1 Introduction topenlarge
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.
2 Neural decompression topenlarge
If open reduction and foraminotomy are required, after exposure is completed, identify and remove small bony fragments from the comminuted fracture zone. They may be located in the transforaminal region and may hinder fracture reduction.
The complete fracture line has to be cleaned out and inspected.
Enhance the exposure by using a lamina (bone) spreader.
Extract fragments that may compromise the sacral nerve roots.
Additional foraminal patency can be achieved with the use of Kerrison rongeurs or high speed rotational burr to expand the nerve root channel.
3 Reduction topenlarge
ISS fixation requires an essentially anatomically reduced sacral fracture. Significant residual displacement renders this procedure unsafe.
Displacement may make it impossible to accomplish ISS fixation without causing nerve root injury or resulting in an extraosseous screw that threatens adjacent neurovascular structures.
If displacement remains significant after closed reduction, open reduction should be considered.
The typical displacements are cranial and posterior together with sagittal plane rotation.
Once the fracture edges have been debrided, the primary reduction maneuver typically involves the use of two pointed reduction forceps (Weber clamps).
These span from the spinous process to the lateral ilium and are used to incrementally obtain a step by step reduction by alternating translation and clamping.
Additional reduction techniques
Preliminarily fix the anatomic reduction with pointed reduction forceps.
If needed, insert Schanz screws into both posterior iliac crests as a reduction aid for better rotational reduction.
4 Insertion of the IS screws topenlarge
Before beginning an ISS screw fixation procedure, appropriate preoperative planning for screw type and location needs to be completed.
Following reduction, the IS screw is inserted.
5 Insertion of the pedicle screws topenlarge
Pedicle screws are inserted bilaterally in L5 and connected with the rod. If there is concern regarding fixation to L5, then more cranial fixation levels can be added.
6 Insertion of iliac screw topenlarge
Iliac screws are inserted in either of the three potential locations
7 Insertion of the connection rod topenlarge
It is important that the iliac screw head and connecting rod lie flush to the bone. Avoiding prominent hardware prevents soft tissue irritation.
With a sacral entry point for the iliac screw there is less concern with screw prominence compared to iliac starting points.
Cut the rod to the appropriate length. Attach it to the screw per the hardware system.