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.
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.
Feigl GC, Kastner M, Ulz H, Breschan C, Dreu M, Likar R. Topography of the lumbar sympathetic trunk in normal lumbar spines and spines with spondylophytes. Br J Anaesth. 2011 Feb;106(2):260-5. Epub 2010 Dec 7. PubMed PMID: 21138903.
PMID: 21138903 (Link to Abstract)
Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009