Use of navigation during spinal instrumentation helps lower the rate of screw misplacement for spinal surgeons who are at the beginning of their learning curve or do not frequently perform this kind of procedure. Navigation-guided spinal instrumentation is more accurate compared with fluoroscopic-guided techniques and appears to have a lower complication rate.

Posterior Facetectomy with Fusion Using a Pedicle Screw for Parallel-shaped Cervical Foraminal Stenosis

Objective

To assess the efficacy and safety of posterior facetectomy with fusion using pedicle screw (PF using FPS) for severe cervical foraminal stenosis of parallel shape.

Methods

Patients (n=8) with 1- or 2-level parallel-shaped cervical foraminal stenosis who underwent posterior facetectomy with fusion using cervical pedicle screw between March 2012 and August 2016 were enrolled. Patients were followed up immediately postoperatively and at 1, 3, 6, and 12 months postoperatively. We assessed arm and neck pains and clinical outcomes using a numeric rating scale (NRS) and neck disability index (NDI). We determined cervical Cobb's and segmental angles by radiological evaluations. We identified screw breech as a neurovascular complication.

Results

Neck and arm pains were significantly reduced postoperatively (neck visual analog scale [VAS]: 4.9±3.7 [preoperative] to 0.4±1.1 [final follow-up]; arm VAS: 9.0±0.8 to 0.4±1.1). Cobb's angle for cervical sagittal alignment improved from 11.1±8.4 to 17.0±5.9. Segmental angle of index surgery was maintained (3.4±7.0–4.9±5.6). NDI was also remained from 36.1±26.3 to 13.8±8.4. There are no injuries to the vertebral arteries and neural tissues because of screw insertion.

Conclusion

PF using FPS is a practical treatment option for parallel-shaped cervical foraminal stenosis.

Effect of Fenestrated Pedicle Screws with Cement Augmentation in Osteoporotic Patients Undergoing Spinal Fusion

OBJECTIVE

Osteoporosis is a well-known risk factor for instrumentation failure and subsequent pseudoarthrosis after spinal fusion. In the present systematic review, we analyzed the biomechanical properties, clinical efficacy, and complications of cement augmentation via fenestrated pedicle screws in spinal fusion.

METHODS

We conducted a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Reports appearing in the PubMed database up to March 31, 2020 were queried using the key words "cement," "pedicle screw," and "osteoporosis." We excluded non-English language studies, studies reported before 2000, studies that had involved use of cement without fenestrated pedicle screws, nonhuman studies, technical reports, and individual case reports.

RESULTS

Twenty-five studies met the inclusion criteria. Eleven studies had tested the biomechanics of cement-augmented fenestrated pedicle screws. The magnitude of improvement achieved by cement augmentation of pedicle screws increased with the degree of osteoporosis. The cement-augmented fenestrated pedicle screw was superior biomechanically to the alternative "solid-fill" technique. Fourteen studies had evaluated complications. Cement extravasation with fenestrated screw usage was highly variable, ranging from 0% to 79.7%. However, cement extravasation was largely asymptomatic. Thirteen studies had assessed the outcomes. The use of cement-augmented fenestrated pedicles decreased screw pull out and improved fusion rates; however, the clinical outcomes were similar to those with traditional pedicle screw placement.

CONCLUSIONS

The use of cement-augmented fenestrated pedicle screws can be an effective strategy for achieving improved pedicle screw fixation in patients with osteoporosis. A potential risk is cement extravasation; however, this complication will typically be asymptomatic. Larger comparative studies are needed to better delineate the clinical efficacy.

Technique of C2 Subfacetal Screw in Patients with High-Riding Vertebral Artery

A C2 pedicle screw provides robust construct for fixation in atlantoaxial dislocation.^1-5 However, inserting a C2 pedicle screw with the standard technique in cases with narrow pedicle and high-riding vertebral artery (VA) may endanger the artery.⁶ A pars screw is also risky and biomechanically inferior.^3-5 This video demonstrates the technique of safe insertion of subfacetal screws, directly into the C2 body while safeguarding the VA in a patient with atlantoaxial dislocation/basilar-invagination with cervicomedullary compression (Video 1). Computed tomography angiography showed a high-riding VA with a thin pedicle. The patient underwent posterior C1-C2 joint manipulation and fixation.^1,2 After the joints were exposed, the VA was dissected from the medial border of the C2 transverse foramen and a subfacetal screw was inserted directly into the C2-body, safeguarding the artery.⁷ The screw trajectory is similar to that described by Goel et al⁸ (15-20 degrees cranial and 30-40 degrees medial). The entry point in the Goel technique is 2 mm below the medial portion of C2 superior articular surface. However, with a high-riding VA, the entry point needs to be shifted medially. C1 lateral mass screws were inserted according to the standard technique and fixed to C2 screws with rods. Postoperatively, the patient improved and radiology showed satisfactory reduction with good flow across the VA on angiography. There is a minimal risk of arterial injury/spasm due to its handling. Nevertheless, the benefit of a strong construct clearly outweighs this risk. Alternatively, one may insert a C2 laminar screw. However, the biomechanical considerations are better with the C2 pedicle screws and the overall construct may be not ideal as the fixation is away from the C1-C2 joint.^3-5,9.

Pedicle Screw Insertion: Is O-Arm-Based Navigation Superior to the Conventional Freehand Technique? A Systematic Review and Meta-Analysis

BACKGROUND

Although O-arm-based navigation (ON) has been considered a better choice than the conventional freehand (FH) technique for spine surgery, clinical evidence showing the accuracy of ON compared with the FH technique is limited. The purpose of this study was to evaluate the accuracy of pedicle screw insertion under ON compared with the FH technique.

METHODS

The Cochrane Library, Ovid, Web of Science, PubMed, Embase, and CNKI online databases were searched up to January 2020. Because only a few randomized controlled trials were anticipated, prospective and retrospective comparative studies were also evaluated to compare the accuracy of pedicle screw insertion between ON and FH. Statistical analysis was performed using Stata 16.0. The primary outcomes extracted from articles that met the selection criteria were expressed as odds ratios for dichotomous outcomes with a 95% confidence interval. A χ² test and I² statistics were used to evaluate heterogeneity.

RESULTS

A total of 20 reviews were included in this meta-analysis without identifying additional studies from the references of published articles. These reviews included 1422 patients and 9982 screws. ON was used to insert 4797 pedicle screws and 5185 pedicle screws were inserted using the conventional FH technique with C-arm assistance. The meta-analysis showed that ON is significantly more accurate than FH pedicle screw insertion (odds ratio, 2.46; 95% confidence interval, 1.92-3.16; I² = 43.4%; P = 0.021). I² indicates that the studies have a moderate statistical heterogeneity; subgroup analysis decreased heterogeneity significantly.

CONCLUSIONS

Compared with conventional methods, navigation provides greater accuracy in the placement of pedicle screws, accelerates the insertion, and reduces the complications associated with screw insertion. However, it may increase exposure time to radiation, which may harm the patient's or surgeon's health.

Placement of Guide-Wireless Sharp Percutaneous Pedicle Screws Utilizing Computed Tomography-Navigation and Sentinel Fluoroscopy: 2-Dimensional Operative Video

Many established techniques exist for minimally invasive pedicle screw placement. Nearly all techniques incorporate the use of a Kershner wire (K-wire) at various points in the work-flow. The use of a K-wire adds an additional step. If its position is lost, it requires repeating all previous steps, and placement is not without complication. The use of a guide-wireless sharp screws allows the surgeon to place a pedicle screw in 1 step with several fluid maneuvers.1 The patient underwent Institutional Review Board-approved consent for this study. Following traditional computed tomography-based navigation, a stab incision is made, followed by fascial dissection with monopolar cautery. The sharp screw is placed percutaneously at the facet-transverse process junction. The precise entry point is confirmed with navigation, followed by a sentinel anterior-posterior fluoroscopic image, verifying the accuracy of the navigation. The cortical bone is traversed by malleting the sharp tip through the cortex. When the cancellous bone is engaged, the screw is then advanced through the pedicle. This set of steps allows for safe, efficient placement of percutaneous pedicle screws without the need for a guidewire. Mal-placement regarding sharp pedicle screw insertion is similar to K-wire-dependent screw placement. Surgeons must be cognoscente of exceptionally sclerotic bone, which can prove difficult to cannulate. Conversely, osteoporotic bone that is liable to a cortical pedicle breach, transverse process fracture, and/or maltrajectory are all considerations when placing a K-wireless, sharp pedicle screw. Anterior-posterior fluoroscopy is utilized to confirm accuracy of image-guided navigation and mitigate malplacement of pedicle screws.

Five or more proximal anchors and including upper end vertebra protects against reoperation in distraction-based growing rods

STUDY DESIGN

Retrospective multi-center enrollment.

OBJECTIVE

To examine the impact of patient and surgical factors on proximal complication and revision rates of early onset scoliosis patients using a multicenter database. Proximal anchor pullout and junctional kyphosis are common causes necessitating revision surgery during growth friendly treatment of early onset scoliosis (EOS). Many options exist for proximal fixation and may impact the rate of these complications.

METHODS

Retrospective review of multicenter database of patients with growth friendly constructs for EOS. Inclusion criteria were patients with index instrumentation < 10 years of age and minimum of 2 year follow-up.

RESULTS

353 patients met the inclusion criteria and had the following constructs: growing rods with spine anchors = 303; growing rods with rib anchors = 15 and VEPTR = 35. Mean age at index instrumentation was 6.0 years. Mean preoperative Cobb angle was 76° and mean kyphosis was 54°. Mean follow-up was 6.0 years. 21.8% of patients (77/353) experienced anchor pullout. Lower anchor pullout rates were associated with a higher numbers of proximal anchors (p = 0.003, r = - 0.157), and 5 or more anchors were associated with lower rates of anchor pullout (p = 0.014). Anchor type (rib hooks vs spine anchors vs rib cradle) did not impact rate of anchor pullout (p = 0.853). Kyphosis data was available for 198 patients. 23.2% (46/198) of these patients required proximal extension of their construct after index surgery. Initial instrumentation below the upper end vertebrae (UEV) of kyphosis was associated with higher rates of subsequent proximal revision; 28.9% (20/69) compared to 20.1% (26/129) for those instrumented at or above the UEV (p = 0.035). Preoperative kyphosis and change in thoracic kyphosis were not associated with anchor pullout (p = 0.436, p = 0.115) or proximal revision rates (p = 0.486, p = 0.401).

CONCLUSION

Five or more anchors are associated with lower rates of anchor pullout. Proximal anchor placement at or above the UEV resulted in a significant decrease in rates of proximal extension of the construct.

Robot-assisted orthopedic surgery in the treatment of adult degenerative scoliosis: a preliminary clinical report

Study design

A single-institution, retrospective cohort study.

Objective

To compare the accuracy and short-term clinical outcomes of pedicle screw placement between robot-assisted (RA) and freehand (FH) technique in the treatment of adult degenerative scoliosis (ADS).

Methods

From February 2018 to October 2019, 97 adult patients with degenerative scoliosis admitted to our department were retrospectively reviewed. Thirty-one patients received robot-assisted pedicle screw placement (RA group), and 66 patients underwent freehand pedicle screw placement (FH group). Patient demographics and short-term clinical outcomes were recorded and compared between two groups. Gertzbein-Robbins grading system was adopted to evaluate the accuracy of pedicle screw placement by means of postoperative CT scan. Short-term clinical outcomes consist of operative time, intraoperative blood loss, length of hospital stay (LOS), radiological parameters, Scoliosis Research Society-22 (SRS-22) scores before the operation, 6 months after operation, adverse events, and revisions.

Results

The accuracy of screw placement was higher than that of the FH group (clinically acceptable 98.7% vs. 92.2%; P< 0.001). Intraoperative blood loss of the RA group was less than those in the FH group (499 vs. 573 ml; P < 0.001). Operative time (283.1 vs. 291.9 min; P = 0.31) and length of stay (12.8 vs. 13.7 days; P = 0.36) were compared between RA and FH groups. In terms of radiological parameters, both of groups were improved postoperatively. The SRS-22 scores at 6 months after operation from both groups were better than those before operation. For surgery-related complication, one case had pressure sores in the RA group while two cases developed dural tears in the FH group. No revision was required in both groups.

Conclusion

Combined with other surgical correction modalities, robot-assisted pedicle screw fixation is an effective and safe method of treating degenerative scoliosis. Due to its satisfactory surgical outcomes such as higher accuracy and less trauma, it provides a good alternative for clinical practice.

Level of evidence

3.

Diagnostic accuracy of perioperative electromyography in the positioning of pedicle screws in adolescent idiopathic scoliosis treatment: a cross-sectional diagnostic study

Background

To investigate in the conventional techniques of the pedicle screws using triggered screw electromyography (t-EMG), considering different threshold cutoffs: 10, 15, 20 25 mA, for predicting pedicle screw positioning during surgery of the adolescent with idiopathic scoliosis (AIS).

Methods

Sixteen patients (4 males, 12 females, average age 16.6 years) were included, with an average curve magnitude of 50 degrees and placement of 226 pedicle screws. Each screw was classified as “at risk for nerve injury” (ARNI) or “no risk for nerve injury” (NRNI) using CT and the diagnostic accuracy of EMG considering different threshold cutoffs (10,15, 20 and 25 mA) in the axial and Sagittal planes for predicting screw positions ARNI was investigated.

Results

The EMG exam accuracy, in the axial plane, 90.3% screws were considered NRNI. In the sagittal plane, 81% pedicle screws were considered NRNI. A 1-mA decrease in the EMG threshold was associated with a 12% increase in the odds of the screw position ARNI. In the axial and sagittal planes, the ORs were 1.09 and 1.12, respectively. At every threshold cutoff evaluated, the PPV of EMG for predicting screws ARNI was very low in the different threshold cutoff (10 and 15); the highest PPV was 18% with a threshold cutoff of 25 mA. The PPV was always slightly higher for predicting screws ARNI in the sagittal plane than in the axial plane. In contrast, there was a moderate to high NPV (78–93%) for every cutoff analyzed.

Conclusions

EMG had a moderate to high accuracy for positive predicting value screws ARNI with increase threshold cutoffs of 20 and 25 mA. In addition, showed to be effective for minimizing false-negative screws ARNI in the different threshold cutoffs of the EMG in adolescent with idiopathic scoliosis (AIS).

Biomechanical Comparison of Pull-out Strength of Different Cementation and Pedicle Screw Placement Techniques in a Calf Spine Model

BACKGROUND

We hypothesized that an entire pedicle screw tract cement augmentation has greater strength than traditional techniques.

METHOD

Twenty-four fresh frozen calf lumbar spines were randomized into three study groups, each having eight vertebrae: (1) screw cemented after vertebroplasty; (2) fenestrated cemented screw; and (3) cementation of the entire pedicle screw tract. For the right side screws, two pedicle screws were inserted in each vertebra with the standard position in the sagittal plane, whereas the left side screws were placed at a 30° angle craniocaudal plane. From the recorded force-displacement curves, the maximum peak load (failure load) of each screw was determined. The mode of failure was screw stripping at all levels tested.

RESULTS

The pull-out strength for standard screw replacement at the sagittal plane was 1843.3 N, 1707.45 N, and 5365.1 N consecutively. The failure load value in the standard position in the sagittal plane in the cementation of the entire pedicle screw tract group was significantly higher than that in the fenestrated cemented screw group and screw cemented after vertebroplasty (p < 0.001 and p < 0.001, respectively). The standard pedicle screw position in the sagittal plane showed a significant pull-out strength than the others (p < 0.001).

CONCLUSION

The pull-out strength of the cementation of the entire pedicle screw tract was 2.5 times higher than the others. The pull-out strength of the pedicle screws in malposition obtained the same strength to the standard positions after the augmentation procedure in our study.

A novel system for accurate lumbar spine pedicle screw placement based on three-dimensional computed tomography reconstruction

Objectives

The accuracy of pedicle screw placement strongly affects the outcome of spinal surgery and has mainly relied on the surgeons’ experience. There is no simple, low-cost, and effective pedicle screw placement system to assist new spinal surgeons with less experience.

Methods

We designed a localization system with six parameters (starting point height [SP-H], starting point length [SP-L], transverse section angle, sagittal section angle [SSA], pedicle width [W] and height [H]) based on preoperative computed tomography reconstruction and combined it with the Roussouly classification to guide lumbar spine pedicle screw placement and analysed the change patterns of the six parameters in 50 participants.

Results

Based on the system, we confirmed that combining SP-H and SP-L can localize the entrance of the pedicle screw. Furthermore, we considered that SP-L and transverse section angle would be a new standard for determination of the transverse orientation of the pedicle screw. More importantly, the linear regression equations between H and W and SP-H and H were concealed. In addition, H and W can guide the appropriate selection of pedicle screw. Moreover, change patterns of SSA combined with the Roussouly classification indicate that SSA of L3 can be used as a benchmark to guide the establishment of sagittal alignment of the lumbar spine.

Conclusions

Understanding and applying the six-parameter localization system are essential for achieving accuracy in lumbar spine pedicle screw placement, and the system is a useful guide in the establishment of sagittal alignment.

The translational potential of this article

This study provides a new pedicle-screw placement system for accurate lumbar spine pedicle screw placement based on three-dimensional CT reconstruction, requiring six parameters to guide the system.

Investigation of the "Superior Facet Rule" Using 3D-Printed Thoracic Vertebrae With Simulated Corticocancellous Interface

BACKGROUND

Pedicle screw placement is the most common method of fixation in the thoracic spine. Use of the "superior facet rule" allows the operator to locate the borders of the pedicle reliably using posterior landmarks alone. This study investigated the ability of 3-dimensionally (3D)-printed thoracic vertebrae, made from combined thermoplastic polymers, to demonstrate pedicle screw cannulation accurately using the superior facet as a reliable landmark.

METHODS

An anonymized computed tomography scan of the thoracic spine was obtained. The T1-T12 thoracic vertebrae were anatomically segmented and 3D-printed. The pedicle diameters and distance from the midpoint of the superior facet to the ventral lamina were recorded. A total of 120 thoracic pedicles in 60 thoracic vertebral models were instrumented using a freehand technique based only on posterior landmarks. The vertebral models were then coronally cut and examined for medial or lateral violations of the pedicle after screw placement.

RESULTS

A total of 120 pedicle screws were placed successfully within the 3D-printed thoracic vertebral models. Average measurements fell within 1 standard deviation of previous population studies. There were no pedicle wall violations using standard posterior element landmarks for instrumentation. There were 3 lateral violations of the vertebral body wall during screw placement, all attributable to the insertion technique.

CONCLUSIONS

3D-printed thoracic vertebral models using combined thermoplastic polymers can accurately demonstrate the anatomical ultrastructure and posterior element relationships of the superior facet rule for safe thoracic pedicle screw placement. This method of vertebral model prototyping could prove useful for surgical education and demonstrating spinal anatomy.

Extraforaminal Vertebral Artery Anomalies and Their Associated Surgical Implications: An Epidemiologic and Anatomic Report on 1000 Patients

OBJECTIVE

Extraforaminal vertebral anomalies involve entry at cervical transverse foramina other than at C6 and can appear with other anatomic variations along the V2 segment. Such unexpected vessel courses can have implications on surgical planning. We sought to evaluate the incidence of anomalous V2 segment entries, as well as their associations with vessel dominance, medialization, and C7 pedicle width.

METHODS

We conducted a retrospective study on 1000 consecutive computed tomography angiograms, documenting level and laterality of vessel of entry, as well as vertebral dominance patterns. Patients with rostral C4 anomalies were assessed for medialization. The pedicle widths ipsilateral to caudal C7 anomalies were compared with those of contralateral and matched controls.

RESULTS

A total of 157 patients were identified with extraforaminal entries, with 25 having bilateral findings. The most common alternative entry was at C5 (70.3%), followed by C4 (17.6%) and C7 (11.5%). Among patients with unilateral anomalies, there was an increased representation of contralateral vertebral dominance, relative to ipsilateral dominance (79.6% vs 20.4%, P < 0.0001). Among anomalous C4 entries, vertebral medialization was seen along the right (35%) and left sides (23.1%) spanning C6-T1. Among C7 anomalous entries there was no statistical difference in pedicle width.

CONCLUSIONS

Extraforaminal anomalies may be more frequent than previously reported and are important considerations during subaxial cervical spine surgery planning. Particular attention should be paid to the contralateral dominance pattern within this subgroup. In patients with anomalous V2 segment entries, adherence to the standard, anatomic landmarks remains desirable.

Pedicle screw fixation of thoracolumbar fractures: conventional short segment versus short segment with intermediate screws at the fracture level-a systematic review and meta-analysis

OBJECTIVE

Posterior short-segment fixation (4-screw construct = 4S) is the conventional surgical technique for thoracolumbar fractures. The effect of adding two intermediate pedicle screws at the fractured level (6-screw construct = 6S) is still a matter of debate. This review aims to compare the results between 4 and 6S pedicle screw fixation for thoracolumbar fractures.

METHODS

A systematic review and meta-analysis were performed. The databases PubMed, Embase and Google Scholar were searched until January 2020. Inclusion criteria were studies comparing 4S and 6S techniques in patients with thoracolumbar fractures. Non-comparative studies and studies without full text were excluded. Cochrane risk of bias was assessed, and the GRADE approach was used to present the quality of evidence.

RESULTS

Twenty-seven studies, of which 21 randomized controlled trials, with a total of 1890 patients (940 with 4S and 950 with 6S) were included. Meta-analysis showed that the 6S technique resulted in significantly lower pain scores, better short-term and long-term Cobb angles, less loss of correction and less implant failures. However, longer operation time and more blood loss were seen with the 6S technique. Length of hospital stay, Oswestry Disability Index scores and infections did not differ significantly between the 6S and 4S techniques. Quality of the evidence according to GRADE was moderate to low.

CONCLUSION

In the treatment of thoracolumbar fractures, adding intermediate screws at the fracture level (6S) results in less post-operative pain, better radiological outcomes and less implant failure at the cost of a longer operation time and higher blood loss.

Techniques and Tips for Freehand Placement of C7 Pedicle Screws With Respect to Cervicothoracic Constructs: 2-Dimensional Operative Video

We present a surgical video highlighting the technical pearls for C7 pedicle screw placement with respect to cervicothoracic constructs. Pedicle screw placement into C7 has been shown to enhance the biomechanical stability of both cervical and cervicothoracic constructs and is safe for patient related outcomes.1,2 Rod placement across the cervicothoracic junction is known to be difficult because of the variable starting point of the C7 pedicle screw, which may cause misalignment of the polyaxial heads with respect to the C7 and C6 screw heads. Using our step-wise method of anatomic screw placement, this potential pitfall is minimized. The T1 pedicle screw is placed first. The C6 lateral mass screw starting point is displaced slightly superiorly from the midpoint of the lateral mass in order to make room for the polyaxial head of the C7 pedicle screw. A small laminotomy is performed in order to find the medial border of the C7 pedicle. Palpation of the medial border allows for an approximation of the pedicle limits. The cranial-caudal angle of drilling is perpendicular to the C7 superior facet, and the medial-lateral trajectory typically falls between 15 and 20 degrees medial. Once the pedicle is cannulated, a ball-tipped probe is used to confirm intraosseous position. A rod is cut and contoured to the appropriate length of the construct. The C7 pedicle screw should capture the rod easily with slight displacement of the polyaxial head. Postinstrumentation anteroposterior and lateral fluoroscopy are performed to confirm good position of the lateral mass and pedicle screws. Patient consent was not required for this cadaveric surgical video.

Short fixation with a 3-rod technique for posterior hemivertebra resection in children younger than 5 years old

IMPORTANCE

Congenital hemivertebra is commonly treated with posterior hemivertebra resection with bilateral transpedicular fixation. However, implant-related complications are common in children younger than 5 years old who undergo this surgical procedure.

OBJECTIVE

To present the preliminary clinical and radiological outcomes of children younger than 5 years old treated by posterior hemivertebra resection and 3-rod fixation technique.

METHODS

From January 2016 to December 2017, 14 consecutive patients of congenital scoliosis with 16 hemivertebrae were retrospectively reviewed, including 5 girls and 9 boys, aged between 25 and 55 months old (average, 37.6 months). All patients underwent posterior hemivertebra resection with short fixation with bilateral pedicle screws and a convex lamina hook. Surgical complications and corrective outcomes were assessed based on the clinical charts and spinal radiographs with a minimum 24-month follow-up.

RESULTS

The mean Cobb angle of the main curve was 38.4° before surgery, 8.5° after surgery, and 8.7° at final follow-up. In the compensatory cranial curve, the preoperative Cobb angle of 16.8° was corrected to 8.1° postoperatively and was 10.3° at final follow-up. In the compensatory caudal curve, the preoperative Cobb angle of 15.9° improved to 5.3° postoperatively and was 7.8° at final follow-up. The segmental kyphosis was corrected from 13.5° to 0.5° and was 1.1° at final follow-up. There were no crankshaft phenomena, no proximal kyphosis, and no complications related to the instrumentation.

INTERPRETATION

Posterior hemivertebra resection with instrumentation with bilateral pedicle screws and a convex lamina hook can achieve rigid fixation and deformity correction.

Intraoperative radiation exposure to patients in idiopathic scoliosis surgery with freehand insertion technique of pedicle screws and comparison to navigation techniques

PURPOSE

In surgical correction of scoliosis with pedicle screw dual-rod systems, frequently used freehand technique of screw positioning is challenging due to 3D deformity. Screw malposition can be associated with serious complications. Image-guided technologies are already available to improve accuracy of screw positioning and decrease radiation to surgeon. This study was conducted to measure intraoperative radiation to patients in freehand technique, evaluate screw-related complications and compare radiation values to published studies using navigation techniques.

METHODS

Retrospective analysis of prospectively collected data of 73 patients with idiopathic scoliosis, who underwent surgical correction with pedicle screw dual-rod system. Evaluated parameters were age, effective radiation dose (ED), fluoroscopy time, number of fused segments, correction and complications. Parameters were compared with regarding single thoracic curve (SC) and double thoracic and lumbar curves (DC), adolescent (10-18 years) or adult (> 18 years) idiopathic scoliosis, length of instrumentation. ED was compared with values for navigation from online database.

RESULTS

Average age was 21.0 ± 9.7 years, ED was 0.17 ± 0.1 mSv, time of fluoroscopy was 24.1 ± 18.6 s, 9.5 ± 1.9 fused segments. Average correction for SC was 75.7%, for DC 69.9% (thoracic) and 76.2% (lumbar). No screw-related complications. ED was significantly lower for SC versus DC (p < 0.01), short versus long fusions (p < 0.01), no significant difference for age (p = 0.1). Published navigation data showed 6.5- to 8.8-times higher radiation exposure for patients compared to our results.

CONCLUSION

Compared to navigation procedures, freehanded positioning of pedicle screws in experienced hands is a safe and effective method for surgical correction of idiopathic scoliosis with a significant decrease in radiation exposure to patients.

Accuracy of t-EMG stimulation of the middle pedicle track to prevent radiculopathies as a result of misplaced lumbar screws

OBJECTIVE

To describe the accuracy of middle pedicle track stimulation for the detection of pedicle breaches causing misplaced lumbar screws and subsequent neurological symptoms.

PATIENTS AND METHODS

In a comparative observational study with two cohorts, 1440 lumbar pedicle screws were implanted using the freehand technique in 242 patients undergoing surgery for spinal deformities. In the first two-year period (2011-2012), the accuracy of screw placement (802 screws) was assessed by conventional intraoperative palpation of the pedicle track, t-EMG screw stimulation, and fluoroscopic monitoring. In the second period (2012-2013), the middle aspect of the lumbar pedicle tracks was systematically stimulated with a probe (638 screws). When thresholds in the middle track showed <9 mA, potential neurological risk was considered, and therefore, new pedicle tracks were performed.

RESULTS

Six patients (4.4 %) in the first period presented postoperative radicular pain and a normal intraoperative screw t-EMG threshold. CT scans showed seven screws (0.9 %) with >2-mm medial-caudal invasion of the foramen. Before screw removal, t-EMG thresholds of these screws were again normal (≥10 mA). After removal of the screws. t-EMG of the middle part of the pedicle track showed thresholds below 9 mA (mean 5.2 mA). In the second period, the pedicle tracks were systematically stimulated. Low t-EMG thresholds (<9 mA) were found in 11 tracks (1.7 %) and were therefore reworked before screw placement. CT scans in these 10 patients showed that all of the 11 screws were correctly repositioned.

CONCLUSIONS

This study shows that caudal or medial pedicle cortical breaches can be detected effectively by stimulating the middle part of the pedicle track. This technique is strongly recommended to prevent postoperative lumbar radiculopathies due to screw malposition.

MRI versus CT: a retrospective investigation of the feasibility and agreeability in post-operative evaluation of screw position after posterior lumbar interbody fusion

PURPOSE

Many patients receive magnetic resonance (MR) and computed tomography (CT) scans post-operatively to review screw placement. Traditionally, CT is diagnostic but as metal artefact reduction sequences are advancing in MR, the necessity for both MR and CT scans is questionable. The objective is to establish the statistical agreeability of MR and CT for evaluation of adequate screw placement in posterior lumbar interbody fusion.

METHODS

This opportunistic retrospective study of 58 patients investigated 297 images of 296 implanted screws. Post-operative MR and CT images were scrutinised for depiction of lumbar pedicle screw position using a 5-point scale. Kappa value for statistical agreeability tested MR against CT.

RESULTS

The 297 images of screws resulted in strong to near-perfect agreement between MR and CT (n = 297 k = 0.8042 p < 0.025). MRI resulted in high sensitivity (88.7%) and positive predictive value (78.3%). MRI demonstrated very high specificity (96.2%) and negative predictive value (98.2%). MR depicted screws (mean 12.6 mm diameter, mean 65.3 mm length) with 50% error in diameter and 30% in length from susceptibility artefact compared to manufacturer dimensions (6.5-7.5 mm diameter, 40-50 mm length). Adequate screw placement was high despite this (85.8%). On MR, the cortex border visibility was 60.7% and the spinal canal visibility was 74.6%.

CONCLUSION

There is strong to near-perfect agreement between MR and CT for evaluating adequate screw position in PLIF surgery. MR alone is useful for analyzing screw placement and should be considered first-line imaging in uncomplicated cases with CT analysis reserved for cases of uncertainty.

LEVEL OF EVIDENCE

Level III retrospective cohort study.

O-arm navigation versus C-arm guidance for pedicle screw placement in spine surgery: a systematic review and meta-analysis

BACKGROUND

O-arm and C-arm are commonly used in spine surgery to guide pedicle screw placement. However, concerning the accuracy and efficiency of them, no systematical review and meta-analyses are available to help surgeons make comparisons.

PURPOSES

This study aims to investigate the accuracy and efficiency of O-arm-navigated versus C-arm-guided pedicle screw placement in thoracic and lumbar spine surgery. It would help surgeons choose the optimal technique for pedicle screw placement.

PATIENTS AND METHODS

A systematic review and meta-analyses were performed after searching the PubMed, Embase, and Cochrane databases to identify all studies that assessed the accuracy and efficiency of navigation coupled with O-arm and conventional C-arm fluoroscopy.

RESULTS

Eight studies were finally recruited in this systematic review, all of which reported pedicle screw placement outcomes related to accuracy or efficiency in both C-arm and O-arm groups. Five studies showed higher screw insertion accuracy in the O-arm group, while one study showed no significant difference. And the pooled results also indicated that the incidence of screw misplacement in the C-arm groups is higher. Moreover, the pooled results from five studies indicated no significant difference in insertion time between C-arm and O-arm.

CONCLUSIONS

Navigation coupled with O-arm imaging displayed a lower efficiency outcome in pedicle screw placement compared to conventional C-arm fluoroscopy. However, in terms of accuracy, O-arm navigation had significant advantages in accuracy over conventional C-arm fluoroscopy.

Probe versus drill: A biomechanical evaluation of two different pedicle preparation techniques for pedicle screw fixation in human cadaveric osteoporotic spine

BACKGROUND

Aim of this biomechanical study was to investigate the anchorage of pedicle screws in osteoporotic vertebrae using two different preparation techniques (probe versus drill-assisted).

METHODS

Twelve thoracic vertebrae were used for the study. The right and left pedicles of the vertebra were prepared with a thoracic probe or a 3.2 mm drill bit and divided into two groups. A standard titanium (diameter: 5.5 mm, length: 45 mm) pedicle screw was then inserted. All pedicle screws were initially loaded with -25 N to +25 N in the cranio-caudal direction. The load was increased by 5 N every 500 cycles up to a maximum load of 10,000 cycles. Loosening was defined as a displacement of the pedicle screw head of >5 mm. The two groups were compared in terms of maximum number of cycles and maximum force until loosening.

FINDINGS

The pedicle screws prepared with the thoracic probe failed on average after 3819 cycles (SD 3281) and the pedicle screws prepared with the 3.2 mm drill after 3335 cycles (SD 3477). There was no significant difference between the two preparation techniques (P = .797). With regard to the maximum force until loosening, there was also no significant difference between the two techniques (thoracic probe: 61 N (SD 33), 3.2 mm drill bit: 56 N (SD 34), P = .791).

INTERPRETATION

Preparation of the pedicle screw hole either with a probe or drill bit doesn't seem to have an influence on pedicle screw loosening rates in the osteoporotic spine.

Is the Risk of Aorta Injury or Impingement Higher During Correction Surgery in Patients with Severe and Rigid Scoliosis?

OBJECTIVE

To evaluate the position of the aorta relative to the spine and the risk of aortic injury during correction surgery in patients with idiopathic severe and rigid scoliosis (main curve Cobb angle >90° and flexibility <30%).

METHODS

Twenty-seven patients with severe right thoracic/thoracolumbar scoliosis were recruited. The entry point-aorta distance (EAD), the left pedicle-aorta angle (α), the left aorta angle (β), and the vertebral rotation angle (γ) were measured from 4 vertebrae above (A4) to 4 below (B4) the apical vertebra (Apex) to quantify the spatial relationship between aorta and spine. We simulated the pedicle screw misplacement with variable direction error, length, and diameter to analyze the potential risk of aortic injury.

RESULTS

The aorta shifted laterally and posteriorly as it descended from A4 and moved back medially and anteriorly from Apex. The potential risk of aortic injury increased with the augment of direction error and/or length of the screw, but the tendency was not significant with the augment of diameter. The risk peaked at A4, A3, and B2, when the screw length was 40 mm and diameter was 5.0 mm, and the direction error was 30°, whereas the risk was lowest at the apical level 14.3% (0%-40.7%) in any scenarios.

CONCLUSIONS

In patients with severe and rigid scoliosis, the aorta shifted more laterally and posteriorly, and the injury risk was lower at the apical level, compared with moderate scoliosis. Most potential risks can be minimized by careful preoperative planning and the assistance of intraoperative navigation or robotics.

Establishing validity of the fundamentals of spinal surgery (FOSS) simulator as a teaching tool for orthopedic and neurosurgical trainees

BACKGROUND CONTEXT

Pedicle screw placement is a demanding surgical skill as a spine surgeon can face challenges including variations in pedicle morphology and spinal deformities. Available CT simulators for spine pedicle placement can be very costly and hands-on cadaver courses are limited by specimen availability and are not readily accessible.

PURPOSE

To conduct validation of a simulated training device for essential spine surgery skills.

DESIGN

Cross-sectional, empirical study of physician performance on a surgical simulator model.

SAMPLE

Spine attending physicians and residents from four different academic institutions across the United States.

OUTCOME MEASURES

Performance metrics on two surgical simulator tasks.

METHODS

After IRB approval, an inexpensive ($30) simulator was developed to test two main psychomotor tasks (1) creation of the pedicle screw path with a standard gearshift probe without cortical breaks and (2) the ability to palpate for the presence or absence of cortical breaches as well as determine the location of wall defects. Orthopedic and neurosurgery residents (N=72) as well as spine attending surgeons (N=26) participated from four different institutions. To test construct validity, performance metrics were compared between participants of different training status through one-way analysis of variance and linear regression analysis, with significance set at p<.05.

RESULTS

Spine attending surgeons consistently scored higher than the residents, in the screw trajectory task with triangular base (p=.0027) and defect probing task (p=.0035). In defect probing, performance improved with linear trend by number of residency training years with approaching significance (p=.0721). In that task, independent of institutional affiliation, PGY-2 residents correctly identified an average of 1.25±0.43 fewer locations compared with attending physicians (p=.0049). More than 80% of the spine attendings reported they would use the simulator for training purposes.

CONCLUSIONS

This low-cost fundamentals of spine surgery simulator detected differences in performances between spine attending surgeons and surgical residents. Programs should consider implementing a simulator such as fundamentals of spine surgery to assess and develop pedicle screw placement ability outside of the operating room.

Biomechanical strength comparison of pedicle screw augmentation using poly-dicalcium phosphate dihydrate (P-DCPD) and polymethylmethacrylate (PMMA) cements

STUDY DESIGN

A basic science, hypothesis-driven experimental study of the biomechanics of two bone cements in their ability to augment pedicle screws in bone foam.

OBJECTIVE

The purpose of our study was to compare the pullout and torque resistance of conventional pedicle screws (CPS) augmented with either polymethylmethacrylate (PMMA) or poly-dicalcium phosphate dihydrate (P-DCPD) cement in polyurethane foam blocks mimicking osteoporotic bone. P-DCPD cement has attractive safety characteristics such as non-exothermic curing and drug-eluting capacity. PMMA cement lacks these safety features yet is the current standard in pedicle screw augmentation.

METHODS

Standardized low-density polyurethane open-cell foam blocks were instrumented with conventional pedicle screws and categorized into three groups of six each. Group 1 was the control group and no cement was used. Groups 2 and 3 were augmented with PMMA and P-DCPD, respectively. An Instron machine applied an axial load to failure at a rate of 2 mm/min for 3 min and a torsional load to failure at a rate of 1°/s. Failure was defined by an evident drop in the load after maximum value.

RESULTS

Maximal pullout load for PMMA and P-DCPD was significantly greater than control (p < 0.0001). Interestingly, there was no significant difference in the pullout load to failure for the PMMA and P-DCPD groups. Analysis showed significant difference in torsional resistance between PMMA and P-DCPD, with PMMA having greater resistance (p = 0.00436).

CONCLUSIONS

No difference was observed between PMMA and P-DCPD in pullout load to failure conducted in low-density open-cell, rigid foam blocks. Although a significant difference did exist in our torque analysis, the clinical significance of such a load on a native spine is questionable. Further investigation is warranted for this promising compound that seems to be comparable in pullout resistance to PMMA and offers attractive safety features.

LEVEL OF EVIDENCE

Basic science, not applicable.

Accuracy of augmented reality surgical navigation for minimally invasive pedicle screw insertion in the thoracic and lumbar spine with a new tracking device

BACKGROUND CONTEXT

Minimally invasive approaches are increasingly used in spine surgery. The purpose of navigation systems is to guide the surgeon and to reduce intraoperative x-ray exposure.

PURPOSE

This study aimed to determine the feasibility and clinical accuracy of a navigation technology based on augmented reality surgical navigation (ARSN) for minimally invasive thoracic and lumbar pedicle screw instrumentation compared with standard fluoroscopy-guided minimally invasive technique.

STUDY DESIGN/SETTING

Cadaveric laboratory study.

METHODS

ARSN was installed in a hybrid operating room, consisting of a flat panel detector c-arm with two dimensional/three dimensional imaging capabilities and four integrated cameras in its frame. The surface-referenced navigation device does not require a bony reference but uses video cameras and optical markers applied to the patient's skin for tracking. In four cadavers, a total of 136 pedicle screws were inserted in thoracic and lumbar vertebrae. The accuracy was assessed by three independent raters in postoperative conventional computed tomography.

RESULTS

The overall accuracy of ARSN was 94% compared with an accuracy of 88% for fluoroscopy. The difference was not statistically significant. In the thoracic region, accuracy with ARSN was 92% compared with 83% with fluoroscopy. With fluoroscopy, unsafe screws were observed in three normal cadavers and one with scoliosis. Using ARSN, unsafe screws were only observed in the scoliotic spine. No significant difference in the median of time for K-wire placement was recorded. As no intraoperative fluoroscopy was necessary in ARSN, the performing surgeon was not exposed to radiation.

CONCLUSIONS

In this limited cadaveric study minimally invasive screw placement using ARSN was demonstrated to be feasible and as accurate as fluoroscopy. It did not require any additional navigation time or use of any intraoperative x-ray imaging, thereby potentially permitting surgery in a protective lead garment-free environment. A well-powered clinical study is needed to demonstrate a significant difference in the accuracy between the two methods.

CLINICAL SIGNIFICANCE

ARSN offers real-time imaging of planned insertion paths, instrument tracking, and overlay of three dimensional bony anatomy and surface topography. The referencing procedure, by optical recognition of several skin markers is easy and does not require a solid bony reference as necessary for conventional navigation which saves time. Additionally, ARSN may foster the reduction of intraoperative x-ray exposure to spinal surgeons.

Impact of lumbar pedicle screw positioning on screw stability - A biomechanical investigation

BACKGROUND

Screw loosening is a major complication following spondylodesis. While several modifications increase screw stability, some, such as screw augmentation, are associated with potential complications; new techniques are needed to minimize the risk of screw loosening without increasing complication rates.

METHODS

13 fresh-frozen human lumbar vertebral bodies (L1 to L5) were dissected. In group 1 (n = 7), pedicle screws were implanted conventionally, while in group 2 (n = 6), the screws were positioned divergent in the sagittal pathway. Screw stability was tested under cyclic axial load; one testing-cycle included 1000 repetitions. The first cycle started with a load of 100 N while the load was increased by +20 N in each following cycle until failure. Failure was defined by either a >5 mm movement of the screw heads or triggering of the switch-off threshold.

FINDINGS

Average number of cycles until failure was increased in group 2 compared with group 1 (12,046 vs 9761 cycles), as was the average load to failure (Fmax 313 N vs 260 N). Overall, in group 2, the number of cycles until screw loosening or failure increased by 23% (p = 0.28), while the required force increased by 20% (p = 0.3). Statistically significant correlation between BMD and increased number of cycles completed as well as with increased load (p < 0.01) could be observed.

INTERPRETATION

The results demonstrate, that divergent screw-drift of pairs of screws in the sagittal plane tends to increase stability, especially in vertebral bodies with lower bone density. Moreover, we could demonstrate a correlation between BMD and stability of screw-fixation.

Augmented reality navigation for spinal pedicle screw instrumentation using intraoperative 3D imaging

BACKGROUND CONTEXT

Due to recent developments in augmented reality with head-mounted devices, holograms of a surgical plan can be displayed directly in the surgeon's field of view. To the best of our knowledge, three dimensional (3D) intraoperative fluoroscopy has not been explored for the use with holographic navigation by head-mounted devices in spine surgery.

PURPOSE

To evaluate the surgical accuracy of holographic pedicle screw navigation by head-mounted device using 3D intraoperative fluoroscopy.

STUDY DESIGN

In this experimental cadaver study, the accuracy of surgical navigation using a head-mounted device was compared with navigation with a state-of-the-art pose-tracking system.

METHODS

Three lumbar cadaver spines were embedded in nontransparent agar gel, leaving only commonly visible anatomy in sight. Intraoperative registration of preoperative planning was achieved by 3D fluoroscopy and fiducial markers attached to lumbar vertebrae. Trackable custom-made drill sleeve guides enabled real-time navigation. In total, 20 K-wires were navigated into lumbar pedicles using AR-navigation, 10 K-wires by the state-of-the-art pose-tracking system. 3D models obtained from postexperimental CT scans were used to measure surgical accuracy. MF is the founder and shareholder of Incremed AG, a Balgrist University Hospital start-up focusing on the development of innovative techniques for surgical executions. The other authors declare no conflict of interest concerning the contents of this study. No external funding was received for this study.

RESULTS

No significant difference in accuracy was measured between AR-navigated drillings and the gold standard with pose-tracking system with mean translational errors between entry points (3D vector distance; p=.85) of 3.4±1.6 mm compared with 3.2±2.0 mm, and mean angular errors between trajectories (3D angle; p=.30) of 4.3°±2.3° compared with 3.5°±1.4°.

CONCLUSIONS

In conclusion, holographic navigation by use of a head-mounted device achieve accuracy comparable to the gold standard of high-end pose-tracking systems.

CLINICAL SIGNIFICANCE

These promising results could result in a new way of surgical navigation with minimal infrastructural requirements but now have to be confirmed in clinical studies.

A minimally invasive, 3D-fluoroscopy-navigation-guided, 3D-controlled pedicle approach in spine surgery: first reliable results and impact on patient safety

PURPOSE

Safe pedicle screw placement is a daily challenge to every spine surgeon. Introduction of minimally invasive approaches in spinal surgery led to an impaired facility of inspection of the surgical field increasing the importance of intraoperative imaging and navigation. During the past years, we established a minimally invasive, navigated approach in our clinical setting.

METHODS

We retrospectively reviewed the accuracy of pedicle approaches in patients treated due to traumatic or osteoporotic fractures, spondylitis/discitis, and tumoral lesions. Guide wires for pedicle screws or kyphoplasty cannulas were inserted in a 3D-navigation-guided, minimally invasive technique. Positioning of the guide wires was verified via 3D-scan, and pedicle screws/kyphoplasty cannulas were then visualized via a.p./lateral radiographs. Accuracy data were compared to a standard navigated open approach control group with indications similar to the MIS-group.

RESULTS

23 MIS patients were included in this study (25-84 years, mean 70 years) with a total of 154 placed guide wires. Handling of the navigated Jamshidi needle was easy and secure. The guide wires showed correct placement in 151/154 cases. Three wires (1.9%) needed correction of placement after control scan. There were no vascular or neurologic complications due to wire misplacement. In the open-surgery control group, 7/181 screws (3.9%) needed intraoperative correction presenting no significant difference compared to the correction rate of the MIS-group (p = 0.35).

CONCLUSION

Our study shows the feasibility and reliability of a navigation-guided, minimally invasive pedicle approach in the clinical setting. Therefore, reduced morbidity due to minimized approaches can be combined with higher accuracy of navigated pedicle screw/kyphoplasty cannula placement improving patient safety.

Pullout force of minimally invasive surgical and open pedicle screws-a biomechanical cadaveric study

Background

To assess whether lumbar pedicle screw placement with a minimally invasive surgical (MIS) vs. open technique imparts different biomechanical parameters and thus may affect failure rates.

Methods

Human cadaveric disarticulated lumbar vertebrae 1-5 were stabilised in cement. Pedicle screws were inserted either via the 'MIS' or 'open' technique, based on previously described anatomical landmarks. Each vertebra had one 'MIS' and one 'open' technique screw. Specimens were tested with an Instron mechanical testing machine, positioned to allow for testing of direct coaxial force. Load was applied until failure occurred, and load-displacement curves generated for each screw.

Results

Average failure load was found to be 685±399 N for MIS, versus 661±323 N for open technique (P=0.75). The average ultimate failure load was 748±421 N for MIS, versus 772±326 N for open (P=0.74). Average displacement until failure was 0.95±0.49 mm for MIS as compared to 0.95±0.62 mm for open (P=0.996). Axial stiffness was 936±217 N/mm for MIS and 1,016±263 N/mm for open (P=0.19). Average work required to result in failure was 0.84±1.09 J for MIS and 0.82±1.05 J for open (P=0.94).

Conclusions

There was no significant difference in the biomechanical properties of the MIS as compared with open lumbar pedicle screws, when tested until failure under direct coaxial force. The clinical implication may be that there is no significant advantage in the biomechanical properties of MIS versus open lumbar pedicle screw insertion techniques.

Biomechanical comparison of cervical discectomy/fusion model using allograft spacers between anterior and posterior fixation methods (lateral mass and pedicle screw)

BACKGROUND

The purpose of this study is to investigate effects of different fixation methods on the physical stress on allospacers, endplate-vertebral body, and implants using finite element model analyses.

METHODS

Stress distribution and subsidence risk according to the fixation methods under the condition of hybrid motion control were analyzed. The detailed finite element model of a previously validated, three-dimensional, intact cervical spinal segment model, with C5-C6 segmental fusion using allospacer, was used to evaluate the biomechanical characteristics of different fixation combinations, such as anterior plate/screws, lateral mass screw, and posterior pedicle screw.

FINDINGS

The load sharing on allospacers increased in extension in order of posterior pedicle screws (21.4%), lateral mass screws (31.5%), and anterior plate/screws (56.6%). lateral mass screw demonstrated the highest load sharing (68.1%) on the allospacer in flexion. The Peak von Mises stress of the allospacer was the lowest in flexion and axial rotation but the highest in extension with anterior plate/screws. Allospacer subsidence risk was the lowest in extension, lateral bending, and axial rotation with posterior pedicle screws but the lowest in flexion with anterior plate/screws. The bone-screw loosening risk was the lowest in all modes with posterior pedicle screws but the highest with anterior plate/screws.

INTERPRETATION

Posterior pedicle screws demonstrated the best mechanical stability of allospacer failure-subsidence and the lowest risk of screw loosening. Different motion restrictions depending on the fixation method should be considered for implant and allospacer safety.

Symptomatic pulmonary cement embolism after pedicle screw polymethylmethacrylate cement augmentation: A case report and review

Background:

In osteoporotic patients, a useful technique for significantly enhancing the strength of a pedicle screw is augmentation with polymethylmethacrylate cement. However, a rare complication of this procedure is a symptomatic pulmonary cement embolism.

Case Description:

A pedicle screw cement augmentation was performed in a middle-aged female for the failed back syndrome. When she developed symptomatic pulmonary cement emboli, she was successfully managed with conservative measures, including anticoagulation.

Conclusion:

Despite the increased use of cement augmentation for pedicle screw placement and the relatively high incidence of cement leakage into the prevertebral venous system, symptomatic cement pulmonary embolism remains rare. The management of such symptomatic CPE should be evaluated and treated based on both the size and location of the embolism. Here, we presented this case while reviewing three symptomatic and four asymptomatic cases from the literature.

Comparison of Different Insertion Techniques for Lumbosacral Fixation Improvement: A Finite Element Study

OBJECTIVE

We create a new S1 cortical screw trajectory technique using 3D reconstruction and the finite element (FE) method to provide a more reliable theoretical basis for clinical practices and to advance internal fixation technology for treatment of lumbosacral degenerative diseases.

METHODS

This retrospective study included patients (aged from 40 to 70 years) who needed intervertebral fusion surgery between August 2016 and August 2017. Data of patients with lumbosacral lesions was scanned and measured by 64-row spiral CT, and were then transmitted to the GE-AW4.3 post-processing system for 3D reconstruction. The trajectories of the three different screws were simulated by FE software and processed by mimics software to simulate the screw path: traditional PS fixation (Model A); traditional cortical screw (Model B); and new cortical screw (Model C). The CT value of the bone around the screw canal was recorded. Biomechanical effects of the three screws were analyzed and compared.

RESULTS

The displacement of flexion and extension, the vertebral body stress of right torsion, and the cage stress of flexion showed no significant differences among the three models (P > 0.05). The results demonstrated that cortical screws exceeded pedicle screws in stability and pullout force. Models B and C showed higher vertebral displacement in left bending (0.41 and 0.31 mm) and right bending (0.58 and 0.40 mm), lower vertebral body stress on extension (48.37 and 38.92 MPa), left bending (0.76 and 0.74 mm) and right bending (0.50 and 0.53 mm), and higher cage stress on left bending (162.19 and 160.63 MPa), right bending (150.02 and 150.05 MPa), left torsion (158.45 and 146.27 MPa) and right torsion (167.33 and 171.15 MPa) (all P < 0.05) compared to model A. Compared to Model B, Model C had higher displacement of left and right torsion, lower pressure in extension and flexion, and lower stress on cages in extension (P < 0.05).

CONCLUSION

The new cortical screw insertion method has similar effects to traditional cortical screw fixation. However, it demonstrated advantages in promoting lumbosacral interbody fusion, which protects vessels and nerves.

A bicortical pedicle screw in the caudad trajectory is the best option for the fixation of an osteoporotic vertebra: An in-vitro experimental study using synthetic lumbar osteoporotic bone models

BACKGROUND

In pedicle screw fixation, the optimal depth and trajectory of insertion are controversial, and this might be because of the wide variations in specimens. The present study aimed to investigate the biomechanically optimal depth and trajectory of screw insertion using synthetic lumbar osteoporotic vertebrae.

METHODS

A total of 27 synthetic osteoporotic lumbar vertebrae (L3) were used to ensure standard vertebral quality and shape. Pedicle screws having two different lengths (unicortical: to the center of the vertebra; bicortical: to the anterior cortex of the vertebra) were inserted in the following three different trajectories: 1) straight-forward (parallel to the superior endplate), 2) cephalad (toward the anterosuperior corner), and 3) caudad (toward the anteroinferior corner). Maximum insertional torque and pull-out strength were measured.

FINDINGS

For the straight-forward, cephalad, and caudad trajectories, the maximum insertional torque (Ncm) values of unicortical screws were 144.4, 143.1, and 148.9, respectively, and those of bicortical screws were 205.5, 156.2, and 207.8, respectively. The maximum insertional torque values were significantly higher for bicortical screws than unicortical screws (p < 0.001). Additionally, regarding bicortical screws, the maximum insertional torque values were significantly lower for the cephalad trajectory than other trajectories (p = 0.002). The pull-out strength (N) values of bicortical screws for the straight-forward, cephalad, and caudad trajectories were 703.3, 783.9, and 981.3, respectively. The pull-out strength values were significantly lower for the straight-forward trajectory than other trajectories (p = 0.034).

INTERPRETATION

A bicortical pedicle screw in the caudad trajectory might be the best option to improve fixation in an osteoporotic lumbar vertebra.

A cost-effectiveness study

Image-guided surgery using intraoperative cone-beam CT and navigation improves screw placement accuracy rates. However, this technology is associated with high acquisition costs. The aim of this study is to evaluate the costs of revision surgery from symptomatic pedicle screw malposition to justify whether the costs of acquiring intraoperative navigation justify the expected benefits. This is a retrospective cost-effectiveness analysis of consecutive patients who had pedicle screw instrumentation using intraoperative cone-beam CT and navigation compared with patients who underwent freehand pedicle screw instrumentation at our institution over 4 years. The costs associated with revision surgery for symptomatic pedicle screw malposition (excess length of stay, intensive care, theatre time, implants and additional outpatient appointments) were calculated. A total of 19 patients had symptomatic screw malpositioning requiring revision surgery. None of these patients had screws inserted under navigation. Revision surgery accounted for an extra 304 bed days and an additional 97 h theatre time. The total extra spent over 4 years was £464,038. When compared to the costs of revision surgery for screw malpositioning, it was cost neutral to acquire and maintain this technology. Intraoperative image-guided surgery reduces reoperation rates for symptomatic screw malposition and is cost-effective in high volume centers with improved patients outcomes. High acquisition and maintenance cost of such technologies is economically justifiable.

Guideline for Thoracolumbar Pedicle Screw Placement Assisted by Orthopaedic Surgical Robot

The pedicle screw placement procedure is the most commonly used technique for spinal fixation and can provide reliable three‐column stabilization. Accurate screw placement is necessary in clinical practice. To avoid screw malposition, which may decrease the stiffness of the screw‐rod construct or increase the likelihood of neural and vascular injuries, the surgeons must fully understand the regional anatomy. Deformities, such as scoliosis, kyphosis or congenital anomalies, may complicate the application of the pedicle screw placement technique and increase the chance of screw encroachments. Incidences of pedicle screw malposition vary in different districts and hospitals and with surgeons and techniques. Today, the minimally invasive spinal surgery is well developed. However, the narrow corridors and limited views for surgeons increase the difficulty of pedicle screw placement and the possibility of screw encroachment. Evidenced by previous studies, robotic surgery can provide accurate screw placement, especially in settings of spinal deformities, anatomical anomalies, and minimally invasive procedures. Based on the consensus of consultant specialists, the literature review and our local experiences, this guideline introduces the robotic system and describes the workflow of robot‐assisted procedures and the precautions to take during procedures. This guideline aims to outline a standardized method for robotic surgery for thoracolumbar pedicle screw placement.

Pedicle screw placement in spinal neurosurgery using a 3D-printed drill guide template: a systematic review and meta-analysis

Background

Many surgeons believe that the use of a 3D-printed drill guide template shortens operative time and reduces intraoperative blood loss compared with those of the free-hand technique. In this study, we investigated the effects of a drill guide template on the accuracy of pedicle screw placement (the screw placed completely in the pedicle), operative time, and intraoperative blood loss.

Materials/Methods

We systematically searched the major databases, such as Medline via PubMed, EMBASE, Ovid, Cochrane Library, and Google Scholar, regarding the accuracy of pedicle screw placement, operative time, and intraoperative blood loss. The χ² test and I² statistic were used to examine heterogeneity. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to calculate the accuracy rate of pedicle screw placement, and weighted mean differences (WMDs) with 95% CIs were utilized to express operative time and intraoperative blood loss.

Results

This meta-analysis included 13 studies (seven randomized controlled trials and six prospective cohort studies) involving 446 patients and 3375 screws. The risk of research bias was considered moderate. Operative time (WMD = − 20.75, 95% CI − 33.20 ~ − 8.29, P = 0.001) and intraoperative blood loss (WMD = − 106.16, 95% CI − 185.35 ~ − 26.97, P = 0.009) in the thoracolumbar vertebrae, evaluated by a subgroup analysis, were significantly different between groups. The 3D-printed drill guide template has advantages over the free-hand technique and improves the accuracy of pedicle screw placement (OR = 2.88; 95% CI, 2.39~3.47; P = 0.000).

Conclusion

The 3D-printed drill guide template can improve the accuracy rate of pedicle screw placement, shorten operative time, and reduce intraoperative blood loss.

Axis vertebral dimensions for safe screw placement: A CT normative data analysis

INTRODUCTION

Morphometric evaluation of the pedicle and isthmus of second cervical vertebra (C2) (Axis) is extremely vital before contemplating any surgical stabilization involving the Craniovertebral region, in view of its proximity to the vertebral artery and the cervical nerve root. The dimensions of pedicles and isthmuses in C2 vary between individuals and there is paucity of data in the Indian population. This study strives to measure the average pedicle and isthmus dimensions in a sample of population, which would enable selection of screws with safest diameters to be used in C2; thereby avoiding injury to adjacent neurovascular structures.

MATERIALS AND METHODS

One Hundred patients in the age group between 18 and 70 years who underwent CT scan of head and neck region were included in the study. The aim of this study was to assess the anatomic suitability of transarticular and pedicle screw placement in Axis vertebrae of Indian population and determine the maximum safe diameter for screw placement. The following parameters were measured in millimeters: Pedicle width, Pedicle angle, Internal height and Isthmic height.

RESULTS

The Mean maximum diameter of potential pedicle screw was 4.99 ± 1.1 mm for the right side with the left side being slightly wider at 5.20 ± 1.16 mm. Twenty eight (28%; 56 out of 200 pedicles) had a measurement < 4.5 mm. The internal height in sagittal images representing the pedicle height was found to be 4.79 ± 0.96 mm on the right side and 4.75 ± 1.04 mm on the left side. Sixty five (65) out of 200 pedicles (32.5%) had measurements < 4.5 mm in sagittal plane. The Mean maximum diameter of potential Transarticular screw (outer diameter of isthmus) was 5.05 ± 0.78 mm for the right side and 5.18 ± 0.84 mm on the left side.

DISCUSSION

Isthmic height < 4.5 mm could potentially violate the vertebral foramen when a 3.5 mm screw is used. In our study 22.5% isthmuses were narrow (<4.5 mm). The mean maximum safe diameter for a potential transarticular screw in the present study was 5.11 mm. Though our patients had smaller isthmus dimensions compared with literature, 77.5% of C2 could take a 4 mm transarticular screw quite comfortably considering the 0.5 mm margin on either side. In the present study, 28% of pedicles were found to be inappropriately sized (<4.5 mm) to accommodate the standard 3.5 mm screw. The mean maximum diameter of a potential pedicle screw in our study was 5.09 mm; and in 72% of patients a 4 mm screw could be placed with confidence. Though our patients on an average can accommodate a 4 mm screw comfortably, we suggest a protocol of obtaining CT measurements of C2 prior to operative intervention for identifying those individuals at risk of neurovascular injury; 22.5% for transarticular screw and 28% for pedicle screw.

Clinical Effects of Oblique Lateral Interbody Fusion by Conventional Open versus Percutaneous Robot-Assisted Minimally Invasive Pedicle Screw Placement in Elderly Patients

OBJECTIVES

To compare the clinical outcomes of percutaneous robot-assisted minimally invasive pedicle screw insertion versus freehand fluoroscopy-assisted pedicle screw insertion using a traditional open technique in elderly patients undergoing an oblique lumbar interbody fusion (OLIF) procedure.

METHODS

Based on the inclusion and exclusion criteria, 80 patients with lumbar degenerative disease who attended the spinal surgery department of the Beijing Jishuitan Hospital between January 2017 and April 2018 were enrolled in the present study. Patients were randomized 1:1 to undergo percutaneous robot-assisted minimally invasive pedicle screw insertion (experimental group, n = 40) or freehand fluoroscopy-assisted pedicle screw insertion using a traditional open technique (control group, n = 40). Outcomes were accuracy of screw placement evaluated on postoperative CT using the modified Gertzbein and Robbins scale, operative time, blood loss, postoperative drainage, lower back and leg pain evaluated using a visual analogue scale (VAS), lumbar function evaluated using the Oswestry disability index (ODI), and complication rates.

RESULTS

A total of 344 vertebral pedicle screws were inserted: 170 screws in the experimental group, and 174 screws in the control group. Accurate screw placement was significantly higher in the experimental group (98.2% [167/170]) than in the control group (93.1% [162/174]). Clinical outcomes showed significant differences between the experimental and control groups in operative time, intraoperative blood loss, and postoperative VAS for lower back pain in the immediate postoperative period.

CONCLUSION

Robot-assisted pedicle screw insertion in OLIF is an effective strategy for the management of elderly patients with lumbar degenerative diseases.

Application of different thresholds for instrumentation device testing in minimally invasive lumbosacral spine fixation

The main aim of this study was evaluating the reliability of stimulus-evoked electromyography (using different thresholds for stimulation of the instrumentation devices) for minimally invasive pedicle screw placement in the lumbosacral spine. A threshold of 5 mA was applied for the pedicle access needle. 7 mA was applied for the tapscrew and pedicle screw stimulation. The existence of threshold differences between vertebral levels was also assessed. All patients underwent postoperative computed tomography (CT) to determine the accuracy of pedicle screw placement. A total of 172 percutaneous pedicle screws were placed in 52 patients. 94.1% of screws were placed at L4, L5 and S1 vertebral levels. No statistically significant differences existed in thresholds of the pedicle access needles, tapscrews and pedicle screws between vertebral levels. In four instances, the pedicle access needle stimulation had a threshold of 5 mA (no breaches were associated). In the rest of occasions, the pedicle access needles had stimulation thresholds above 5 mA. In all instances, tapscrew and pedicle screw thresholds were above 7 mA; the tapscrews and pedicle screws had significantly greater thresholds than the pedicle access needles. No statistically significant differences existed in thresholds between tapscrews and pedicle screws. Postoperative CT imaging revealed one lateral pedicle violation. Both breach rate and false negative rate were 0.5%. No false positive cases were observed. No patients experienced postoperative pedicle screw-related neurologic deficits. A threshold of 5 mA for the pedicle access needle stimulation seems to be safe. Greater than 7 mA should be used for the tapscrew and pedicle screw stimulation.

A biomechanical investigation of the retentive force of pedicle screw structures for different screw tulip designs

BACKGROUND

Pedicle screw based spinal fixation systems have been widely used for treating a variety of spinal diseases. The retentive force is an important factor that determines structural stability. The screw tulip design and the magnitude of nut tightening torque influence the retentive force. This study investigated the influences of varied tilt angles between the shaft-rod interface and varied nut tightening torques on the retentive force of the monoaxial, polyaxial, and uniplanar screws.

METHODS

Three types of tulip constructs were biomechanically tested. Two parameters that affect the retentive force include the tilt angle and the nut tightening torque. The retentive force was investigated by an axial gripping capacity test and axial torque gripping capacity test.

FINDING

Among all combinations of screw designs and tilt angles, the 12 Nm nut tightening torque offered a greater retentive force than the 8 Nm, except for monoaxial screws with a 0 degree tilt angle. For monoaxial screws, the retentive force was negatively correlated with increasing tilt angles. For polyaxial and uniplanar screws, the retentive forces remained constant with increasing tilt angles.

INTERPRETATION

In monoaxial screws, when the axis of the shaft isn't perpendicular to the axis of the rod, a gap is formed between the tulip-rod interface. This results in a decreased retentive force. In polyaxial and uniplanar screws, the contact surfaces were the same in different tilt angles, therefore, the retentive force remained constant, which was attributed to the adjustable tulips always being perpendicular to the axis of the rods.

A comparative study between the Universal Spinal System® (USS) and the CD Horizon® Legacy™ (CDH) in the management of thoracolumbar fractures

Introduction: For the treatment of unstable non-osteoporotic thoracolumbar fractures, the clinical and radiological outcome of short-segment fixation with the USS™ – Universal Spine System (DePuy Orthopedics, Inc., Warsaw, IN, USA) and the CD HORIZON^® LEGACY™ 5.5 Spinal System, (Medtronic Sofamor Danek USA, Inc., Memphis, TN, USA) were compared.

Methods: From March 2015 to January 2016, 40 consecutive patients with unstable traumatic thoracolumbar fractures who met our inclusion criteria were treated with either the USS system or CDH Legacy system. Segmental kyphosis angle (SKA) and anterior body height (ABH) of fractured vertebrae, and ASIA Impairment Scale (AIS) were evaluated. Radiological fusion was confirmed with plain X-rays and when indicated with computerized tomography (CT).

Results: The mean immediate kyphotic angle correction was 16.6° for the Schanz and 6.4 for the Legacy system, and the immediate mean anterior vertebral body height correction was 0.92 cm for the Schanz and 0.51 cm for the Legacy system. Our study shows a significant statistical difference between Schanz and Legacy systems regarding post-operative segmental kyphosis and height correction immediately postoperatively, at 6 months and at one-year follow-up (p-value < 0.005). The degree of pain reduction and neurological improvement was not influenced by the screw system.

Conclusion: Usage of USS in thoracolumbar fracture as a short-segment fixation led to a near anatomical reduction when compared to the Legacy system. However, there was no advantage regarding pain reduction and neurological outcome.

Surgical Treatment With Thoracic Pedicle Screw Fixation of Vertebral Osteomyelitis With Long-Term Follow-up

BACKGROUND

While recent data has demonstrated the utility of lumbar pedicle screws for the treatment of vertebral osteomyelitis, the data are limited for thoracic pedicle screws.

OBJECTIVE

To investigate the effectiveness of thoracic pedicle screws for the surgical treatment of vertebral osteomyelitis.

METHODS

A retrospective review of all operations performed by 2 spinal neurosurgeons from 1999 to 2012 yielded 30 cases of vertebral osteomyelitis that were treated with thoracic pedicle screws. Sixteen (53%) of which underwent combined anterior and posterior fusion and 14 patients (47%) underwent standalone posterior fusion. Postoperative records were analyzed for pertinent clinical, laboratory, and radiographic data.

RESULTS

Of the 30 patients, 21 were males (70%), 8 were females (27%), and 1 was transsexual (3%). The mean age was 47 yr (range 18-69). The most common organism cultured was Staphylococcus aureus in 12 cases (50%). The mean patient stay in the hospital was 12.4 d after surgery (range 5-38 d). The mean antibiotic duration after discharge was 8 wk (range 1-24 wk). Of the 25 patients with long-term follow-up (mean, 49 mo), 92% had improved back pain (6/25 marked improvement, 17/25 complete resolution), 83% had improved muscle weakness (8/18 marked improvement, 7/18 complete resolution), and 100% had improved urinary incontinence (3/8 marked improvement, 5/8 complete resolution). Two patients (7%) required additional surgical revision due to instrumentation failure or wound infection.

CONCLUSION

This study demonstrates the efficacy of utilizing thoracic pedicle screws as a primary intervention to treat vertebral osteomyelitis.

Accuracy and reliability of spinal navigation: An analysis of over 1000 pedicle screws

Purpose

To estimate the rate of pedicle screw malpositioning associated with placing pedicle screws using intraoperative computed tomography (CT)-guided spinal navigation.

Methods

We analysed the records of 219 patients who underwent pedicle screw fixation using O-arm-based navigation. Screw placement accuracy was evaluated on intraoperative CT scans acquired after pedicle screw insertion. Breaches were graded according to the Gertzbein classification (grade 0-III).

Results

Of 1152 pedicle screws included, 47 had pedicle violations noted on intraoperative CT. Pedicle screw violation was noted for 17 of 241 screws placed in the cervical spine (overall breach rate, 7.05%; 3.73% and 3.3% with grade I and II, respectively), for 11 of 300 screws placed in the thoracic spine (overall breach rate, 3.67%; 2%, 1%, and 0.67% with grade I, II, and III, respectively), and for 22 of 611 screws placed in the lumbar spine (overall breach rate, 3.6%; 2.29% and 0.82% with grade I and II, respectively). The rate of accuracy of pedicle screw fixation was 93%, 96.33%, and 96.4% for the cervical, thoracic, and lumbar spine, respectively.

Conclusions

Using O-arm-based intra-operative three-dimensional scans for navigation can improve the reliability, accuracy, and safety of pedicle screw placement, reducing the risk for reoperation and hospitalization due to implant-related complications. Further improvement may be achieved by adequate consideration of potential sources of errors.

percutaneous dorsal instrumentation after traumatic spinal fracture

OBJECTIVE

Dorsal stabilization is a frequently used procedure in the treatment of acute traumatic vertebral body fractures. Besides the traditional open surgical procedure, the percutaneous positioning of pedicle screws is now widely used. The aim of the current study is to compare pedicle screw misplacement following open vs. percutaneous dorsal instrumentation after traumatic spinal fracture of the thoracic and lumbar spine and to assess possible risk factors associated with pedicle screw misplacement.

METHODS

All patients who suffered a traumatic spinal fracture that were treated with dorsal stabilization in our level I trauma center in the period from 01/2007 to 03/2014 were included in this retrospective therapeutic cohort study. From 01/2007 to 06/2009, an open surgical procedure was used, and from 06/2009 to 03/2014, the percutaneous procedure was used for all types of fractures. Retrospectively, the positioning of every single pedicle screw was evaluated in the post-operative computed tomography scan and classified. Epidemiological data were also documented to compare the two treatment groups.

RESULTS

A total of 491 patients with 681 vertebral body fractures were included. Of 733 pedicle screws placed during the open surgery procedure, 96.0% were within the safe zone. There was no significant difference compared with pedicle screws placed percutaneously (95.3% of 1884 screws). In all other categories, the number of misplaced pedicle screws also showed no differences between the two treatment groups. There is a positive correlation between pedicle screw misplacement and duration of the operation. Most pedicle screws are misplaced at the levels T12, L1 and T7, T8.

CONCLUSION

The current study shows that percutaneous surgery using dorsal stabilization allows the positioning of pedicle screws in an equivalently safe manner compared with an open surgical procedure in the acute care of spinal trauma.

A comparison of rigid, semi-rigid and flexible spinal stabilization devices: A finite element study

Pedicle-screw-based spinal fixation system has shown its success for treating degenerative disc disease-related back pain and spinal instability. In the last few decades, several non-fusion implants ( 'flexible' or 'dynamic' fixation) are developed for treating slight degenerate disc disease. The aim of this study is to characterize and compare the biomechanical responses of pedicle-screw-based fusion with various rod materials and a flexible spinal stabilization device on the lumbar spine (L3L5). Computed tomography scan-based finite element model and pedicle screw fixation with rigid rod material stainless steel rod, semi-rigid rod material poly-ether-ether-ketone and flexible rod device made of stainless steel are used in this study. Intact model of the lumbar spine and treated with all the different implants are simulated under typical physiological loading conditions. Compared with the intact model, pedicle screw with the stainless steel rod fixation system is found to offer very less range of motion. Poly-ether-ether-ketone rod system increased range of motion 3.8, 7 and 1.8 times for axial rotation, lateral bending and flexion-extension, respectively, compared to the stainless steel rod system. The flexible rod device rod system is found to reduce stress on vertebral body, carrying out more loads as compared to poly-ether-ether-ketone rods. In the case of stainless steel rods, range of motion is almost restricted on the fusion zone, which is overcome by the poly-ether-ether-ketone rod system to some extent and farther improved by the flexible rod device rod system. So, the poly-ether-ether-ketone rod and flexible rod device rod systems may be implemented for better clinical results after succeeding experimental validation and clinical trial.