What Is the Lumbar Plexus?

The anterior branch of the spinal nerve distributes the plexus that innervates the muscles and skin of the waist and reproductive functions. The lumbar plexus consists of a small part of the anterior branch of the 12th thoracic nerve, a part of the anterior branch of the 1-3 lumbar nerve, and a part of the anterior branch of the 4th lumbar nerve. Located within the psoas muscle, just before the lumbar vertebra process. In addition to the lumbar plexus, the following branches control the psoas and iliopsoas muscles, and the following branches are distributed in the anterior and medial part of the thigh, as well as the groin area. inferior iliac nerve and iliac inguinal nerve; femoral nerve; obturator nerve; reproductive femoral nerve; lateral femoral cutaneous nerve.

The anterior branch of the spinal nerve distributes the plexus that innervates the muscles and skin of the waist and reproductive functions. The lumbar plexus consists of a small part of the anterior branch of the 12th thoracic nerve, a part of the anterior branch of the 1-3 lumbar nerve, and a part of the anterior branch of the 4th lumbar nerve. Located within the psoas muscle, just before the lumbar vertebra process. In addition to the lumbar plexus, the following branches control the psoas and iliopsoas muscles, and the following branches are distributed in the anterior and medial part of the thigh, as well as the groin area. inferior iliac nerve and iliac inguinal nerve; femoral nerve; obturator nerve; reproductive femoral nerve; lateral femoral cutaneous nerve.

Chinese name

Lumbar plexus

Foreign name

lumbar plexus

Meaning

Part of the anterior branch of the 12th thoracic nerve

Branch

Inferior ventral nerve

Lumbar plexus anatomy

Lumbar plexus and inferior ventral nerve:

Starting from the 12th thoracic nerve and the 1th lumbar nerve. From the upper lateral edge of the psoas major, obliquely through the dorsal side of the lower kidney, on the ventral side of the psoas muscle, above the diaphragm, through the transverse abdominis fascia, between the transverse abdominis and the internal oblique, divided into Dermal branch (inferior ventral branch) and lateral cutaneous branch (condylar branch).

Anterior cutaneous branch: between the internal abdominal oblique and transverse abdominal muscle, obliquely forward and downward, about 2 cm from the medial anterior superior iliac spine, pierce the internal oblique muscle, and run on the inferior side of the external oblique tendon Inferiorly, approximately 3 cm above the subcutaneous ring of the inguinal canal, it penetrates the external oblique tendon and dominates the skin of the pubic area.

Lateral cutaneous branch: on the upper side of the anterior, middle 1/3 junction, on the posterior side of the lateral cutaneous branch of the 12th thoracic nerve, pass through the internal oblique muscle and external oblique muscle, and descend to the superficial fascia. Distributed on the front of the buttocks.

Lumbar plexus inguinal nerve:

Contains fibers from the 1st lumbar nerve and fibers from the 12th thoracic nerve. This nerve runs along the lateral border of the psoas major muscle, along the front of the psoas muscle, behind the kidney, and then through the front of the diaphragm, through the transverse abdominal muscle and the oblique muscle into the inguinal canal. It descends along the lower and outer side of the spermatic cord, passes through the subcutaneous ring of the tube to the superficial fascia, and is distributed on the skin inside the upper thigh. Concurrent branches are distributed in the skin of the root of the penis and the scrotum (women's labia), called the anterior scrotal nerve (women's anterior labial nerve). Its muscular branches are distributed in and control the abdominal wall muscles through which the groin nerve passes.

Lumbar plexus femoral nerve:

The femoral nerve (lumbar _2-4 ) is the largest branch of the lumbar plexus, descending between the psoas major and diaphragm muscles, and branching to this muscle. Accompany with the psoas major muscle. It enters the thigh through the midpoint of the inguinal ligament and divides into several branches.

(1) Muscle branch, the femoral nerve is a motor nerve of the thigh anterior muscle group. It emerges immediately after the midpoint of the inguinal ligament and branches immediately. Its muscle branch enters and controls the sartorius muscle, rectus femoris muscle, lateral femoris muscle, and intermediate femur muscle , Nerve femoral muscle nerve branches to the knee joint muscles; another branch to the pubic muscle; muscle branches issue small joints into the hip and knee joints.

(2) Anterior cutaneous branch, often two, on the thigh, near the middle 1/3 junction, inside the sartorius muscle, passing through the sartorius muscle (dominates this muscle) to the deep side of the broad fascia, and then through The broad fascia is distributed on the skin in the front, middle and lower part of the thigh. There are branches down to the knee joint, and there is a branch to the sacroiliac nerve branch, which participates in the phrenic nerve plexus.

The saphenous nerve (lumbar _3-4 ) belongs to the cutaneous branch, which is the longest terminal branch of the femoral nerve, with the femoral artery descending into the adductor tube. In the lower part of the tube, the branch of the descending knee artery passes through the adductor aponeurosis and then in the suture The rear of the carcass muscles goes straight down the medial side of the knee joint, and the subcutaneous skin from the sartorius muscles to the gracilis muscles is shallowed from the medial tibial tuberosity. Following the great saphenous vein, it descends along the medial edge of the tibia to the medial edge of the foot and branches along the way Distributed on the skin. After the saphenous nerve emerges from the adductor tube, it sends out the inferior iliac branch. The inferior zygomatic branch is connected to the cutaneous nerves on the medial, lateral, and medial thighs, as well as short branches of the saphenous nerve, to form the zygomatic plexus.

Variation: The femoral nerve consisting of lumbar _1-4 is a common type, about 67.9%. Sometimes, an extra branch is issued between the femoral nerve and the obturator nerve. It is called the parafemoral nerve and is located in the lumbar great (small) muscles and iliac crest. Between the lumbar fascia and the femoral nerve, it was also distributed in the femoral nerve distribution area (5.6%).

Lumbar plexus obturator nerve:

The obturator nerve (lumbar _2-4 ) is the branch of the lumbar plexus, which exits from the medial edge of the psoas major muscle and descends into the pelvis to the posterior common iliac artery. It continues on the superficial surface of the obturator inner muscle and accompanies the obturator vessels. , Through the obturator tube into the femoral part, divided into two branches before and after (see the "sacral plexus and tail plexus" bar chart). Anterior branch: the joint branch is sent to the hip joint; the other branch is to the obturator external muscle, long adductor and gracilis, and often branches to the pubis and short adductor. The terminal branch of the anterior branch is a cutaneous nerve that travels between the long adductor and gracilis muscle, and is distributed on the lower third of the skin of the medial thigh. Posterior branch: It passes through and dominates the obturator external muscle, and the secondary branches are distributed in a part of the large adductor muscle and the short adductor muscle. Nerves continue down to the knee joint, this branch often communicates with the saphenous nerve.

Variation: Some of the fibers of the obturator nerve do not enter the pelvis, but accompany the extrasacral blood vessels, pass through the deep surface of the inguinal ligament to the pubic muscle, and these fibers constitute the paraocclusal nerve. The prevalence in China is about 2.9%.

Lumbar plexus femoral nerve:

Most of the fibers come from the second lumbar nerve, and a small part comes from the first lumbar nerve. Pass through the psoas muscle and run down its front. Outside the common iliac artery, the posterior side of the ureter is divided into two branches:

1. The femoral branchthat is, the lumbar inguinal nerve, descends along the external iliac artery, passes through the deep side of the inguinal ligament, inside the femoral vascular sheath, through the outer side of the femoral artery to the femur; slightly below the inguinal ligament, passes through the anterior wall and broad The fascia may emerge from the oval fossa and become a cutaneous nerve, which is distributed on the femoral triangle skin.

2. The reproductive branch is the external spermatic nerve, which descends outside the external iliac artery, and the hair branch reaches the psoas muscle. This trunk descends through the inguinal canal and around the outside of the inferior abdominal wall into the inguinal canal. Men are accompanied by spermatic cord (women are accompanied by round ligament of the uterus), dominate the cremaster muscle; and branch to the skin of the scrotum (or labia majora).

Lumbar plexus lateral cutaneous nerve:

The lateral femoral cutaneous nerve (lumbar _2-3 ) exits from the outer edge of the psoas major muscle, going down and down along the surface of the diaphragm, passing through the deep side of the inguinal ligament before or after the sartorius muscle, or passing through the upper part of the muscle, divided into The anterior and posterior branches, the posterior branch 5 cm below the anterior superior iliac spine, penetrated the broad fascia and were distributed on the anterolateral skin of the thigh. When performing anterior and lateral incisions on hip joints, be careful not to damage them. The lateral femoral cutaneous nerve passes through a narrow fissure between the two layers of the lateral end of the inguinal ligament inside the anterior superior iliac spinethe lateral cutaneous nerve fiber tube. The length and width of the inlet of the pipe are larger than the length and width of the outlet. The exit is closer to the anterior superior iliac spine, and the surrounding structure is dense. These factors may be the reason why the lateral femoral cutaneous nerve exits the bone fiber tube, which is prone to compression at the thigh wide fascia. In addition, the strength of the flat muscles of the three layers of the iliopsoas and abdominal wall, and the thickness of the second layer of aponeurosis that forms the bone fiber tube at the outer end of the inguinal ligament are also related to whether the lateral femoral cutaneous nerve is subject to compression.