Anatomical measurement and design of modified iliac screw technique by 3D printing technique

Abstract

Objective To investigate the feasibility of improved iliac screw technique by using 3D printing technique to observe the related anatomy and design the screw track. Methods From April 2015 to March 2017, 60 mature skeletal development patients without other causes of pelvic diseases were randomly selected in Foshan Hospital of Traditional Chinese Medicine , 30 males and 30 females, aged 21-65 years old. With the patient's CT DICOM data, the 3D model of all the patient's pelvic were reconstructed using Mimics Research 21.0 software, and the model was manufactured with 3D printing technology. On the 3D model of pelvis of 60 cases, two different methods of traditional iliac screw(control group) and modified iliac screw(modified group) were used to simulate the screw implantation. The maximum depth of screw insertion(Maximum depth, MD), Sagittal angle(SA), Transverse angle(TA), the vertical distance between the point of screw insertion and the highest point of posterior iliac crest(Distance to highest point, DHP), the distance between the point of screw insertion and the midline(Distance from med-line, DM), and the diameter of the narrowest iliac bone(Iliac width, IW) were measured. The data were included in the control group and the modified group. and were compared between groups and within groups. The modified iliac screw technique was used to simulate on the 3D printed model using iliac screw with diameter of 7.5 mm and length of 80 mm, to observe the success rate of screw implantation and whether the screw was penetrated or the nail path was blocked. Results In the group of modified iliac screw canal, which chose 1 cm to the caudal side of the posterior superior iliac spine and the inner half central point of the ilium as the screw entry point, the best direction was the middle point of anterior inferior iliac spine and superior border of acetabulum, the sagittal angle was 28.6°±4.2° and transverse angle was 32.8°±4.9°(P>0.05). The measurements from the control group for MD, IW, SA and TA were(123.6±5.0)mm, (14.5±3.6)mm, 29.5°±2.1° and 31.4°±5.1° respectively, whereas the measurements from the improved group for MD, IW, SA and TA were (122.1±5.8)mm, (15.4±2.7)mm, 28.6°±4.20°and 32.8°±4.9° respectively. There were no significant differences between the control group and the improved group in MD, IW, SA and TA (all P values>0.05). The measurements from the control group for DM and DHP were(0.0±0.0)mm and(44.3±4.9)mm respectively, whereas the measurements from the improved group for DM and DHP were(16.5±2.9)mm and(32.1±4.3)mm respectively. There were significant differences between 2 groups(t=44.072, 14.496, all P value 0.05). There were significant differences between the male and female patients in SA and the measurements were 30.3°±3.6° and 26.9°±4.5°, respectively (t=3.232, P<0.05). Iliac screws were also successfully simulated in all 3D printed models. Conclusions MD, IW, SA and TA of the modified iliac screw paths are consistent.It is safe, which meets the requirements of the clinical iliac screw implantation with a length of 8 cm and a diameter of 7.5 mm.The modified screw insertion point is closer to the straight line of the insertion point of L5 and S1 pedicle screw than the traditional iliac screw insertion point, so it is more convenient to install, descend incisions at the point of insertion and reduce complications.The modified technique of ilium screw is a better method for iliolumbar fixation. Key words: Internal fixators; 3D printing; Pelvic model; Modified technique of iliac screw technique; Iliolumbar fusion