Surgical Anatomy of the Lumbar Plexus with Emphasis on Landmarks
Abstract
Surgical landmarks for identifying the branches of the lumbar plexus as found on the posterior abdominal wall are lacking in the English literature. Many surgical complications have involved these nerves, highlighting the significance of the development of a clear topographical map for use in their identification. The surgeon who operates in this region needs a good working knowledge of the nerves of the lumbar plexus on the posterior abdominal wall. Our measurements will hopefully aid the surgeon who wishes to expose or most certainly avoid these nerves, thus lessening patient morbidity.
Keywords: complications, operative, exposure, surgery, nervous, lumbosacral
26.1 Introduction
Although much less common than injuries of the brachial plexus, injuries to the lumbar plexus do occur and the surgeon must be familiar with this region in order to evaluate and potentially treat such problems. Lesions of the lumbar plexus are most commonly iatrogenic but can be due to birth trauma, 9 hematoma, entrapment in fibrous or muscular bands, 13 tumors both intrinsic and extrinsic, or wounds such as incurred by a sharp object or gunshot. Additionally, ablative procedures for pain involving any branch of the lumbar plexus demands a thorough knowledge of this anatomy. 2, 4, 14, 22
Peripheral nerve surgery is a common neurosurgical procedure. However, the lumbar plexus and its branches are dealt with infrequently. One reason for this is the relative inaccessibility of this region and the infrequency with which the neurosurgeon performs deep dissections within the abdominal and pelvic cavities. Benzel 2 referred to the lumbosacral plexus and lesions of these nerves as a “no-man’s-land” and stated that “unfortunately, an inappropriately conservative approach is often undertaken in patients harboring these lesions because of the suspected degree of difficulty of the surgical approach.” However, there has been a recent increase in the use of endoscopic approaches to the retroperitoneum for various spinal disorders. 20 Congruently, injury to branches of the lumbar plexus has been estimated at approximately 2% for laparoscopic hernioplasties. 23 Approaches to the lumbosacral plexus in the abdomen and pelvis include a lateral extracavitary approach to the spine, 3 an anterolateral extraperitoneal approach to the spine, 12 a pelvic brim extraperitoneal approach, 12 a Pfannenstiel infraperitoneal approach, 11 and a transperitoneal approach. 1 The anterolateral extraperitoneal approach is essentially the same corridor used by surgeons to access the sympathetic trunk in the lumbosacral region. The lumbar veins and arteries can be obstacles to very medial dissections. 2 The pelvic brim extraperitoneal approach allows the lower branches of the lumbar plexus (e.g., the obturator nerve) to be accessed. The Pfannenstiel infraperitoneal approach also allows for access to lower branches of the lumbar plexus such as the femoral nerve. The transperitoneal approach to the lumbar plexus is perhaps the best method to use when a wide exposure is needed such as for tumors of neural origin. 2
26.2 General Anatomy
The lumbar plexus is formed in the retroperitoneal abdomen from the ventral rami of spinal nerves T12 to L4 (▶ Fig. 26.1). 30 This pattern can be different if the plexus is pre- or postfixed (i.e., fiber contributions are moved cranially or caudally, respectively). 7, 24 Most of these branches traverse the psoas major muscle proximally. They include the subcostal (T12), iliohypogastric (T12–L1), ilioinguinal (L1), lateral femoral cutaneous (L2–L3), genitofemoral (L1–L2), femoral (L2–L4), and obturator (L2–L4) nerves (▶ Fig. 26.1, ▶ Fig. 26.2). The subcostal, iliohypogastric, and ilioinguinal nerves innervate the abdominal wall musculature and aid in supplying the dermatomes of T12 through L1. The iliohypogastric nerve can also innervate the pyramidalis muscle when present. As implied, the lateral femoral cutaneous supplies the skin of the lateral thigh. The genitofemoral nerve innervates a small patch of skin over the proximal anterior thigh, scrotum and labia majora, and also the cremaster muscle. The femoral nerve innervates most of the anterior thigh musculature, much of the skin of the anterior thigh and medial leg, and both the hip and knee joints. The obturator nerve innervates a small patch of skin of the medial thigh, provides most of the motor innervation to the medial thigh muscles, and sends articular branches to the hip and knee joints. An accessory obturator nerve is also encountered in up to 30% of individuals. 29 Each of these branches has both a sensory and motor component with the exception of the lateral femoral cutaneous, which as its name implies, has no somatic motor component.
Fig. 26.1 Schematic view of the branches of the lumbar plexus. (Reproduced with permission from Gilroy AM, MacPherson BR, Ross LM, Schuenke M, Schulte E, Schumacher U. Atlas of Anatomy. 2nd ed. New York, NY: Thieme Medical Publishers; 2005. Illustration by Karl Wesker.)
(From THIEME Gilroy Atlas of Anatomy, 2e, © Thieme 2005, Illustration by [Karl Wesker])
Fig. 26.2 Schematic representation of the posterior abdominal wall with the distances measured in this study. A = distance from midline to branches of the lumbar plexus at their emergence site through the psoas major muscle (the nerve in this example is the lateral femoral cutaneous nerve), B = distance superior to the supracristal plane (the tips of the iliac crests are connected with the horizontal line to create this plane) on a vertical line through a midpoint between the anterior superior iliac spine and midline for nerves of the lumbar plexus (the nerve in this example is the subcostal nerve), C = distance inferior to the supracristal plane on a vertical line through a midpoint between the anterior superior iliac spine and midline for nerves of the lumbar plexus (the nerve in this example is the femoral), D = distance inferior to L1 vertebra that GF emerges through the psoas major muscle, E=distance inferomedial from the anterior superior iliac spine for LFC. L1, first lumbar vertebra.
26.3 Landmarks
In a previous anatomical study, mean distances from the midline at their emergence through or lateral to the psoas major muscle to the subcostal, iliohypogastric, ilioinguinal, lateral femoral cutaneous, genitofemoral, and femoral nerves measured 5.5, 6, 6.5, 6, 4.5, and 4.5 cm, respectively (▶ Table 26.1, ▶ Fig. 26.2). 29 ▶ Fig. 26.2 illustrates these and the following distances. The obturator nerve had a mean distance of 3 cm lateral to the midline. At a vertical line through the anterior superior iliac spine, the subcostal, iliohypogastric, and ilioinguinal nerves were superior to the supracristal plane by mean distances of 8, 4, and 5 cm, respectively. Inferior to the supracristal plane and in a vertical line through a midpoint between the anterior superior iliac spine and midline, the lateral femoral cutaneous and femoral nerves had mean distances of 5 and 5.5 cm, respectively. The lateral femoral cutaneous nerve (LFCN) had a mean distance 1.5 cm inferomedial to the anterior superior iliac spine. The subcostal nerve had a mean distance of 1 cm inferior to the 12th rib. The genitofemoral nerve emerged from the center of the psoas major in all specimens and divided into its genital and femoral components at a mean distance of 6 cm inferior to its exit from the psoas major, which had a mean distance of 6.5 cm inferior to the attachment of the psoas major to the L1 vertebra.
Nerve | Distance | Range (cm) | Mean (cm) | SD |
Subcostal | A | 4.5–7 | 5.5 | 1.7 |
Iliohypogastric | A | 5–8 | 6 | 1.5 |
Ilioinguinal | A | 5.5–8.5 | 6.5 | 1.9 |
Genitofemoral | A | 3.5–6.5 | 4.5 | 2.1 |
Lateral femoral cutaneous | A | 5–7.5 | 6 | 1.3 |
Femoral | A | 4–5.5 | 4.5 | 1.1 |
Obturator | A | 2.5–4 | 3 | 0.9 |
Subcostal | B | 5–10 | 8 | 2.2 |
Iliohypogastric | B | 3–6 | 4 | 1.5 |
Ilioinguinal | B | 4–7 | 5 | 1.7 |
Lateral femoral cutaneous | C | 4–7 | 5 | 1.2 |
Femoral | C | 4.5–7.5 | 5.5 | 0.9 |
Genitofemoral | D | 4–8 | 6.5 | 2.3 |
Lateral femoral cutaneous | E | 0.5–3.5 | 1.5 | 0.8 |
Abbreviations: GF, genitofemora; LFC, lateral femoral cutaneous; SD, standard deviation. Note: See ▶ Fig. 26.2 Related posts: Stay updated, free articles. Join our Telegram channel
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