Cage Obliquity in Oblique Lumbar Interbody Fusion-How Common Is It and What Are the Effects on Fusion Rates, Subsidence, and Sagittal Alignment? A Computed Tomography-Based Analysis

Oblique lumbar interbody fusion (OLIF) through a prepsoas approach was identified as an alternative to alleviate complications associated with direct lateral interbody fusion. Cage placement is known to influence cage subsidence and fusion rates due to suboptimal biomechanics. There are limited studies exploring cage obliquity as a potential factor influencing fusion outcomes. Hence, our objective was to assess the effects of cage obliquity and position on fusion rates, subsidence, and sagittal alignment in patients who underwent OLIF. Patients who underwent OLIF for levels L1 to L5 in our center, performed by a single surgeon and with a minimum of 12 months of follow-up, were included in the study. Cage obliquity and sagittal placement were measured, and their correlation with fusion, subsidence, and sagittal alignment correction was assessed. Fusion and subsidence were evaluated using the Bridwell Criteria and Marchi Criteria, respectively. Among the included patients (age, 67.5 ± 7.93 years; 16 men and 37 women), 97 fusion levels were studied. The mean cage obliquity was 4.2° ± 2.8°. Ninety-six levels (99.0%) were considered to have achieved fusion with a Bridwell score of 1 or 2. Eighty-one (83.5%), 14 (14.4%), and 2 (2.06%) operated levels had a Marchi score of 0, 1, and 2, respectively. A Marchi grade of 1 or higher was considered indicative of significant subsidence. There was good improvement in both the segmental lordosis angle (4.2° ± 5.7°; < 0.0001) and disc height (4.5 ± 3.8 mm; < 0.0001). Cage placement did not have any statistical correlation with fusion rates, subsidence, or sagittal alignment. Our results indicate that OLIF facilitates appropriate cage placement with only a minor degree of cage obliquity, typically less than 20°. This minor obliquity does not lead to lower fusion rates, increased subsidence, or sagittal malalignment. Despite subsidence being common, the majority of these cases resulted in complete fusion.