The standard method for treating posterior pelvic ring injuries involves sacroiliac joint cannulated lag screw fixation, necessitating repeated fluoroscopy and leading to radiation exposure. The O-arm navigation system, designed for spine screw fixation, is applied in pelvic injuries to enhance precision. A successful case involved a 39-year-old male with a complex pelvic injury, where sacroiliac screw fixation was performed in the prone position using the O-arm guide. The patient, injured at a construction site, showed fractures and widening of the symphysis pubis and right sacroiliac joint. Surgery was planned for both lumbar and pelvic regions due to an L3 burst fracture. The O-arm system demonstrated efficacy in precise screw placement, reducing surgical duration, and minimizing complications. The discussion emphasizes early pelvic fixation benefits, with percutaneous iliosacral screws standing out. Conventional fluoroscopy-guided methods pose challenges, and the O-arm system proves advantageous, especially for less experienced surgeons. Future advancements may enable pelvic surgery using the O-arm without C-arm guidance if instrumentation for pelvis fixation is developed.

Objective
The purpose of this study is to investigate the radiological risk factors and differences in spinopelvic parameters for radiologic degenerative changes in the sacroiliac joint after lumbar or lumbosacral fusion surgery.
Materials and Methods
From 2019 to 2020, 116 patients diagnosed with lumbar and sacral degenerative diseases who underwent lumbar or lumbar sacral fusion were included. The degenerative changes of the sacroiliac joint were measured by CT performed before and 6 months after surgery, and divided into two groups according to the presence or absence of radiographic degeneration. Evaluation factors for radiographic degeneration include sclerotic changes, erosion, osteophyte formation, intra-articular bone formation, joint space narrowing, intra-articular gas formation and subchondral cysts were evaluated. Spinopelvic radiologic parameters and surgery-related parameters including lumbar lordosis, sacral slope, pelvic incidence, global tilts, and T1PA between the two groups were analyzed using Student's t-tests and chi-square tests to determine the difference between continuous and non-continuous variables between groups. Logistic regression analysis was used for the analysis of risk factors for degeneration for SI joints after lumbar or lumbosacral fusion surgery.
Results
There was no statistically significant difference between the demographic data and surgery-related data between the group with and without sacroiliac joint degenerative changes. There was also no statistical difference in the rate of degenerative changes in the sacroiliac joint according to the presence or absence of S1 in the fusion segment. (degeneration group vs non-degeneration group; 45.5% vs 39.8%, p: 0.574) There were statistically significant differences between the two groups in lumbar lordosis (LL), pelvic angle of incidence (PI), and PI-LL. (LL; 27.2±12.0 vs. 39.8±11.3, PI; 51.3±12.0 vs. 57.2±12.6. and PI-LL; 24.1±17.0 vs 17.4±13.9, p: <0.001, 0.023, and 0.030) As risk factors for radiographic degenerative changes in the sacroiliac joint, lumbar lordosis (LL), pelvic incidence (PI), sacral inclination (SS), and sagittal vertical axis (SVA) were statistically significant factors. (lumbar lordosis Odd ratio: 0.851, 95% CI: 0.791-0.917, p-value <0.001)
Conclusions
Lumbar lordosis and pelvic incidence are related as risk factors for radiographic degenerative changes in the sacroiliac joint after surgery in patients with lumbar spinal fusion.