Safe and accurate midcervical pedicle screw insertion procedure with the patient-specific screw guide template system

Design and application of a novel 3D printing digital navigation template for cubitus varus deformity in children

Background

This study was aimed to assess the feasibility and efficacy of 3D printing digital template for treatment of cubitus varus deformity.

Methods

32 patients who underwent lateral closing osteotomy were evaluated between January 2018 and January 2020 in this retrospective study. Navigation templates were used in 17 cases, while conventional surgery in 15 cases. The carrying angles before and after surgery, operation time and elbow joint function were compared.

Results

Navigation templates matched well with the anatomical markers of the lateral humerus. More accurate osteotomy degrees, shorter operation time and less radiation exposure were achieved in the navigation template group (p < 0.05). At the last follow-up time, significant difference was found based on the Bellemore criteria (p = 0.0288).

Conclusions

The novel navigation template can shorten operation time, improve the lateral closing osteotomy accuracy and improve postoperative elbow joint function.

Instrumentation of hypoplastic pedicles with patient-specific guides

PURPOSE

Hypoplastic pedicles of the thoracolumbar spine (<5 mm diameter) are often found in syndromic deformities of the spine and pose a challenge in pedicle screw instrumentation. 3D-printed patient-specific guides might help overcome anatomical difficulties when instrumenting pedicles with screws, thereby reducing the necessity for less effective fixation methods such as hooks or sublaminar wires. In this study, the surgical feasibility and clinical outcome of patients with hypoplastic pedicles following pedicle screw instrumentation with 3D-printed patient-specific guides were assessed.

METHODS

Hypoplastic pedicles were identified on preoperative computed tomography (CT) scans in six patients undergoing posterior spinal fusion surgery between 2017 and 2020. Based on these preoperative CT scans, patient-specific guides were produced to help with screw instrumentation of these thin pedicles. Postoperatively, pedicle-screw-related complications or revisions were analyzed.

RESULTS

93/105 (88.6%) pedicle screws placed with patient-specific guides were instrumented. 62/93 (66.7%) of these instrumented pedicles were defined as hypoplastic with a mean width of 3.07 mm (SD  ±0.98 mm, 95% CI [2.82-3.32]). Overall, 6 complications in the 62 hypoplastic pedicles (9.7%) were observed and included intraoperatively managed 4 cerebrospinal fluid leaks, 1 pneumothorax and 1 delayed revision due to 2 lumbar screws (2/62, 3.3%) impinging the L3 nerve root causing a painful radiculopathy. The mean follow-up time was 26.7 (SD  ±11.7) months. Complications were only noted when the pedicle-width-to-screw-diameter ratio measured less than 0.62.

CONCLUSION

Patient-specific 3D-printed guides can aid in challenging instrumentation of hypoplastic pedicles in the thoracolumbar spine, especially if the pedicle-width-to-screw-diameter ratio is greater than 0.62.

Assessing the Accuracy and Safety Thresholds of Patient-Specific Screw Guide Template System in Cervical and Thoracic Spine Surgeries Using DAST Measurements

Introduction

To analyze the reliability of the newly developed patient-specific Screw Guide Template (SGT) system as an intraoperative navigation device for spinal screw insertion.

Methods

We attempted to place 428 screws for 51 patients. The accuracy of the screw track was assessed by deviation of the screw axis from the preplanned trajectory on postoperative CT. The safety of the screw insertion was evaluated by the bone breach of the screw. The bone diameter available for screw trajectory (DAST) was measured, and the relations to the bone breach were analyzed.

Results

In the inserted screws, 98.4% were defined as accurate, and 94.6% were contained in the target bone. In the cervical spine, the screw deviation between breaching (0.57 mm) and contained screws (0.43 mm) did not significantly differ, whereas DAST for breaching screws (3.62 mm) was significantly smaller than contained screws (5.33 mm) (p<0.001). Cervical screws with ≥4.0 mm DAST showed a significantly lower incidence of bone breach (0.4%) than ≤3.9 mm DAST (28.3%) (p<0.001). In the thoracic spine, screw deviation and DAST had significant differences between breaching (1.54 mm, 4.41 mm) and contained (0.75 mm, 6.07 mm) (p<0.001). The incidence of the breach was significantly lower in thoracic screws with ≥5.0 mm (1.9%) than ≤4.9 (21.9%) DAST (p<0.001).

Conclusions

This study demonstrated that our SGT system could support precise screw insertion for 98.4% accuracy and 94.6% safety. DAST was recommended to be ≥4.0 and ≥5.0 mm in the cervical and thoracic spines for safe screw insertion.

Accurate Placement and Revisions for Cervical Pedicle Screws Placed With or Without Navigation: A Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVES

To evaluate the accuracy of placement for cervical pedicle screws with and without the use of spinal navigation.

METHODS

A structured search was conducted in electronic databases without any language or date restrictions. Eligible studies reported the proportion of accurately placed cervical pedicle screws measured on intraoperative or postoperative 3D imaging, and reported whether intraoperative navigation was used during screw placement. Randomized Studies (MINORS) criteria were used to evaluate the methodological quality of how accuracy was assessed for cervical pedicle screws.

RESULTS

After screening and critical appraisal, 4697 cervical pedicle screws from 18 studies were included in the meta-analysis. The pooled proportion for cervical pedicle screws with a breach up to 2 mm was 94% for navigated screws and did not differ from the pooled proportion for non-navigated screws (96%). The pooled proportion for cervical pedicle screws placed completely in the pedicle was 76% for navigated screws and did not differ from the pooled proportion for non-navigated screws (82%). Intraoperative screw reposition rates and screw revision rates as a result of postoperative imaging also did not differ between navigated and non-navigated screw placement.

CONCLUSIONS

This systematic review and meta-analysis found that the use of spinal navigation systems does not significantly improve the accuracy of placement of cervical pedicle screws compared to screws placed without navigation. Future studies evaluating intraoperative navigation for cervical pedicle screw placement should focus on the learning curve, postoperative complications, and the complexity of surgical cases.

Ex vivo comparison of pin placement with patient-specific drill guides or freehand technique in canine cadaveric spines

OBJECTIVE

To compare vertebral implant placement in the canine thoracolumbar spine between 3D-printed patient-specific drill guides (3DPG) and the conventional freehand technique (FH).

STUDY DESIGN

Ex vivo study.

ANIMALS

Cadaveric canine spines (n = 24).

METHODS

Implant trajectories were established for the left and right sides of the T10 through L6 vertebrae based on computed tomography (CT) imaging. Customized drill guides were created for each vertebra of interest. Each cadaver was randomly assigned to one of six veterinarians with varying levels of experience placing vertebral implants. Vertebrae were randomly assigned a surgical order and technique (3DPG or FH) for both sides. Postoperative CT images were acquired. A single, blinded observer assessed pin placement using a modified Zdichavsky classification.

RESULTS

A total of 480 implants were placed in 240 vertebrae. Three sites were excluded from the analysis; therefore, a total of 238 implants were evaluated using the FH technique and 239 implants using 3DPG. When evaluating implant placement, 152/239 (63.6%) of 3DPG implants were considered to have an acceptable placement in comparison with 115/248 (48.32%) with FH. Overall, pin placement using 3DPG was more likely to provide acceptable pin placement (p < .001) in comparison with the FH technique for surgeons at all levels of experience.

CONCLUSION

The use of 3DPG was shown to be better than the conventional freehand technique regarding acceptable placement of implants in the thoracolumbar spine of canine cadavers.

CLINICAL SIGNIFICANCE

Utilizing 3DPG can be considered better than the traditional FH technique when placing implants in the canine thoracolumbar spine.

Cervical Posterior Instrumentation Surgery Using a Patient-Specific Screw Guide Templating System: A Case Report

Posterior cervical pedicle screw (CPS) is one of the most robust forms of posterior instrumentation. Nonetheless, the spinal cord, nerve roots, and vertebral artery are situated in proximity to the cervical pedicle, engendering a significant risk of damage to these structures during CPS insertion. Here, we report a case of cervical posterior instrumentation surgery using a patient-specific three-dimensional (3D) screw guide templating system approved for the cervical spine (Myspine Cervical®). A 62-year-old man presented to our hospital with progressive numbness and paresthesia in both hands and fingers, as well as gait disturbance, which had persisted for one year. A neurological examination revealed severe myelopathy. Imaging findings showed severe spinal cord compression due to ossification of the posterior longitudinal ligament (OPLL) from C3/4 to C6/7. On the diagnosis of compression myelopathy due to cervical OPLL, we performed a posterior decompression and fusion surgery using a patient-specific 3D screw guide templating system (Myspine Cervical®). No severe complications occurred during the surgery. Evaluation of the CPS position by postoperative CT showed that all the CPS placements were accurate. The implementation of the patient-specific 3D screw guide templating system facilitated the secure and precise insertion of CPS in comparison to other surgical assist devices.

Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine (C2-T1): systematic review and meta-analysis comprising 4,165 patients and 16,669 screws

Lateral mass screw (LMS) and cervical pedicle screw (CPS) fixation are among the most popular techniques for posterior fusion of the cervical spine. Early research prioritized the LMS approach as the trajectory resulted in fewer neurovascular complications; however, with the incorporation of navigation assistance, the CPS approach should be re-evaluated. Our objective was to report the findings of a meta-analysis focused on comparing the LMS and CPS techniques in terms of rate of various complications with inclusion of all levels from C2 to T1. We conducted a systematic review of PubMed and EMBASE databases with final inclusion criteria focused on identifying studies that reported outcomes and complications for either the CPS or LMS technique. These studies were then pooled, and statistical analyses were performed from the cumulative data. A total of 60 studies comprising 4165 participants and 16,669 screws placed within the C2-T1 levels were identified. Within these studies, the LMS group had a significantly increased odds for lateral mass fractures (odds ratio [OR] = 43.2, 95% confidence interval [CI] = 2.62-711.42), additional cervical surgeries (OR = 5.56, 95%CI = 2.95-10.48), and surgical site infections (SSI) (OR = 5.47, 95%CI = 1.65-18.16). No other significant differences between groups in terms of complications were identified. Within the subgroup analysis of navigation versus non-navigation-guided CPS placement, no significant differences were identified for individual complications, although collectively significantly fewer complications occurred with navigation (OR = 5.29, 95%CI = 2.03-13.78). The CPS group had significantly fewer lateral mass fractures, cervical revision surgeries, and SSIs. Furthermore, navigation-assisted CPS placement was associated with a significant reduction in complications overall.

Review of Enhanced Handheld Surgical Drills

The handheld drill has been used as a conventional surgical tool for centuries. Alongside the recent successes of surgical robots, the development of new and enhanced medical drills has improved surgeon ability without requiring the high cost and consuming setup times that plague medical robot systems. This work provides an overview of enhanced handheld surgical drill research focusing on systems that include some form of image guidance and do not require additional hardware that physically supports or guides drilling. Drilling is reviewed by main contribution divided into audio-, visual-, or hardware-enhanced drills. A vision for future work to enhance handheld drilling systems is also discussed.

Evaluating the contact anatomy and contact bone volume of spinal screws using a novel drilled surface image

Intraoperative navigation systems have been widely applied in spinal fusion surgery to improve the implantation accuracy of spinal screws using orthogonal tomographic and surface-rendering imaging. However, these images contain limited anatomical information and no information on bone volume contact by the implanted screw, which has been proven to affect the stability of implanted screws. This study proposed a novel drilled surface imaging technique that displays anatomical integration properties to calculate the contact bone volume (CBV) of the screws implanted along an implantation trajectory. A cylinder was used to represent the area traversed by the screws, which was manually rotated and translated to a predetermined implantation trajectory according to a vertebra model obtained using computed tomography (CT) image volumes. The drilled surface image was reconstructed by interpolating the CT numbers at the predefined sampling points on the cylinder surface. The anatomical integration property and CBV of the screw implanted along the transpedicular trajectory (TT) and cortical bone trajectory (CBT) were evaluated and compared. The drilled surface image fully revealed the contact anatomical structure of the screw under the trajectories, improving the understanding of the anatomical integration of the screw and surrounding tissues. On average, the CBV of the CBT was 30% greater than that of the TT. The proposed drilled surface image may be applied in preoperative planning and integrated into intraoperative navigation systems to evaluate the anatomical integration and degree of bone contact of the screw implanted along a trajectory.

An improved path planning algorithm based on artificial potential field and primal-dual neural network for surgical robot

Safety and accuracy are essential for path planning in a surgical navigation system. In this paper, an improved path planning algorithm is proposed to increase the autonomous level of spine surgery robots for higher safety and accuracy. Firstly, the dynamic gravitational constant and piecewise repulsion function are adopted to improve the traditional Artificial Potential Field algorithm to solve the common issues of path planning, including local minimum, unable to reach the target near obstacles. To better control the pose of the end-effector in an operation space, the positions of the two endpoints of the end-effector are further constrained. Secondly, an improved Primal-Dual Neural Network with multiple constraints is proposed to minimize the joint angular velocity norm. The multiple constraints are formulated according to the planned path, the obstacle avoidance of the robot and the joint limits. Moreover, a real-time planned velocity scheme is applied to prevent the accumulation of position errors. The simulation results of the pedicle screw implantation demonstrate that the robot can find the collision-free trajectory and arrive at the target position in various complicated situations. More specifically, the error between two endpoints of the end-effector and the target pose is below 0.1 mm in reaching the surgical tool pose, while the maximum position error is around 0.05 mm when performing the planned path. Moreover, two experiments are conducted in the real-world to verify the proposed algorithm is effective in practice.

3D-printed guides for cervical pedicle screw placement in primary spine tumor: Case report and technical description

Introduction

For spine surgeons, dealing with unstable cervical spine has been usually challenging, and this becomes more difficult when facing a primary craniovertebral junction tumor. Primary spine tumor surgery should always include column reconstruction in order to guarantee biomechanical stability of the spine, but surgeons should always be aware that instrumentations could create interferences with postoperative radiations. However, although carbon fiber instrumentations have started to be used in thoracolumbar oncology for few years, these options are still not available for cervical spine. In the reported case, the adopted strategy to obtain adequate column reconstruction was based on the idea of reducing the amount of titanium needed for posterior fixation and maximizing the distance between the radiation target and titanium rods.

Case report and aim

We present the case of a 53-year-old woman harboring a craniovertebral junction chordoma. A short occipito-C3 construct was selected. Specifically, titanium cervical pedicle screws were placed by using a new technology consisting in patient-tailored and customized 3D-printed guides. The aim of this case report is to determine the feasibility and safety of 3D-printed guides for cervical pedicle screw (CPS) positioning, even in the case of cervical spine tumor.

Conclusion

CPS could represent a good solution by providing strong biomechanical purchase and tailored 3D-printed guides could increase the safety and the accuracy of this challenging screw placement, even in oncological patients.

Accuracy of Lumbosacral Pedicle Screw Placement in Dogs: A Novel 3D Printed Patient-Specific Drill Guide versus Freehand Technique in Novice and Expert Surgeons

OBJECTIVE

 The aim of this study was to compare the accuracy of pedicle screw placement at the canine lumbosacral junction using a novel unilateral three-dimensional printed patient-specific guide (3D-PSG) versus a freehand drilling technique. Additionally, accuracy of screw placement between a novice and an experienced surgeon was determined.

STUDY DESIGN

 Preoperative computed tomography images from 20 lumbosacral cadaveric specimens were used to design a novel unilateral 3D-PSG for the L7 and sacral vertebrae which was printed in acryl-nitrile butadiene styrene plastic. A novice and an expert surgeon each placed 3.5mm cortical screws in 10 cadavers; on the left using the unilateral 3D-PSG and by the freehand (anatomic landmark) technique on the right.

RESULTS

 Sixty screws were placed using the unilateral 3D-PSG and 60 using the freehand technique. There was no statistical difference in accuracy for the comparison between methods performed by the expert (p = 0.679) and novice (p = 0.761) surgeon, nor between an expert and novice surgeon overall (p = 0.923). Unexpectedly, the use of a unilateral 3D-PSG increased variability for the expert surgeon in our study (p = 0.0314).

CONCLUSION

 Using a novel unilateral 3D-PSG did not improve the accuracy of screw placement for lumbosacral stabilization by a novice surgeon compared with an expert surgeon in lumbar spine surgery. This may reflect a suboptimal PSG design.

The Accuracy of Patient-Specific Spinal Drill Guides Is Non-Inferior to Computer-Assisted Surgery: The Results of a Split-Spine Randomized Controlled Trial

In recent years, patient-specific spinal drill guides (3DPGs) have gained widespread popularity. Several studies have shown that the accuracy of screw insertion with these guides is superior to that obtained using the freehand insertion technique, but there are no studies that make a comparison with computer-assisted surgery (CAS). The aim of this study was to determine whether the accuracy of insertion of spinal screws using 3DPGs is non-inferior to insertion via CAS. A randomized controlled split-spine study was performed in which 3DPG and CAS were randomly assigned to the left or right sides of the spines of patients undergoing fixation surgery. The 3D measured accuracy of screw insertion was the primary study outcome parameter. Sixty screws inserted in 10 patients who completed the study protocol were used for the non-inferiority analysis. The non-inferiority of 3DPG was demonstrated for entry-point accuracy, as the upper margin of the 95% CI (−1.01 mm−0.49 mm) for the difference between the means did not cross the predetermined non-inferiority margin of 1 mm (p < 0.05). We also demonstrated non-inferiority of 3D angular accuracy (p < 0.05), with a 95% CI for the true difference of −2.30°−1.35°, not crossing the predetermined non-inferiority margin of 3° (p < 0.05). The results of this randomized controlled trial (RCT) showed that 3DPGs provide a non-inferior alternative to CAS in terms of screw insertion accuracy and have considerable potential as a navigational technique in spinal fixation.

Clinical applications and prospects of 3D printing guide templates in orthopaedics

Background

With increasing requirements for medical effects, and huge differences among individuals, traditional surgical instruments are difficult to meet the patients' growing medical demands. 3D printing is increasingly mature, which connects to medical services critically as well. The patient specific surgical guide plate provides the condition for precision medicine in orthopaedics.

Methods

In this paper, a systematic review of the orthopedic guide template is presented, where the history of 3D-printing-guided technology, the process of guides, and basic clinical applications of orthopedic guide templates are described. Finally, the limitations of the template and possible future directions are discussed.

Results

The technology of 3D printing surgical templates is increasingly mature, standard, and intelligent. With the help of guide templates, the surgeon can easily determine the direction and depth of the screw path, and choose the angle and range of osteotomy, increasing the precision, safety, and reliability of the procedure in various types of surgeries. It simplifies the difficult surgical steps and accelerates the growth of young and mid-career physicians. But some problems such as cost, materials, and equipment limit its development.

Conclusions

In different fields of orthopedics, the use of guide templates can significantly improve surgical accuracy, shorten the surgical time, and reduce intraoperative bleeding and radiation. With the development of 3D printing, the guide template will be standardized and simplified from design to production and use. 3D printing guides will be further sublimated in the application of orthopedics and better serve the patients.

The translational potential of this paper

Precision, intelligence, and individuation are the future development direction of orthopedics. It is more and more popular as the price of printers falls and materials are developed. In addition, the technology of meta-universe, digital twin, and artificial intelligence have made revolutionary effects on template guides. We aim to summarize recent developments and applications of 3D printing guide templates for engineers and surgeons to develop more accurate and efficient templates.

The feasibility of creating Image-Based Patient-Specific Drill Guides for the Atlantoaxial Instabilities using open-source CAD software and desktop 3D printers

OBJECTIVE

C1/2 cervical pedicle screw fixation is a well-known procedure for treating severely damaged and unstable C1/2 fractures. On the other hand, C1/C2 screw fixation is not safe and can lead to potentially disastrous consequences. The importance of personalized 3D printed navigational guides in avoiding these consequences cannot be overstated.

MATERIALS AND METHODS

We retrospectively reviewed the neuroimaging data of 16 patients who had undergone fixation for treatment of C1/2 diseases. We created patient-specific C1/2 models and drill guide models using open-source 3D editing software and a desktop 3D printer. The drill guides were then placed over the respective vertebrae models and fixated with 3.5 mm screws. Following fixation, the parts were scanned with a thin-slice (01 mm) CT scan, and the screw trajectories in the transverse and sagittal planes were measured at each level.

RESULTS

Of the total of 62 screws, 58 were type I (93.54%), 4 were type II (6.45%), and no screws were type III (Tab 2). The results showed that there was no significant deviation in the screw trajectories and the accuracy of the drill guides was 93.54% (Table 3). In our study, type I and type II screws were deemed acceptable, and the acceptable rates of C1/2 screw fixation were 100%.

CONCLUSIONS

In this preclinical study, we demonstrated that it is possible to create patient-specific pedicle drill guides using open source editing software and a commercially available desktop PLA printer, resulting in high accuracy rates in pedicle screw placement in C1/2 patient models.

Accuracy of pedicle screw placement using patient-specific template guide system

BACKGROUND

Despite repeated efforts for accurate cervical pedicle screw insertion, malpositioning of the inserted screw is commonly noted. To avoid neurovascular complications during cervical pedicle screw insertion, we have developed a new patient-specific screw guide system. This study aimed to evaluate the accuracy of cervical PS placement using the new patient-specific screw guide system.

METHODS

This study is a retrospective clinical evaluation of prospectively enrolled patients. Seventeen consecutively enrolled patients who underwent posterior cervical fusion using the guide system were included. Firstly, three-dimensional planning of pedicle screw placement was done using simulation software. A screw guide for each vertebra was constructed preoperatively. A total of 77 screws were inserted with the guides. Postoperative computed tomography was used to evaluate pedicle perforation, and screw deviations, between the planned and actual screw positions, were measured.

RESULTS

A total of 76 screws (98.7%) were completely inside the pedicle (C3-7), without neurovascular injuries. The mean screw deviations from the planned trajectory at the narrowest point of the pedicle and at the entry point in the axial and sagittal planes were 0.56 ± 0.43 mm and 0.43 ± 0.35 mm and 0.43 ± 0.30 mm and 0.63 ± 0.50 mm, respectively. There were no significant differences in any parameter at different spinal levels. Angular deviations in the sagittal and axial planes were 2.94 ± 2.04° and 2.53 ± 1.85°, respectively. Sagittal angular deviations tended to increase in the cranial vertebra (C3 and C4) compared to the middle cervical spine.

CONCLUSIONS

We demonstrated that our patient-specific screw guide is vital for guiding precise screw insertion in the cervical pedicle. This technique may be an effective solution for achieving precise screw insertion and reducing the incidence of complications.

Evaluation of the accuracy of three-dimensionally printed patient-specific guides for transsphenoidal hypophysectomy in small-breed dogs

OBJECTIVE

To assess the accuracy of transsphenoidal hypophysectomy using 3-D printed patient-specific guides (3D-PSGs) in small-breed dogs.

ANIMALS

Heads obtained from the cadavers of 19 small-breed dogs (ex vivo portion of study) and 3 healthy adult (3 to 4 years) purpose-bred Beagles with a median body weight of 9.2 kg.

PROCEDURES

In the ex vivo study, CT images of the cadavers were collected. The position, width, and length of the pituitary fossa and the pilot hole (insertion angle and place) were measured. Using PSGs, 19 pilot holes were made for the pituitary gland fossa, and CT was performed to assess the position accuracy. In the in vivo study, 3 surgical windows from the pilot holes were made using PSGs. Repeated CT and MRI were performed to evaluate the safeness and effectiveness of PSGs, followed by necropsy.

RESULTS

In the ex vivo study, the median (interquartile range) difference between the pre- and postoperative insertion angles was 2° (0° to 3.5°) and the median deviation of the pilot hole was 0.46 mm (0 to 1.58 mm). In the in vivo study, the surrounding structures were not damaged, and favorable outcomes were evident in terms of the shape, size, and position of the surgical window.

CLINICAL RELEVANCE

3D-PSGs provided a safe and effective surgical window for transsphenoidal hypophysectomy. Our findings emphasized the applicability of PSGs in brain surgery, in terms of accuracy and effectiveness.

Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine: systematic review and meta-analysis comprising 1768 patients and 8636 screws

Lateral mass screw (LMS) fixation for the treatment of subaxial cervical spine instability or deformity has been traditionally associated with few neurovascular complications. However, cervical pedicle screw (CPS) fixation has recently increased in popularity, especially with navigation assistance, because of the higher pullout strength of the pedicle screws. To their knowledge, the authors conducted the first meta-analysis comparing the complication rates during and/or after CPS and LMS placement for different pathologies causing cervical spine instability. A systematic literature search of PubMed and Embase from inception to January 12, 2021 was performed to identify studies reporting CPS and/or LMS-related complications. Complications were categorized into intraoperative and early postoperative (within 30 days of surgery) and late postoperative (after 30 days from surgery) complications. All studies that met the prespecified inclusion criteria were pooled and cumulatively analyzed. A total of 24 studies were conducted during the time frame of the search and comprising 1768 participants and 8636 subaxially placed screws met the inclusion criteria. The CPS group experienced significantly more postoperative C5 palsy (odds ratio [OR] = 3.48, 95% confidence interval [CI] = 1.27-9.53, p < 0.05). Otherwise, there were no significant differences between the LMS and CPS groups. There were no significant differences between the CPS and LMS groups in terms of neurovascular procedure-related complications other than significantly more C5 palsy in the CPS group.

Computed Tomography-Based Navigation System in Current Spine Surgery: A Narrative Review

The number of spine surgeries using instrumentation has been increasing with recent advances in surgical techniques and spinal implants. Navigation systems have been attracting attention since the 1990s in order to perform spine surgeries safely and effectively, and they enable us to perform complex spine surgeries that have been difficult to perform in the past. Navigation systems are also contributing to the improvement of minimally invasive spine stabilization (MISt) surgery, which is becoming popular due to aging populations. Conventional navigation systems were based on reconstructions obtained by preoperative computed tomography (CT) images and did not always accurately reproduce the intraoperative patient positioning, which could lead to problems involving inaccurate positional information and time loss associated with registration. Since 2006, an intraoperative CT-based navigation system has been introduced as a solution to these problems, and it is now becoming the mainstay of navigated spine surgery. Here, we highlighted the use of intraoperative CT-based navigation systems in current spine surgery, as well as future issues and prospects.

Cervical Spine Pedicle Screw Accuracy in Fluoroscopic, Navigated and Template Guided Systems-A Systematic Review

Background: Pedicle screws provide excellent fixation for a wide range of indications. However, their adoption in the cervical spine has been slower than in the thoracic and lumbar spine, which is largely due to the smaller pedicle sizes and the proximity to the neurovascular structures in the neck. In recent years, technology has been developed to improve the accuracy and thereby the safety of cervical pedicle screw placement over traditional fluoroscopic techniques, including intraoperative 3D navigation, computer-assisted Systems and 3D template moulds. We have performed a systematic review into the accuracy rates of the various systems. Methods: The PubMed and Cochrane Library databases were searched for eligible papers; 9 valid papers involving 1427 screws were found. Results: fluoroscopic methods achieved an 80.6% accuracy and navigation methods produced 91.4% and 96.7% accuracy for templates. Conclusion: Navigation methods are significantly more accurate than fluoroscopy, they reduce radiation exposure to the surgical team, and improvements in technology are speeding up operating times. Significantly superior results for templates over fluoroscopy and navigation are complemented by reduced radiation exposure to patient and surgeon; however, the technology requires a more invasive approach, prolonged pre-operative planning and the development of an infrastructure to allow for their rapid production and delivery. We affirm the superiority of navigation over other methods for providing the most accurate and the safest cervical pedicle screw instrumentation, as it is more accurate than fluoroscopy and lacks the limitations of templates.

The comparative accuracy and safety of fluoroscopic and navigation-based techniques in cervical pedicle screw fixation: systematic review and meta-analysis

OBJECTIVE

The goal of this study was to evaluate the comparative accuracy and safety of navigation-based approaches for cervical pedicle screw (CPS) placement over fluoroscopic techniques.

METHODS

A systematic search of the literature published between January 2006 and December 2019 relating to CPS instrumentation and the comparative accuracy and safety of fluoroscopic and intraoperative computer-based navigation techniques was conducted. Several databases, including the Cochrane Library, PubMed, and EMBASE, were systematically searched to identify potentially eligible studies. Data relating to CPS insertion accuracy and associated complications, in particular neurovascular complications, were extrapolated from the included studies and summarized for analysis.

RESULTS

A total of 17 studies were identified from the search methodology. Eleven studies evaluated CPS placement under traditional fluoroscopic guidance and 6 studies addressed outcomes following navigation-assisted placement (3D C-arm or CT-guided placement). Overall, a total of 4278 screws were placed in 1065 patients. Misplacement rates of CPS were significantly lower (p < 0.0001) in navigation-assisted techniques (12.51% [range 2.5%-20.5%]) compared to fluoroscopy-guided techniques (18.8% [range 0%-43.5%]). Fluoroscopy-guided CPS insertion was associated with a significantly higher incidence of postoperative complications relating to neurovascular injuries (p < 0.038), with a mean incidence of 1.9% compared with 0.3% in navigation-assisted techniques.

CONCLUSIONS

This systematic review supports a logical conclusion that navigation-based techniques confer a statistically significantly more accurate screw placement and resultant lower complication rates.

A semi-automatic seed point-based method for separation of individual vertebrae in 3D surface meshes: a proof of principle study

PURPOSE

The purpose of this paper is to present and validate a new semi-automated 3D surface mesh segmentation approach that optimizes the laborious individual human vertebrae separation in the spinal virtual surgical planning workflow and make a direct accuracy and segmentation time comparison with current standard segmentation method.

METHODS

The proposed semi-automatic method uses the 3D bone surface derived from CT image data for seed point-based 3D mesh partitioning. The accuracy of the proposed method was evaluated on a representative patient dataset. In addition, the influence of the number of used seed points was studied. The investigators analyzed whether there was a reduction in segmentation time when compared to manual segmentation. Surface-to-surface accuracy measurements were applied to assess the concordance with the manual segmentation.

RESULTS

The results demonstrated a statically significant reduction in segmentation time, while maintaining a high accuracy compared to the manual segmentation. A considerably smaller error was found when increasing the number of seed points. Anatomical regions that include articulating areas tend to show the highest errors, while the posterior laminar surface yielded an almost negligible error.

CONCLUSION

A novel seed point initiated surface based segmentation method for the laborious individual human vertebrae separation was presented. This proof-of-principle study demonstrated the accuracy of the proposed method on a clinical CT image dataset and its feasibility for spinal virtual surgical planning applications.

Accuracy of cervical pedicle screw placement with four different designs of rapid prototyping navigation templates: a human cadaveric study

PURPOSE

Due to the high perforation rate of cervical pedicle screw placement, we have designed four different types of rapid prototyping navigation templates to enhance the accuracy of cervical pedicle screw placement.

METHODS

Fifteen human cadaveric cervical spines from C2 to C7 were randomly divided into five groups, with three specimens in each group. The diameter of pedicle screw used in this study was 3.5 mm. Groups 1-4 were assisted by the two-level template, one-level bilateral template, one-level unilateral template and one-level point-contact template, respectively. Group 5 was without any navigation template. After the surgery, the accuracy of screw placement in the five groups was evaluated using postoperative computed tomographic scans to observe whether the screw breached the pedicle cortex.

RESULTS

A total of 180 pedicle screws were inserted without any accidents. The accuracy rate was 75%, 100%, 100%, 91.7%, and 63.9%, respectively, from Groups 1 to 5. All the template groups were significantly higher than Group 5, though the two-level navigation template group was significantly lower than the other three template groups. The operation time was 4.72 ± 0.28, 4.81 ± 0.29, 5.03 ± 0.35, 8.42 ± 0.36, and 10.05 ± 0.52 min, respectively, from Groups 1 to 5. The no template and point-contact procedures were significantly more time-consuming than the template procedures.

CONCLUSION

This study demonstrated that four different design types of navigation templates achieved a higher accuracy in assisting cervical pedicle screw placement than no template insertion. However, the two-level template's accuracy was the lowest compared to the other three templates. Meanwhile, these templates avoided fluoroscopy during the surgery and decreased the operation time. It is always very challenging to translate cadaveric studies to clinical practice. Hence, the one-level bilateral, unilateral, and point-contact navigation templates designed by us need to be meticulously tested to verify their accuracy and safety.

Surgical treatment for upper cervical deformity with atlantoaxial joint dislocation using individualized 3D printing occipitocervical fusion instrument: A case report and literature review

To introduce a novel technique of using individualized 3D printing occipitocervical fusion instrument (3D-OCF) for the treatment of upper cervical deformity with atlantoaxial joint dislocation.The surgery for deformity of the craniocervical junction area is a challenge in the field of spine. If the surgical deviation is too large to injure the spinal cord or vertebral artery, it will cause catastrophic damage to the patient. Therefore, it is controversial whether these patients should undergo surgical treatment. We provide a novel surgical approach for the challenging upper cervical surgery through 3D-OCF and a typical patient.We present a 54-year-old female patient, who suffered from dizziness and numbness in her limbs for 8 months. After the patient was admitted, we performed the three-dimensional CT scan, modeled using Mimics software 17.0, and designed customized occipitocervical fusion instrument. Besides, we repeatedly perform simulated surgery based on 3D-printed models before surgery.The operative time was 142 minutes and the intraoperative blood loss was 700 mL. X-ray showed reduction of atlantoaxial dislocation and accurate position of internal fixation. The patient's symptoms were significantly relieved: the sensation of dizziness and numbness of limbs was obviously relieved, and the sense of banding in chest, abdomen, and ankle was disappeared. At the last follow-up, imaging showed that 3D-OCF had bone-integration and Syringomyelia was disappeared. The patient's cervical JOA (Japanese Orthopaedic Association) score increased from 10 points to 17 points.Individualized 3D-OCF can improve the safety and accuracy of upper cervical surgery, reduce the operative time and the number of fluoroscopy. Our study provides a novel surgical approach for the challenging upper cervical surgery.

Safety and Feasibility of Cervical Pedicle Screw Insertion in Pediatric Subaxial Cervical Spine Without Navigation: A Retrospective Cohort Study

BACKGROUND

The use of cervical pedicle screws (CPSs) in pediatric subaxial cervical spine has been scarcely reported in the literature. The biomechanical superiority of CPS over other methods of fixation is beneficial in surgery for correcting severe, rigid cervical/cervicothoracic deformity. Our study aims to assess the safety, efficacy, and feasibility of CPS fixation in pediatric subaxial cervical spine without intraoperative navigation.

METHODS

Eight pediatric patients requiring rigid subaxial cervical spine fixation for complex cervical deformities were operated at a single center between 2014 and 2016. Their hospital records and imaging were retrospectively studied. The feasibility of inserting CPS was assessed by studying pedicle morphometry on preoperative computed tomography (CT) scans. Aberrant vertebral artery anatomy was ruled out using CT angiography. CPS were inserted into selected pedicles without navigation. Postoperative CT scans were studied to look for screw containment within pedicles. Complications were noted and clinicoradiologic follow-up was for a minimum of 36 months.

RESULTS

Thirty-seven CPS were inserted in 8 pediatric patients with a mean age of 9.2 years (range: 5 to 13 y). Surgery was done for complex cervical deformities due to various causes-neglected cervical spine trauma (n=3), posttubercular kyphosis (n=2), cervicothoracic scoliosis (n=2), and cervicothoracic osteoblastoma (n=1). The level-wise distribution of the inserted CPS was: C3=4, C4=6, C5=10, C6=10, and C7=7. Postoperative CT scans showed grade-1 medial cortical breach in 5/37 screws and grade-2 medial cortical breach in a single screw (16%). No perioperative complications were noted. At a mean follow-up of 3.6 years (range: 3 to 4.33 y), no patient had implant failure or deformity progression.

CONCLUSIONS

CPS insertion in pediatric subaxial cervical spine without neuronavigation is safe, feasible, and effective in carefully selected cases. Biomechanical advantages of CPS can be extended to the pediatric subaxial cervical spine.

LEVEL OF EVIDENCE

Level IV-retrospective cohort.

Accuracy of Patient-Specific 3D-Printed Drill Guides for Pedicle and Lateral Mass Screw Insertion: An Analysis of 76 Cervical and Thoracic Screw Trajectories

STUDY DESIGN

Single-center retrospective case series.

OBJECTIVE

The purpose of this study was to assess the safety and accuracy of three-dimensional (3D)-printed individualized drill guides for pedicle and lateral mass screw insertion in the cervical and upper-thoracic region, by comparing the preoperative 3D surgical plan with the postoperative results.

SUMMARY OF BACKGROUND DATA

Posterior spinal fusion surgery can provide rigid intervertebral fixation but screw misplacement involves a high risk of neurovascular injury. However, modern spine surgeons now have tools such as virtual surgical planning and 3D-printed drill guides to facilitate spinal screw insertion.

METHODS

A total of 15 patients who underwent posterior spinal fusion surgery involving patient-specific 3D-printed drill guides were included in this study. After segmentation of bone and screws, the postoperative models were superimposed onto the preoperative surgical plan. The accuracy of the realized screw trajectories was quantified by measuring the entry point and angular deviation.

RESULTS

The 3D deviation analysis showed that the entry point and angular deviation over all 76 screw trajectories were 1.40 ± 0.81 mm and 6.70 ± 3.77°, respectively. Angular deviation was significantly higher in the sagittal plane than in the axial plane (P = 0.02). All screw positions were classified as "safe" (100%), showing no neurovascular injury, facet joint violation, or violation of the pedicle wall.

CONCLUSIONS

3D virtual planning and 3D-printed patient-specific drill guides appear to be safe and accurate for pedicle and lateral mass screw insertion in the cervical and upper-thoracic spine. The quantitative 3D deviation analyses confirmed that screw positions were accurate with respect to the 3D-surgical plan.Level of Evidence: 4.

Accurate and Minimally Invasive Cervical Pedicle Screw Insertion Procedure Using the Bone Biopsy Needle as Drill Guide

Introduction

Cervical pedicle screw (CPS) fixation provides the strongest mechanical stability. It needs, however, wide soft tissue detachment to expose the entry point and carries the potential risk of iatrogenic damage to neurovascular structures. Malposition of the CPS cannot be completely avoided even using the navigation system.

Technical Note

Using the bone biopsy needle as drill guide, we developed a novel accurate CPS insertion technique. (1) The entry point of CPS was exposed using Southwick's technique for anterior fixation or Tokioka's technique for posterior fixation. (2) A 13G bone biopsy needle was inserted from the entry point established by the fluoroscopy-assisted pedicle axis view technique described by Yukawa et al. to within a few millimeters of the pedicle. (3) The external sleeve of the bone biopsy needle was left in place as a drill guide, and the 1.25 mm guidewire for a 4.0 mm cannulated screw was then inserted into the pedicle cavity. (4) The external sleeve of the bone biopsy needle was removed, and the screw trajectory was created by a 2.7 mm cannulated drill bit over the guidewire. (5) Tapping was conducted prior to CPS insertion.

Using this method, 29 CPSs in nine patients were inserted. Postoperative computed tomography scans revealed that all the CPSs were placed accurately.

Conclusions

Utilizing the bone biopsy needle as drill guide, our procedure enables accurate positioning of CPS without expensive instruments.

3D printing-assisted percutaneous fixation makes the surgery for scaphoid nonunion more accurate and less invasive

Purpose

The study was to explore whether the 3-dimensional printing guiding plate system could facilitate the modified procedure for arthroscopic treatment of nondisplaced scaphoid nonunion.

Methods

Patients, diagnosed with scaphoid nonunion without displacement, were randomly assigned into two groups. In Group A, the 3-dimensional printing guiding plate system was used for guiding fixation during the surgery. In Group B, fixation was performed with intra-operative fluoroscopy. The bone operation time was recorded during the surgery. The patients were evaluated before surgery and followed-up after six post-operative months, including motion ratio, strength ratio, Visual Analogue Scale, modified Mayo Scores, Patient Rated Wrist Evaluation scores, plain radiography and CT scan.

Results

Sixteen patients were recruited for the study. The average bone operation time in Group A was statistically shorter than that in Group B.

Conclusions

3-dimensional printing technique-assisted arthroscopic bone graft and fixation of scaphoid nonunion constitute an effective and accurate clinical treatment option.

The translational potential of this article

The concept and technique of 3D printing assisted percutaneous fixation introduced in this paper have the potential to be applied in a variety of operations requiring accurate percutaneous fixation, especially for the joint injuries.

Vertebral Artery Terminating Posterior Inferior Cerebellar Artery (PICA-VA) as a Potential Risk Factor in Cervical Spine Surgery

OBJECTIVE

Unilateral vertebral artery (VA) injury is thought to not result in serious complications. The dominant-side VA should be preserved, although the importance of the nondominant-side VA has not been discussed. The injury of VA terminating posterior inferior cerebellar artery (PICA-VA) may result in cerebellar infarction. The characteristics of PICA-VA were evaluated.

METHODS

In study 1, results of head and neck magnetic resonance angiography were reviewed for 358 consecutive cases. VA diameter was measured at the V2 segment. Relationships between frequency of PICA-VA and asymmetry and diameter of the VA were analyzed. In study 2, results of magnetic resonance angiography were measured for 62 consecutive cases aged ≤39 years. Frequency of PICA-VA was compared between this young age group and 324 of the 358 cases aged ≥50 years.

RESULTS

Mean age for the total cohort was 67.8 ± 13.8 years (range, 10-94 years). PICA-VA was identified in 44 cases (12.3%). Mean diameter of all VAs was 3.2 ± 0.76 mm. Mean diameter of PICA-VA was 2.0 ± 0.55 mm, significantly smaller than the nondominant side in Confluence (+) (2.8 ± 0.59 mm; P < 0.001). Among the 56 VAs <2.0 mm, 26 (46.4%) were PICA-VA. PICA-VA was seen in 1 of the 62 cases aged ≤39 years (1.6%), and in 43 of the 324 cases aged ≥50 years (13.3%), showing a significantly lower frequency in the younger population (P < 0.001).

CONCLUSIONS

Whether PICA-VA injury causes complications is not obvious. However, PICA-VA should also be preserved considering that potential risks exist. If the VA is small or shows a large difference in diameter between sides, special care should be taken during cervical spine surgery.

A feasibility study of individual 3D-printed navigation template for the deep external fixator pin position on the iliac crest

Background

The aim of this study was to investigate the feasibility of an individual navigation template for the deep pin position on the iliac crest, based on digital design and 3D printing technology.

Methods

The preoperative CT images of 8 patients with pelvic fractures were collected. The data were reconstructed using a 3D imaging reconstruction workstation. An individual navigation template for the deep pin position on the iliac crest was designed on a virtual 3D model. The individual drill template and the solid pelvic model were produced using the 3D printing technology. The individual drill template was used for intraoperative deep pin position on the iliac crest after the preoperative simulation was completed.

Results

Thirty-two external fixator pins were inserted using the individual drill template. The average depth of pins was 84.82 mm. The trajectories were appropriate based on the postoperative X-ray and CT scan. No significant difference in the entry point, convergence angle, and caudal angle of the pins were noted before and after the operation (all P > 0.05). Finite element analysis indicated that the deep external fixator pin position could more reasonably distribute the stress in the cortical and spongy bones in the pelvis. All patients could perform partial weight-bearing activity 6 weeks postoperatively. No loosening and rupture of the pin, infection, and no damage of blood vessels and nervous tissue were found during the entire follow-up period.

Conclusions

The individual drill template technique is an improvement of the traditional technique, which could increase precision and the depth of pin position. In addition, good mechanical stability and low risk of pin-related complications occurred due to the individual drill template, which makes the external fixation technique a potential alternative.

Biomechanical Evaluation and the Assisted 3D Printed Model in the Patient-Specific Preoperative Planning for Thoracic Spinal Tuberculosis: A Finite Element Analysis

Posterior fixation is superior to anterior fixation in the correction of kyphosis and maintenance of spinal stability for the treatment of thoracic spinal tuberculosis. However, the process of selecting the appropriate spinal fixation method remains controversial, and preoperative biomechanical evaluation has not yet been investigated. In this study, we aimed to analyze the application of the assisted finite element analysis (FEA) and the three-dimensional (3D) printed model for the patient-specific preoperative planning of thoracic spinal tuberculosis. An adult patient with thoracic spinal tuberculosis was included. A finite element model of the T7−T11 thoracic spine segments was reconstructed to analyze the biomechanical effect of four different operative constructs. The von Mises stress values of the implants in the vertical axial load and flexion and extension conditions under a 400-N vertical axial pre-load and a 10-N⋅m moment were calculated and compared. A 3D printed model was used to describe and elucidate the patient’s condition and simulate the optimal surgical design. According to the biomechanical evaluation, the patient-specific preoperative surgical design was prepared for implementation. The anterior column, which was reconstructed with titanium alloy mesh and a bone graft with posterior fixation using seven pedicle screws (M+P) and performed at the T7–T11 level, decreased the von Mises stress placed on the right rod, T7 pedicle screw, and T11 pedicle. Moreover, the M+P evaded the left T9 screw without load bearing. The 3D printed model and preoperative surgical simulation enhanced the understanding of the patient’s condition and facilitated patient-specific preoperative planning. Good clinical results, including no complication of implants, negligible loss of the Cobb angle, and good bone fusion, were achieved using the M+P surgical design. In conclusion, M+P was recommended as the optimal method for preoperative planning since it enabled the preservation of the normal vertebra and prevented unnecessary internal fixation. Our study indicated that FEA and the assisted 3D printed model are tools that could be extremely useful and effective in the patient-specific preoperative planning for thoracic spinal tuberculosis, which can facilitate preoperative surgical simulation and biomechanical evaluation, as well as improve the understanding of the patient’s condition.

The Subaxial Cervical Pedicle Screw for Cervical Spine Diseases: The Review of Technical Developments and Complication Avoidance

This study aimed to review information on the subaxial cervical pedicle screw (CPS) including recent anatomical considerations, entry points, placement techniques, accuracy, learning curve, and complications. Relevant literatures were reviewed, and the authors’ experiences were summarized. The CPS is used for reconstruction of unstable cervical spine and achieves superior biomechanical stability compared to other fixation techniques. Various insertion and guidance techniques are established, among which, lateral fluoroscopy-assisted placement is the most common and cost-effective technique. Generally, placement under imaging guidance is more accurate than other techniques, and a three-dimensional template allows optimal trajectory for each pedicle regardless of intraoperative changes in spinal alignment. The free-hand technique using a curved pedicle probe without a funnel-like hole increases screw stability and reduces operation time, radiation exposure, and soft tissue injury. Compared to conventional lateral fluoroscopy-assisted placement, free-hand CPS placement by trained surgeons achieves superior accuracy comparable to that of image-guided navigation; in general, 30 training cases are sufficient for learning a safe and accurate technique for CPS placement. The complications of subaxial CPS are classified into three categories: complications due to screw misplacement, complications without screw misplacement, and others. Inexperienced surgeons may benefit from advanced techniques; however, the accuracy of CPS ultimately depends on the surgeon’s experience. Inexperienced surgeons should master the placement of the thoracolumbar pedicle screw in real practice and practice CPS insertion using cadavers. During the initial phase of the learning curve, careful preparation of surgery, reiterated identification, patterned safety steps, and supervision of the expert are necessary.

Cervical Pedicle Screw Insertion Using O-Arm-Based 3D Navigation: Technical Advancement to Improve Accuracy of Screws

OBJECTIVE

This study aimed to report the technical advancement to improve the accuracy of cervical pedicle screw (CPS) placement using O-arm-based 3D navigation.

METHODS

Sixty-four patients who underwent CPS using O-arm in the spine level of C2 to C7 between June 2013 and February 2020 were involved. In the first phase, a reference frame was placed onto the spinous process of the cranial vertebrae and used it at a maximum of 3 vertebral levels. The navigation guide sleeve was used to drill a screw hole. In the second phase, a reference frame that can hold 3 vertebrae was introduced. In the third phase, a drill guide sleeve to minimize bending of the drill tip was developed. In the fourth phase, navigated surgical drill was introduced. Screw accuracy was assessed using Neo classification: grade (G) 0, no perforation; G1, perforation <2 mm; G2, perforation 2-4 mm; and G3, perforation >4 mm.

RESULTS

Mean age at surgery was 67 (19-88) years. A total of 317 CPSs were inserted. In total, 83 screws were inserted in the first phase, 60 in the second phase, 87 in the third phase, and 87 in the fourth phase. The total proportion of malpositioning was 3.8% (12/317 screws) and all were G1; 6.0% (5/83 screws) in the first phase, 8.3% (5/60 screws) in the second phase, 1.2% (1/87 screws) in the third phase, and 1.2% (1/87 screws) in the fourth phase (P < 0.05).

CONCLUSIONS

O-arm use improved CPS placement accuracy with the advancement of techniques and instruments.

Influence of a customized three-dimensionally printed drill guide on the accuracy of pedicle screw placement in lumbosacral vertebrae: An ex vivo study

OBJECTIVE

To compare the accuracy of pedicle screw insertion (PSI) into canine lumbosacral vertebrae with custom-made three-dimensionally (3D)-printed drill guides or freehand insertion.

STUDY DESIGN

Ex vivo study.

SAMPLE POPULATION

Nineteen canine lumbosacral specimens.

METHODS

Drill guides for PSI were designed on the basis of safe screw insertion trajectories by using preoperative computed tomography (CT) and produced by 3D printing of templates. Right and left sides of the specimens were randomly allocated to two groups; 4-mm pedicle screws were inserted in L5-L6 and L7-S1 spinal segments either freehand (control group) or with custom-made drill guides (guide group). Sixty-six screws were inserted with each method. Insertion angles (α, β), bone stock, and vertebral canal breach were assessed according to postoperative CT. χ² Tests were used to compare vertebral canal breach between groups and vertebrae.

RESULTS

Breaches in the vertebral canal were less common (P < .001) when screws were placed with a guide in the guide group (9/66, 14%) than without a guide (30/66, 45%). The rate of vertebral canal breach differed at L5 (P = .021) but not at L6 (P = .05), L7 (P = .075) or S1 (P = .658). The angle of insertion (α) did not differ between specimens with and without breaches (guide, P = .068; control, P = .394).

CONCLUSION

The use of a customized 3D-printed guide generally improved the accuracy of PSI in canine lumbosacral vertebrae, although statistical significance was reached only at L5.

CLINICAL SIGNIFICANCE

The use of customized drill guides may be considered as an alternative to freehand PSI in the lumbosacral area, especially for L5-L6 vertebrae.

3D Printing Navigation Template Used in Total Hip Arthroplasty for Developmental Dysplasia of the Hip

BACKGROUND

The purpose of our study was to explore the feasibility of 3D printing navigation template used in total hip arthroplasty (THA) for adult developmental dysplasia of the hip (DDH).

MATERIALS AND METHODS

25 patients who received THA for DDH from February 2014 to May 2018 were randomized into the control or intervention group. Of these patients, 12 received THAs assisted with 3D printing navigation templates, 13 THAs underwent THAs without navigation templates. The mean follow-up was 1.6 (range, 1.2-3.8) years. Clinical scores and radiographic results were evaluated for two groups.

RESULTS

Operating time, intra- and postoperative hemorrhage and Harris Hip Score (HHS) at 6 months postoperatively in the 3D printing group were better than those for patients in the conventional hip replacement group, while infection and implant loosening were 0 in the two groups. There were no significant differences in anteversion angle, abduction angle and the distance from rotation center to the ischial tuberosity line in 3D printing group as compared to the normal side. The abduction angle and the distance from rotation center to the ischial tuberosity line were significantly different between the two sides in the traditional group.

CONCLUSION

Application of the 3D printing template for THA with DDH can facilitate the surgical procedure and create an ideal artificial acetabulum placement.

Clinical application of individualized 3D-printed navigation template to children with cubitus varus deformity

Background

Cubitus varus deformity is a common sequela of elbow fractures in children. Cubitus varus deformity treatment is tending toward 3D correction, which is challenging for orthopedic surgeons. This study aims to explore whether individualized 3D-printed navigation templates can assist with accurate and effective corrective treatment of children with cubitus varus deformity.

Methods

Thirty-five patients were treated for cubitus varus deformity from June 2015 to April 2017, including 21 boys and 14 girls, aged 4.6–13.2 years (average, 7.5 years). Of these cases, 17 deformities were on the left side and 18 were on the right side. All were treated with wedge osteotomy of the lateral distal humerus. 3D-printed navigation templates were used in 16 cases, while traditional surgery was used in 19 cases. All patients underwent computed tomography scans before surgery. Computer software was used to analyze the measurements and design and print individualized navigation templates. The navigation templates were matched, and surgery was initially simulated. Intraoperative individualized navigation templates were used to assist with accurate osteotomy and Kirschner wire fixation. Operation times were recorded in all cases, the carrying angles before and after surgery were assessed by computer, and postoperative elbow joint function was evaluated using Bellemore criteria. All measurement data were presented as means ± SD, and Student’s t test was used to examine differences between groups. All count data between both groups were compared using the chi-square test or Fisher’s exact test analysis.

Results

All individualized navigation templates matched well with the corresponding anatomical markers and were consistent with preoperative planning, simulated surgery, and intraoperative procedures. Average operation times from clear exposure to fixed Kirschner wire were 11.69 min (9.6–13.5 min) for the individualized navigation template group and 22.89 min (17.7–26.8 min) for the traditional operation group (p < 0.001). Average differences in postoperation carrying angles between affected and healthy sides were 1.13° (0–2.0°) and 4.21° (0–7.5°), respectively (p < 0.001). Follow-up 6–12 months postoperation showed that elbow function did not differ significantly between groups using the Bellemore criteria (p > 0.05).

Conclusions

Individualized navigation templates simplify procedures, reduce operation time, and improve accuracy when used in orthopedic surgery to treat children with cubitus varus deformity.

Comparing the Treatment of Congenital Spine Deformity Using Freehand Techniques In Vivo and 3D-Printed Templates In Vitro (Prospective-Retrospective Single-Center Analytical Single-Cohort Study)

INTRODUCTION

Hemivertebrae excision with local posterior instrumentation is the most common technique for treatment of patients with congenital spine deformity-it is performed at a very young age. We conducted a comparative analysis for accuracy of pedicle screw positioning in infants with congenital scoliosis of the thoracolumbar area inserted using freehand technique in vivo and 3D-printed guiding templates in vitro.

METHODS

The study analyzes the results of 10 surgically treated patients with congenital deformity of the thoracolumbar spine due to vertebrae failure of formation. These patients were included in group 1 (in vivo) comprising six boys and four girls with a mean age of 3 years 8 months (2 years 2 months-6 years 8 month). Group 2 (in vitro) consisted of 27 plastic 3D-printed models of congenitally deformed spine of the same 10 patients in which screws were placed using 3D-printed guiding templates. The accuracy of screw position was assessed using computer tomography data performed postoperatively with Gertzbein-Robbins classification.

RESULTS

Results of our study show that screw insertion using 3D-printed guiding templates during surgical treatment of infants with congenital spine deformities is more accurate than using freehand technique (96.3% vs. 78.8% p = 0.011).

CONCLUSION

The data show that this method of screw insertion is very promising and can be used in surgical treatment of infants with congenital spine deformities.

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.

Accuracy of three-dimensional printed patient-specific drill guides for treatment of canine humeral intracondylar fissure

OBJECTIVE

To determine the accuracy of three-dimensional printed patient-specific drill guides (3D-PDG) as treatment of humeral intracondylar fissures (HIF) in dogs.

STUDY DESIGN

Retrospective consecutive case series.

ANIMALS

Client-owned dogs with HIF treated with a 5-mm transcondylar screw (TCS) placed from medial to lateral with a 3D-PDG.

METHODS

The proposed TCS entry point and trajectory were planned using computed tomography (CT) data and computer-aided design software (CAD), and a 3D-PDG was produced. During surgery the 3D-PDG was used to drill the pilot hole from medial to lateral; the guide was then removed, the pilot hole was overdrilled, and a 5-mm TCS was placed. Postoperative CT data were imported into CAD software, and the entry points, exit points, and trajectories were compared between the planned and actual screw locations.

RESULTS

Sixteen elbows from 11 dogs were included. Mean (SD) entry point translation was 1.3 mm (0.64), with all screws entering cranial to the proposed location. Mean maximum screw angulation was 5.2° (2.10°), with most screws directed caudodistal to the desired trajectory. Mean (SD) exit point translation was 1.8 mm (0.89) from the planned location. There was no intra-articular screw placement.

CONCLUSION

Use of a 3D-PDG permitted accurate placement of a mediolateral 5-mm locking TCS within the humeral condyle.

CLINICAL SIGNIFICANCE

Three-dimensional printed patient-specific drill guides should be considered as accurate and consistent for placing TCS for treatment of HIF in dogs.

Precision and safety of Multilevel Cervical Transpedicular Screw Fixation with 3D Patient-Specific Guides; A Cadaveric Study

The aim is to design a patient-specific instrument (PSI) for multilevel cervical pedicle screw placement from C2 to C7, as well as verifying reliability and reproducibility. Computed tomography (CT) scans were obtained from 7 cadaveric cervical spines. Using Mimics software, semiautomatic segmentation was performed for each cervical spine, designing a 3D cervical spine bone model in order to plan transpedicular screw fixation. A PSI was designed according to the previously cited with two cannulated chimneys to guide the drill. The guides were 3D printed and surgeries performed at the laboratory. Postoperative scans were obtained to study screw placement. Sixty-eight transpedicular screws were available for study. 61.8% of all screws were within the pedicle or partially breached <4 mm. No differences were observed between cervical levels. None of these screws had neurovascular injury. Of the 27 screws with a grade 3 (screw outside the pedicle; 39.7%), only 2 had perforation of the transverse foramen and none of them would have caused a neural injury. In conclusion, multilevel PSI for cervical pedicle screw is a promising technology that despite showing improvements regarding free-hand technique requires further studies to improve the positioning of the PSI and their accuracy.

Three-Dimensional Printing in Minimally Invasive Spine Surgery

PURPOSE OF REVIEW

To summarize the recent advances in 3D printing technology as it relates to spine surgery and how it can be applied to minimally invasive spine surgery.

RECENT FINDINGS

Most early literature about 3D printing in spine surgery was focused on reconstructing biomodels based on patient imaging. These biomodels were used to simulate complex pathology preoperatively. The focus has shifted to guides, templates, and implants that can be used during surgery and are specific to patient anatomy. However, there continues to be a lack of long-term outcomes or cost-effectiveness analyses. 3D printing also has the potential to revolutionize tissue engineering applications in the search for the optimal scaffold material and structure to improve bone regeneration without the use of other grafting materials. 3D printing has many potential applications to minimally invasive spine surgery requiring more data for widespread adoption.

Accurate placement of cervical pedicle screws using 3D-printed navigational templates : An improved technique with continuous image registration

OBJECTIVE

Accurate placement of cervical pedicle screws remains a surgical challenge. This study aimed to test the feasibility of using a novel three-dimensional (3D-)printed navigational template to overcome this challenge.

METHODS

Cervical spines were scanned using computed tomography (CT). A 3D model of the cervical spines was created. The screw trajectory was designed to pass through the central axis of the pedicle. Thereafter, a navigational template was designed by removing the soft tissue from the bony surface in the 3D model. A 3D printer was used to print the navigational template. The screws were then placed in the cadavers following CT scanning. The 3D model of the designed trajectory and the placed screws were registered. The coordinates of the entry and exit points of the designed trajectory and the actual trajectory were recorded. The numbers of qualified points that met the different degrees of accuracy were compared using a χ² test.

RESULTS

A total of 158 screws were placed. Five screws breached the pedicle cortex with a distance <2 mm. There was no significant difference between the pre- and postoperative entry points with a degree of accuracy ≥1.7 mm (P = 0.131). Meanwhile, there was no significant difference between the pre- and postoperative exit points with degrees of accuracy ≥6.4 mm (P = 0.071).

CONCLUSION

A navigational template can be designed by removing the soft tissue from the bony surface in a CT-generated 3D model. This guiding tool may effectively prevent intraoperative drifting and accurately places cervical pedicle screws.

3D printing in spine surgery

The applications of three-dimensional (3D) printing, or additive manufacturing, to the field of spine surgery continue to grow in number and scope especially in recent years as improved manufacturing techniques and use of sterilizable materials have allowed for creation of 3D printed implants. While 3D printing in spine surgery was initially limited to use as visual aids in preoperative planning for complex pathology, it has more recently been used to create intraoperative patient-specific screw guides and templates and is increasingly being used in surgical education and training. As patient-specific treatment and personalized medicine gains popularity in medicine, 3D printing provides a similar option for the surgical fields, particularly in the creation of customizable implants. 3D printing is a relatively new field as it pertains to spine surgery, and as such, it lacks long-term data on clinical outcomes and cost effectiveness; however, the apparent benefits and seemingly boundless applications of this growing technology make it an attractive option for the future of spine surgery.

Application of patient-specific 3D navigation templates for pedicle screw fixation of subaxial and upper thoracic vertebrae

Objective. To analyze the safety and accuracy of pedicle screw placement in the subaxial cervical and upper thoracic spine using patient-specific 3D navigation templates.

Material and Methods. The study included 16 patients who underwent transpedicular implantation of screws in the subaxial cervical and upper thoracic vertebrae using patient-specific 3D navigation templates. A total of 88 screws were installed. All patients underwent preoperative CT angiography to assess visualization of the vertebral artery. Customized vertebral models and navigation templates were created using 3D printing technology. Models and templates were sterilized and used during surgery. The results of screw implantation, as well as the safety and accuracy of the placement, were assessed by postoperative CT.

Results. The average deviation from the planned trajectory was 1.8 ± 0.9 mm. Deviation was estimated as class 1 (<2 mm) for 57 (64.77 %) screws, class 2 (2–4 mm) for 29 (32.95 %), and class 3 for two (2.27 %). The safety of screw implantation of grade 0 (the screw is completely inside the bone structure) was in 79 (89.77 %) cases, of grade 1 (<50 % of the screw diameter perforates the bone) – in 5 (5.68 %), and of grade 3 – in 2 (2.27 %).

Conclusion. Using 3D navigation templates is an affordable and safe method of installing pedicle screws in the cervical and upper thoracic spine. The method can be used as an alternative to intraoperative CT navigation.

Accuracy and Safety of Lateral Vertebral Notch-Referred Technique Used in Subaxial Cervical Pedicle Screw Placement

BACKGROUND

Biomechanical studies revealed that pedicle screw instrumentation has a superior stabilizing effect compared with other internal fixations in reconstructing the subaxial cervical spine. However, severe neurovascular risks preclude surgeons from routinely conducting pedicle screw manipulation in cervical spine.

OBJECTIVE

To evaluate the accuracy and safety of the lateral vertebral notch (LVN)-referred technique used in subaxial cervical pedicle screw (CPS) placement.

METHODS

One hundred thirty-five consecutive retrospective patients with cervical disorders underwent the LVN-referred technique for CPS placements in 3 spine centers. Postoperative pedicle perforations were confirmed by CT scans to assess the technical accuracy. Neurovascular complications derived from CPS misplacements were recorded to evaluate the technical safety.

RESULTS

A total of 718 CPSs were inserted into subaxial cervical spine. Postoperative CT scans revealed that the accuracy of CPS placement was superior. Neither vertebral artery injury nor spinal cord injury occurred. One radiculopathy was from a unilateral C6 nerve root compression. A screw-related neurovascular injury rate of 0.7% occurred in this cohort. Additionally, there was no significant difference in the accuracy of CPS placement among 3 surgeons (H = 1.460, P = .482). The relative standard deviation values revealed that technical reproducibility was acceptable. Furthermore, there was no significant difference between the patients' pedicle transverse angles and inserted CPS transverse angles from C3 to C7 (all P > .05).

CONCLUSION

The LVN is a reliable and consistent anatomic landmark for CPS placement. The accuracy and safety of subaxial CPS placement by using LVN-referred technique are highly acceptable, which may endow this technique to be practicably performed in selected patients.