The template group consisted of 6 male and 2 female patients who were treated using this new type of screw guide template from July 2017 to July 2018. The inclusion criteria were as follows: (1)closed pelvic unstable fracture (Tpye B); (2) without severe internal
organ injury; (3)without obvious fracture displacement, or displacement can be reducted by pre-operative exteral fixation. The exclusion criteria were as follows: (1) severe open fracture; (2) fracture requiring open reduction and internal fixation. The average age was 52.3 years (range 23–78 years). The mean body mass index (BMI) was 22.7 ( rang 20.5–26.3). According to the Tile classification, there were two type B1, four type B2.1, and two type B3 fractures. The average injury severity score (ISS) was 15.2( range 11–27). 3 patients only had unstable pelvic fractures, 3 patients combined with multiple rib fractures and pleural effusion, 1 patient combined with subarachnoid hemorrhage, and 1 patient combined with multiple lumbar fractures and bilateral femoral fractures. All patients underwent external fixation to achieve damage control and a closed reduction at the same time in the emergency room during the first stage (Figs. 1 and 2). The external fixation (Trauson, China) was performed with a Carefix composite scaffold, which consists of 6-mm diameter stainless steel spicules, an 8-mm diameter aluminum alloy bar material, and an 8-mm diameter carbon fiber/PEEK unilateral connecting rod. When the vital signs of the patients became stable, we evaluated the fracture site, if the fracture was non-displaced or minimally displaced and did not need to reset during the operation, we used our 3D template for screw placement. The mean surgical waiting time to insert the pelvic screw was 4.2 days ( rang 3–8 days). This study got approval from the ethics review committee of the Qingpu branch of Zhongshan Hospital of Fudan University and written informed consent was obtained from each patient.
In the fluoro-navigation group, there were 10 patients, inculding 7 men and 3 female. The mean age was 45.2 years (range 28–58). According to the Tile classification, there were three type B1, four type B2.1, and three type B3 fractures. The fracture sites also did not need to be resetted during the operation. The surgical technqiue was described in our previous paper .
Template design and printing
Before the final operation, patients with external fixation were examined with a 64-slice spiral computed tomography (CT) scanner (GE, Boston, MA, USA), with 5-mm slice thickness. The images were stored in DICOM format and analyzed with Mimics 10.01 software (Materialise, Louvain, Belgium). The trajectory and the depth of the screws were designed in 3D format. We adopted 6.5 mm as the optimal diameter of the screw. The direction was adjusted until the optimal screw path was found using a reverse engineering technique to make sure that the virtual cylindrical implant was totally in the bony structure and did not penetrate the acetabulum, the pubis rim cortex, or the sacral foramen. In addition, 2D images of the pelvis in transverse, coronal, and sagittal planes were observed to confirm that the virtual cylindrical implant was intraosseous. We also measured the length of the cylindrical implant. After the screw entry point and the tip of the screw were determined, the data were saved in STL format(Fig. 3D).
The above data were input into the Geomagic studio 2012 software (3D Systems, Morrisville, NC, USA). Next, the patient-specific screw guide template was designed (Fig. 2D, 3E). Following that design, the patient-specific template was subsequently manufactured using a 3D printing system (Liantai RS6000) with photosensitive resin material (Fig. 2E, Fig. 3F).
The cost for the design and printing of the template is about 200 US dollars. We needed about 2 hours to design the template and about 8 hours to print it, after which it was sterilized with ethylene oxide.
After general anesthesia, the patient was placed in the supine position and the assistant connected the 3D printing template to the external fixation. A 1.5 cm incision was made according to the direction of the guide hole on the template. The assistant used one hand to stabilize the template and external fixation. The surgeon drilled 2.5 mm relatively rigid K-wires along the guide hole to the pubic rim or S1 body. When the screws were inserted into the pubic rim, there was a slope due to the irregular shape of the iliac wing. In order to reduce sliding of the K-wire, we also used a sleeve of our own design to guide the insertion of the K-wire (Fig. 4). The C-arm was used to confirm the position of the K-wire during the insertion process. When the K-wire was in the right position, the template was removed and the length of the screw was measured. Appropriate 6.5 mm cannulated screws (AO, Synthes, Stratec Medical, Oberdorf, Switzerland) were inserted along the K-wires, which were of similar length as in the preoperative plan. The C-arm was used again to assure the position and length of the screw. Finally, the K-wire was removed and the incision was sutured (Figs. 2,3)
Measurement and analysis
The amount of time required for screw insertion and radiation were recorded for analysis. Radiographic imaging in the form of X-rays and CT scan was repeated after surgery and used to check for fracture reduction and hardware placement. We also calculated the screw deviation from the planned trajectory. Quantitative data are presented as the mean ± standard deviation. Between-group differences were evaluated using independent sample Student’s t-test, the chi-squared test, and Fisher’s exact test, as appropriate for the data type and distribution. All analyses were performed using SPSS (version 17.0; Chicago, IL, USA).