Study design: Prospective single-cohort observational study.
Objectives: To compare cage settling rates after extreme lateral interbody fusion (XLIF) across various implant sizes and fixation types. Secondary objectives were to detect factors associated with cage settling and correlation with clinical and radiographical improvement.
Summary of background data: Intervertebral cage settling can occur postoperatively after interbody fusion, limiting the long-term correction achieved with surgery.
Methods: Clinical and radiographical data were collected on 140 consecutive patients treated with extreme lateral interbody fusion at 223 levels (range, 1-5). All patients received supplemental pedicle screw fixation or lateral plating.
Results: Average follow-up was 15.5 months (range, 12-36 mo). At 12 months, disability improved by 44%, low back pain improved by 49%, leg pain improved by 48%, and quality of life improved by 50% (P < 0.001). Foraminal height improved from 15.7 mm to 21.2 mm, disc height improved from 4.6 mm to 9.4 mm, discal lordosis improved from 4.0 to 8.1, and segmental lordosis improved from 10.7 to 13.7 (P < 0.001). Cage settling 1 mm or more occurred in 20% of cages immediately postoperatively and in 62% at 12 months. Settling more than 4 mm occurred in 5% of cages immediately postoperatively and in 24% at 12 months postoperatively. Pedicle screw fixation was associated with a higher rate of cage settling 1 mm or more compared with lateral plating, though magnitude of settling at the anterior inferior endplate was higher for lateral plating (4.9 mm vs. 3.5 mm). Taller cage height, narrower cage width, and shorter cage length were significantly associated with increased risk of cage settling more than 4 mm at 12 months postoperatively. In patients with no cage settling immediately postoperatively, risk of settling more than 4 mm at 12 months was 6.8 times greater with narrower cages.
Conclusion: Risk of cage settling after extreme lateral interbody fusion may be reduced with the use of wider cages to engage more central endplate bone, longer cages to span the ring apophysis and osteophytes, and avoid overdistraction of the intervertebral disc space with shorter cages.
Level of evidence: 3.