Oblique Lateral Lumbar Interbody Fusion at L2-L5: Proposal of a New CT-based Preoperative Assessment to Minimize Risks

Objective: Oblique anterior to psoas (ATP) interbody lumbar fusion is associated with advantag-es such as sufficient indirect decompression and restoration of lordosis. Therefore, a compre-hensive preoperative assessment that includes the location of entry into the disc space, a feasible trajectory to complete the intervertebral space procedure, and the possible retraction of the psoas muscle is necessary to correctly and safely perform the technique. Methods: From January 2019 to January 2020, 160 lumbar CT scans were evaluated. Only 124 images from the L2-L3, L3-L4, and L4-L5 levels met the inclusion criteria. The length of the anterior vertebral line (AVL) and the middle-third of the disc in the anteroposterior axis were measured to localize the entry point (EP). The distance between the anterior arterial vessel (AV) and the EP was also measured. The trajectory commonly used to set the surgical instruments into the disc space was called α, and a new proposed trajectory termed β was calculated. The psoas cross-sectional area anterior to the β angle trajectory was measured to determine any possible retraction using this parameter. Results: The EP-AVL distances were L2-L3 11.49 ± 0.89 mm, L3-L4 11.54 ± 0.88 mm, and L4-L5 11.57 ± 0.87 mm. The EP-AV lengths were 17.64 ± 5.62 mm, 19.36 ± 5.49 mm, and 16.48 ± 6.47 mm at L2-L3, L3-L4, and L4-L5, respectively. The average α and β trajectory angles re-ported were 39.91º and 14.48º, respectively. Psoas muscle retraction was primarily noted at the L4-L5 level. Conclusion: This article’s proposed parameters represent a routine preoperative safety assessment in patients previously selected for oblique ATP lumbar interbody fusion.