Robotic versus freehand S2 alar iliac fixation: in-depth technical considerations.

Achieving fixation and fusion across the lumbosacral junction has been a challenge for spinal deformity surgeons ever since the development of instrumentation. The S2 alar-iliac (S2AI) trajectory has been introduced as a method of pelvic fixation to decrease strain on S1 screws. The S2AI screws differ in several ways from traditional iliac screws.