Patient-specific Drill Template Research Articles

Accuracy and Safety of Pedicle Screw Placement for Treating Adolescent Idiopathic Scoliosis: A Narrative Review Comparing Available Techniques.

Posterior spinal fusion and segmental spinal instrumentation using pedicle screws (PS) is the most used procedure to correct adolescent idiopathic scoliosis. Computed navigation, robotic navigation, and patient-specific drill templates are available, besides the first described free-hand technique. None of these techniques are recognized as the gold standard. This review compares the PS placement accuracy and misplacement-related complication rates achieved with the techniques mentioned above. It further reports PS accuracy classifications and anatomic PS misplacement risk factors. The literature suggests a higher PS placement accuracy for robotic relative to computed navigation and for the latter relative to the free-hand technique (misplacement rates: 0.4-7.2% versus 1.9-11% versus 1.5-50.7%) using variable accuracy classifications. The reported PS-misplacement-related complication rates are, however, uniformly low (0-1.4%) for every technique, while robotic and computed navigation induce a roughly fourfold increase in the patient's intraoperative radiation exposure relative to the free-hand technique with fluoroscopic implant positioning control. The authors, therefore, recommend dedicating robotic and computed navigation for complex deformities or revisions with altered landmarks, underline the need for a generally accepted PS accuracy classification, and advise against PS placement in grade 4 pedicles yielding higher misplacement rates (22.2-31.5%).

Low-cost 3D Modeling Software for Generating Patient-specific Drill Guide Templates for Cervical Pedicle Screw Insertion: An In Vitro Study

Background. Instrumented posterior cervical spine surgery (IPCSS) can be conducted using screws inserted through the pedicles of the vertebra. A safe IPCSS method uses 3D-printing to produce templates that will serve as drill guides for screw placement.Objectives. This study describes the generation of 3D-printed drill guides using low-cost general purpose 3D modeling software and the comparison of screw insertion accuracy scores against the traditional landmark method and guides created using commercial grade software.Methods. Twenty-five (25) subaxial pedicles of five cadaveric spines were selected and scanned using computedtomography (CT). A digital reconstruction of the five cadaveric spines were created based on the CT DICOM data. A low-cost 3D modeling software, Rhinoceros 3D, was utilized for trajectory planning and generation of a patientspecific drill template using the digital reconstruction. The templates were then fabricated in ABS plastic using a fused deposition modeling (FDM) 3D printer. Insertion of cervical pedicle screws on the cadaveric spines was done by an orthopedic resident using the 3D printed guides. Postoperative CT scans were obtained, and placement accuracy of the screws were scored by two assessors utilizing a four-point rating system. Screws in correct placement were scored Grade 0 while misplaced screws with neurovascular damage were given a score of Grade 3.Results. Accuracy scores for the 3D-printed drill guides were 52% for assessor 1 and 44% for assessor 2. Forassessor 1, screw placement in C3, C6, and C7 received the highest scores. For assessor 2, the highest scores were achieved in C3 and C7. The hybrid method of Bundoc et al. achieved scores of 94% while 3D printed guides utilizing commercial software like Materialise Mimics, Geomagic Freeform, or UG Imageware achieved scores of 80-100%. The traditional landmark method had scores ranging from 12% to 94% depending on the skill of the surgeon.Conclusion. Commercial medical 3D image-based engineering software has high acquisition costs that might be beyond the reach of most institutions. A sub-$1000 general purpose 3D modeling software can be used to create drill templates. Several factors were identified in the design and fabrication of the template that can be addressed to increase accuracy. Trajectory planning can also be improved by automating the process. The researchers recommend further studies in these areas specially in the context of developing 3D printing as a support service for surgical operations in the Philippines.

Patient-specific drill template for C2 transoral pedicle insertion in complete reduction of atlantoaxial dislocation: cadaveric efficacy and accuracy assessments

BackgroundThe transoral atlantoaxial reduction plate (TARP) is an effective advance in the treatment of atlantoaxial dislocation (AAD) and can enable the performance of anterior atlantoaxial release, reduction, decompression, and internal fixation in a one-stage operation. However, accurate transoral C2 pedicle insertion (C2TOPI) remains a challenge. The aim of this study is to develop a grouped patient-specific drill template (PDT) specifically for AAD with complete reduction and, furthermore, to compare its efficacy and accuracy in facilitating C2TOPI.MethodsAfter CT scanning, ten cadaveric C2 specimens were randomly assigned to two groups (the PDT and freehand group). A grouped PDT specifically for AAD with complete reduction was designed and manufactured. C2TOPI was performed using the PDT or the fluoroscopy-guided freehand technique. Postoperative CT scans were subsequently performed to analyze the deviations at the centroid of the cross section at the midpoint of the pedicle. Screw position grades were also assessed in both groups.ResultsCompared to the freehand group, the PDT group had a significantly shorter surgery time (p < 0.001). Significant differences between the two groups were observed in the absolute value of the deviations at the centroid of the pedicle on either the axial or sagittal planes (p < 0.05). No significant difference was found in the screw positions between the two groups (p > 0.05); however, two unacceptable breaches (20%) occurred in the freehand group.ConclusionA specifically designed PDT could provide an accurate and easy-to-apply method for C2TOPI in AAD with complete reduction.

A Method to Design and Manufacture Low-Cost Patient-Specific Templates for Spinal Surgery: Evaluation of Multiple Additive Manufacturing Methods

Aim: This study aims to detail an interactive process to design, fabricate and test patient-specific drill templates and surgical training models, and to determine the advantages and disadvantages of multiple low-cost additive manufacturing methods in this application. Materials &amp; methods: Image data from one patient were used to develop and manufacture both patient-specific drill templates for spinal surgery and replica spine models for surgical training with three, low-cost additive manufacturing methods. With the input of an orthopedic surgeon, the models were analyzed based on function, production time, cost, durability and appearance. Results &amp; conclusion: Although differences were observed in the spinal surgery training models, the performance of the drill template models showed little variance across fabrication methods and template materials.

Outcome and safety analysis of 3D-printed patient-specific pedicle screw jigs for complex spinal deformities: a comparative study

Background ContextSpinal deformities are very challenging to treat and have a great risk of neurologic complications because of hardware placement during corrective surgery. Various techniques have been introduced to ensure safe and accurate placement of pedicle screws. Patient-specific screw guides with predrawn and prevalidated trajectory seem to be an attractive option. PurposeWe have focused on developing three-dimensional (3D) printing technique for complex spinal deformities in India. This study also aimed to compare the placement of pedicle screw with 3D printing and freehand technique. Study Design/SettingsThis is a retrospective comparative clinical study in an academic institutional setting. Patient SampleA total of 20 patients were enrolled during the study: 10 were operated on with the help of 3D printing (Group 1) and 10 were operated on with freehand technique (Group 2). Group 1 included six patients with congenital scoliosis, three patients with adolescent idiopathic scoliosis (AIS), and one patient with post-tubercular kyphosis, and Group 2 included five patients with congenital scoliosis, four patients with AIS, and one patient with post-tubercular kyphosis. Outcome MeasuresPrimary outcomes were measured in terms of screw violation, and secondary outcomes were measured in terms of surgical time, blood loss, radiation exposure (number of shoots required), and complications. Materials and MethodsMIMICS Base v18.0 software was used for 3D reconstruction from computed tomography scan images of all the patients. 3-Matic software was used to create a drill guide. A 3D printer from Stratasys Mojo with ABS P430 model material cartilage (a thermoplastic material) was used for the printing of the vertebra model and jigs. A two-sample test of proportion was used to compare correctly and wrongly placed pedicle screws with 3D printing and freehand technique. t Test with equal variance was used for operating surgical time and blood loss. ResultsNo superior or inferior screw violation was observed in any of our patients in either group. We found a significant difference (p=.03) between the two groups regarding perfect screw placement in favor of 3D printing. There were 13 Grade 2 medial perforations in the freehand group and 3 in the 3D printing group. There was no Grade 3 medial perforation in either group. Six Grade 2 lateral perforations in the freehand group and seven in the 3D printing group were observed. Three Grade 3 lateral perforations in the freehand group and two in 3D printing group were observed. Analysis showed a statistically significant (p=.005) medial violation in the freehand group. Surgical time was significantly less (p=.03) in the 3D printing group compared with the freehand group. Mean blood loss was higher in the freehand group but was not statistically significant (p=.3) in the 3D printing group. Fluoroscopic shots required were less in number in the 3D printing group compared with the freehand group. There was no neurologic deficit in any of the patients in the two groups. ConclusionsIn our study, focusing on spinal deformities with statistically significant higher rates of accurate screw positioning and higher numbers of inserted screws with 3D printing was possible because of enhanced safety, particularly at apical levels. As such, spinal deformities are difficult to treat worldwide. In India, these deformities are often neglected and present at a very late and a much more deformed state when their treatment becomes even more challenging. Developing these patient-specific drill templates will enable an average spine surgeon to treat these patients with much ease and safety.

Is a patient-specific drill template via a cortical bone trajectory safe in cervical anterior transpedicular insertion?

BackgroundThis study aimed to develop patient-specific drill templates by computer numerical control or three-dimensional printing via two cortical bone trajectories (CBTs) and to evaluate their efficacies and accuracies in cervical anterior transpedicular insertion.MethodsPreoperative CT images of 20 cadaveric cervical vertebrae (C3–C7) were obtained. After image processing, patient-specific drill templates were randomly assigned to be constructed via two CBTs (CBT0 and CBT0.7) and manufactured by two methods (computer numerical control and three-dimensional printing). Guided by patient-specific drill templates, 3.5-mm-diameter screws were inserted into the pedicles. Postoperative CT scans were performed to evaluate the screw deviation in the entry point and midpoint of the pedicle. The screw positions were also graded.ResultsComputer numerical control patient-specific drill templates had a significantly shorter manufacturing time compared to three-dimensional-printed patient-specific drill templates (p < 0.01). Absolute deviations at the entry point and midpoint of the pedicle had no significant differences on the transverse and sagittal planes (p > 0.05). There were no significant differences in screw positions (p = 0.3). However, three screw positions were in grade 3 in CBT0, while the others were in grade 1.ConclusionsCBT0.7 appears to be a safe and feasible trajectory for cervical anterior transpedicular insertion. Bio-safe computer numerical control patient-specific drill templates can facilitate cervical anterior transpedicular insertion with good feasibility and accuracy.

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.

Prospective clinical pilot study. 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. 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. 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. 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. 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. 5.

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

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

Innovative approach in the development of computer assisted algorithm for spine pedicle screw placement

Pedicle screws are typically used for fusion, percutaneous fixation, and means of gripping a spinal segment. The screws act as a rigid and stable anchor points to bridge and connect with a rod as part of a construct. The foundation of the fusion is directly related to the placement of these screws. Malposition of pedicle screws causes intraoperative complications such as pedicle fractures and dural lesions and is a contributing factor to fusion failure. Computer assisted spine surgery (CASS) and patient-specific drill templates were developed to reduce this failure rate, but the trajectory of the screws remains a decision driven by anatomical landmarks often not easily defined. Current data shows the need of a robust and reliable technique that prevents screw misplacement. Furthermore, there is a need to enhance screw insertion guides to overcome the distortion of anatomical landmarks, which is viewed as a limiting factor by current techniques. The objective of this study is to develop a method and mathematical lemmas that are fundamental to the development of computer algorithms for pedicle screw placement. Using the proposed methodology, we show how we can generate automated optimal safe screw insertion trajectories based on the identification of a set of intrinsic parameters. The results, obtained from the validation of the proposed method on two full thoracic segments, are similar to previous morphological studies. The simplicity of the method, being pedicle arch based, is applicable to vertebrae where landmarks are either not well defined, altered or distorted.

Feasibility of 3D-printed patient-specific drill template for cervical pedicle screw placement

Objective To evaluated the effect of computer-assisted pedicle screw placement using the 3D-printed patient-specific drill template. Methods CT scan was performed on each cervical vertebra of 8 cadavers (4 males and 4 females) and data were saved in Dicom format. 3D reconstruction models were generated with the Mimics to simulate bilateral C3-C6 pedicle screw placement and a drill template was designed. The drill template was manufactured by 3D printing using the photosensitive resin and applied to assist the pedicle screw placement. Accuracy of screw placement was assessed with radiographic examination. Results A total of 64 pedicle screws were inserted with 62 screws entirely inside the pedicle and 2 screws violated into vertebral artery orifice. Accuracy of screw placement was 97%. Conclusions 3D-printed patient-specific drill template is easy to apply and accurate in assisting cervical screw placement. The potential use of drill template to place cervical pedicle screws is promising. Key words: Cervical vertebrae; Imaging, three-dimensional; Computer-aided design; Rapid prototyping

Construction and Accuracy Assessment of Patient-Specific Biocompatible Drill Template for Cervical Anterior Transpedicular Screw (ATPS) Insertion: An In Vitro Study

BackgroundWith the properties of three-column fixation and anterior-approach-only procedure, anterior transpedicular screw (ATPS) is ideal for severe multilevel traumatic cervical instabilities. However, the accurate insertion of ATPS remains challenging. Here we constructed a patient-specific biocompatible drill template and evaluated its accuracy in assisting ATPS insertion.MethodsAfter ethical approval, 24 formalin-preserved cervical vertebrae (C2–C7) were CT scanned. 3D reconstruction models of cervical vertebra were obtained with 2-mm-diameter virtual pin tracts at the central pedicles. The 3D models were used for rapid prototyping (RP) printing. A 2-mm-diameter Kirschner wire was then inserted into the pin tract of the RP model before polymethylmethacrylate was used to construct the patient-specific biocompatible drill template. After removal of the anterior soft tissue, a 2-mm-diameter Kirschner wire was inserted into the cervical pedicle with the assistance of drill template. Cadaveric cervical spines with pin tracts were subsequently scanned using the same CT scanner. A 3D reconstruction was performed of the scanned spines to get 3D models of the vertebrae containing the actual pin tracts. The deviations were calculated between 3D models with virtual and actual pin tracts at the middle point of the cervical pedicle. 3D models of 3.5 mm-diameter screws were used in simulated insertion to grade the screw positions.FindingsThe patient-specific biocompatible drill template was constructed to assist ATPS insertion successfully. There were no significant differences between medial/lateral deviations (P = 0.797) or between superior/inferior deviations (P = 0.741). The absolute deviation values were 0.82±0.75 mm and 1.10±0.96 mm in axial and sagittal planes, respectively. In the simulated insertion, the screws in non-critical position were 44/48 (91.7%).ConclusionsThe patient-specific drill template is biocompatible, easy-to-apply and accurate in assisting ATPS insertion. Its clinical applications should be further researched.

Accuracy and efficacy of thoracic pedicle screws in scoliosis with patient-specific drill template

With the rapid increase in the use of thoracic pedicle screws in scoliosis, accurate and safe placement of screw within the pedicle is a crucial step during the scoliosis surgery. To make thoracic pedicle screw placement safer various techniques are used, Patient-specific drill template with pre-planned trajectory has been thought as a promising solution, it is critical to assess the efficacy, safety profile with this technique. In this paper, we develop and validate the accuracy and safety of thoracic transpedicular screw placement with patient-specific drill template technique in scoliosis. Patients with scoliosis requiring instrumentation were recruited. Volumetric CT scan was performed on each desired thoracic vertebra and a 3-D reconstruction model was generated from the CT scan data. The optimal screw size and orientation were determined and a drill template was designed with a surface that is the inverse of the posterior vertebral surface. The drill template and its corresponding vertebra were manufactured using rapid prototyping technique and tested for violations. The navigational template was sterilized and used intraoperatively to assist with the placement of thoracic screws. After surgery, the positions of the pedicle screws were evaluated using CT scan and graded for validation. This method showed its ability to customize the placement and the size of each pedicle screw based on the unique morphology of the thoracic vertebra. In all the cases, it was relatively very easy to manually place the drill template on the lamina of the vertebral body during the surgery. This method significantly reduces the operation time and radiation exposure for the members of the surgical team, making it a practical, simple and safe method. The potential use of such a navigational template to insert thoracic pedicle screws in scoliosis is promising. The use of surgical navigation system successfully reduced the perforation rate and insertion angle errors, demonstrating the clear advantage in safe and accurate pedicle screw placement of scoliosis surgery.

Engineering patient-specific drill templates and bioabsorbable posterior cervical plates: a feasibility study

The authors describe a method of using computer models to generate customized cervical implants. A promising yet challenging technique in cervical spine surgery involves the use of pedicle screws to assist with posterior instrumentation. Surrounding anatomical structures such as the vertebral arteries and cervical nerve roots present challenges for safe screw placement; however, the use of computer-generated templates seems to be a promising method to assist with placement. In this study, the authors explore the use of computer-generated templates and introduce their methods for creating custom, bioabsorbable posterior cervical implants. The cervical spines (C2-T1) from 4 cadavers were scanned with volumetric CT. Using commercially available software, the authors generated volumetric models of a cervical drill template and the mold for a cervical plate spanning a desired number of vertebrae. The computer generated models of the cervical drill template and cervical plate mold were converted into physical models using a rapid prototyping machine. The biopolymer polylactic acid resin was heated to 250 degrees C and resolidified to form thin approximately 5-mm-thick plates. The newly formed plates were reheated to 60 degrees C and cast on the cervical mold. The resulting translucent plates were found on visual inspection to have a secure lock-and-key fit on the original cadaver spine, and the techniques used were robust and reproducible. The process described in this brief report provides the background to proceed with development and testing of these patient-absorbable templates. The creation and use of patient-specific bioabsorbable posterior cervical plates in conjunction with multilevel drill templates appear promising. Additional feasibility studies are planned, and in vitro studies are required to determine the safety and efficacy of using patient-specific drill templates and converting them into bioabsorbable implants.