Radiographic Analysis of Early Changes in Upper Adjacent Segments After Fusion Surgery: OLIF vs. PLIF

<b>Background:</b> Oblique lumbar interbody fusion (OLIF) has recently gained popularity as a minimally invasive surgical technique for lumbar fusion. While OLIF is superior in restoring disc height and lumbar lordosis compared to posterior lumbar interbody fusion (PLIF), its biomechanical effect on adjacent segments remains unclear. <b>Methods:</b> We retrospectively analyzed 236 patients who underwent one- or two-level OLIF (<i>n</i> = 95) or PLIF (<i>n</i> = 141) between 2013 and 2020. Radiographic outcomes, including lumbar lordosis, upper adjacent segmental lordosis, retrolisthesis, and foraminal height, were evaluated preoperatively and at 3 days and 1, 3, 6, and 12 months postoperatively. Patient-reported outcomes (VAS for back/leg pain and Oswestry Disability Index [ODI]) were assessed preoperatively and at 12 months. <b>Results:</b> OLIF provided superior restoration of lumbar lordosis (4.03 ± 4.38° vs. 1.63 ± 5.11°, <i>p</i> = 0.001) and disc height (5.50 ± 3.39 mm vs. 2.71 ± 2.18 mm, <i>p</i> < 0.0001) compared with PLIF. However, OLIF was associated with higher incidence (76.9% vs. 24.6%, <i>p</i> < 0.0001) and degree of retrolisthesis (1.69 ± 1.09 mm vs. 0.29 ± 0.70 mm, <i>p</i> < 0.0001), and decreased foraminal height (-1.43 ± 2.12 mm vs. 0.54 ± 2.53 mm, <i>p</i> < 0.0001) in the upper adjacent segment. Importantly, there was no significant difference in clinical outcomes (VAS and ODI) between the two groups at 12 months (all <i>p</i> > 0.05). <b>Conclusions:</b> While OLIF achieves superior restoration of lumbar lordosis and disc height compared to PLIF, it also induces early radiographic deterioration in the upper adjacent segment. Importantly, these findings represent radiographic changes observed within 1 year, without significant differences in clinical outcomes, and longer-term follow-up is required to determine their clinical relevance.