Quantitative Threshold of Intraoperative Radiological Parameters for Suspecting Oblique Lumbar Interbody Fusion Cage Malposition Triggering Contralateral Radiculopathy

Background: This study aimed to clarify the quantitative threshold of intraoperative radiological parameters for suspecting posterior malposition of the oblique lumbar interbody fusion (OLIF) cage triggering contralateral radiculopathy. Methods: We measured the sagittal center and axial rotation angle (ARA) of the cage using postoperative computed tomography (CT) in 130 patients (215 cages) who underwent OLIF. The location of the cage tip was determined from axial magnetic resonance imaging in selected cases based on CT simulations to assess whether the cage was in contact with the contralateral exiting nerve or whether the surgical instruments could contact the nerve during intradiscal maneuvers. Results: The sagittal center of the cages was on average 41.5% from the anterior edge of the endplate (shown as AC/ AP value: anterior end plate edge- cage center/anterior- posterior endplate edge x100%), and posterior cage positioning >= 50% occurred in 14% of the cages. The ARA was-2.9 degrees, and posterior oblique rotation of the cages >= 10 degrees (ARA <=-10 degrees) was observed in 13%. CT simulation showed that the cage tip could directly contact the contralateral nerve when the cage was placed deep in the posterior portion >= 50% of the AC/AP values with concomitant posterior axial rotation >= 10 degrees (ARA <=-10 degrees), or deep in an extremely rare portion >= 60% of the AC/AP values with posterior axial rotation >= 0 degrees (ARA <= 0 degrees). Six percent of the cages (13/215) were placed in these posterior oblique areas (potential contact area: PCA). Three cages in the PCA were in direct contact with the contralateral nerves, and 9 were placed deep just anterior to the nerves. Symptomatic contralateral radiculopathy occurred in 2 cages (2/13/215, 15.3%/0.9%). Conclusions: Two intraoperative radiological parameters (AC/AP and ARA) measurable during OLIF procedures may become practical indicators for suspecting cage malposition in PCA and may be available when determining whether to consider cage revision intraoperatively to a more ventral disc space or anteriorly from the opposite endplate edge. Level of Evidence: 4.