Triangular osteosynthesis is a subcategory of spinopelvic fixation. It combines
- lumbo-pelvic fixation ((usually unilateral) from the pedicle of L5 to the ipsilateral posterior ilium, and
- transverse sacral alar fracture fixation (iliosacral screw/s, sacral plate, etc.)
This technique offers mechanically better fixation for highly unstable, vertical shear sacral alar fractures. The lumbo-pelvic fixation, applied after reduction of the pelvic ring injury, helps prevent recurrent vertical displacement of the unstable hemipelvis.
As a result, early mobilization of the patient may be achieved, with avoidance of late deformity. However, prominent hardware, impaired healing, nerve root injury, and need for hardware removal are potential concerns. Improved techniques may reduce complication rates, especially reduction and fixation of the sacral fracture, with preliminary neural decompression, before applying distraction to the lumbo-sacral instrumentation.
For illustration purposes, we show here only the spinopelvic fixation which follows the IS screw insertion. Typically iliosacral screw fixation precedes spinopelvic fixation because of the tight anatomical constraints to iliosacral screw placement.