Deviation analysis of C2 translaminar screw placement assisted by a novel rapid prototyping drill template: a cadaveric study

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.

Freehand power-assisted pedicle screw placement in scoliotic patients: results on 5522 consecutive pedicle screws

Pedicle screws is the current gold standard in spine surgery, achieving a solid tricolumnar fixation which is unreachable by wires and hooks. The freehand technique is the most widely adopted for pedicle screws placing. While freehand technique has been classically performed with manual tools, there has been a recent trend toward the use of power tools. However, placing a pedicle screw remains a technically demanding procedure with significant risk of complications. The aim of this article is to retrospectively evaluate safety and accuracy of free-hand power-assisted pedicle screw placement in a cohort of patients who underwent correction and fusion surgery for scoliosis (both idiopathic and non-idiopathic) in our department. A retrospective review of all patients with scoliosis who underwent surgery and received a postoperative CT scan in our department in a 9-year period was undertaken. Screw density, number and location of pedicle screws were measured using pre and postoperative full-length standing and lateral supine side-bending radiographs. Then, postoperative CT scan was used to assess the accuracy of screw placement according to Gertzbein-Robbins scale. Malpositioned screws were divided according to their displacement direction. Finally, intra and postoperative neurological complications and the need for revision of misplaced screws were recorded. A total of 205 patients were included, with a follow-up of 64.9 ± 38.67 months. All constructs were high density (average density 1.97 ± 0.04), and the average number of fusion levels was 13.72 ± 1.97. A total of 5522 screws were placed: 5308 (96.12%) were grade A, 141 (2.5%) grade B, 73 (1.32%) grade C. Neither grade D nor grade E trajectories were found. The absolute accuracy (grade A) rate was 96.12% (5308/5522) and the effective accuracy (within the safe zone, grade A + B) was 98.6% (5449/5522). Of the 73 misplaced screws (grade C), 59 were lateral (80.80%), 8 anterior (10.95%) and 6 medial (8.22%); 58 were in convexity, while 15 were in concavity (the difference was not statistically significant, p = 0.33). Intraoperatively, neither neurological nor vascular complications were recorded. Postoperatively, 4 screws needed revision (0.072% of the total): Power-assisted pedicle screw placing may be a safe an accurate technique in the scoliosis surgery, both of idiopathic and non-idiopathic etiology. Further, and higher quality, research is necessary in order to better assess the results of this relatively emerging technique.

Anatomical study of the technique of the axis laminar screws and development of guide

PURPOSE

To develop a bidirectional slide guide to assist screw placement in the axial lamina and to preliminarily discuss the accuracy and feasibility of auxiliary screw placement.

METHODS

CT data from 40 randomly selected patients were imported into the software for modelling, and cross-pinning was used to simulate pinning. According to the different crossing methods of the upper and lower laminar screws, they are divided into two groups. In the software, the position of the needlepoint of each screw is accurately measured, and the needle point is kept unchanged to simulate the movable range of the screw tail under the condition that the body does not penetrate the cortical bone. The data were compared by grouping and gender. Finally, the guide was designed by combining the screw exit point and fine adjustment angle data of all patients with the centripetal principle of the slide rail.

RESULTS

The needle exit data L1/L2/L3/L4 were 6.44 ± 0.52 mm, 7.05 ± 0.48 mm, 3.55 ± 0.75 mm and 5.09 ± 0.74 mm, respectively, and the fine adjustment angle of the slide rail was 10.51° ± 0.87°. There was no significant difference between the two groups or between men and women (p > 0.05).

CONCLUSION

In this experiment, using the data obtained from the simulation of screw insertion, a two-way slide guide was designed to assist the insertion of axial laminar screws. The guide locks the screw outlet point to position and guides the screw inlet point, which improves the accuracy and safety of screw placement.

Use of a 3D-printed body surface percutaneous puncture guide plate in vertebroplasty for osteoporotic vertebral compression fractures

BACKGROUND

Percutaneous vertebroplasty (PVP) has been used widely to treat osteoporotic vertebral compression fractures (OVCFs). However, it has many disadvantages, such as excessive radiation exposure, long operation times, and high cement leakage rates. This study was conducted to explore the clinical effects and safety of the use of a three-dimensional (3D)-printed body-surface guide plate to aid PVP for the treatment of OVCFs.

METHODS

This prospective cohort study was conducted with patients with OVCFs presenting between October 2020 and June 2021. Fifty patients underwent traditional PVP (group T) and 47 patients underwent PVP aided by 3D-printed body-surface guide plates (3D group). The following clinical and adverse events were compared between groups: the puncture positioning, puncture, fluoroscopy exposure and total operation times; changes in vertebral height and the Cobb angle after surgery relative to baseline; preoperative and postoperative visual analog scale and Oswestry disability index scores; and perioperative complications (bone cement leakage, neurological impairment, vertebral infection, and cardiopulmonary complications.

RESULTS

The puncture, adjustment, fluoroscopy, and total operation times were shorter in the 3D group than in group T. Visual analog scale and Oswestry disability index scores improved significantly after surgery, with significant differences between groups (both p < 0.05). At the last follow-up examination, the vertebral midline height and Cobb angle did not differ between groups. The incidence of complications was significantly lower in the 3D group than in group T (p < 0.05).

CONCLUSION

The use of 3D-printed body-surface guide plates can simplify and optimize PVP, shortening the operative time, improving the success rate, reducing surgical complications, and overall improving the safety of PVP.

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.

Accuracy of patient-specific drill guide template for bilateral C1-C2 laminar screw placement: a cadaveric study

OBJECTIVE

To evaluate the accuracy of using patient-specific drill guides to place bilateral laminar screws in C1 and C2.

METHODS

Nine cervical specimens (8 male; mean age: 66.6 (56-73)) with the occiput attached (C0-C3) were used in this study. Pre-operative CT scans were used to create digital anatomic models for templating and guide creation. A total of 36 screws were placed with the aid of 3D printed patient-specific guides (2 screws at C1 and C2). Post-operative CT scans were performed following screw insertion. The planned and actual trajectories were compared using pre- and post-operative imaging based on the angular and entry point deviation. After screw placement and post-operative imaging, each specimen was dissected and performed a visual inspection for breaches.

RESULTS

No breaches or violations were observed on post-procedure CT and visual inspection. The average variation of the entry point in the X, Y, and Z-axis was 0.3±0.28, 0.41±0.38, and 0.29±0.24, respectively. No statistically significant difference (p>0.05) was observed between the planned and obtained entry points. There was no significant difference (p>0.05) in the deviation analysis between the planned and obtained angles in the axial and coronal planes.

CONCLUSION

The study demonstrates that patient-specific drill guides allow for accurate C1 and C2 bilateral laminar screw placement, with a low risk of cortical breach.

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.

Retracted Article: Application of 3D printing technology in orthopedic medical implant - Spinal surgery as an example

Additive manufacturing has been used in complex spinal surgical planning since the 1990s and is now increasingly utilized to produce surgical guides, templates, and more recently customized implants. Surgeons report beneficial impacts using additively manufactured biomodels as pre-operative planning aids as it generally provides a better representation of the patient's anatomy than on-screen viewing of computed tomography (CT) or magnetic resonance imaging (MRI). Furthermore, it has proven to be very beneficial in surgical training and in explaining complex deformity and surgical plans to patients/parents. This paper reviews the historical perspective, current use, and future directions in using additive manufacturing in complex spinal surgery cases. This review reflects the authors' opinion of where the field is moving in light of the current literature. Despite the reported benefits of additive manufacturing for surgical planning in recent years, it remains a high niche market. This review raises the question as to why the use of this technology has not progressed more rapidly despite the reported advantages - decreased operating time, decreased radiation exposure to patients intraoperatively, improved overall surgical outcomes, pre-operative implant selection, as well as being an excellent communication aid for all medical and surgical team members. Increasingly, the greatest benefits of additive manufacturing technology in spinal surgery are custom-designed drill guides, templates for pedicle screw placement, and customized patient-specific implants. In view of these applications, additive manufacturing technology could potentially revolutionize health care in the near future.

The effectiveness and safety of 3-dimensional printed composite guide plate for atlantoaxial pedicle screw: A retrospective study

This study aims to evaluate the effectiveness and safety of the application of a 3-dimensional (3D)-printed composite guide plate for atlantoaxial pedicle screw.This was a retrospective study. A total of 43 atlantoaxial dislocation patients admitted in our hospital between January 2014 and October 2016 were retrospectively analyzed. According to the different methods of operation, patients were divided into 2 groups: 3D-printed plate group (n = 19) and traditional fixation group (n = 24). Placement time, operation duration, fluoroscopy number, intraoperative bleeding volume, and the neck and shoulder pain visual analog scale and Japanese Orthopaedic Association cervical nerve function scores were compared between pre- and postoperation.Differences in general data between these 2 groups were not statistically significant (P > .05). For patients in the 3D-printed plate group, a total of 68 assisting screws were placed at the pedicle, the accuracy rate of screw placement was 94.1%, placement time was 2.2 ± 0.4 minutes, fluoroscopy number was 4.6 ± 1.1 times, operation duration was 197 ± 41 minutes, and intraoperative bleeding volume was 395 ± 64 mL. In the traditional fixation group, a total of 76 screws were placed at the pedicle of patients, the accuracy rate of screw placement was 76.3%, placement time was 3.4 ± 0.7 minutes, fluoroscopy number was 9.4 ± 2.7 times, operation duration was 245 ± 67 minutes, and intraoperative bleeding volume was 552 ± 79 mL. Differences in accuracy rate, placement time, fluoroscopy number, operation duration, and intraoperative bleeding volume between these 2 groups were statistically significant (P < .05).The effectiveness and safety of 3D-printed composite guide plate for atlantoaxial pedicle screw were better than traditional method.

Prospective Multicenter Study of a Multistep Screw Insertion Technique Using Patient-Specific Screw Guide Templates for the Cervical and Thoracic Spine

STUDY DESIGN

A prospective clinical study of a multistep screw insertion method using a patient-specific screw guide template system (SGTS) for the cervical and thoracic spine.

OBJECTIVE

To evaluate the efficacy of SGTS for inserting screws into the cervical and thoracic spine.

SUMMARY OF BACKGROUND DATA

Posterior screw fixation is a standard procedure for spinal instrumentation; however, screw insertion carries the risk of injury to neuronal and vascular structures.

METHODS

Preoperative bone images of the computed tomography (CT) scans were analyzed using 3D/multiplanar imaging software, and the screw trajectories were planned. Plastic templates with screw-guiding structures were created for each lamina using 3D design and printing technology. Three types of templates were made for precise multistep guidance, and all the templates were specially designed to fit and lock onto the lamina during the procedure. In addition, plastic vertebra models were generated, and preoperative screw insertion simulation was performed. This patient-specific SGTS was used to perform the surgery, and CT scanning was used to postoperatively evaluate screw placement.

RESULTS

Enrolled to verify this procedure were 103 patients with cervical, thoracic, or cervicothoracic pathologies. The SGTS were used to place 813 screws. Preoperatively, each template was found to fit exactly and to lock onto the lamina of the vertebra models. In addition, intraoperatively, the templates fit and locked onto the patient lamina, and the screws were inserted successfully. Postoperative CT scans confirmed that 801 screws (98.5%) were accurately placed without cortical violation. There were no injuries to the vessels or nerves.

CONCLUSION

The multistep, patient-specific SGTS is useful for intraoperative pedicle screw (PS) navigation in the cervical and thoracic spine. This method improves the accuracy of PS insertion and reduces the operating time and radiation exposure during spinal fixation surgery.

LEVEL OF EVIDENCE

3.

Anatomical and radiologic characteristics of isthmus parameters in guiding pedicle screw placement

Objective To study the clinical application of lumbar isthmus parameters in guiding pedicle screw placement. Methods Lumbar isthmus parameters were measured in normal lumbar x-rays and cadaveric specimens from a Chinese Han population. Distance between the medial pedicle border and lateral isthmus border was recorded as a 'D' value and was compared between X-rays and cadavers. Orthopaedic surgeons estimated different distances (2-6 mm) and angles (5-20°), and bias ratios between estimated and real values were compared. Orthopaedic residents placed pedicle screws on cadaveric specimens before and after application of the 'D' value, and screw placement accuracy was compared. Results Except for L4 vertebrae, significant differences in the 'D' value were found between 25 cadaveric specimens and x-ray films from 120 patients. Distances and angles estimated by 40 surgeons were significantly different from all real values, except 2 mm distance. Accuracy of pedicle screw placement by six orthopaedic residents was significantly improved by applying the 'D' value. Conclusions Surgeon estimates of distance were more accurate than angle estimates. Addition of a 'D' value to conventional parameters may significantly improve pedicle screw placement accuracy in lumbar spine surgery.

Preparation and Assessment of an Individualized Navigation Template for Lower Cervical Anterior Transpedicular Screw Insertion Using a Three-Dimensional Printing Technique

STUDY DESIGN

Prospective trial.

OBJECTIVE

To establish an individualized navigation template for safe and accurate insertion of lower cervical anterior transpedicular screw (ATPS) based on a three-dimensional (3D) printing technique.

SUMMARY OF BACKGROUND DATA

Conventional screw insertion manually under fluoroscopy easily leading to deviation of ATPS screw channel, cervical instrumentation procedures demand the need for a precise technique for screw placement.

METHODS

Twenty adult cervical spine specimens (10 men and 10 women, with a mean age of 50.29 ± 6.98) were selected for computed tomography pre- and postoperatively. A 3D lower cervical spine model was reconstructed using Mimics software to measure the screw-related parameters and generate a reverse template with optimal screw channel as well as a prototype using 3D printing. Assisted by the navigation template, bilateral ATPS were inserted into the cadavers.

RESULTS

The mean outer width and height of pedicle were 5.31 ± 1.23 and 6.78 ± 1.10 mm, respectively. The average length, sagittal, and axial angles of the optimal screw channel obtained through the optimal entry point were 36.34 ± 4.39 mm, 40.67° ± 5.10°, and 93.7° ± 7.96°, respectively. The adjustable safe ranges of sagittal and axial angles were 3.89° ± 1.13° and 5.64° ± 0.97°, respectively. The axial and sagittal accuracies of the 200 screws were 99.5% and 97%, respectively. The average deviations of the actual entry point and the preset opening in the X, Y, and Z axes were 0.39 ± 0.43, 0.21 ± 0.41, and 0.29 ± 0.14 mm, respectively (P > 0.05).

CONCLUSION

An individualized ATPS navigation template was developed using Mimics software and 3D printing prototyping, based on computed tomography, for highly accurate screw insertion.

LEVEL OF EVIDENCE

4.

Computer-assisted Patient-specific Prototype Template for Thoracolumbar Cortical Bone Trajectory Screw Placement: A Cadaveric Study

The cortical bone trajectory (CBT) screw technique yields effective mechanical and clinical results, improving the holding screw strength with a less invasive exposure. Accurate and safe screw placement is crucial. A patient-specific drill template with a preplanned trajectory was considered a promising solution; however, it is critical to assess the efficacy and safety of this technique. This study aims to evaluate the accuracy of patient-specific computed tomography (CT)-based rapid prototype drill guide templates for the CBT technique. CT scanning was performed in 7 cadaveric thoracolumbar spines, and a 3-dimensional reconstruction model was generated. By using computer software, we constructed drill templates that fit onto the posterior surface of thoracolumbar vertebrae with drill guides to match the CBT. In total, 80 guide templates from T11 to L5 were created from the computer models by using rapid prototyping. The drill templates were used to guide the drilling of CBT screws without any fluoroscopic control, and CT images were obtained after fixation. The entry point and direction of the planned and inserted screws were measured and compared. In total, 80 screws were inserted from T11 to L5. No misplacement or bony perforation was observed on postoperative CT scan. The patient-specific prototype template system showed the advantage of safe and accurate cortical screw placement in the thoracolumbar spine. This method showed its ability to customize the patient-specific trajectory of the spine, based on the unique morphology of the spine. The potential use of drill templates to place CBT screws is promising.

Unilateral Spinous Process Noncovering Hook Type Patient-specific Drill Template for Thoracic Pedicle Screw Fixation: A Pilot Clinical Trial and Template Classification

STUDY DESIGN

Prospective clinical pilot study.

OBJECTIVE

To confirm the accuracy of thoracic pedicle screw placement by using the unilateral spinous noncovering hook type patient-specific drill template (PSDT) made through rapid prototyping (RP) and to analyze previously reported PSDT designs and their characteristics.

SUMMARY OF BACKGROUND DATA

Pedicle screw fixation is the most common form of the posterior instrumentation of the thoracic and lumbar spine. Various techniques have been introduced to improve pedicle screw placement. Among them PSDT with a preplanned trajectory has been considered a promising solution; however, we don't have consensus on proper character of the template.

METHODS

Preoperative spiral three-dimensional (3D) computed tomography (CT) was performed on the thoracic spine. The images were stored in DICOM format and transferred to a workstation running MIMICS 17.0 software to generate a 3D reconstruction template for the desired thoracic vertebra. The accurate trajectory and screw diameter and length were calculated with UG Imageware 12.1. The guide template was sterilized and used intraoperatively to assist with the placement of thoracic pedicle screws. After all pedicle trajectory screws had been inserted. We reviewed 12 previous reports and classified them according to the shape and system of PSDT that met the inclusion criteria of the review.

RESULTS

Ten screws were placed by using the PSDT without violating the single laminar cortex. There was no violation of the spinal canal or the cortex of pedicle on postoperative CT scans. The results of 13 PSDT types included in the current study suggested that there is no significant difference in accuracy between the PSDTs.

CONCLUSION

The unilateral spinous process noncovering hook type PSDT made through RP provided an accurate trajectory for the thoracic vertebra, and the classification of PSDT in this study could be helpful for further studies.

LEVEL OF EVIDENCE

5.

Are computer numerical control (CNC)-manufactured patient-specific metal templates available for posterior thoracic pedicle screw insertion? Feasibility and accuracy evaluation

PURPOSE

Accurate and safe posterior thoracic pedicle insertion (PTPI) remains a challenge. Patient-specific drill templates (PDTs) created by rapid prototyping (RP) can assist in posterior thoracic pedicle insertion, but pose biocompatibility risks. The aims of this study were to develop alternative PDTs with computer numerical control (CNC) and assess their feasibility and accuracy in assisting PTPI.

METHODS

Preoperative CT images of 31 cadaveric thoracic vertebras were obtained and then the optimal pedicle screw trajectories were planned. The PDTs with optimal screw trajectories were randomly assigned to be designed and manufactured by CNC or RP in each vertebra. With the guide of the CNC- or RP-manufactured PDTs, the appropriate screws were inserted into the pedicles. Postoperative CT scans were performed to analyze any deviations at entry point and midpoint of the pedicles.

RESULTS

The CNC group was found to be significant manufacture-time-shortening, and cost-decreasing, when compared with the RP group (P < 0.01). The PDTs fitted the vertebral laminates well while all screws were being inserted into the pedicles. There were no significant differences in absolute deviations at entry point and midpoint of the pedicle on either axial or sagittal planes (P > 0.05). The screw positions were grade 0 in 90.3% and grade 1 in 9.7% of the cases in the CNC group and grade 0 in 93.5% and grade 1 in 6.5% of the cases in the RP group (P = 0.641).

CONCLUSION

CNC-manufactured PDTs are viable for assisting in PTPI with good feasibility and accuracy.

Optimal Entry Point and Trajectory for Anterior C1 Lateral Mass Screw

STUDY DESIGN

A radiographic analysis of the anatomy of the C1 lateral mass using computed tomography (CT) scans and Mimics software.

OBJECTIVE

To define the anatomy of the C1 lateral mass and make recommendations for optimal entry point and trajectory for anterior C1 lateral mass screws.

SUMMARY OF BACKGROUND DATA

Although various posterior insertion angles and entry points for screw insertion have been proposed for posterior C1 lateral mass screws, no large series have been performed to assess the ideal entry point and optimal trajectory for anterior C1 lateral mass screw placement.

MATERIALS AND METHODS

The C1 lateral mass was evaluated using CT scans and a 3-dimensional imaging application (Mimics software). Measuring the space available for the anterior C1 lateral mass screw (SAS) at different camber angles from 0 to 30 degrees (5-degree intervals) was performed to identify the ideal camber angle of insertion. Measuring the range of sagittal angles was performed to calculate the ideal sagittal angle. Other measurements involving the height of the C1 lateral mass were also made.

RESULTS

The optimal screw entry point was found to be located on the anterior surface of the atlas 12.88 mm (±1.10 mm) lateral to the center of the anterior tubercle. This optimal entry point was found to be 6.81 mm (±0.59 mm) superior to the anterior edge of the atlas inferior articulating process. The mean ideal camber angle was 20.92 degrees laterally and the mean ideal sagittal angle was 5.80 degrees downward.

CONCLUSIONS

These measurements define the optimal entry point and trajectory for anterior C1 lateral mass screws and facilitate anterior C1 lateral mass screw placement. A thorough understanding of the local anatomy may decrease the risk of injury to the spinal cord, vertebral artery, and internal carotid artery. Delineating the anatomy in each case with preoperative 3D CT evaluation is recommended.

A New Navigational Tool for Pedicle Screw Placement in Patients With Severe Scoliosis: A Pilot Study to Prove Feasibility, Accuracy, and Identify Operative Challenges

STUDY DESIGN

Pilot study.

OBJECTIVE

To develop and validate the feasibility and accuracy of a newly designed navigational spinal instrument guiding tool for patient-matched thoracic and lumbar pedicle screw placement in patients with severe scoliosis, and to identify intraoperative challenges that may be relevant.

SUMMARY OF BACKGROUND DATA

Pedicle screw placement is challenging in severely rotated scoliotic spine with small diameters and asymmetrical shape of the pedicles and vertebrae. Patient-specific drill/positioning guides with preplanned trajectory have been developed as a promising solution in spinal surgery for precise screw insertion.

METHODS

In 4 patients with severe scoliosis, navigational templates and models of all vertebrae to be instrumented were manufactured using a computed tomography (CT)-based 3-dimensional model of the thoracic and lumbar spine. The guides were designed differently for thoracic and lumbar segments according to the individual anatomy to achieve an optimal coupling to the surface of the patient's spine, to maximize the stability of the device itself, and to increase user friendliness for the complete screw positioning process. Intraoperative challenges and opportunities for device and process improvements regarding the handling of the guides during the surgery were recorded. Postoperatively, the intrapedicular screw positions were evaluated versus the preoperative plan and evaluated for cortical violation based on CT scans.

RESULTS

A total of 76 pedicle screws were implanted (56 thoracic, 20 lumbar). Two screws (2.6%) were assessed to be misplaced intraoperatively and repositioned. Eighty-four percent of the pedicle screws were completely intrapedicular, 96.1% within <2 mm cortical breech. CT scans did not demonstrate medial pedicle violation, or misplaced screw contact to neurovascular structures. No screw-related clinical complaints were reported postoperatively.

CONCLUSIONS

The new custom-made positioning guide is a feasible navigational tool that permits a safe and accurate implantation of pedicle screws in patients with severe scoliosis.

A Modified Personalized Image-Based Drill Guide Template for Atlantoaxial Pedicle Screw Placement: A Clinical Study

Background

Atlantoaxial posterior pedicle screw fixation has been widely used for treatment of atlantoaxial instability (AAI). However, precise and safe insertion of atlantoaxial pedicle screws remains challenging. This study presents a modified drill guide template based on a previous template for atlantoaxial pedicle screw placement.

Material/Methods

Our study included 54 patients (34 males and 20 females) with AAI. All the patients underwent posterior atlantoaxial pedicle screw fixation: 25 patients underwent surgery with the use of a modified drill guide template (template group) and 29 patients underwent surgery via the conventional method (conventional group). In the template group, a modified drill guide template was designed for each patient. The modified drill guide template and intraoperative fluoroscopy were used for surgery in the template group, while only intraoperative fluoroscopy was used in the conventional group.

Results

Of the 54 patients, 52 (96.3%) completed the follow-up for more than 12 months. The template group had significantly lower intraoperative fluoroscopy frequency (p<0.001) and higher accuracy of screw insertion (p=0.045) than the conventional group. There were no significant differences in surgical duration, intraoperative blood loss, or improvement of neurological function between the 2 groups (p>0.05).

Conclusions

Based on the results of this study, it is feasible to use the modified drill guide template for atlantoaxial pedicle screw placement. Using the template can significantly lower the screw malposition rate and the frequency of intraoperative fluoroscopy.

Accurate and Simple Screw Insertion Procedure With Patient-Specific Screw Guide Templates for Posterior C1-C2 Fixation

STUDY DESIGN

Prospective clinical trial of the screw insertion method for posterior C1-C2 fixation utilizing the patient-specific screw guide template technique.

OBJECTIVE

To evaluate the efficacy of this method for insertion of C1 lateral mass screws (LMS), C2 pedicle screws (PS), and C2 laminar screws (LS).

SUMMARY OF BACKGROUND DATA

Posterior C1LMS and C2PS fixation, also known as the Goel-Harms method, can achieve immediate rigid fixation and high fusion rate, but the screw insertion carries the risk of injury to neuronal and vascular structures. Dissection of venous plexus and C2 nerve root to confirm the insertion point of the C1LMS may also cause problems. We have developed an intraoperative screw guiding method using patient-specific laminar templates.

METHODS

Preoperative bone images of computed tomography (CT) were analyzed using three-dimensional (3D)/multiplanar imaging software to plan the trajectories of the screws. Plastic templates with screw guiding structures were created for each lamina using 3D design and printing technology. Three types of templates were made for precise multistep guidance, and all templates were specially designed to fit and lock on the lamina during the procedure. Surgery was performed using this patient-specific screw guide template system, and placement of the screws was postoperatively evaluated using CT.

RESULTS

Twelve patients with C1-C2 instability were treated with a total of 48 screws (24 C1LMS, 20 C2PS, 4 C2LS). Intraoperatively, each template was found to exactly fit and lock on the lamina and screw insertion was completed successfully without dissection of the venous plexus and C2 nerve root. Postoperative CT showed no cortical violation by the screws, and mean deviation of the screws from the planned trajectories was 0.70 ± 0.42 mm.

CONCLUSION

The multistep, patient-specific screw guide template system is useful for intraoperative screw navigation in posterior C1-C2 fixation. This simple and economical method can improve the accuracy of screw insertion, and reduce operation time and radiation exposure of posterior C1-C2 fixation surgery.

LEVEL OF EVIDENCE

3.

CLINICAL APPLICATION OF A DRILL GUIDE TEMPLATE FOR PEDICLE SCREW PLACEMENT IN SEVERE SCOLIOSIS

OBJECTIVE

To evaluate the accuracy and the effect of drill guide template for pedicle screw placement in severe scoliosis.

METHOD

Eight patients with rigid scoliosis were enrolled, five males and three females, ranging from nine to 23 years old. A three-dimensional CT scan of the spine was performed and saved as a DICOM file type. The multi-level template was designed by Mimics software and manufactured according to the part of the most severe deformity. The drill template was placed on the corresponding vertebral surface. Pedicle screws were carefully inserted across the trajectory of the template. Postoperatively, the positions of the pedicle screws were evaluated by CT scan and graded for validation.

RESULTS

No spinal cord injury or nerve damage occurred. All patients had satisfactory outcomes. The abnormalities and the measures observed during operation were the same as those found in the preoperative period. The position of the pedicle screws was accurate, according to the postoperative X-ray and CT scan. The rate of scoliosis correction was 60%. Compared with controls, surgery time, blood loss and radiation were significantly lower.

CONCLUSION

With the application of multi-level template, the placement of pedicle screws shows high accuracy in scoliosis with shorter surgical time, less blood loss and less radiation exposure. Level of Evidence III, Retrospective Comparative Study.

Accuracy Assessment of Using Rapid Prototyping Drill Templates for Atlantoaxial Screw Placement: A Cadaver Study

Purpose. To preliminarily evaluate the feasibility and accuracy of using rapid prototyping drill templates (RPDTs) for C1 lateral mass screw (C1-LMS) and C2 pedicle screw (C2-PS) placement. Methods. 23 formalin-fixed craniocervical cadaver specimens were randomly divided into two groups. In the conventional method group, intraoperative fluoroscopy was used to assist the screw placement. In the RPDT navigation group, specific RPDTs were constructed for each specimen and were used intraoperatively for screw placement navigation. The screw position, the operating time, and the fluoroscopy time for each screw placement were compared between the 2 groups. Results. Compared with the conventional method, the RPDT technique significantly increased the placement accuracy of the C2-PS (p < 0.05). In the axial plane, using RPDTs also significantly increased C1-LMS placement accuracy (p < 0.05). In the sagittal plane, although using RPDTs had a very high accuracy rate (100%) in C1-LMS placement, it was not statistically significant compared with the conventional method (p > 0.05). Moreover, the RPDT technique significantly decreased the operating and fluoroscopy times. Conclusion. Using RPDTs significantly increases the accuracy of C1-LMS and C2-PS placement while decreasing the screw placement time and the radiation exposure. Due to these advantages, this approach is worth promoting for use in the Harms technique.

Accuracy assessment of atlantoaxial pedicle screws assisted by a novel drill guide template

INTRODUCTION

Posterior atlantoaxial pedicle screw fixation is an effective technique for atlantoaxial instability (AAI). However, because of the complex anatomy of the cranio-cervical junction, it remains challenging to insert atlantoaxial pedicle screw precisely and safely. A novel drill guide template was designed for atlantoaxial pedicle screw placement in this study. The purpose of this study is to quantitatively evaluate the accuracy of atlantoaxial pedicle screw placement using the novel drill guide template.

MATERIALS AND METHODS

Between June 2014 and September 2015, 32 consecutive patients with AAI were included. Using the Mimics v17.0 and 3-matic v9.0 softwares, a novel drill guide template with two location holes and guide rods was designed. All patients underwent posterior atlantoaxial pedicle screw fixation assisted by the novel drill guide template. After surgery, the entry point and directions of actual and ideal screw trajectories were measured and compared.

RESULTS

All patients underwent surgery successfully assisted by the novel drill guide template. A total of 128 atlantoaxial pedicle screws were placed for 32 AAI patients. Postoperative CT scans showed two screws in atlas deviated medially from the pedicle cortex and entered the spinal canal about 1 mm but without symptoms. For both atlas and axis, there were no significant differences in entry point or directions between the ideal and actual screw trajectories (P > 0.05). Significant differences were found in preoperative and postoperative Japanese Orthopaedic Association score and Visual Analogue Score (P < 0.001).

CONCLUSIONS

It is feasible to use the novel drill guide template for atlantoaxial pedicle screw placement. The accuracy of screw placement assisted by the novel template is high. More studies are needed to confirm the efficacy of this template.

Applications of 3D printing in the management of severe spinal conditions

The latest and fastest-growing innovation in the medical field has been the advent of three-dimensional printing technologies, which have recently seen applications in the production of low-cost, patient-specific medical implants. While a wide range of three-dimensional printing systems has been explored in manufacturing anatomical models and devices for the medical setting, their applications are cutting-edge in the field of spinal surgery. This review aims to provide a comprehensive overview and classification of the current applications of three-dimensional printing technologies in spine care. Although three-dimensional printing technology has been widely used for the construction of patient-specific anatomical models of the spine and intraoperative guide templates to provide personalized surgical planning and increase pedicle screw placement accuracy, only few studies have been focused on the manufacturing of spinal implants. Therefore, three-dimensional printed custom-designed intervertebral fusion devices, artificial vertebral bodies and disc substitutes for total disc replacement, along with tissue engineering strategies focused on scaffold constructs for bone and cartilage regeneration, represent a set of promising applications towards the trend of individualized patient care.

Utility of a custom screw insertion guide and a full-scale, color-coded 3D plaster model for guiding safe surgical exposure and screw insertion during spine revision surgery

Several articles have described the use of screw insertion guides during primary spine surgery; however, the use of such a guide during revision surgeries has not been described. The purpose of this study is to describe the utility of a custom screw insertion (CSI) guide assembled using a novel method and a full-scale, color-coded 3D plaster (FCTP) model for safe and accurate revision surgery.

The authors applied the CSI guide and the FCTP model in 3 cases. In the first case, a patient with multiple failed cervical spine surgeries underwent occipitocervicothoracic fusion. After a successful result for this patient, the authors applied the CSI guide in 2 other patients who underwent revision lumbar fusion surgeries to confirm the accuracy and the efficacy of the CSI guides in such cases. The models and guides were fabricated using rapid prototyping technology. The effectiveness of these methods was examined.

The FCTP model was designed using CT data. During model assembly, implants inserted during previous surgery were removed virtually, and for the cervical spine, vertebral arteries were colored red for planning. The CSI guide was designed with 5 or 6 arms to fit the bone surface precisely after removing artifacts. Surgery was performed by referring to the FCTP model. Because the actual structure of the bone surface was almost identical to that of the FCTP model, surgical exposure around the complex bone shape proceeded smoothly. The CSI guides were positioned accurately to aid the successful insertion of a pedicle screw into the C-2 vertebra in the case of cervical revision surgery, and 4 pedicle screws for lumbar vertebrae in the 2 other patients. Postoperative CT scans showed that all screw positions closely matched those predicted during the preoperative planning. In conclusion, the FCTP models and the novel CSI guides were effective for safe and accurate revision surgery of the spine.

Cervical screw placement using rapid prototyping drill templates for navigation: a literature review

PURPOSE

Due to the high screw malposition rate and the potential risk of neurovascular injury in cervical fixation surgeries, guided tools, mainly computer-assisted surgery navigation systems and rapid prototyping drill templates (RPDTs) have increasingly been developed to help surgeons improve screw placement accuracy. Although RPDTs have been used in cervical surgeries for almost 2 decades, no specific review has been performed detailing the state of this technique. Thus, in the current review, we fully discuss the status of applying RPDTs in cervical surgeries.

METHODS

Studies that tested the accuracy and reliability of RPDTs in guiding cervical screw placements were included in this review. The fabrication workflow and usage of RPDTs, the accuracy and reliability of using RPDTs for screw and plate placement, the advantages and disadvantages of RPDTs and their prospects for future applications as a part of cervical fixation instrumentation are discussed.

RESULTS

As the design of RPDTs becomes more rational, the accuracy and reliability of these devices have significantly improved in cervical fixation surgeries. Moreover, RPDTs decrease the intraoperative radiation exposure for surgeons and patients relative to conventional methods. However, some disadvantages also exist. The fabrication of RPDTs is time-consuming, and the time required to learn the related software is long.

CONCLUSION

We believe that because of their merits, the RPDT technique is worth promoting for use in cervical surgeries. However, the time-consuming fabrication workflow and the long period required to learn the related software might limit its widespread use. In the future, the workflow should be simplified to reduce the extra workload for surgeons. Moreover, more clinical studies with high-level evidence are still needed to further test its accuracy and feasibility.

Rapid prototyping for patient-specific surgical orthopaedics guides: A systematic literature review

There has been a lot of hype surrounding the advantages to be gained from rapid prototyping processes in a number of fields, including medicine. Our literature review aims objectively to assess how effective patient-specific surgical guides manufactured using rapid prototyping are in a number of orthopaedic surgical applications. To this end, we carried out a systematic review to identify and analyse clinical and experimental literature studies in which rapid prototyping patient-specific surgical guides are used, focusing especially on those that entail quantifiable outcomes and, at the same time, providing details on the guides’ design and type of manufacturing process. Here, it should be mentioned that in this field there are not yet medium- or long-term data, and no information on revisions. In the reviewed studies, the reported positive opinions on the use of rapid prototyping patient-specific surgical guides relate to the following main advantages: reduction in operating times, low costs and improvements in the accuracy of surgical interventions thanks to guides’ personalisation. However, disadvantages and sources of errors which can cause patient-specific surgical guide failures are as well discussed by authors. Stereolithography is the main rapid prototyping process employed in these applications although fused deposition modelling or selective laser sintering processes can also satisfy the requirements of these applications in terms of material properties, manufacturing accuracy and construction time. Another of our findings was that individualised drill guides for spinal surgery are currently the favourite candidates for manufacture using rapid prototyping. Other emerging applications relate to complex orthopaedic surgery of the extremities: the forearm and foot. Several procedures such as osteotomies for radius malunions or tarsal coalition could become standard, thanks to the significant assistance provided by rapid prototyping patient-specific surgical guides in planning and performing such operations.

A semi-automatic computer-aided method for surgical template design

This paper presents a generalized integrated framework of semi-automatic surgical template design. Several algorithms were implemented including the mesh segmentation, offset surface generation, collision detection, ruled surface generation, etc., and a special software named TemDesigner was developed. With a simple user interface, a customized template can be semi- automatically designed according to the preoperative plan. Firstly, mesh segmentation with signed scalar of vertex is utilized to partition the inner surface from the input surface mesh based on the indicated point loop. Then, the offset surface of the inner surface is obtained through contouring the distance field of the inner surface, and segmented to generate the outer surface. Ruled surface is employed to connect inner and outer surfaces. Finally, drilling tubes are generated according to the preoperative plan through collision detection and merging. It has been applied to the template design for various kinds of surgeries, including oral implantology, cervical pedicle screw insertion, iliosacral screw insertion and osteotomy, demonstrating the efficiency, functionality and generality of our method.

Clinical Use of 3D Printing Guide Plate in Posterior Lumbar Pedicle Screw Fixation

Background

This study aimed to evaluate the clinical efficacy of use of a 3D printing guide plate in posterior lumbar pedicle screw fixation.

Material/Methods

We enrolled 43 patients receiving posterior lumbar pedicle screw fixation. The experimental group underwent 3D printing guide plate-assisted posterior lumbar pedicle screw fixation, while the control group underwent traditional x-ray-assisted posterior lumbar pedicle screw fixation. After surgery, CT scanning was done to evaluate the accuracy of screw placement according to the Richter standard.

Results

All patients were followed up for 1 month. The mean time of placement for each screw and the amount of hemorrhage was 4.9±2.1 min and 8.0±11.1 mL in the experimental group while 6.5±2.2 min and 59.9±13.0 mL in the control group, respectively, with significant differences (p<0.05). The fluoroscopy times of each screw placement was 0.5±0.4 in the experimental group, which was significantly lower than that in the control group 1.2±0.7 (p<0.05). The excellent and good screw placement rate was 100% in the experimental group and 98.4% in the control group, without any statistical difference (P>0.05). No obvious complications were reported in either group.

Conclusions

Compared with the traditional treatment methods, the intra-operative application of 3D printing guide plate can shorten the operation time and reduce the amount of hemorrhage. It can also reduce the fluoroscopy times compared with the traditional fluoroscopy, which cannot improve the accuracy rate of screw placement.

Improved accuracy of 3D-printed navigational template during complicated tibial plateau fracture surgery

This study was aimed to improve the surgical accuracy of plating and screwing for complicated tibial plateau fracture assisted by 3D implants library and 3D-printed navigational template. Clinical cases were performed whereby complicated tibial plateau fractures were imaged using computed tomography and reconstructed into 3D fracture prototypes. The preoperative planning of anatomic matching plate with appropriate screw trajectories was performed with the help of the library of 3D models of implants. According to the optimal planning, patient-specific navigational templates produced by 3D printer were used to accurately guide the real surgical implantation. The fixation outcomes in term of the deviations of screw placement between preoperative and postoperative screw trajectories were measured and compared, including the screw lengths, entry point locations and screw directions. With virtual preoperative planning, we have achieved optimal and accurate fixation outcomes in the real clinical surgeries. The deviations of screw length was 1.57 ± 5.77 mm, P > 0.05. The displacements of the entry points in the x-, y-, and z-axis were 0.23 ± 0.62, 0.83 ± 1.91, and 0.46 ± 0.67 mm, respectively, P > 0.05. The deviations of projection angle in the coronal (x-y) and transverse (x-z) planes were 6.34 ± 3.42° and 4.68 ± 3.94°, respectively, P > 0.05. There was no significant difference in the deviations of screw length, entry point and projection angle between the ideal and real screw trajectories. The ideal and accurate preoperative planning of plating and screwing can be achieved in the real surgery assisted by the 3D models library of implants and the patient-specific navigational template. This technology improves the accuracy and efficiency of personalized internal fixation surgery and we have proved this in our clinical applications.