Introduction:

Steerable “banana” cages have been posited to increase segmental lordosis in short-segment transforaminal lumbar interbody fusions (TLIF). The same is not necessarily true for straight “bullet” cages. While increased lordosis is generally thought to be advantageous, a potential complication is decreased foraminal height. Here we evaluate for any association between cage type and change in foraminal height and clinical outcomes following short-segment TLIFs.

Methods:

We retrospectively reviewed consecutive one- and two-level TLIFs with bilateral facetectomies with minimum one-year clinical and radiographic follow-up. Two cohorts were based on cage morphology: steerable “banana” cage or straight “bullet” cage. Patient reported outcome measures (PROMs), radiographic measurements, and revision rates were compared.

Results:

46 patients with 53 straight and 95 patients with 131 steerable cage levels were included. Steerable cages showed increased segmental lordosis (9.1 vs 13.5°, p<0.001) and decreased foraminal height (20.3 vs 18.5 mm, p<0.001) after surgery. Straight cages demonstrated similar segmental lordosis (8.7 vs 8.1°, p=0.30) and foraminal height (19.4 vs 20.0 mm, p=0.065). Both cohorts showed improved PROMs at last follow-up (p≤0.005). Sub-analysis comparing patients that had increased or decreased foraminal height revealed similarly improved PROMs between cohorts. Revision rates at one-year were similar between cohorts (4.3% for straight and 3.2% for steerable group, p=0.72).

Conclusion:

Although the increased segmental lordosis afforded by placement of steerable cages may decrease foraminal height after short segment TLIF, clinical outcomes are not negatively affected by this association.