Fusion rates of PLIF using expandable cage for pear-shaped discs, a risk factor of cage retropulsion

Abstract

Introduction: A previous study showed that pear-shaped discs are a risk factor of cage retropulsion in posterior lumbar interbody fusion (PLIF) because a pear-shaped disc does not tend to make contact with the four cage corners in sagittal plane, and that expandable cages should be used in cases of the unstable contact between the endplates and the cage. Therefore we hypothesized that a pear-shaped disc may be a risk factor of nonunion after PLIF, and I evaluated surgical results of PLIF using expandable cages for pear-shaped discs.

Methods: We analyzed 68 patients who underwent single- or 2-level PLIF for degenerative lumbar diseases between 2015 and 2018. Ninety-four discs of 68 patients were categorized to 2-groups, the group P with pear-shaped discs (20 discs) and the group C without it (74 discs).

Results: Fusion rates on CT 6 months after surgery were 50% in the group P and 79.7% in the group C, that made a significant difference (P = 0.01), and fusion rates evaluating flexion-extension X-ray images were 85% in the group P and 94.6% in the group C, that showed no significant difference (P = 0.16).

Conclusions: Although fusion rates on CT 6 months after surgery were higher in the group C than those in the group P, fusion rates on X-ray images a year after surgery were similar in both groups. Therefore, expandable cages were useful in undergoing PLIF for pear-shaped discs.