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Lumbarized Sacrum as a Relative Contraindication for Lateral Transpsoas Interbody Fusion at L5-6

D. Smith, William MD*,†,‡; Youssef, Jim A. MD§; Christian, Ginger BS*,‡; Serrano, Sherrie BS; Hyde, Jonathan A. MD

Journal of Spinal Disorders & Techniques: July 2012 - Volume 25 - Issue 5 - p 285–291
doi: 10.1097/BSD.0b013e31821e262f
Original Articles

Study Design: Retrospective review.

Objective: To determine if lumbarized sacra at the L5-6 level (functional L4-5) are a contraindication to a lateral transpsoas approach.

Summary of background Data: Transitional 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.

Methods: Three 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.

Results: Of 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.

Conclusions: Treating 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.

*Western Regional Center for Brain and Spine Surgery

University Medical Center

NNI Research Foundation, Las Vegas, NV

§Durango Orthopedic Associates, P.C./Spine Colorado, Durango, CO

South Florida Spine Institute, Miami Beach, FL

Sources of support or funding (including NIH, Wellcome Trust, Howard Hughes Medical Institute, and others): None.

Reprints: William D. Smith, MD, Neurosurgery, University Medical Center, 1800 W. Charleston, Las Vegas, NV 89102 (e-mail:

Received February 7, 2011

Accepted April 5, 2011

© 2012 Lippincott Williams & Wilkins, Inc.