Preoperative Placement of Rigid Markers for the Treatment of Tibial Fractures Using 3D Printed External Repositioning Model Combined With External Fixator

Purpose: To investigate the effectiveness of preoperative placement of a rigid marker 3D printed external repositioning model combined with an external xation frame in patients with tibial fractures. Methods: Fifty-ve patients with tibial fractures treated from June 2019 to August 2020 were used as study subjects. Patients were divided into a control group and an observation group according to the order of their admission to the hospital. Patients in the control group were treated with conventional surgery, and patients in the observation group were treated with preoperative placement of rigid markers 3D printed external repositioning models combined with external xators. The treatment results of the two groups were compared. Results: Patients in the observation group had signicantly shorter operative time, hospital stay and fracture healing time than patients in the control group, and intraoperative bleeding was signicantly less than that in the control group (P<0.05). The pain level decreased in both groups as the time lengthened after surgery. At the same time point, the degree of pain in the observation group was signicantly lower than that in the control group (P<0.05). The incidence of postoperative complications was 6.66% in the observation group and 36% in the control group, and the incidence of postoperative complications was signicantly lower in the observation group than in the control group (P<0.05). The excellent rate of fracture healing was 60% in the observation group and 86.67% in the control group, and the difference in the excellent rate of fracture healing between the two groups was signicant (P<0.05). Patients in both groups gradually recovered their knee and ankle functions after surgery with the extension of time. At the same time point, the HSS and Maryland scores of patients in the observation group were signicantly higher than those in the control group (P<0.05). Conclusion(cid:0)By using preoperative placement of rigid markers 3D printed external repositioning model combined with external xator treatment. No further incision or uoroscopic closed reduction is required. This reduces the patient's pain and improves the patient's fracture healing results.


Introduction
Most tibial fractures are caused by high-energy injuries, which can easily lead to serious soft tissue damage. Due to the complex mechanism of injury, the degree of injury to the injured person is serious, which makes treatment and postoperative recovery di cult [1,2].The medial soft tissue of the tibia is thin, and the anterior medial musculature and blood vessels are few, which can lead to tibial fracture once a high energy impact is delivered [3].The incidence of tibial fractures is higher than the incidence of fractures in other parts of the body, and there is a greater chance of exposure of the tibial fracture site [4].Due to the lack of soft tissue protection and poor skeletal blood circulation, tibial fractures are prone to fracture non-union. Once a tibial fracture does not heal, the continuity of the fracture end cannot be restored, the tibia cannot bear weight and force, and the sequelae remain serious and affect normal life [5].
Currently, tibial fractures are mainly treated surgically with the help of two-dimensional imaging data such as X-rays, CT, and MRI. The patient's fracture condition is judged and the surgical plan is designed.
However, due to the problems of overlapping bone blocks and uoroscopic angles, the imaging is prone to deviations.Therefore, precise data cannot be provided, which increases the risk of surgery [6,7].Steel plate internal xation is no longer the main treatment method due to the high trauma and disruption of fracture blood circulation. Intramedullary nail for tibial fractures has improved the fracture healing rate, but it cannot fully achieve satisfactory repositioning, requires a small incision to place the intramedullary pin, and is more traumatic to the medullary cavity. Although the external xator can promote healing of the fracture break end by means of pressure and traction, it is not possible to completely and accurately place the conventional auxiliary device in the appropriate position intraoperatively due to individual differences and factors such as in ammation and sprain [8].In this study, we analyzed the feasibility of this treatment method by preoperatively placing a 3D printed external repositioning model with rigid markers in combination with an external xaor in patients with tibial fractures.

General information
Fifty-ve patients with tibial fractures treated in the orthopedic department of our hospital from June 2019 to August 2020 were divided into a control group (n=25) and an observation group (n=30) according to the order of patient admission. Inclusion criteria: Diagnosis of fresh tibial fracture was con rmed by X-ray , and patients signed an informed consent form. Exclusion criteria: patients with combined hypertension, blood disorders, diabetes mellitus, patients with severe lower extremity vascular or nerve injury, patients who abandoned treatment midway or lost to postoperative follow-up. This study was reviewed and approved by Cangzhou Hospital of integrated traditional Chinese medicine and Western medicine.

Operative technique
Control group: Patients were treated with conventional surgery. Preoperative X-ray was taken at the fracture site, and the surgical plan was determined according to the imaging results.
Observation group: Patients were treated with preoperative placement of hard markers in 3D-printed fracture models combined with external xation frames. After admission, a 3.5-mm Kirschner pin was inserted through each side of the fracture under local anesthesia as a stiff marker, and the data of the stiff marker were recorded by CT scan (Fig. 1, A).The image data of the hard markers were transferred to the computer, and the Mimics software was used to preprocess the images, segment the area, select the bone region, and remove excess tissue to simulate the reset fracture end, and obtain a three-dimensional reconstruction model of the reset fracture end, and a four-piece extracorporeal fracture template was designed to closely t the Kirschner pin with the shape of the major skin contour of the lower leg ( Fig.1,   B). The fracture ends can be repositioned by template alignment, and a 3D printed fracture reduction model is performed based on the 3D reconstruction model (Fig. 1, C).During surgery, the corresponding four fracture resetting templates are threaded through the positioning holes onto the Kirschner pins of the affected limb and the four templates are docked by traction on the foot of the affected limb. This completes the repositioning of the fracture break end by means of the hard marker repositioning template, and when the fracture break end returns to the normal docking position, all the positioning Kirschner pins are repositioned and both fracture break ends are aligned. The external xation frame is attached and the repositioning template is retained as an auxiliary xation to complete the surgical treatment of the tibial fracture (Fig. 1, D).
Post-operative follow up protocol Follow up visits were scheduled at six weeks, three and six months post-operatively.During each visit, the patients were evaluated clinically using Johner Wruhs postoperative evaluation criteria for tibial fractures,Hospital for special surgery score(HSS) and Maryland score.

Statistical analysis
Statistical analysis was performed using SPSS 20.0 statistical software. The measurement data were presented as the mean ± standard deviation, and independent-samples t-test was used to compare the data between groups. The counting data were presented as the rate, and the chi-square test was used to compare groups. Differences with P <0.05 were considered statistically signi cant.

Results
There was no statistically signi cant difference between the two groups compared to the general data of gender, age, and mechanism of injury (P>0.05)(Tab.1).The operative time, hospital stay and fracture healing time of the patients in the observation group were signi cantly shorter than those of the patients in the control group. Intraoperative bleeding was signi cantly less in the observation group than in the control group (Fig. 2). It was demonstrated that the shorter the operative time, the less the hospital stay, and the relatively shorter the fracture healing time for the patients treated by preoperative placement of the 3D printed fracture external repositioning model with rigid markers combined with external xators.Using the VAS scale scores, it was found that the pain level decreased with increasing time in both groups after surgery. At the same time point, the pain level of patients in the observation group was signi cantly lower than that of patients in the control group (Fig. 3). This demonstrates that the preoperative placement of a 3D printed fracture model with a rigid marker combined with external xation can improve the postoperative pain level and psychological status of the patients.The incidence of postoperative complications was 6.66% in the observation group and 36% in the control group. The incidence of postoperative complications in the observation group was signi cantly lower than that in the control group (Fig. 3). This demonstrates that the patients were better treated by preoperative placement of 3D printed fracture models with rigid markers combined with external xators, and the postoperative complication rate was lower.The excellent rate of fracture healing was 60% in the observation group and 86.67% in the control group, and the difference between the two groups was signi cant (P<0.05), so the fracture healing in the observation group was signi cantly better than that in the control group (Fig. 4).
This demonstrates that the preoperative placement of 3D printed fracture models with rigid markers combined with external xators can improve the healing outcome of patients, promote bone formation and growth, accelerate the healing rate, and thus improve the quality of life of patients.Using the HSS scale scores, it was found that patients in both groups gradually recovered knee function as time increased after surgery. At the same time point, the HSS scores of patients in the observation group were signi cantly higher than those in the control group (Fig.5, A). Using the Maryland scale, it was found that the ankle function gradually recovered with time after surgery in both groups. At the same time, the Maryland score was signi cantly higher in the observation group than in the control group (Fig.5, B). This demonstrates that preoperative placement of a 3D-printed fracture model with a rigid marker combined with external xation can improve the functional recovery of the knee and ankle joints after surgery.

Discussion
Currently, most tibial fractures are treated surgically. Although the traditional surgical treatment is more effective, the soft tissues at the fracture site need to be stripped during the surgery, which causes soft tissue damage and affects the blood circulation at the fracture site, thus increasing the incidence of postoperative complications in patients [13,14].
In recent years, 3D printing technology has been widely used in the eld of orthopaedic trauma, and this technology can transform two-dimensional images into solid models [15].3D images allow for more accurate pre-operative planning, simulation of surgery, and other operations, leading to a complete and personalized surgical plan [16,17].By creating a 3D model, the surgeon has a clearer understanding of the patient's fracture, which provides a basis for the selection and placement of xation and increases the likelihood of fracture reduction [18].Xie and Shen compared 3D printing with incisional internal xation in the treatment of tibial plateau fractures, and showed that 3D printing shortened operative time and fracture site healing time, and reduced operative bleeding [19,20].Ren, Jian et al. tested a common plate and a new anatomically locked plate by 3D printing technology, respectively, and the newly designed xation material is stable and reliable, and more suitable for clinical application [21,22].However, there are no reports on the use of 3D printed fracture external repositioning models with preoperative placement of rigid markers.
In this study, patients in the observation group were treated with a 3D printed fracture model with rigid markers combined with an external xator. The 3D printed fracture model was used to reset the fracture ends without incision or X-rays, and then an external xator was applied. After treatment, all the observed indexes of the patients were reduced compared with the control group. The postoperative pain level was signi cantly reduced, the complication rate was reduced, the healing of the fracture site was signi cantly improved, and the function of the knee and ankle joint was basically restored about 6 months after surgery, which improved the prognosis of the patients.
In this study, we introduced a rigid marker by inserting a locating Kirschner pin on both sides of the fracture, and then performed a CT scan to collect data, input the data into the computer, simulate the repositioning and design a repositioning model to t the marker. The 3D-printed model was used to determine the position of the pins outside the patient's body during surgery, and the tibial fracture was then repositioned. The disadvantages are as follows: (1) The 3D printing modeling relies on preoperative imaging data, but there are also modeling errors due to muscle pulling at the fracture site and bone block occlusion.
(2) 3D printing modeling is time-consuming and cannot be used in emergency surgery. To address these shortcomings, the next step is to investigate more convenient and e cient 3D modeling methods to provide a detailed theoretical basis for the accurate repositioning treatment of more tibial fracture patients.

Conclusion
Preoperative placement of a 3D-printed fracture model with a rigid marker combined with an external xator in patients with tibial fractures allows for minimally invasive repositioning that is easy for the surgeon to perform. This treatment can reduce the pain of patients and improve the healing of fracture ends, which is of clinical signi cance.

Declarations
Thanks for the contribution of the tracking system.
available from the corresponding author on reasonable request.

Ethics approval and consent to participate
This study was approved by the medical ethics review board of Cangzhou Hospital of integrated traditional Chinese medicine and Western medicine.
All methods in the study were carried out in accordance with the Helsinki guidelines and declaration.
All procedures were undertaken by the senior author after obtaining informed consent for all patients.

Consent for publication
Participate in our study involving human subjects,signed informed consent was obtained from all participants.

Competing interests
No competing interest to report.  Comparison of perioperative indicators between two groups of patients.

Figure 3
Page 12/12 Comparison of postoperative pain between two groups of patients.

Figure 4
Comparison of fracture healing in the two groups.

Figure 5
Comparison of functional recovery of knee and ankle joints between two groups.

Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download. Table1.pdf Table2.pdf