An Overview of the Sacral Plexus

In This Article

The sacral plexus is a network of nerves emerging from the lower part of the spine. These nerves provide motor control to and receive sensory information from most of the pelvis and leg. 

A plexus is a web of nerves that share roots, branches, and functions. There are several plexi (plural of plexus) throughout the body, and the sacral plexus covers a large area of the body in terms of its motor and sensory nerve function. Often described as part of the lumbosacral plexus, the sacral plexus is located lower in the body than any of the other nerve plexi. 

Anatomy

The sacral plexus is formed by the lowest lumbar spinal nerves, L4 and L5, as well as sacral nerves S1 through S4. Several combinations of these six spinal nerves merge together and then divide into the branches of the sacral plexus.

Every person has two sacral plexi, one on the right side and one on the left side; the two sides are symmetrical in structure and function.

Structure

Spinal nerves L4 and L5 make up the lumbosacral trunk. And the anterior rami of sacral spinal nerves S1, S2, S3 and S4 join the lumbosacral trunk to form the sacral plexus. 

At each level of the spine, an anterior motor root and a posterior sensory root join to form a spinal nerve. Each spinal nerve then divides into an anterior (ventral) and a posterior (dorsal) rami (portion), each of which can have motor and/or sensory functions.

The sacral plexus divides into several nerve branches, which include:

  • Superior gluteal nerve, formed by sections of L4, L5, and S1
  • Inferior gluteal nerve, formed by sections of L5, S1, and S2
  • Sciatic nerve, which is the largest nerve of the sacral plexus and among the largest nerves in the body, formed by sections of L4, L5, S1, S2, and S3
  • The common fibular nerve (formed by L4 through S2) and tibial nerves (formed by L4 through S3) are branches of the sciatic nerve 
  • Posterior femoral cutaneous nerve, formed by sections of S1, S2, and S3
  • Pudendal nerve, formed by sections of S2, S3, and S4
  • The nerve to the quadratus femoris muscle is formed by L4, L5, and S1
  • The nerve to the obturator internus muscle is formed by L5, S1, and S2
  • The nerve to the piriformis muscle is formed by S1 and S2

Location

The spinal nerves that comprise the sacral plexus emerge from the lateral (sides) regions spinal cord. Each of these nerves travels through its corresponding spinal foramen (opening) before they join in their various combinations to form the sacral plexus in the back of the pelvis. 

The sacral plexus branches into smaller nerves within the pelvis. Some of the nerves remain the pelvis and some extend down the leg. Some nerves of the sacral plexus exit the pelvis through the greater sciatic foramen—a large opening comprised of pelvic bones that contain muscles, nerves, and blood vessels—and then travel down the leg. 

Anatomical Variations 

There are a number of natural variations in the structure of the sacral plexus. These variations typically do not cause any clinical problems, but they may be detected on an imaging study, or they can be observed during a surgical procedure.

Sometimes, nerves of the sacral plexus may be larger or smaller than average, or a spinal nerve that typically contributes nerve fibers to a nerve of the sacral plexus might not do so. The plexus may form or divide at a higher or lower region in the pelvis than expected.

Function

The sacral plexus has extensive functions throughout the pelvis and legs. Its branches provide nerve stimulation to a number of muscles. The nerve branches of the sacral plexus also receive sensory messages from the skin, joints, and structures throughout the pelvis and legs. 

Motor

Motor nerves of the sacral plexus receive their messages from the motor area of the brain, which sends the messages down the ventral (front) column of the spine, out to the sacral plexus, and eventually to the motor nerve branches of the sacral plexus to stimulate muscle contraction (movement).

Motor nerves of the sacral plexus include:

Superior gluteal nerve: This nerve provides stimulation to the gluteus minimus, gluteus medius, and tensor fascia lata, which are muscles that help move the hip laterally (away from the center of the body). 

Inferior gluteal nerve: This nerve provides stimulation to the gluteus maximus, a large muscle that moves the hip laterally. 

Sciatic nerve: The sciatic nerve has a tibial portion and a common fibular portion, which have motor and sensory functions.

  • The tibial portion stimulates the adductor magnus on the inner part of the thigh as well as muscles in the back of the thigh, which moves the upper part of the leg in towards the body. The tibial portion also activates muscles in the back of the leg and the sole of the foot.
  • The common fibular portion of the sciatic nerve stimulates the short head of biceps femoris, which moves the thigh and knee. This common fibular nerve also stimulates muscles in the front and sides of the legs and the extensor digitorum brevis, which extends toes to straighten them out. 

Pudendal nerve: The pudendal nerve (which also has sensory functions) stimulates the muscles of the urethral sphincter to control urination and muscles of the anal sphincter to control defecation (pooping). 

The nerve to the quadratus femoris stimulates the muscle to move your thigh. 

The nerve to the obturator internus muscle stimulates the muscle to rotate the hip and stabilize your body when you walk. 

The nerve to the piriformis muscle stimulates the muscle to move your thigh away from your body. 

Sensory

The sensory fibers of the sacral plexus receive nerve messages from the skin, joints, and muscles. These messages are sent up through the nerves of the sacral plexus and to the spine, where they travel in the dorsal (back) column of the spine and up to the sensory regions of your brain to make you aware of your sensations.

Sensory nerves of the sacral plexus include:

Posterior femoral cutaneous nerve: This nerve receives sensory messages from the skin on the back of the thigh and leg, as well as the pelvis.

Sciatic nerve: The tibial and common fibular portions of the sciatic nerve both receive sensory information from the leg. The tibial portion receives sensory information from most of the foot. The common fibular portion receives sensory messages from the front and sides of the leg and from the back of the foot. 

Pudendal nerve: This nerve receives sensory information from the skin of the genital areas.

Associated Conditions

The sacral plexus, or parts of the sacral plexus, can be affected by disease, traumatic damage, or cancer. 

Because this network of nerves has many branches and portions, the symptoms can be confusing. You may experience sensory loss or pain of regions in your pelvis and leg, with or without muscle weakness.

The pattern might not necessarily correspond to a single nerve, making it difficult to identify which parts of the sacral plexus are affected.

Imaging studies, such as pelvic computerized tomography (CT) or magnetic resonance imaging (MRI) may identify cancer or traumatic injuries. Electrical studies such as nerve conduction studies (NCV) or electromyography (EMG) can often identify the specific nerve branches that have been injured or have been affected by diseases such as neuropathy. 

Conditions that affect the sacral plexus include:

  • Neuropathy: Nerve impairment can affect the sacral plexus or parts of it. Diabetic neuropathy is a nerve disease that results from diabetes, particularly from diabetes that is not well controlled. Neuropathy can also occur due to vitamin B12 deficiency, certain medications (such as chemotherapeutic medications) toxins (such as lead), alcohol, and metabolic illnesses. 
  • Cancer: Cancer arising in the pelvis or spreading to the pelvis from somewhere else in the body can compress or infiltrate the sacral plexus, impairing nerve function. 
  • Injury: A traumatic injury of the pelvis can stretch, tear, or harm the nerves of the sacral plexus. Bleeding may compress the nerves, interfering with their function. 
  • Infection: An infection of the spine or the pelvic region may spread to nerves of the sacral plexus or may produce an abscess, causing symptoms of nerve impairment, as well as pain and tenderness of the infected region. 

Rehabilitation

Recovery and rehabilitation of a disease or injury of the sacral plexus is possible. In general, recovery is better when the symptoms are detected early and the illness is diagnosed before serious nerve damage has occurred. Less extensive damage and involvement of fewer nerve branches is also associated with better recovery. 

Treatment of the Underlying Medical Problem

Rehabilitation begins with treatment of the cause of the problem—such as treatment for cancer (surgery, chemotherapy and/or radiation) or antibiotic treatment for an infection. Treatment of neuropathy is often complicated because the cause may be unclear, and a person can experience several causes of neuropathy at the same time. Healing after a major pelvic trauma (such as from a car accident) can take months, especially if you have had multiple bone fractures.

Motor and Sensory Recovery

Physical therapy and occupational therapy can help you regain your strength and motor control as you are healing from a sacral plexus disease or injury.

Adapting to sensory deficits is an important part of rehabilitation and recovery from a sacral plexus problem. Sensory problems can interfere with your ability to walk, as you might not be able to properly feel your own position as you are moving.

Sensory deficits may make you less sensitive to pain, which can worsen the effects of injuries (when you don’t take care of them or avoid further trauma).

And sometimes, rehabilitation for bowel and bladder function may require exercises, as well as medication that can help control these functions.

Was this page helpful?

Article Sources