Sacroiliac (SI) joint dysfunction is responsible for 15–30% of non-radicular lower back pain cases. When conservative treatment fails, minimally invasive sacroiliac joint fusion (SIJF) can be performed using three triangular implants to stabilize the joint. Accurate implant placement is critical but challenging under conventional 2D fluoroscopy due to anatomical variability and limited spatial information. Navigation systems can improve accuracy but are costly and not standard available. Patient-specific surgical guides (PSGs) offer an alternative; however, previous designs required bone exposure, increasing invasiveness and soft-tissue damage. This study evaluated the clinical feasibility of a minimally invasive PSG with radiopaque alignment features to achieve proper positioning by aligning the features to the patient’s anatomy using 2D fluoroscopy. Four patients underwent primary SIJF using the lateral transiliac approach with triangular titanium implants in a standard parallel configuration. Implant trajectories were planned preoperatively and translated to the PSG design for intraoperative execution. Postoperative CT scans were analyzed for positional and angular deviations. Twelve implants were placed successfully using the PSG with a mean 3D positional deviation of 6.9 ± 3.1 mm and an angular deviation of 2.5 ± 1.2°. All implants were intraosseous (Grade 0), and in one case, a minor complication occurred as two implants made contact. No other surgical complications occurred. Although the PSG enabled safe implant placement, the observed positional deviations indicate that the workflow lacks robustness for broader clinical adoption, as accuracy was inferior to a previous study that assessed the accuracy of virtual surgical planning alone.