Preliminary design of 3D patient-specific drill template based on bone cement accumulation for lag screw placement in minimal invasive retrograde intramedullary fixation of the superior pubic ramus

Objective To investigate the feasibility of 3D patient-specific drill template based on bone cement accumulation for lag screw placement in minimal invasive retrograde intramedullary fixation of the superior pubic ramus. Methods The clinical data of 5 cases of pelvic fracture were reviewed retrospectively, including 3 males and 2 females, with average age of 49. According to the Young & Burgess classification, the type of pelvic fracture was 4 cases of LC Ⅱ and 1 case of LC Ⅲ. Three cases were left lateral superior pubic fracture and 2 cases were right. Pro/E software was used to simulate the 1.5 mm Kirschner wire, selected the base plane, drew the 1.5 mm Kirschner wire through the stretching function of Pro/E software, and saved it in STL format. The virtual screw placement was inserted by using the registration tool in Medcad module of the Mimics software. The Kirschner wire and the model were integrated by Boolean calculation. According to CT scan images, 3D reconstruction model of the pelvis were established by image screening, mask editing, threshold extraction, image filling and segmentation, smoothing and reduction triangular facets. The pelvic reconstructed data and the virtual Kirschner's data were processed in STL format to print 1:1 three dimensional model, The screw channel and the individual drill template was designed by bone cement accumulation technique to observe if the Kirschner wires were located in the bone canal. Results Three dimensional pelvic model and digital, individual drill template confirmed the effectiveness of superior ramus of pubis fracture, all of Kirschner wires were located in the bone canal. Kirschner was placed and the accuracy of screw placement was confirmed with X-ray and CT scanning. Template and the corresponding anatomical landmark fitted well. Conclusion By means of individual bone cement technique and 3D printing technology, accurate and minimal invasive placement of superior ramus of lateral pubis fracture screws can be finished. This technology is helpful to reduce the operation time and X-rays exposure of the patient and staff.