Teaching Case of the Week: SI Joint Fixation

Patient had a sacroiliac joint fusion with posterior lateral-oblique transfixation technique. Patient had radicular symptoms localized to the S1 nerve. What is the problem?

Lessons:

The second screw was placed too medial and breached the S1 foramen. Note the tip of the screw is medial to the lateral border of the L5 vertebral body, a sign of being too medial. In this case, the ilium is low to the sacrum so the starting point of the screw is unusually close to the back of the sacrum, seen on the lateral view. It is likely the physician came in at a flat angle greater than 10 degrees to the vertical which directed the screw more medially.