Purposes: This study aimed to evaluate the clinical effect of the unlocking closed reduction technique (UCRT) for the displaced posterior pelvic ring fractures and to analyze the factors associated with failure of closed reduction and fixation. Patients and methods: Data from patients admitted with displaced posterior pelvic ring fractures initially treated with the URCT from July 2017 to January 2020 were extracted. Clinical and radiological factors including fracture classification, interval days from injury to surgery, number of screws, and type of fixation for the posterior pelvic ring were analyzed to evaluate their correlation with closed reduction failure, reduction quality, and fixation failure. Then a logistic regression model was used for statistical analysis to eliminate confusion factors. Results: Ninety-seven patients with displaced posterior pelvic ring fractures were followed for a mean of 1.7 years after surgery. Successful closed reduction and percutaneous fixation were achieved for 89 patients (91.8%), of which 82 patients (92.1%) achieved an excellent or good reduction. Closed reduction failure which converted to open reduction was recorded for eight patients (8.2%). AO/OTA type C3 fracture (p = 0.036) and osteoporosis (p = 0.012) were significant factors for closed reduction failure. Excellent was recorded for 76 patients (78.4%) and acute (1-21 days) interval days from injury to surgery was an associated factor for reduction quality. For AO/OTA type C1 fractures, no more than two short screws (unilateral iliosacral screws) or a single long screw (transiliac-transsacral screws) were independent prognostic factors of fixation failure (p = 0.026). Conclusions: Displaced posterior pelvic ring fractures treated with the UCRT are associated with excellent/ good radiological results. However, in patients with AO/OTA type C3 pelvic fracture and osteoporosis, the backup plan of open reduction should be routinely prepared. The patient should be brought to the operating room within three weeks to get a good reduction result. Two long screws or one long screw combined with two short screws are required to create a strong construct for AO/OTA type C1 pelvic fractures. (c) 2022 Elsevier Ltd. All rights reserved.