Journal of Neurosurgery: Spine
February 2009 Volume 10, Number 2

An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine
Laboratory investigation

David M. Benglis Jr., M.D., Steve Vanni, D.O., and Allan D. Levi, M.D., Ph.D.
Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, Florida

Abbreviations used in this paper: DLIF = direct lateral interbody fusion; EMG = electromyographic; XLIF = extreme lateral interbody fusion.

Address correspondence to: Allan D. Levi, M.D., Ph.D., Department of Neurosurgery, University of Miami, Lois Pope Life Center, 1095 NW 14th Terrace, D4-6, Miami, Florida 33136.
DOI: 10.3171/2008.10.SPI08479

Object
Minimally invasive anterolateral approaches to the lumbar spine are options for the treatment of a number of adult degenerative spinal disorders. Nerve injuries during these surgeries, although rare, can be devastating complications. With an increasing number of spine surgeons utilizing minimal access retroperitoneal surgery to treat lumbar problems, the frequency of complications associated with this approach will likely increase. The authors sought to better understand the location of the lumbar contribution of the lumbosacral plexus relative to the disc spaces encountered when performing the minimally invasive transpsoas approach, also known as extreme lateral interbody fusion or direct lateral interbody fusion.

Methods
Three fresh cadavers were placed lateral, and a total of 3 dissections of the lumbar contribution of the lumbosacral plexus were performed. Radiopaque soldering wire was then laid along the anterior margin of the nerve fibers and the exiting femoral nerve. Markers were placed at the disc spaces and lateral fluoroscopy was used to measure the location of the lumbar plexus along each respective disc space in the lumbar spine (L1–2, L2–3, L3–4, and L4–5).

Results
The lumbosacral plexus was found lying within the substance of the psoas muscle between the junction of the transverse process and vertebral body and exited along the medial edge of the psoas distally. The lumbosacral plexus was most dorsally positioned at the posterior endplate of L1–2. A general trend of progressive ventral migration of the plexus on the disc space was noted at L2–3, L3–4, and L4–5. Average ratios were calculated at each level (location of the plexus from the dorsal endplate to total disc length) and were 0 (L1–2), 0.11 (L2–3), 0.18 (L3–4), and 0.28 (L4–5).

Conclusions
This anatomical study suggests that positioning the dilator and/or retractor in a posterior position of the disc space may result in nerve injury to the lumbosacral plexus, especially at the L4–5 level. The risk of injuring inherent nerve branches directed to the psoas muscle as well as injury to the genitofemoral nerve do still exist.

KEYWORDS: direct lateral interbody fusion; extreme lateral interbody fusion; lumbar spine; lumbosacral plexus; psoas muscle; retroperitoneal approach.

©1990-2009 by the American Association of Neurological Surgeons