Sciatica

Definitions & Key takeaways

Sciatica is a term used to describe symptoms of lower back pain, numbness, or tingling that originate in the lower back and travel down the sciatic nerve. It is often due to a spinal disc herniation pressing on one of the lumbar or sacral nerve roots. Other common causes are spinal stenosis, degenerative disc diseases. Treatment options include physical therapy, pain medication, exercise, and in some cases, surgery.

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Introduction0:00–0:21

Sciatica is a condition where there’s pain that starts in the lower back which then travels down the leg. Since the pain is associated with injury or compression of the sciatic nerve and follows the path of the sciatic nerve, it makes sense to name it sciatica.The sciatic nerve is the longest and widest nerve in the body.

Anatomy and physiology0:21–2:39

It’s formed by the spinal nerves L4, L5, and S1-3, which leave the spinal canal through intervertebral foramen, an opening located between the vertebrae and behind the intervertebral discs.
These nerves travel to the area in front of the sacrum, and join to make the sacral plexus.All the nerves in the plexus, except S3 are split into two divisions: anterior and posterior.
Anterior divisions of the L4, L5, S1, S2 and the entire S3 nerve create the tibial nerve, while posterior divisions of the L4, L5, S1 and S2 form the common fibular nerve.
These two nerves are bound together by connective tissue and make up the sciatic nerve.The sciatic nerve then passes beneath the piriformis muscle and through the greater sciatic foramen which is an opening formed by the pelvic bone, sacrospinous, and sacrotuberous ligaments.It then travels down the back of the thigh to the back of the knee where it splits into the tibial and common fibular nerves.
The sciatic nerve innervates the muscles in the back of the thigh. The Tibial nerve innervates the muscles of the posterior compartment of the leg and intrinsic flexors of the foot.The Common fibular nerve is in charge of the muscles in the anterior and lateral compartments of the leg and intrinsic extensors of the foot.
Now, each spinal nerve is in charge of the sensation of a specific area of the skin, called a dermatome.Dermatomes of the spinal nerves of the sacral plexus cover almost the entire surface of the thigh, leg and foot.
L4 covers the medial side of the leg, L5 covers the lateral side. S1 covers part of the dorsum and the entire sole of the foot, S2 the back of the leg, while S3 covers the back of the thigh.
Skin sensations like touch, temperature, pain, and pressure are carried to the spinal cord and then to the brain where we register the sensations.Sciatica occurs when there’s irritation to any part of the sciatic nerve or the spinal nerves that form it.

Pathology2:39–5:40

The causes of sciatica can be divided into two groups - spinal, and non-spinal.Spinal causes are related to the spinal column.
The most common one is intervertebral disc herniation. The intervertebral discs lie between vertebrae, and act as shock absorbers.
Each disk is made of two parts. The outer fibrous ring called the annulus fibrosus, and the inner gel-like pulp called the nucleus pulposus.Poor posture, traumas, physical activity and strong rotational movement can cause herniations where the disk bulges out in one direction.
If it bulges out towards the center of the spinal cord, it could compress multiple nerve roots on both sides, or laterally, compressing one nerve root on one side.In some cases, the nucleus macrophages attack the nucleus pulposus and start secreting inflammatory cytokines like tumor necrosis factor alpha and interleukin 1 and interleukin 6.
The inflammation and swelling which result from this reaction compresses the nerves even further.Another cause of nerve compression is spinal stenosis which is the narrowing of the spinal canal or intervertebral foramen.
This is often due to degenerative disorders of the bone, trauma, or inflammatory disease like rheumatoid arthritis.Spondylolisthesis is a condition where one vertebra slips or becomes displaced due to trauma, surgery or degenerative spinal disease and presses on the nearby nerve roots.
Finally any growths within the spinal canal like tumors, cysts, or abscesses can cause compression on the spinal nerves.Non-spinal causes occur outside of the spinal region and cause compression or damage to the sciatic nerve itself.
The most common one is piriformis syndrome. The piriformis muscle and sciatic nerve are very close to each other, so if the piriformis muscle gets irritated, it can cause muscle inflammation or muscle spasms that can compress the sciatic nerve.A more recent phenomenon is the so-called wallet sciatica or credit-carditis.
Many people carry their wallets or other objects in their back pockets. So when they sit down, these objects put pressure on the gluteal muscles which compress the sciatic nerve, causing sciatica.Pregnancy is another potential cause of sciatica.
When sitting, the fetal head presses down on the sciatic nerve, just before it exits the pelvis. Other non spinal causes include trauma to the leg and pelvic tumors which can damage or compress the nerve directly.In sciatica, the main symptom is aching and sharp leg pain.

Symptom5:40–6:59

It radiates along the middle or lower buttock, and on the back or the outer side of the thigh. Below the knee, the pain usually follows the dermatome distribution.
For example, if the L4 nerve root is compressed, the pain would radiate along the medial side of the leg. If the S2 nerve root is compressed, the pain would mostly be felt along the back of the leg.
This pain could begin suddenly, usually with disk herniation, piriformis syndrome, or trauma. It could also develop slowly, like if it’s caused by a tumor or spinal stenosis, where the pain increases over time.Sciatic pain is typically unilateral, meaning it’s only located on one side.
Bilateral sciatica, where both legs are affected, can occur with central disc herniation, lumbar stenosis or spondylolisthesis.
Sometimes the pain can be accompanied by other sensory and motor dysfunctions like numbness, motor weakness and reduction or loss of reflexes.
S1 spinal nerve compression affects the ankle-jerk reflex, while L4 nerve compression affects the knee-jerk reflex.To diagnose sciatica there are some classic physical exam findings.

Diagnosis6:59–7:37

The Lasègue's sign, also called the straight leg raise test, is most often used to check for spinal causes. In this test, a person lays down on their back, and an examiner lifts each leg with the knees straight.
This stretches the nerve roots over the herniated disk or the object causing compression. If the sciatic pain worsens when the legs are between 30 and 70 degrees the test is positive.
Finally, A CT or MRI should be done to look for the cause.Sciatic pain caused by inflammation often resolves on its own over time.

Treatment7:37–7:58

With pain medication and anti-inflammatories, the pain can be relieved in a few weeks to a few months. Surgical treatment is required if the sciatica was caused by tumors, cysts, abscesses or injury to the spinal cord.All right, as a quick recap… Sciatica refers to aching and sharp leg pains that radiate below the knee.

Review7:58–8:22

It is caused by irritation or damage to the sciatic nerve and spinal nerve roots of the sacral plexus, most commonly as a result of disc herniation.
Typically the pain resolves on its own over a few weeks to months, but sometimes surgery is required.