Can posterior stand-alone expandable cages safely restore lumbar lordosis? A minimum 5-year follow-up study

Abstract

Background: Lumbar lordosis (LL) can be restored, and screw-related complications may be avoided with the stand-alone expandable cage method. However, the long-term spinopelvic changes and safety remain unknown. We aimed to elucidate the long-term radiologic outcomes and safety of this technique. Methods: Data from patients who underwent multi-level stand-alone expandable cage fusion and 80 patients who underwent screw-assisted fusion between February 2007 and December 2012, with at least 5 years of follow-up, were retrospectively analyzed. Segmental angle and translation, short and whole LL, pelvic incidence, pelvic tilt, sacral slope (SS), sagittal vertical axis, thoracic kyphosis, and presence of subsidence, pseudoarthrosis, retropulsion, cage breakage, proximal junctional kyphosis (PJK), and screw malposition were assessed. The relationship between local, lumbar, and spinopelvic effects was investigated. The implant failure rate was considered a measure of procedure effectiveness and safety. Results: In total, 69 cases were included in the stand-alone expandable cage group and 150 cases in the control group. The stand-alone group showed shorter operative time (58.48±11.10 versus 81.43±13.75, P=.00028), lower rate of PJK (10.1% versus 22.5%, P=.03), and restoration of local angle (4.66±3.76 versus 2.03±1.16, P=.000079) than the control group. However, sagittal balance (0.01±2.57 versus 0.50 ±2.10, P=.07) was not restored, and weakness showed higher rate of subsidence (16.31% versus 4.85 %, P=.0018), pseudoarthrosis (9.92% versus 2.42%, P=.02), cage, and retropulsion (3.55% versus 0, P=.01) than the control group.Conclusions: Stand-alone expandable cage fusion can restore local lordosis; however, global sagittal balance was not restored. Furthermore, implant safety has not yet been proven.