What Is the Lumbosacral Plexus?

Andrew Kirmayer

The lumbosacral plexus is a series of nerves with branches near the lumbar, or middle spine, and sacral, or lower part of the spinal column. Normally situated toward the front side of the body, it usually consists of the lumbar and sacral nerves. The coccygeal nerve is typically a part of the lumbosacral plexus as well; these nerves are often referred to as the lumbar nerves and are typically located within a muscle called the Psoas major, which sits in front of spinal bones called vertebrae. Nerves that originate in this area generally form a branch-like pattern throughout the lower body and also into the legs.

Severe chronic lower back pain is frequently treated through a nerve block at the lumbar plexus.
Severe chronic lower back pain is frequently treated through a nerve block at the lumbar plexus.

One of three parts to the overall structure, the lumbar plexus often includes parts of other major spinal nerves, and splits into different major nerves of the abdomen. The femoral nerves, which normally extend into and down the legs, also arise from this area. Other branches go into the thigh as well as the reproductive organs, while some are also associated with muscles such as the quadriceps in the leg. Another branch-off is typically associated with the structure of the knee.

Divisions of the lumbar nerves usually begin at nerve structures called ganglia on the sides of the vertebrae. Each nerve division of the lumbosacral plexus, from the top down, is often larger than the one above it. The first three typically separate and are re-connected by structures called anastomotic loops; the lumbar plexus also consists of fourth and fifth nerves. These usually join together to form another part called the sacral plexus.

The sacral plexus is normally located from where a major leg nerve, called the sciatic, branches off. Typically the largest in the body, the sciatic nerve can provide sensation for the entire skin surface of the leg, and connect to muscles from the thigh to the foot. Even lower in the abdomen is the pudendal plexus, which normally passes near the rectum and parts of the lower pelvis. Branches from these nerve structures also often travel to the back of the thigh as well.

Abnormalities of the lumbosacral plexus can occur in humans and other animals, and are sometimes present at birth or develop throughout life. Malformed spinal bones as well as arthritis can affect the nerves. Injuries, infections, and degenerative diseases can also lead to conditions in which the nerves of the lumbosacral plexus are compromised. These problems may affect sensation, mobility, as well as other biological functions.

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