Patient-Specific Guide using Radiopaque Alignment for Minimally Invasive Sacroiliac Joint Fusion

1. Introduction
Severe pelvic instability accounts for up to 30% of low back pain. When conservative treatment fails, sacroiliac joint fusion (SIJF) may be indicated to reduce pain by placing three implants inside the joint. SIJF is commonly performed using 2D fluoroscopic guidance. Due to anatomical variability, poor visibility during intraoperative imaging, and the absence of 3D spatial information, placing the implants without damaging neural structures is challenging.
2. Objectives
To improve patient outcomes, a workflow with a patient-specific guide (PSG) using alignment tools has been developed. A human cadaveric test was performed to assess whether the workflow can be safely implemented in clinical practice.
3. Methods
During typical PSG surgeries, a guide is seated onto the bone based on bony landmarks, enabling guided cutting or drilling according to a prespecified plan. Since SIJF is a minimally invasive procedure, bone seating is not possible. Therefore, a novel alignment tool was incorporated in the PSG, allowing it to be aligned using 2D fluoroscopy. The PSG was applied to five specimens, with both SI joints fused, comprising ten surgeries. Implant malposition complications and implant placement accuracy were determined.
4. Results
Thirty implants were placed with two malposition complications. Implant placement accuracy showed a positional deviation of 8.4 ± 3.5 mm and an angular deviation of 3.2 ± 1.9°.
5. Conclusion
Using radiopaque alignment tools in a PSG is a novel approach for guide alignment. However, the results were inferior to a previously developed technique involving virtual surgical planning. More research is necessary to optimize the workflow.