A novel computer-assisted drill guide template for lumbar pedicle screw placement: a cadaveric and clinical study

3D printing for spine pathologies: a state-of-the-art review

Three-Dimensional Printing has advanced throughout the years in the field of biomedical science with applications, especially in spine surgeries. 3D printing has the ability of fabricating highly complex structures with ease and high dimensional accuracy. The complexity of the spine's architecture and the inherent dangers of spinal surgery bring the evaluation of 3D printed models into consideration. This article summarizes the benefits of 3D printing based models for application in spine pathology. 3D printing technique is extensively used for fabrication of anatomical models, surgical guides and patient specific implants (PSI). The 3D printing based anatomical models assist in preoperative planning and training of students. Furthermore, 3D printed models can be used for improved communication and understanding of patients about the spinal disorders. The use of 3D printed surgical guides help in the stabilization of the spine during surgery, improving post procedural outcomes. Improved surgical results can be achieved by using PSIs that are tailored for patient specific needs. Finally, this review discusses the limitations and potential future scope of 3D printing in spine pathologies. 3D printing is still in its infancy, and further research would provide better understanding of the technology's true potential in spinal procedures.

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.

Dimensional accuracy of 3D printing navigation templates of chemical-based sterilisation

3D printed navigational templates have facilitated the accurate treatment of orthopaedic patients. However, during practical operation, it is found that the location hole occasionally deviates from the ideal channel. As such, there will be a security risk in clinical applications. The purpose of this study was to evaluate the influence of chemical-based sterilisation methods on the dimensional accuracy of different materials and the influence of module parameters on the degree of deformation. We found that polylactic (PLA) modules sterilised with ethylene oxide (EO) would undergo micro-deformation, and these micro-deformation characteristics depend on the building direction, i.e., the module stretches in the Z direction and shrinks in the X and Y directions. Heat-resisting polylactide (HR-PLA) has the same melting temperature (T_m) as PLA, but its glass transition temperature (T_g) is greater than the EO sterilisation temperature, so there is no obvious deformation after EO sterilisation. The layer height of the module were inversely proportional to the degree of deformation in the same sterilisation method. The deformation time of the module is concentrated within 2 h after heating. The micro-deformation of the 3D printing module depends on its T_g, sterilisation temperature, and duration of the sterilisation cycle.

Patient-specific template-guided versus standard freehand lumbar pedicle screw implantation: a randomized controlled trial

OBJECTIVE

Patient-specific template-guided (TG) pedicle screw placement currently achieves the highest reported accuracy in cadaveric and early clinical studies, with reports of reduced use of radiation and less surgical time. However, a clinical randomized controlled trial (RCT) eliminating potential biases is lacking. This study compares TG and standard freehand (FH) pedicle screw insertion techniques in an RCT.

METHODS

Twenty-four patients (mean age 64 years, 9 men and 15 women) scheduled consecutively and independently from this study for 1-, 2-, or 3-level lumbar fusion were randomized to either the FH (n = 12) or TG (n = 12) group. Accuracy of pedicle screw placement, intraoperative parameters, and short-term complications were compared.

RESULTS

A total of 112 screws (58 FH and 54 TG screws) were implanted in the lumbar spine. Radiation exposure was significantly less in the TG group (78.0 ± 46.3 cGycm2) compared with the FH group (234.1 ± 138.1 cGycm2, p = 0.001). There were 4 pedicle screw perforations (6.9%) in the FH group and 2 (3.7%) in the TG group (p > 0.99), with no clinical consequences. Clinically relevant complications were 1 postoperative pedicle fracture in the FH group (p > 0.99), 1 infection in the FH group, and 2 infections in the TG group (p > 0.99). There were no significant differences in surgical exposure time, screw insertion time, overall surgical time, or blood loss between the FH and TG groups.

CONCLUSIONS

In this RCT, patient-specific TG pedicle screw insertion in the lumbar region achieved a high accuracy, but not better than a standardized FH technique. Even if intraoperative radiation exposure is less with the TG technique, the need for a preoperative CT scan counterbalances this advantage. However, more difficult trajectories might reveal potential benefits of the TG technique and need further research.

Accuracy and safety of three-dimensionally printed animal-specific drill guides for thoracolumbar vertebral column instrumentation in dogs: Bilateral and unilateral designs

OBJECTIVE

To evaluate the safety and accuracy of a unilateral three-dimensionally printed animal-specific drill guide (3DASDG) design for unilateral stabilization in the thoracolumbar vertebral column of dogs compared to a bilateral design.

STUDY DESIGN

Cadaveric study.

SAMPLE POPULATION

Fifty-two corridors in one canine cadaver.

METHODS

Two 3DASDG designs with 2 drilling tubes each were created from T8 to L7 vertebrae. Fifty-two corridors were drilled on the right and the left sides by using unilateral and bilateral designs, respectively. Planned and postoperative trajectories (entry point, exit point, angle) were compared to establish the accuracy. Statistical analysis was used for accuracy comparison between designs. Safety was evaluated by using Zdichavsky classification.

RESULTS

Unilateral and bilateral drill guide designs were not different for entry point and angle deviations; however, they were different for the exit point deviations. Two corridors breached outside the vertebra. For all guides, mean entry and exit point deviations were less than 1 and 2 mm, respectively. The maximum entry or exit point deviation in both groups was 4.7 mm. The mean angle deviation was <3.5°, and the maximum angle deviation was 9.3°.

CONCLUSION

No difference was detected in accuracy of entry points and angle deviations between drill guide designs tested in normal vertebrae. The technique was classified as highly safe.

CLINICAL SIGNIFICANCE

A unilateral drill guide design may be a safe alternative to bilateral guides for unilateral stabilization of the thoracolumbar vertebral column in dogs.

An experimental study on the safe placement of sacroiliac screws using a 3D printing navigation module

Background

In this experimental study, we evaluated the use of digital 3D navigation printing in minimizing complications arising from sacroiliac screw misplacement.

Methods

A total of 13 adult pelvic specimens were studied using 3D navigation printing. Mimics software was used for preoperative planning and for obtaining sacrum median sagittal resection and long axis resection of the S1 pedicle center by 3D segmentation. The ideal screw path had its origin at the post-median part of the auricular surface of the sacroiliac joint, the midpoint at the mid-position of the lateral recess and outlet of the anterior sacral foramina; and the endpoint at the S1 sagittal resection. A sacroiliac screw fixed the pelvic specimens with the assistance of the navigation module. The distance between the start point (ilium surface) and endpoint (sacral median sagittal resection) of the screw path was measured after the pre- and postoperative 3D pelvis module was 3D-registered according to the standard precision range. The origin/endpoint qualified rates of the postoperative (n/26) and preoperative (26/26) screw paths were analyzed by the chi-square test.

Results

No screw misplacement occurred in the screw paths of any of the 13 pelvic specimens. The mean distance between the preoperative and postoperative origin of the screw path was 1.5415±0.6806 mm, and the mean distance between the preoperative and postoperative endpoint was 2.2809±0.4855 mm. The qualified rate of origin was 23/26 when the precision grade was 2.4 mm (P>0.05, χ²=1.41), while the qualified rate of endpoint was 21/26 when the precision grade was 2.7 mm (P>0.05, χ²=3.54).

Conclusions

In this experimental study, using a 3D printing navigation module helped attain an accurate and safe sacroiliac screw implantation.

Comparison of the 3D-printed operation guide template technique and the free-hand technique for S2-alar-iliac screw placement

BACKGROUND

To compare the safety and accuracy of the 3D-printed operation guide template technique and the free-hand technique in the placement of the S2-alar-iliac (S2AI) screw.

METHODS

We conducted a retrospective analysis of 47 patients undergoing S2AI screw placement in our hospital, divided into the 3D-printed operation guide template group and the free-hand screw placement group. The duration of single S2AI screw placement was documented in all patients. A postoperative CT scan was performed to assess screw placement effectiveness according to the distance from the screw tip to the breach of the cortical bone wall.

RESULTS

In total, 42 screws were placed in the guide template group, with an average screw placement duration of 151.6 ± 44.8 s. Screw placement grading was as follows: 40 screws in grade 0, two in grade 1, and none in grades 2 and 3. This grading resulted in excellent and good rates of 95.2% and 100%, respectively. In total, 52 screws were placed in the free-hand group, with an average screw placement duration of 138.3 ± 45.9 s. Screw placement grading was as follows: 42 screws in grade 0, seven in grade 1, three in grade 2, and none in grade 3. This grading resulted in excellent, good and acceptable rates 80.8%, 94.2% and 100%, respectively. Screw placement duration did not significantly differ between the groups (p > 0.05). The excellent rate of screw placement was greater in the guide template group than in the free-hand group (p < 0.05), but the good and acceptable rates did not significantly differ between the two groups (p > 0.05).

CONCLUSION

Both techniques can be applied to S2AI screw placement. The 3D-printed guide technique is superior to the free-hand technique in terms of safety and accuracy.

Accuracy of S2 Alar-Iliac Screw Placement Under the Guidance of a 3D-Printed Surgical Guide Template

OBJECTIVE

To evaluate the safety and accuracy of S2 alar-iliac (S2AI) screw placement guided by a 3-dimensional (3D)-printed surgical guide template.

METHODS

The data of 27 patients treated with S2AI screws were analyzed. S2AI surgical guide templates were designed and printed, and S2AI screw placement was completed intraoperatively with the guide templates. Postoperative computed tomography was performed to measure screw path parameters, namely the sagittal angle (SA), the transverse angle (TA), the horizontal distance (HD) between the entry point of the screw and the median sacral crest, and the vertical distance (VD) between the entry point of the screw and the lower edge of the first posterior sacral foramen. Screw placement was graded according to the Oh grading criteria.

RESULTS

A total of 54 S2AI screws were placed. The screw grades were as follows: 52 screws were considered grade 0, 2 were grade 1, none were grade 2, and none were grade 3. Thus grade 0 accounted for 96.3% of the screws. When the preoperatively planned SA (32.3° ± 2.0°), TA (42.1° ± 3.9°), HD (5.1 ± 1.1) mm, and VD (19.0 ± 2.4) mm were compared with the corresponding postoperative SA (31.9° ± 3.8°), TA (42.5° ± 4.0°), HD (4.9 ± 1.1) mm, and VD (19.1 ± 2.3) mm, no significant differences were identified (P > 0.05).

CONCLUSIONS

S2AI screw placement assisted by a 3D-printed surgical guide is safe and accurate.

Design, application, and evaluation of a novel method for determining optimal trajectory of thoracic pedicle screws

Background

This is an experimental study performed on 15 adult cadavers. In this cadaveric study, we designed and evaluated a novel methodology for determining the optimal trajectory for the placement of thoracic pedicle screws. The accuracy of thoracic pedicle screw placement is critical to the spinal surgery. The concept, implement method, and significance of the optimal thoracic pedicle trajectory have not been reported.

Methods

The experimental study was performed on 15 adult cadavers. The Mimics software was used to design optimal trajectory through the pedicle central axis. Using three-dimensional (3D) printing, a navigation module with a locating facet and a stabilizing facet was developed. The thoracic pedicle screws were inserted with the help of the navigation module. The three-dimensional coordinates for the entry and the exit points of the screws were compared between the planned trajectories and the postoperative trajectories. The differences in coordinates were analyzed to evaluate the precision of the screw placement.

Results

The trajectories through the pedicle central axis showed an excellent symmetry between the single segments and for all thoracic vertebrae. Out of a total of 358 screws that were inserted, 15 (4.2%) screws breached the pedicle cortex with a breach distance of <2 mm. The qualifying rate was 98.6% (353/358) for the entry point precision of ≥3.2 mm, and 98.9% (354/358) for the exit point precision of ≥6.4 mm. In comparison to the designed qualified rate of 100% (358/358), the χ² was 3.22 and 2.26, respectively (P>0.05).

Conclusions

The optimal trajectory was obtained through the pedicle central axis, which significantly reduced the risk of cortex breach. A high degree of precision was obtained for the entry and the exit points of the screws when the postoperative trajectory was compared with the designed trajectory.

Three-dimensional printing in spine surgery: a review of current applications

In recent years, the use of three-dimensional printing (3DP) technology has gained traction in orthopedic spine surgery. Although research on this topic is still primarily limited to case reports and small cohort studies, it is evident that there are many avenues for 3DP innovation in the field. This review article aims to discuss the current and emerging 3DP applications in spine surgery, as well as the challenges of 3DP production and limitations in its use. 3DP models have been presented as helpful tools for patient education, medical training, and presurgical planning. Intraoperatively, 3DP devices may serve as patient-specific surgical guides and implants that improve surgical outcomes. However, the time, cost, and learning curve associated with constructing a 3DP model are major barriers to widespread use in spine surgery. Considering the costs and benefits of 3DP along with the varying risks associated with different spine procedures, 3DP technology is likely most valuable for complex or atypical spine disorder cases. Further research is warranted to gain a better understanding of how 3DP can and will impact spine surgery.

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.

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.

The Accuracy of 3D Printing Assistance in the Spinal Deformity Surgery

Background

The pedicle screw is one of the main tools used in spinal deformity correction surgery. Robotic and navigated surgeries are usually used, and they provide superior accuracy in pedicle screw placement than free-hand and fluoroscopy-guided techniques. However, their high cost and space limitation are problematic. We provide a new solution using 3D printing technology to facilitate spinal deformity surgery.

Methods

A workflow was developed to assist spinal deformity surgery using 3D printing technology. The trajectory and profile of pedicle screws were determined on the image system by the surgical team. The engineering team designed drill templates based on the bony surface anatomy and the trajectory of pedicle screws. Their effectiveness and safety were evaluated during a preoperative simulation surgery. The surgery consisted in making a pilot hole through the drill template on a computed tomography- (CT-) based, full-scale 3D spine model for every planned segment. Somatosensory evoke potential (SSEP) and motor evoke potential (MEP) were used for intraoperative neurophysiological monitoring. Postoperative CT was obtained 6 months after the correction surgery to confirm the screw accuracy.

Results

From July 2015 to November 2016, we performed 10 spinal deformity surgeries with 3D printing technology assistance. In total, 173 pedicle screws were implanted using drill templates. No notable change in SSEP and MEP or neurologic deficit was noted. Based on postoperative CT scans, the acceptable rate was 97.1% (168/173). We recorded twelve pedicle screws with medial breach, six with lateral breach, and five with inferior breach. Medial breach (12/23) was the main type of penetration. Lateral breach occurred mostly in the concave side (5/6). Most penetrations occurred above the T8 level (69.6%, 16/23).

Conclusion

3D printing technology provides an effective alternative for spinal deformity surgery when expensive medical equipment, such as intraoperative navigation and robotic systems, is unavailable.

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.

Clinical Applications of 3-Dimensional Printing Technology in Hip Joint

Three‐dimensional (3D) printing is a digital rapid prototyping technology based on a discrete and heap‐forming principle. We identified 53 articles from PubMed by searching “Hip” and “Printing, Three‐Dimensional”; 52 of the articles were published from 2015 onwards and were, therefore, initially considered and discussed. Clinical application of the 3D printing technique in the hip joint mainly includes three aspects: a 3D‐printed bony 1:1 scale model, a custom prosthesis, and patient‐specific instruments (PSI). Compared with 2‐dimensional image, the shape of bone can be obtained more directly from a 1:1 scale model, which may be beneficial for preoperative evaluation and surgical planning. Custom prostheses can be devised on the basis of radiological images, to not only eliminate the fissure between the prosthesis and the patient's bone but also potentially resulting in the 3D‐printed prosthesis functioning better. As an alternative support to intraoperative computer navigation, PSI can anchor to a specially appointed position on the patient's bone to make accurate bone cuts during surgery following a precise design preoperatively. The 3D printing technique could improve the surgeon's efficiency in the operating room, shorten operative times, and reduce exposure to radiation. Well known for its customization, 3D printing technology presents new potential for treating complex hip joint disease.

Design and Application of Individualized, 3-Dimensional-Printed Navigation Template for Placing Cortical Bone Trajectory Screws in Middle-Upper Thoracic Spine: Cadaver Research Study

OBJECTIVE

To evaluate the safety and accuracy of use of a 3-dimensional printed navigation template in the placement of a cortical bone trajectory (CBT) screw in the middle-upper thoracic spine.

METHODS

Ten human cadavers were included in the study. Sixty CBT screws were placed on 1 side, using the free-hand technique, and 60 CBT screws were placed on the other side, using the navigation template that was designed and printed using data from 10 cadavers. The safety and accuracy of use of the CBT screws were directly evaluated by radiography and computed tomography.

RESULTS

Computed tomography revealed that 2 and 3 of 60 screws, placed using the navigation template, were broken in the medial or lateral areas and in the superior or inferior pedicle wall, respectively. Furthermore, 8 screws were broken in the medial or lateral areas and 11 screws were broken in the superior or inferior pedicle wall when the free-hand technique was used. Radiography revealed that 3 screws in zone I, 55 screws in zone II, and 2 screws in zone III were placed using the navigation template. Furthermore, 7 screws in zone I, 45 screws in zone II, and 8 screws in zone III were placed using the free-hand technique.

CONCLUSIONS

In this cadaver study, insertion of the CBT screws in the middle-upper thoracic spine with the assistance of the navigation template was safe and convenient.

Design of a 3D navigation template to guide the screw trajectory in spine: a step-by-step approach using Mimics and 3-Matic software

Rapid development of 3D printing techniques has led to the design of navigation templates to assist with accurate insertion of pedicle screws in last decades. However, there are still without the precise step-by-step methods to design 3D navigation templates from computed tomography (CT) images. Our present article provides a detailed protocol to allow the readers or researchers to obtain the 3D navigation template easily, and assist with pedicle screw insertion in their future research and surgery. Using 3D navigation template-assisted pedicle screw fixation in spine surgery is low cost and can decrease the radiation exposure to both patients and surgeons.

Feasibility and accuracy of computer-assisted individual drill guide template for minimally invasive lumbar pedicle screw placement trajectory

OBJECTIVE

To discuss the feasibility and accuracy of a specific computer-assisted individual drill guide template (CIDGT) for minimally invasive lumbar pedicle screw placement trajectory (MI-LPT) through a bovine cadaveric experimental study.

DESIGN

A 3-D reconstruction model, including lumbar vertebras (L1-L5), was generated, and the optimal MI-LPTs were determined. A drill guide template with a surface made of the antitemplate of the vertebral surface, including the spinous process and the entry point vertebral surface, was created by reverse engineering and rapid prototyping techniques. Then, MI-LPTs were determined by the drill guide templates, and the trajectories made by K-wires were observed by postoperative CT scan.

SETTING

General Hospital of Shenyang Military Area Command of Chinese PLA.

RESULTS

In total, 150 K-wires for MI-LPTs were successfully inserted into L1-L5. The required mean time and fluoroscopy times between fixation of the template to the spinous process, entry point vertebral surface, and insertion of the K-wires for minimally invasive lumbar pedicle screw placement trajectories into each vertebra were 79.4 ± 15.0 s and 2.1 ± 0.8 times. There were no significant differences between the preoperative plan and postoperative assessment in the distance from the puncture to the midline and inclination angles according to the different levels (P > 0.05, respectively). The mean deviation between the preoperative plan and postoperative assessment in the distance from the puncture to the midline and inclination angles were 0.8 ± 0.5 mm and 0.9 ± 0.5°, respectively.

CONCLUSIONS

The potential use of the novel CIDGT, which was based on the unique morphology of the lumbar vertebra to place minimally invasive lumbar pedicle screws, is promising and could prevent too much radiation exposure intraoperatively.

The potential of 3D printing in urological research and patient care

3D printing is an evolving technology that enables the creation of unique organic and inorganic structures with high precision. In urology, the technology has demonstrated potential uses in both patient and clinician education as well as in clinical practice. The four major techniques used for 3D printing are inkjet printing, extrusion printing, laser sintering, and stereolithography. Each of these techniques can be applied to the production of models for education and surgical planning, prosthetic construction, and tissue bioengineering. Bioengineering is potentially the most important application of 3D printing, as the ability to produce functional organic constructs might, in the future, enable urologists to replicate and replace abnormal tissues with neo-organs, improving patient survival and quality of life.

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.

Accuracy of thoracic pedicle screw placement in adolescent patients with severe spinal deformities: a retrospective study comparing drill guide template with free-hand technique

PURPOSE

Patients with severe spinal deformities often have small pedicle diameters, and pedicle dimensions vary between segments and individuals. Free-hand pedicle screw placement can be inaccurate. Individualized drill guide templates may be used, but the accuracy of pedicle screw placement in severe scoliosis remains unknown. The accuracy of drill guide templates and free-hand technique for the treatment of adolescent patients with severe idiopathic scoliosis are compared in this study.

METHODS

This study included 37 adolescent patients (mean age 16.4 ± 1.3 years) with severe idiopathic scoliosis treated surgically at a single spine center between January 2014 and June 2017. Spinal deformities were corrected using posterior pedicle screw fixation. Patients in group I were treated with rapid prototype drill guide template technique (20 patients; 396 screws) and patients in group II were treated with free-hand technique (17 patients; 312 screws). Outcomes that included operative time, correction rate, and the incidence and distribution of screw misplacement were evaluated.

RESULTS

Operative time in group I was 283 ± 22.7 min compared to 285 ± 25.8 min in group II (p = 0.89). The scoliosis correction rate was 55.0% in group I and 52.9% in group II (p = 0.33). Based on both axial and sagittal reconstruction images, the accuracy rate of pedicle screw placement was 96.7% in group I and 86.9% in group II (p = 0.000).

CONCLUSION

The drill guide template technique has potential to offer more accurate and thus safer placement of pedicle screws than free-hand technique in the treatment of severe scoliosis in adolescents.

A medium invasiveness multi-level patient's specific template for pedicle screw placement in the scoliosis surgery

Background

Several methods including free-hand technique, fluoroscopic guidance, image-guided navigation, computer-assisted surgery system, robotic platform and patient’s specific templates are being used for pedicle screw placement. These methods have screw misplacements and are not always easy to be applied. Furthermore, it is necessary to expose completely a large portions of the spine in order to access fit entirely around the vertebrae.

Methods

In this study, a multi-level patient’s specific template with medium invasiveness was proposed for pedicle screw placement in the scoliosis surgery. It helps to solve the problems related to the soft tissues removal. After a computer tomography (CT) scan of the spine, the templates were designed based on surgical considerations. Each template was manufactured using three-dimensional printing technology under a semi-flexible post processing. The templates were placed on vertebras at four points—at the base of the superior-inferior articular processes on both left–right sides. This helps to obtain less invasive and more accurate procedure as well as true-stable and easy placement in a unique position. The accuracy of screw positions was confirmed by CT scan after screw placement.

Results

The result showed the correct alignment in pedicle screw placement. In addition, the template has been initially tested on a metal wire series Moulage (height 70 cm and material is PVC). The results demonstrated that it could be possible to implement it on a real patient.

Conclusions

The proposed template significantly reduced screw misplacements, increased stability, and decreased the sliding & the intervention invasiveness.

Three-Dimensional Bioprinting and Its Potential in the Field of Articular Cartilage Regeneration

Three-dimensional (3D) bioprinting techniques can be used for the fabrication of personalized, regenerative constructs for tissue repair. The current article provides insight into the potential and opportunities of 3D bioprinting for the fabrication of cartilage regenerative constructs. Although 3D printing is already used in the orthopedic clinic, the shift toward 3D bioprinting has not yet occurred. We believe that this shift will provide an important step forward in the field of cartilage regeneration. Three-dimensional bioprinting techniques allow incorporation of cells and biological cues during the manufacturing process, to generate biologically active implants. The outer shape of the construct can be personalized based on clinical images of the patient's defect. Additionally, by printing with multiple bio-inks, osteochondral or zonally organized constructs can be generated. Relevant mechanical properties can be obtained by hybrid printing with thermoplastic polymers and hydrogels, as well as by the incorporation of electrospun meshes in hydrogels. Finally, bioprinting techniques contribute to the automation of the implant production process, reducing the infection risk. To prompt the shift from nonliving implants toward living 3D bioprinted cartilage constructs in the clinic, some challenges need to be addressed. The bio-inks and required cartilage construct architecture need to be further optimized. The bio-ink and printing process need to meet the sterility requirements for implantation. Finally, standards are essential to ensure a reproducible quality of the 3D printed constructs. Once these challenges are addressed, 3D bioprinted living articular cartilage implants may find their way into daily clinical practice.

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.

Systematic review of 3D printing in spinal surgery: the current state of play

Three-dimensional printing (3DP), also known as "Additive Manufacturing", is a rapidly growing industry, particularly in the area of spinal surgery. Given the complex anatomy of the spine and delicate nature of surrounding structures, 3DP has the potential to aid surgical planning and procedural accuracy. We perform a systematic review of current literature on the applications of 3DP in spinal surgery. Six electronic databases were searched for original published studies reporting cases or outcomes for 3DP surgical models, guides or implants for spinal surgery. The findings of these studies were synthesized and summarized. These searches returned a combined 2,411 articles. Of these, 54 were included in this review. 3DP is currently used for surgical planning, intra-operative surgical guides, customised prostheses as well as "Off-the-Shelf" implants. The technology has the potential for enhanced implant properties, as well as decreased surgical time and better patient outcomes. The majority of the data thus far is from low-quality studies with inherent biases linked with the excitement of a new field. As the body of literature continues to expand, larger scale studies to evaluate advantages and disadvantages, and longer-term follow up will enhance our knowledge of the effect 3DP has in spinal surgery. In addition, issues such as financial impact, time to design and print, materials selection and bio-printing will evolve as this rapidly expanding field matures.

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.

3D printing technology used in severe hip deformity

This study was designed to assess the use of a 3D printing technique in total hip arthroplasty (THA) for severe hip deformities, where new and improved approaches are needed. THAs were performed from January 2015 to December 2016. Bioprosthesis artificial hip joints were used in both conventional and 3D printing hip arthroplasties. A total of 74 patients (57 cases undergoing conventional hip replacements and 17 undergoing 3D printing hip replacements) were followed-up for an average of 24 months. The average age of the patients was 62.7 years. Clinical data between the patients treated with different approaches were compared. Results showed that the time to postoperative weight bearing and the Harris scores of the patients in the 3D printing group were better than those for patients in the conventional hip replacement group. Unfortunately, the postoperative infection and loosening rates were higher in the 3D printing group. However, there were no significant differences in femoral neck anteversion, neck shaft, acetabular or sharp angles between ipsilateral and contralateral sides in the 3D printing group (P>0.05). The femoral neck anteversion angle was significantly different between the two sides in the conventional hip replacement group (P<0.05). Based on these results, we suggest that the 3D printing approach provides a better short-term curative effect that is more consistent with the physiological structure and anatomical characteristics of the patient, and we anticipate that its use will help improve the lives of many patients.

Patient-specific core decompression surgery for early-stage ischemic necrosis of the femoral head

Introduction

Core decompression is an efficient treatment for early stage ischemic necrosis of the femoral head. In conventional procedures, the pre-operative X-ray only shows one plane of the ischemic area, which often results in inaccurate drilling. This paper introduces a new method that uses computer-assisted technology and rapid prototyping to enhance drilling accuracy during core decompression surgeries and presents a validation study of cadaveric tests.

Methods

Twelve cadaveric human femurs were used to simulate early-stage ischemic necrosis. The core decompression target at the anterolateral femoral head was simulated using an embedded glass ball (target). Three positioning Kirschner wires were drilled into the top and bottom of the large rotor. The specimen was then subjected to computed tomography (CT). A CT image of the specimen was imported into the Mimics software to construct a three-dimensional model including the target. The best core decompression channel was then designed using the 3D model. A navigational template for the specimen was designed using the Pro/E software and manufactured by rapid prototyping technology to guide the drilling channel. The specimen-specific navigation template was installed on the specimen using positioning Kirschner wires. Drilling was performed using a guide needle through the guiding hole on the templates. The distance between the end point of the guide needle and the target was measured to validate the patient-specific surgical accuracy.

Results

The average distance between the tip of the guide needle drilled through the guiding template and the target was 1.92±0.071 mm.

Conclusions

Core decompression using a computer-rapid prototyping template is a reliable and accurate technique that could provide a new method of precision decompression for early-stage ischemic necrosis.

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.

Accuracy of Computer-Aided Techniques in Orthopaedic Surgery: How Can It Be Defined, Measured Experimentally, and Analyzed from a Clinical Perspective?

Surgical accuracy is multifactorial. Therefore, it is crucial to consider all influencing factors when investigating the accuracy of a surgical procedure, such as the surgeon's experience, the assistive technologies that may be used by the surgeon, and the patient factors associated with the specific anatomical site. For in vitro preclinical investigations, accuracy should be linked to the concepts of trueness (e.g., distance from the surgical target) and precision (e.g., variability in relation to the surgical target) to gather preclinical, quantitative, objective data on the accuracy of completed surgical procedures that have been performed with assistive technologies. The clinical relevance of improvements in accuracy that have been observed experimentally may be evaluated by analyzing the impact on the risk of failure and by taking into account the level of tolerance in relation to the surgical target (e.g., the extent of the safety zone). The International Organization for Standardization (ISO) methodology enables preclinical testing of new assistive technologies to quantify improvements in accuracy and assess the benefits in terms of reducing the risk of failure and achieving surgical targets with tighter tolerances before the testing of clinical outcomes.

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.

Individualized 3D printing navigation template for pedicle screw fixation in upper cervical spine

PURPOSE

Pedicle screw fixation in the upper cervical spine is a difficult and high-risk procedure. The screw is difficult to place rapidly and accurately, and can lead to serious injury of spinal cord or vertebral artery. The aim of this study was to design an individualized 3D printing navigation template for pedicle screw fixation in the upper cervical spine.

METHODS

Using CT thin slices data, we employed computer software to design the navigation template for pedicle screw fixation in the upper cervical spine (atlas and axis). The upper cervical spine models and navigation templates were produced by 3D printer with equal proportion, two sets for each case. In one set (Test group), pedicle screws fixation were guided by the navigation template; in the second set (Control group), the screws were fixed under fluoroscopy. According to the degree of pedicle cortex perforation and whether the screw needed to be refitted, the fixation effects were divided into 3 types: Type I, screw is fully located within the vertebral pedicle; Type II, degree of pedicle cortex perforation is <1 mm, but with good internal fixation stability and no need to renovate; Type III, degree of pedicle cortex perforation is >1 mm or with the poor internal fixation stability and in need of renovation. Type I and Type II were acceptable placements; Type III placements were unacceptable.

RESULTS

A total of 19 upper cervical spine and 19 navigation templates were printed, and 37 pedicle screws were fixed in each group. Type I screw-placements in the test group totaled 32; Type II totaled 3; and Type III totaled 2; with an acceptable rate of 94.60%. Type I screw placements in the control group totaled 23; Type II totaled 3; and Type III totaled 11, with an acceptable rate of 70.27%. The acceptability rate in test group was higher than the rate in control group. The operation time and fluoroscopic frequency for each screw were decreased, compared with control group.

CONCLUSION

The individualized 3D printing navigation template for pedicle screw fixation is easy and safe, with a high success rate in the upper cervical spine surgery.

Deviation analysis for C1/2 pedicle screw placement using a three-dimensional printed drilling guide

Cervical transarticular fixation is a technically demanding procedure. This study aimed to develop a safer and more accurate method for C1/2 pedicle screw placement using a three-dimensional printed drilling guide. A total of 20 patients with C1/2 fractures and dislocations were recruited, and their computed tomography scans were evaluated. Under the assistance of the three-dimensional printed drilling guide, bilateral C1/2 pedicle screws were successfully placed in the three-dimensional C1/2 models. Then, sagittal and axial computed tomography scans were obtained, and the accuracy and safety of screw placement were evaluated based on X-Y-Z axis setup. The average depths for C1 and C2 pedicle screws were 30.1 ± 1.12 and 31.81 ± 0.85 mm on the left side and 29.54 ± 1.01 and 31.35 ± 0.27 mm on the right side, respectively. The average dimensional parameters for C1/C2 pedicle screw of both sides were measured and analyzed, which showed no statistically significant differences in the ideal and the actual entry points, inclined angles, and tailed angles. The method of developing a three-dimensional printed drilling guide is an easy and safe technique. This novel technique is applicable for C1/2 pedicle screw fixation; the potential use of the three-dimensional printed guide to place C1/2 pedicle screw is promising.

A low invasiveness patient’s specific template for spine surgery

Free-hand pedicle screw placement is still conventional in surgery, although it has potentially high risks. The surgical procedures such as pedicle screw placement are usually designed based on medical imaging, but during surgery, the procedures are not normally followed due to the fact that some points are missed in two-dimensional images and seen only during surgery. In this regards, some highly accurate computer-assisted systems have been proposed and are currently used. Moreover, it is possible to reduce or completely avoid hand working by applying modern digital technology. Therefore, using these technologies has remarkable advantages. In this study, we have presented a new approach of pedicle screw placement in the lumbar and sacral regions using a specific drill guide template. The template was created by additive manufacturing technology and was verified in a clinical study as well. The main aim of this research includes the following: design, analyze, manufacture and evaluate the accuracy of a new patient-specific drill guide template, for lumbar pedicle screw placement, and compare the template to the free-hand technique under fluoroscopy supervision. Our results show that the incidence of cortex perforation is substantially reduced compared to existing methods. Finally, we believe that this approach remarkably lowers the incidence of cortex perforation and could be potentially used in clinical applications, particularly in certain selected cases.

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.

3D-printing techniques in a medical setting: a systematic literature review

BACKGROUND

Three-dimensional (3D) printing has numerous applications and has gained much interest in the medical world. The constantly improving quality of 3D-printing applications has contributed to their increased use on patients. This paper summarizes the literature on surgical 3D-printing applications used on patients, with a focus on reported clinical and economic outcomes.

METHODS

Three major literature databases were screened for case series (more than three cases described in the same study) and trials of surgical applications of 3D printing in humans.

RESULTS

227 surgical papers were analyzed and summarized using an evidence table. The papers described the use of 3D printing for surgical guides, anatomical models, and custom implants. 3D printing is used in multiple surgical domains, such as orthopedics, maxillofacial surgery, cranial surgery, and spinal surgery. In general, the advantages of 3D-printed parts are said to include reduced surgical time, improved medical outcome, and decreased radiation exposure. The costs of printing and additional scans generally increase the overall cost of the procedure.

CONCLUSION

3D printing is well integrated in surgical practice and research. Applications vary from anatomical models mainly intended for surgical planning to surgical guides and implants. Our research suggests that there are several advantages to 3D-printed applications, but that further research is needed to determine whether the increased intervention costs can be balanced with the observable advantages of this new technology. There is a need for a formal cost-effectiveness analysis.

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.

3D-printed guiding templates for improved osteosarcoma resection

Osteosarcoma resection is challenging due to the variable location of tumors and their proximity with surrounding tissues. It also carries a high risk of postoperative complications. To overcome the challenge in precise osteosarcoma resection, computer-aided design (CAD) was used to design patient-specific guiding templates for osteosarcoma resection on the basis of the computer tomography (CT) scan and magnetic resonance imaging (MRI) of the osteosarcoma of human patients. Then 3D printing technique was used to fabricate the guiding templates. The guiding templates were used to guide the osteosarcoma surgery, leading to more precise resection of the tumorous bone and the implantation of the bone implants, less blood loss, shorter operation time and reduced radiation exposure during the operation. Follow-up studies show that the patients recovered well to reach a mean Musculoskeletal Tumor Society score of 27.125.

Comparison Between Gearshift And Drill Techniques For Pedicle Screw Placement By Resident Surgeons

BACKGROUND

Various techniques have been described for pedicle screw placement with established clinical and radiological success. Suboptimal screw trajectories can compromise bony purchase and, worse yet, cause neurological and vascular injuries. Thus, it is of paramount importance to achieve maximum accuracy of screw placement. Our objective is to evaluate the accuracy of pedicle screw placement in the thoracolumbar spine by resident surgeons. Two popular techniques, gearshift versus drill, were compared.

METHODS

This is a a cadaveric surgical technique comparison study. Six resident surgeons instrumented the spine from T1 to S1 using both gearshift and drill techniques. Each pedicle was randomly assigned to either of the techniques. Pedicle screws were placed freehand without radiographic guidance. Violations (medial, lateral, anterior, superior and inferior) were recorded by studying the computerized tomographic scans of instrumented cadavers by blinded observers. Critical perforations were defined as greater than 2mm breach of the pedicle wall.

RESULTS

A total of 100 vertebrae (200 pedicles) were instrumented in the six cadavers. 103 pedicles were breached (51.5% of total pedicles). Lateral violations were the most encountered (65% of violations, 67 total, 48 critical, 19 noncritical) followed by medial (24%, 25 total, 13 critical, 12 noncritical), and the rest were anterior (3%), superior (4%) and inferior (4%). There was no overall difference in violations comparing the gearshift technique (49.5%, 51 total, 37 critical, 14 noncritical) with drill technique (50.5%, 52 total, 33 critical, 19 noncritical). Analyzing the breaches at individual vertebra indicated most violations at T6 (11), T5 (10), followed by T3 (9) and T4 (9), decreasing towards the lumbosacral vertebrae.

CONCLUSION

The results of this study suggest that the gearshift and drill techniques for placement of pedicle screws in the thoracolumbar spine fare similarly with regards to risk of breach when applied by resident surgeons.

Application of the polystyrene model made by 3-D printing rapid prototyping technology for operation planning in revision lumbar discectomy

OBJECTIVE

The objective was to evaluate the effectiveness of 3-D rapid prototyping technology in revision lumbar discectomy. 3-D rapid prototyping technology has not been reported in the treatment of revision lumbar discectomy.

METHODS

Patients with recurrent lumbar disc herniation who were preparing to undergo revision lumbar discectomy from a single center between January 2011 and 2013 were included in this analysis. Patients were divided into two groups. In group A, 3-D printing technology was used to create subject-specific lumbar vertebral models in the preoperative planning process. Group B underwent lumbar revision as usual. Preoperative and postoperative clinical outcomes were compared between groups included operation time, perioperative blood loss, postoperative complications, Oswestry Disability Index (ODI), Japan Orthopaedics Association (JOA) scores, and visual analogue scale (VAS) scores for back pain and leg pain.

RESULTS

A total of 37 patients were included in this study (Group A = 15, Group B = 22). Group A had a significantly shorter operation time (106.53 ± 11.91 vs. 131.92 ± 10.81 min, P < 0.001) and significantly less blood loss (341.67 ± 49.45 vs. 466.77 ± 71.46 ml, P < 0.001). There was no difference between groups for complication rate. There were also no differences between groups for any clinical metric.

CONCLUSION

Using the 3-D printing technology before revision lumbar discectomy may reduce the operation time and the perioperative blood loss. There does not appear to be a benefit to using the technology with respect to clinical outcomes. Future prospective studies are needed to further elucidate the efficacy of this emerging technology.

Additive-manufactured patient-specific titanium templates for thoracic pedicle screw placement: novel design with reduced contact area

PURPOSE

Image-based navigational patient-specific templates (PSTs) for pedicle screw (PS) placement have been described. With recent advances in three-dimensional computer-aided designs and additive manufacturing technology, various PST designs have been reported, although the template designs were not optimized. We have developed a novel PST design that reduces the contact area without sacrificing stability. It avoids susceptibility to intervening soft tissue, template geometric inaccuracy, and difficulty during template fitting.

METHODS

Fourteen candidate locations on the posterior aspect of the vertebra were evaluated. Among them, locations that had high reproducibility on computed tomography (CT) images and facilitated accurate PS placement were selected for the final PST design. An additive manufacturing machine (EOSINT M270) fabricated the PSTs using commercially pure titanium powder. For the clinical study, 36 scoliosis patients and 4 patients with ossification of the posterior longitudinal ligament (OPLL) were treated with thoracic PSs using our newly developed PSTs. We intraoperatively and postoperatively evaluated the accuracy of the PS hole created by the PST.

RESULTS

Based on the segmentation reproducibility and stability analyses, we selected seven small, round contact points for our PST: bilateral superior and inferior points on the transverse process base, bilateral inferior points on the laminar, and a superior point on the spinous process. Clinically, the success rates of PS placement using this PST design were 98.6 % (414/420) for scoliosis patients and 100 % (46/46) for OPLL patients.

CONCLUSION

This study provides a useful design concept for the development and introduction of patient-specific navigational templates for placing PSs.

Robotics and the spine: a review of current and ongoing applications

OBJECT

Robotics in the operating room has shown great use and versatility in multiple surgical fields. Robot-assisted spine surgery has gained significant favor over its relatively short existence, due to its intuitive promise of higher surgical accuracy and better outcomes with fewer complications. Here, the authors analyze the existing literature on this growing technology in the era of minimally invasive spine surgery.

METHODS

In an attempt to provide the most recent, up-to-date review of the current literature on robotic spine surgery, a search of the existing literature was conducted to obtain all relevant studies on robotics as it relates to its application in spine surgery and other interventions.

RESULTS

In all, 45 articles were included in the analysis. The authors discuss the current status of this technology and its potential in multiple arenas of spinal interventions, mainly spine surgery and spine biomechanics testing.

CONCLUSIONS

There are numerous potential advantages and limitations to robotic spine surgery, as suggested in published case reports and in retrospective and prospective studies. Randomized controlled trials are few in number and show conflicting results regarding accuracy. The present limitations may be surmountable with future technological improvements, greater surgeon experience, reduced cost, improved operating room dynamics, and more training of surgical team members. Given the promise of robotics for improvements in spine surgery and spine biomechanics testing, more studies are needed to further explore the applicability of this technology in the spinal operating room. Due to the significant cost of the robotic equipment, studies are needed to substantiate that the increased equipment costs will result in significant benefits that will justify the expense.

Computer-Assisted Planning and Patient-Specific Instruments for Bone Tumor Resection within the Pelvis: A Series of 11 Patients

Pelvic bone tumor resection is challenging due to complex geometry, limited visibility, and restricted workspace. Accurate resection including a safe margin is required to decrease the risk of local recurrence. This clinical study reports 11 cases of pelvic bone tumor resected by using patient-specific instruments. Magnetic resonance imaging was used to delineate the tumor and computerized tomography to localize it in 3D. Resection planning consisted in desired cutting planes around the tumor including a safe margin. The instruments were designed to fit into unique position on the bony structure and to indicate the desired resection planes. Intraoperatively, instruments were positioned freehand by the surgeon and bone cutting was performed with an oscillating saw. Histopathological analysis of resected specimens showed tumor-free bone resection margins for all cases. Available postoperative computed tomography was registered to preoperative computed tomography to measure location accuracy (minimal distance between an achieved and desired cut planes) and errors on safe margin (minimal distance between the achieved cut planes and the tumor boundary). The location accuracy averaged 2.5 mm. Errors in safe margin averaged −0.8 mm. Instruments described in this study may improve bone tumor surgery within the pelvis by providing good cutting accuracy and clinically acceptable margins.