Effect of Cage Type on Short-Term Radiographic Outcomes in Transforaminal Lumbar Interbody Fusion

Background: The effect of expandable versus static cage type on radiographic outcomes in transforaminal lumbar interbody fusion (TLIF) has not been well studied in the literature. We studied the effect of 3 cage types on change in foraminal height (FH), disk height (DH), subsidence, and segmental lordosis (SL).

Methods: We conducted a retrospective review of patients who underwent TLIF in a single institution from 2014 to 2019. The following 3 cage types were identified: banana cage, bullet, and expandable cage. Computed tomography (CT) scans of the lumbar spine or lumbar radiographs (when CT scan was not available) with 6-week follow-up time were used for radiographic assessment.

Results: One hundred patients with 133 fused segments were identified. The average age was 60.9 years, and 40% were men. A banana cage was used in 19 segments (14.3%), a bullet cage was used in 47 (35.4%), and an expandable cage was used in 67 segments (50.4%). There were no significant differences in FH (average increase, 0.7 mm; P = 0.771), subsidence (average, 2.3 mm; P = 0.554), DH (average decrease, 1.0 mm; P = 0.769), or clinically significant subsidence (>4 mm; P = 0.174). Expandable cages demonstrated a positive 1.2° gain in SL, whereas both other cages demonstrated a decrease in SL on average (P = 0.05). This result held up on multivariate analysis (P = 0.031).

Conclusions: The average increase in the foraminal height in TLIF is small (0.7 mm) and is not different between the cage types; therefore, direct decompression is crucially important in this procedure. Although TLIF is often considered to be a kyphotic procedure, an expandable cage demonstrated superiority in terms of segmental lordosis improvement.

Keywords: Cage; Interbody spacer; Radiographic outcomes; Subsidence; TLIF.