|Year : 2016 | Volume
| Issue : 3 | Page : 113-119
Application of three-dimensional-printed navigation template in pediatric femoral neck fracture
Pengfei Zheng1, Qingqiang Yao2, Peng Xu1, Kai Tang1, Jie Chen1, Yong Li1, Bo Jiang1, Liming Wang2, Yue Lou1
1 Department of Pediatric Orthopaedics, Nanjing Children's Hospital Affiliated to Nanjing Medical University; Department of 3D Printing, Digital Medicine Insitute, Nanjing Medical University, Nanjing, Jiangsu, China
2 Department of 3D Printing, Digital Medicine Insitute; Department of Orthopedics, Nanjing First Hospital, Nanjing Medical University, Nanjing, Jiangsu, China
|Date of Web Publication||24-Nov-2016|
Dr. Liming Wang
68 Changle Road, Nanjing First Hospital, Nanjing Medical University, Nanjing, Jiangsu 210000
Dr. Yue Lou
72 Guangzhou Road,Nanjing Children's Hospital Affiliated to Nanjing Medical University, Nanjing, Jiangsu 210000
Source of Support: None, Conflict of Interest: None
Background and Objectives: Pediatric femoral neck fracture is a serious and disabling injury that is prone to complications. This study examined the feasibility, accuracy, and efficiency of treating the fracture through a three-dimensional (3D)-printed navigation template that was used to guide placement of cannulated screws and locking compression-pediatric hip plates (LC-PHPs). Materials and Methods: Template-guided surgeries were carried out on nine children with femoral neck fracture from 1, 2012 to 12, 2014, and the resulting data were analyzed retrospectively. From preoperative computed tomography data, a 3D model of the proximal femur and a matching navigation template were created for guiding placement of cannulated screws or LC-PHP. Finally, the template-guided operation was performed, and the outcomes were compared to those from control patients undergoing the same surgery without navigation templates (n = 10). Results: The navigation templates were found to match the individual proximal femurs well. Two to three screws were accurately inserted in the femoral neck, and the end of the fracture was successfully stabilized. Implantation of the cannulated screws or LC-PHP took an average of 13.6 and 24.5 min, respectively, whereas intraoperative X-ray was used an average of 4.2 times for the former and 5.5 times for the latter. This was compared to 37.6 and 59.6 min, and 11.4 and 15.4 X-rays, for the controls. Postoperative X-ray showed a great reduction of the femoral neck fracture. Six- to twelve-month follow-ups indicated that the fracture had healed and the function of hip joint was excellent for seven of the children and good for two (Ratliff's criteria). Conclusions: Using 3D-printed guides, accurate and effective placement of cannulated screws and LC-PHPs is realized in the femoral neck. The method reduces operation time, intraoperative bleeding, radiation exposure, and iatrogenic damage to the vasculature, femoral neck, and epiphysis.
Keywords: Cannulated screw, locking compression, navigation template, pediatric femoral neck fracture, pediatric hip plate, three-dimensional printing technology
|How to cite this article:|
Zheng P, Yao Q, Xu P, Tang K, Chen J, Li Y, Jiang B, Wang L, Lou Y. Application of three-dimensional-printed navigation template in pediatric femoral neck fracture. Digit Med 2016;2:113-9
|How to cite this URL:|
Zheng P, Yao Q, Xu P, Tang K, Chen J, Li Y, Jiang B, Wang L, Lou Y. Application of three-dimensional-printed navigation template in pediatric femoral neck fracture. Digit Med [serial online] 2016 [cited 2020 Apr 4];2:113-9. Available from: http://www.digitmedicine.com/text.asp?2016/2/3/113/194699
| Introduction|| |
Pediatric femoral neck fracture (PFNF) is a type of catastrophic fracture with more complications than most other pediatric fractures;  femoral head necrosis, hip inversion, and bone nonunion are the major ones. Its cause is most often a high-energy impact such as those resulting from traffic accidents and high-altitude falls. The injury is disabling and can seriously affect the physical and mental health of the injured child, particularly if complications arise.
Cannulated (hollow) screws and a locking compression-pediatric hip plate (LC-PHP) are usually used to treat it; ,,, however, they are difficult to insert because of the anatomical structure of pediatric femoral neck. First, the small and narrow neck, which differs across individuals, provides only a small volume, in which to insert the screws, thus making it difficult to correctly position and direct them. Second, operator damage to the femoral epiphysis or its blood supply can influence the child's growth, even causing femoral head necrosis. , The challenging and sensitive nature of the procedure means that repeated intraoperative X-rays are needed, thereby increasing the associated risk of carcinogenesis. Thus, technologies and techniques that increase the accuracy and success rate of plate and screw implantation in this region would be of great benefit.
The development of clinical tools for digital design and three-dimensional (3D) printing has led to many advances in orthopedics. At present, the technology is used for numerous purposes such as preoperation planning, and the production of navigation templates and personalized implants. Navigation templates are generally used to guide surgical insertion of internal fixation screws and plates; ,,, however, there have been no previous reports concerning its use in PFNF. This retrospective study examined the practicality, accuracy, and efficacy of designing and implementing a navigation template for the placement of cannulated screws and LC-PHPs in the femoral neck during fracture reduction surgery.
| Materials and methods|| |
General study information
This research was authorized by our hospital's Ethics Committee, and all patients were given detailed information on the study and their situation; all signed the informed consent form. The study sample consisted of nine cases: Six boys and three girls. In five cases, the fracture was on the left side, and it was on the right in the remainder. Patients' age ranged from 3 to 10 years (average, 7.4). According to the Delbet fracture classification system, two cases were Type II, three were Type III, and the rest were Type IV. Open reduction with an LC-PHP was used for Delbet Type IV fractures, whereas open reduction with cannulated screws was used for Type-II and Type-III fractures.
Preoperative computed tomography (CT) images were acquired on a 64-MDCT scanner (Philips, The Netherlands) using a voltage of 120 kV, a current of 160 mA, and a section thickness of 1 mm. The resulting data were stored in the Digital Imaging and Communications in Medicine format.
Fracture reduction and optimization of screw paths
In the following sections, we will use a Type IV case to explain the details of our method; such cases, involving an LC-PHP and insertion of three screws through the femoral neck, were the most challenging.
We first imported the preoperative CT data into the Mimics 17.0 software package (Materialise, Belgium). We separated the fracture fragments accurately in 3D space. Then, we translated and rotated those fragments to reset them. Once the fracture was reset, we measured the width of the most narrowed region of the femoral neck and the diameter of the proximal femoral backbone. We then selected an appropriate LC-PHP. In this case, one with a diameter of 3.5 mm and an angle of 120° (Synthes, Switzerland). Next, we established the optimal insertion point and angle for a fixing screw through the femoral neck using the computer model. We observed its trajectory inside the femoral neck, ensuring that all three screws were in the center of the neck and make sure that all screws would not damage the epiphysis [Figure 1]a-f and [Figure 2]a-c. All data were saved in Standard Tessellation Language (STL) format.
|Figure 1: Representative case of a locking compression-pediatric hip plate implantation with software-based preoperative design, simulation of the operation, use of intraoperative navigation template, and postoperative imaging. (a) Right femoral neck fracture of a 3-year-old male. Coronal computed tomography image of Delbet Type IV femoral neck fracture. (b-d) Digital model of the proximal femur. (c and d) Coronal and sagittal sections after reduction were simulated. (e and f) Optimization of screw path and screw length. (g) Printed polymer models of the reduced proximal femur and the navigation template, showing a high degree of matching. (h-k) Physical simulation of the operation: X-ray images indicate that the direction of the catheter and the length of the screws were suitable. (l-q) The matching degree of the navigation template was high, and the guide pins and locking compression-pediatric hip plate screws were successfully inserted on the first attempt. (r and s) Three weeks postoperative, the X-ray images show a good outcome with callus formation and no fracture line|
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|Figure 2: Representative case of cannulated-screw implantation with software-based preoperative design, simulation of the operation, use of intraoperative navigation template, and postoperative imaging. (a) Left femoral neck fracture of a 10-year-old male. Coronal computed tomography image showing Delbet Type III femoral-neck fracture. (b and c) Coronal and sagittal sections through digital model of the reduced (simulated) proximal femur. (d) Printed polymer models of the reduced proximal femur and navigation template showing a high degree of matching. (e-j) Physical simulation of the operation: X-ray images indicate that the direction of the catheter and the length of the screws were suitable. It was almost the same as the result simulated by computer. (k and l) The matching degree of the navigation template was high, and the guide pins and cannulated screws were inserted successfully on the first attempt. (m) X-ray image from after the operation shows a good reduction, and the position of the two cannulated screws was suitable though they were slightly lower than those in the simulation. (n and o) Three weeks postoperative, the X-ray images show a good outcome for the reduction, with callus formation and no fracture line|
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Design and printing of navigation template
After extracting the data from inside and outside, the level of the greater trochanter of the femoral neck and the anatomy of the corresponding distal bony surface, and the treatment of reversing thickening of 5 mm, we generated a proximal femur model that was morphologically consistent with the real proximal femur. We then combined this femur data with that of the screw paths to generate the navigation template. We added a casing (diameter, 8 mm; length, 30 mm) to the operator-facing surface of the template; this would surround and support the guide pins [Figure 1]h. With the aid of the Boolean operation, we formed the screw paths (empty space) and finished the template.
After amending errors in the model through Magic17.0, we exported it as an STL file for 3D printing (Fuxiang Technology, China). Using medical grade polylactic acid (PLA), we printed the reduced proximal femur model and the navigation template. To verify that the navigation template matched the lateral bony surface of the femoral neck, we placed it in the appropriate position on the femur model [Figure 1]g.
Preoperative testing with the proximal femur model and the navigation template
After correct positioning of the navigation template on femur model, we drilled three guide pins into femur neck directed by the navigation template and control the depth according to computer measure. Then, we placed the three proximal holes of the LC-PHP over the three guide pins and drilled with a matched gouge bit down to the appropriate depth, which was 1.0 cm shorter than the guide pin depth. The next step was to pull out the gouge bit one by one and replace them with 3.5 mm screws, which were preselected to be of appropriate length. After that, we secured the distal plate with screws. X-ray imaging was used to check that the length and position of the screws were suitable, and to compare the result with the preoperative design.
Operation and postoperative treatment
Before surgery, the model and navigation template were plasma sterilized. The proximal femur was exposed, and fracture was reset. The navigation template was attached to the matching region of the great trochanter. At this stage, assistance was needed to maintain the stability of the fractured end. It required the operator to stably maintain the position and orientation of the template with his left hand, while simultaneously inserting two 2 mm (diameter) guide pins to designed depth using an electric drill [Figure 1]l, m and 2k, l. Once the first two were in place, X-ray images were taken to confirm that the fracture reduction and pin positioning were suitable. After these checks, the third guide pin was inserted along the catheter. The next steps were the same as the preoperative testing; again, X-ray was used to confirm a good fracture reduction and that screw and plate positioning was as sufficiently close to the preoperative design.
Method for evaluation of curative effect
Ratliff's criteria  were used to evaluate the function of the hip joint after the operation. There are four criteria: Pain, joint activity, athletic ability, and imaging evaluation; each graded as excellent, good, or bad.
| Results|| |
Computer design and simulation of operation using models and templates
The separation and reduction of the femoral neck fracture were simulated effectively on the computer, allowing for optimization of the screw orientation and length, along with the precise design of the navigation template based on the specific anatomical structure of the fracture region and the screw angles. The femur models and navigation templates were then successfully printed in PLA [Figure 1]g.
After matching all navigation templates to the models of the reduced proximal femur, we drilled the model in the direction given by the navigation template and implanted two to three length-optimized guide pins. After replacing these with the screws, their orientation and depth were assessed through X-ray imaging. The results matched the preoperative designs very well [Figure 1]h-k and [Figure 2]d-j.
The LC-PHP procedures took 24.5 min on average; from the completion of the reduction to completion of the LC-PHP implantation. X-ray was used to check the position of the guide pins and screws an average of 5.5 times. The guide pins, the hollow drill, and the screws did not damage the epiphysis. Compared with five cases of the same type of operation over the same period, but without the use of a navigation template or preoperative simulation, the guided operation took substantially less time and required much less use of X-ray [Table 1]. The operators adequately removed soft tissue from the surface of the large rotor of the femur, and after this, the navigation templates and the real anatomic features fit together tightly. Following template-directed insertion of the guide pins, X-ray imaging showed that the results closely matched the preoperative design. The positioning of the implanted screws was good, and no epiphyseal damage was observed. In addition, the plate was securely fixed and well positioned [Figure 1]n-s.
|Table 1: Comparison between template-guided locking compression-pediatric hip plate operation and traditional locking compression-pediatric hip plate template-free operation |
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The cannulated screw procedures took an average of 13.6 min; from the completion of the reduction until implantation of the two cannulated screws was complete. X-ray was used an average of 4.2 times to make sure that the guide pins and cannulated screws were correctly positioned. The guide pins, the hollow drill, and screws did not damage the epiphysis. Compared with five cases of the same type of operation over the same period, but without a navigation template or preoperative simulation, the operation required substantially less time and X-ray exposure [Table 2]. X-ray imaging confirmed that the end of the fracture was stable. The positioning of the implanted screws was suitable, and no epiphyseal injury was observed [Figure 2]m-o.
|Table 2: Comparison between template-guided cannulated-screw operation and traditional cannulated-screw template-free operation |
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Six months after the operation, hip joint function was excellent in seven cases and good in two cases (Ratliff criteria), and there were no cases of femoral head necrosis or hip deformity.
| Discussion|| |
Early reduction and strong internal fixation are the basic principles behind treatment of PFNF. Fixation with two to three cannulated screws or an LC-PHP is always applied as the treatment. The main use of the cannulated screw procedure is for Delbet Type-II and Type-III fractures.  Moreover, LC-PHP is mainly used for Type IV and some Type III fractures. , The appropriate diameter and length of the screws are very important to the stability of the fracture and the decrease of the complications. In addition, the femoral neck is irregular in shape, and neck-shaft angle and anteversion angle add operation difficulty. Therefore, implantation of the cannulated screws in the correct location requires a highly skilled surgeon with a wealth of clinical experience. The patients need to be X-rayed repeatedly to check and adjust the pin angle and depth. Even experienced surgeons often need several attempts at getting the guide pins into the ideal position [Figure 3]. However, repeated insertion and withdrawal of the guide pins increase the risk of injury to peripheral nerves and blood vessels. In addition, the larger the number of X-rays required, the greater the exposure of surgical personnel and patients to radiation, and therefore the greater the risk of cancer and other associated diseases. Thus, new techniques for implanting screws that are practical, easy to carry out, low cost, and easy to promote are urgently needed. Therefore, this study addressed the use of computer-based orthopedic technology to improve the success rate and reduce the risk of femoral neck fixation.
|Figure 3: The angle and length of the guide pins were adjusted repeatedly. (a-d) Delbet Type IV femoral neck fracture of a 7-year-old male. A locking compression-pediatric hip plate was used to fix the fracture. The direction and length of the guide pins were adjusted repeatedly. The patients and the clinical personnel were exposed to X-ray radiation 17 times by the end of the operation|
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The greater trochanter is one of the major anatomical landmarks of the proximal femur. Therefore, the navigation template set it as an important bone marker. In the surgery, full greater trochanter exposure was necessary to ensure a sufficiently close fit between the navigation template and accurate placement of the guide pins. The guide pins were inserted successfully in all nine patients, and only once with the help of a guide plate. The cannulated screws were implanted first time along the guide of guide pins. The procedure avoided repeated screw path corrections and X-ray scans, and it was generally more convenient than the ten traditional surgeries. As a result, the average time to complete screw implantation was less than half that of the traditional surgeries. The number of X-ray exposures was also more than halved, and the number of epiphyseal injuries was reduced to zero. Several intraoperative X-ray examinations were performed to verify each step in the guided insertion and implantation processes, but they worked first time and did not need to be repeated to improve positioning. With increased application and experience and improved technical proficiency, the verification steps could be reduced in number or even removed. The same is true of the guide pins: Eventually, appropriate screws may be implanted safely and accurately into holes drilled with only the aid of the template and the preoperative design.
Through the experience of treating these nine cases, we can summarize the advantages of using a navigation template for implantation of femoral neck screws: (1) Based on individualized anatomical X-ray data, the computer software can be used to determine the screw depth, diameter, and angle that maximizes fixation, while minimizing unintended damage and the incidence of complications. (2) It makes the operation simpler and less technically challenging, thereby generally increasing the chances of positive results. The most important operational step for achieving accurate screw positioning and orientation is the matching of the navigation template to the corresponding anatomical structure, but this requires no special experience and therefore also less training time. (3) When the technology is mature, only a single positive lateral X-ray should be needed; after completion of screw implantation. This would substantially decrease patient and clinician exposure to intraoperative radiation, while also reducing valuable operation time and bleeding. (4) Expensive equipment such as a computer-aided navigation system is not required, making the technology relatively low cost.
In spite of these advantages, there are a number of issues associated with the template design process: (1) There should be more bone markers to increase the degree of fitting and the stability of the plate. Templates with wings to better wrap the femur improve both these aspects, but the length of the wings needs to be appropriate. If the wings are too short, it is easy for the template to move and if they are too long, it is difficult to place and remove it. (2) The diameter of the guide path should be designed in relation to that of the guide pins. Often it is best to make the guide path diameter 3-5 mm larger than that of the guide pins. (3) The external length of pipeline should be sufficient to optimize its accuracy as a guide. External pipeline should be strong, and it is better if a few pipelines form the overall structure; otherwise, it becomes easy for them to break when being disinfected or guiding the pins.
To the best of our knowledge, this is the first study to report that navigation templates were used to guide insertion of cannulated screws and LC-PHP in PFNF; however, there were still some limitations. The number of patients in each group was too small to establish significance in many parameters. Another shortcoming was the lack of long-time follow-up. Future studies should aim for larger sample sizes as well as long-time follow-up.
| Conclusions|| |
Use of individualized, 3D-printed navigation templates improved accuracy when implanting cannulated screws and LC-PHPs in the femoral neck of children. It also reduced iatrogenic damage to the femoral neck, epiphysis, and vasculature, while also reducing intraoperative hemorrhaging and decreasing implantation time and X-ray exposure. With such increases in efficiency and safety, we feel that the technique is worthy of more widespread adoption in treating femoral neck fractures. In addition, the scope of application should be expanded : p0 atients with femoral neck fractures or a slipped capital femoral epiphysis can use pins to fix through the femoral neck fracture, and LC-PHPs can be used in the treatment of hip dislocation.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]