Oblique Lumbar Interbody Fusion Fails to Reduce Distal Fusion Levels in Skeletally Mature Idiopathic Scoliosis

Study Design: A retrospective case series. Objective: To evaluate the feasibility of oblique lumbar interbody fusion (OLIF) in reducing the distal fusion level during deformity correction for skeletally mature idiopathic scoliosis (IS). Summary of Background Data: Although pedicle screw instrumentation (PSI) achieves sufficient curve correction in IS, it has limitations in controlling apical translation (AT), which may result in the adding-on phenomenon as a compensatory mechanism. Considering the corrective effect of OLIF on vertebral tilting, we hypothesized that adding OLIF could stabilize the lowest instrumented vertebra (LIV) level and thereby reduce the need for distal fusion level. Methods: Eight consecutive IS patients who underwent deformity correction with adding OLIF were retrospectively assessed, with a minimum 2-year follow-up. Radiologic variables included coronal and sagittal parameters, such as main Cobb angle, LIV tilt, and disc angle. The LIV-related complications included fusion mass shifting (FMS), adding-on phenomenon, coronal decompensation, distal screw pull-out, and adjacent segment degeneration. Results: Although the median main Cobb angle was significantly corrected from 61.7 to 17.5 degrees ( P <0.001), there was no statistical difference in both LIV tilt ( P =0.206) and disc angle ( P =0.122). The median FMS was 54.5 mm at postoperative follow-up and 55.9 mm at last follow-up with no statistical difference ( P =0.575). Six of 8 cases experienced unbalanced FMS with adding-on phenomenon. Conclusions: Our case series demonstrated that adding OLIF did not provide a significant corrective effect on the tilted LIV, resulting in unbalanced FMS and the adding-on phenomenon after deformity correction in skeletally mature IS. Consequently, adding OLIF at the distal fusion level offered no benefit in reducing the extent of distal fusion.