Retroperitoneal (Anterolateral) Approach to the Lumbar Spine

DISCUSSION: Number 3 represents the genitofemoral nerve.

The retroperitoneal approach to the lumbar spine is commonly used for anterior lumbar corpectomies, fusions, and total disc replacements. The approach is usually performed from the left as the aorta is more resistant to damage than the inferior vena cava (IVC). The bifurcation occurs over the vertebral body of L4. Therefore, L4/5 discectomies are performed by working on the left side of the aorta, while L5/S1 discectomies are performed by working between the bifurcation of the common iliac vessels. Anatomic features which are important to identify include the genitofemoral nerve, ureter, lumbar sympathetic chain, and lumbar segmental vessels.

Feigl et al performed an anatomic study looking at the effect of lumbar spondylosis on the anatomic position of the lumbar sympathetic chain (LST). They found the LST entered the retroperitoneal space at the level of the vertebral body of L2 in 62% of cadavers and showed the most consistent relationship with the medial margin of the psoas muscle at intervertebral disc level L2/3. They concluded degenerative changes can affect the anatomic position of the sympathetic chain.

Illustration A labels a cadaveric specimen. The sympathetic chain can be seen running down the lateral aspect of the vertebral bodies and is labeled with the white arrows. The genitofemoral nerve (GFN) runs along the surface of the the psoas muscles (PM). The lumbar segmental vessels branch from the aorta roughly at the midpoint of the vertebral bodies (L5 = magenta, L4 = blue, L3 = green, L2 = yellow). The intervertebral discs are shown in white and labeled b (L2/3), c (L3/4), and d (L4/5). When working at L2 or above the renal arteries (LRV) must be identified.

Incorrect Answers:
Answer 1: Label 1 identifies the lumbar segmental vessels.
Answer 2: Label 2 identifies the sympathetic chain.
Answer 4: Label 4 identifies the psoas muscle.
Answer 5: Label 5 identifies the left renal vein.

DISCUSSION: The level of the bifurcation of the great vessels can vary, but most commonly is located at or near the L4 vertebral body. Direct anterior exposure of the L4-5 disc space usually requires lateral retraction of the great vessels. Exposure of the L5-S1 disc space usually can be performed by working in between the bifurcation of the aorta.

Hoppenfeld's Surgical Exposures states "The aorta divides on the anterior surface of the L4 vertebra into the two common iliac arteries. Just below this bifurcation, the common iliac vessels divide in turn at about the S1 level into the internal and external iliac vessels."

Khamanarong et al showed in a study of 197 cadavers that "the abdominal aorta descended and bifurcated into two common iliac arteries at the level of L4 vertebra in 131 cases (70.1%), at the fourth lumbar intervertebral disc in 23 cases (12.3%), and at the level of L5 vertebra in 33 cases (17.6%).

Illustration A shows a cadaveric specimen. The bifurcation sits over the vertebral body of L4. The sympathetic chain can be seen running down the lateral aspect of the vertebral bodies. The genitofemoral nerve (GFN) runs along side the psoas muscles (PM) along with the ureter which is not shown in this dissection. The lumbar segmental vessels branch from the aorta roughly at the midpoint of the vertebral bodies (L5 = magenta, L4 = blue, L3 = green, L2 = yellow). When working at L2 or above the renal arteries (LRV) must be identified.

DISCUSSION: The segmental lumbar arteries branch directly off the aorta and run anterior to posterior along the lateral border of the lumbar vertebrae. During a retroperitoneal approach to the spine it is important to identify and tie off the segmental arteries to avoid excessive bleeding.
The sympathetic chain (5) runs longitudinal along the lateral aspect of the vertebral column. It would not show up on an aortogram. The anatomic course of the artery shown in Figure A is not consistent with the superior mesenteric artery, inferior mesenteric artery, or the hypogastic plexus.