• William D Smith, Jim A Youssef, Ginger Christian, Sherrie Serrano, and Jonathan A Hyde.
• Western Regional Center for Brain and Spine Surgery, Las Vegas, NV, USA.
• J Spinal Disord Tech. 2012 Jul 1; 25 (5): 285-91.

Study DesignRetrospective review.ObjectiveTo determine if lumbarized sacra at the L5-6 level (functional L4-5) are a contraindication to a lateral transpsoas approach.Summary Of Background DataTransitional vertebrae at the lumbosacral junction present mechanical and morphologic changes, though these changes have not been characterized with respect to the feasibility of a lateral transpsoas approach.MethodsThree hundred fifty-one patients were scheduled for lumbar interbody fusion using a mini-open lateral transpsoas approach (XLIF) at L4-5 from 2004 to 2008 at a single institution. In patients with 6 lumbar vertebrae, accessibility, based on neuromonitoring, of the L5-6 level (functional L4-5) was reviewed. Qualitative assessments using axial magnetic resonance imaging (MRI) were performed and compared with a sample of patients with normal anatomy treated at L4-5.ResultsOf the 351 patients scheduled for treatment at L4-5, 10 (2.8%) were determined to have 6 lumbar vertebrae with the symptomatic level at L5-6. Of those 10, 2 (20%) could be treated using a lateral transpsoas approach, and 8 (80%) were converted to another approach after a corridor through the psoas muscle was not found, based on neuromonitoring feedback. Review of axial MRI showed a teardrop-shaped psoas detached from the lateral border of the disc space in patients with transitional anatomy unapproachable at L5-6, resemblant of L5-S1 in normal anatomy. In the 2 patients who could be safely approached, the psoas anatomy at L5-6 was similar to a normal L4-5 level, with a domed/helmet shape, attached laterally to the disc space.ConclusionsTreating the L5-6 level using a lateral transpsoas approach in individuals with lumbarized sacra can be challenging due to anatomy more similar to the L5-S1 level in normal patients. Preoperative planning using axial MRI and intraoperative adherence to advanced neuromonitoring can aid in identifying and avoiding injury in these rare patients.

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