Abstract:[Objective] To compare the clinical efficacy of the 3D printed twistlock guider assisted transverse lengthening sacroiliac screw versus traditional freehand technique in the treatment of unstable pelvic fractures. [Methods] A retrospective study was conducted on 44 patients who received surgical treatment for unstable pelvic fractures in our hospital from July 2020 to July 2022. According to the consequence of doctor-patient communication, 25 patients had the screw placed with 3D printed twistlock guider (the guider group), while the other 19 patients were by the traditional freehand technique (the freehand group). The perioperative period, follow-up and imaging data of the two groups were compared. [Results] The guider group proved significantly superior to the freehand group in terms of operation time [(82.4±20.1) min vs (106.8±22.4) min, P＜0.05] and intraoperative fluoroscopy [(7.2±2.0) times vs (24.9±2.3) times, P＜0.05], despite that the former had significantly greater total incision length than the latter [(16.8±2.5) cm vs (8.1±1.5) cm, P＜0.05]. There were no significant differ- ences in intraoperative blood loss, walking time, incision healing grade and hospital stay between the two groups (P＞0.05). All patients in both groups were followed up for (21.5±3.4) months on an average, and there was no a significant difference in the time to resume full weight-bearing activities between the two groups (P＞0.05). The VAS score significantly decreased (P＜0.05), while Majeed score and Harris score significantly increased in both groups over time postoperatively (P＜0.05), whereas which were not statistically significant between the two groups at any time points accordingly (P＞0.05). Regarding imaging, the postoperative Matta's scales were significantly improved in both groups compared with those before surgery (P＜0.05). Although there was no a significant difference in Matta's grade between the two groups before surgery (P＞0.05), the guider group was significantly superior to the freehand group in Matta's grade postoperatively [excellent/good/fair/poor, (24/1/0/0) vs (14/5/0/0), P＜0.05]. In addition, the guider group was also significantly better than the freehand group in term of the position of implant placed [excellent/good/fair/poor, (23/2/0/0) vs (13/6/0/0), P＜0.05]. By the latest follow-up, fracture union on images was achieved in all patients of both groups without significant adverse imaging findings. [Conclusion] Compared with traditional freehand place- ment, the 3D printed twistlock guider assisted transverse lengthening sacroiliac screw for pelvic unstable fracture is more accurate, with shorter operation time, less fluoroscopy time, and better reduction quality.