Predictors of maximizing the degree of listed interbody lordosis imparted during one- or two-level transforaminal lumbar interbody fusion for degenerative pathology.

Abstract

Objective: Lordotic devices have garnered increased attention for improving the segmental lordosis (SL) achieved with transforaminal lumbar interbody fusion (TLIF). However, it is unclear the degree to which surgeons maximize the "ideal" or listed lordosis of the interbody device.

Methods: Patients undergoing one- or two-level TLIF for degenerative pathologies were identified and data were extracted on demographics, baseline lumbopelvic radiographic parameters, and TLIF details. The primary outcome of interest was the degree to which postoperative SL approximated the listed cage lordosis (Δtarget). Change in SL was a secondary outcome. Linear mixed-effects modeling was used to identify significant predictors of the percentage of ideal lordosis achieved.

Results: A total of 239 treated levels were included (median patient age 66.6 years; 56.9% female); 151 levels were part of single-level TLIF constructs. The median segmental corrections were a 2.8° increase in SL and 2.8 mm in disc height. The median difference between listed cage lordosis and postoperative SL (Δtarget) was 0.5°. However, only 56.1% of levels achieved at least the listed cage lordosis. Linear mixed-effects modeling found that independent predictors of Δtarget were lower implant lordosis (estimate -1.01° [95% CI -1.15° to -0.87°] per degree, p < 0.001), greater preoperative SL (estimate 0.38° [95% CI 0.28°-0.48°] per degree, p < 0.001), greater preoperative PI (estimate 0.06° [95% CI 0.02°-0.11°] per degree, p = 0.007), and closer approximation of the anterior apophyseal ring of the caudal vertebrae (estimate -0.27° [95% CI -0.39° to -0.15°] per mm, p < 0.001). Similarly, independent predictors of postoperative SL were larger implant lordosis (estimate 0.16° [95% CI 0.05°-0.27°] per degree, p = 0.004), lower preoperative SL (estimate -0.70° [95% CI -0.79° to -0.62°] per degree, p < 0.001), greater preoperative PI (estimate 0.08° [95% CI 0.04°-0.12°] per degree, p < 0.001), and closer approximation of the anterior apophyseal ring of the cranial vertebrae (estimate -0.15° [95% CI -0.28° to -0.03°] per mm, p = 0.014).

Conclusions: The present results suggest that while lordosing, only 56% TLIF operations obtain the listed interbody lordosis ("target" lordosis). Anterior placement within the disc space is the only modifiable intraoperative technical factor for maximizing lordosis for a given interbody, highlighting the importance of effective disc space exenteration.