A Case of U-shaped Sacral Fracture After Longstanding Spinopelvic Fixation Treated With Percutaneous Sacroiliac Joint Fusion and Iliosacral Osteosynthesis.

Sacral fractures are pelvic ring injuries that usually occur following a fall from height and may present with neurological injury. They are divided into several subtypes based on the pattern and location of injury. Certain subtypes require operative management due to the risk of neural compromise and inadequate axial load transfer, limiting mobility. Spinopelvic fixation has been reported as an efficient surgical treatment to restore the stability of U-shaped sacral fractures and to accelerate healing by relieving sacral stress. It is unclear if low-velocity sacral fractures occurring after longstanding lumbosacral fusion with pelvic fixation require additional surgical intervention. An elderly female with osteoporosis and prior T4-pelvis instrumented fusion sustained a fragility sacral fracture and was treated conservatively. At follow-up, she developed a symptomatic U-shaped sacral fracture. The increased fracture displacement and nonunion were chiefly attributed to sacroiliac joint hypermobility. A percutaneous osteosynthesis at the S1 and S2 levels was performed with a novel type of implant to achieve concomitant sacroiliac joint stabilization and fusion. Implants were placed with the help of intraoperative three-dimensional imaging and image-guided navigation to avoid the previously installed pelvic hardware. In summary, U-shaped fractures can develop nonunion despite pre-existing spinopelvic fixation and can be treated adequately with percutaneous iliosacral osteosynthesis. A sacroiliac joint fixation and fusion should be considered in the same setting as sacroiliac joint instability may contribute to or exacerbate nonunion.