PURPOSE: Simultaneous ipsilateral sacroiliac joint (SIJ) injury and acetabular fracture are relatively common. Inadequate SIJ reduction may compromise the anatomical alignment of associated acetabular fractures. However, the optimal surgical approach for managing both injuries remains uncertain. In this study, we aimed to compare the efficacy of pelvic ring injury reduction using either the lateral window or the pararectus approach and to analyze associated radiological outcomes in patients with concurrent SIJ injury and acetabular fracture. METHODS: This retrospective study included 44 patients who underwent open reduction and internal fixation (ORIF) for SIJ injury. Patients were divided into two groups based on the surgical approach: L group (lateral window of the ilioinguinal approach) and P group (pararectus approach). A subgroup of patients with simultaneous ipsilateral SIJ injury and acetabular fracture was selected for comparative analysis using postoperative computed tomography (CT) to assess SIJ reduction and acetabular fracture alignment. RESULTS: Improvements in SIJ distance on axial and coronal CT planes were observed in both groups, with greater reductions observed in the P group. Among patients with combined injuries, the P group demonstrated significantly improved SIJ reduction in the coronal plane (P = 0.008), which was associated with smaller residual fracture gaps and articular step-offs in the axial, coronal, and sagittal planes. CONCLUSION: When ORIF is indicated for SIJ injury, the pararectus approach may offer enhanced SIJ reduction in the coronal plane. This technique is also associated with improved acetabular fracture alignment in patients with simultaneous ipsilateral injuries.