"Insert flipping technique:" An effective way of restoring segmental lordosis and disc height with tall bullet cages

The study design was a retrospective study.

The objectives of the present study are dual; to describe a simple and effective way of restoring intervertebral disc (IVD) height by the "Insert Flip Technique" of cage insertion and to demonstrate effective restoration of IVD height and segmental lordosis (SL) and their influence on the functional outcome postoperatively.

IVD height and SL were recorded pre- and postoperatively. Each motion segment was instrumented with pedicle screws to allow segmental stabilization. Patients were called for follow-up at 6 weeks, 3 months, and 1 year postoperatively and were assessed clinically for back pain and leg pain (VAS and Oswestry Disability Index scores recorded).The bullet cages are designed such that they are lordotic in the superior-inferior plane and neutral in the mediolateral plane. Usually, the cage is inserted with superior and inferior surfaces of the cage impacting against superior and inferior end plates of the adjacent vertebral body. However, with the proposed technique, the cages were inserted such that the narrower mediolateral surfaces of the cage engaged with superior and inferior vertebral end plates. The cage was then flipped within the disc space such that the superior-inferior surfaces of the bullet cage impacted against the superior and inferior end plates of the vertebral body to create desired lordosis.

There was a significant improvement seen in the postoperative Cobb's angle and disc height after placement of a tall bullet cage compared to the preoperative Cobb's angle and disc height.

This modification of technique helped in gaining lordosis with taller bullet cages in minimally invasive surgery transforaminal lumbar interbody fusion with no/minimal complication and also reduced the need for bone resection during insertion of the cage.