S1 Radiculopathy Caused by Disc Herniation

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S1 Radiculopathy Caused by Disc Herniation

Lumbar disc herniation with radiculopathy typically occurs when disc material protrudes beyond the normal boundaries of the intervertebral disc space. This displacement can lead to pain, weakness, or numbness in areas corresponding to specific nerve roots.

The clinical presentation of lumbosacral radiculopathy depends on the affected nerve root level. Lumbar disc herniations most commonly involve the L4-L5 and L5-S1 levels, with herniations at these sites more frequent than in the upper lumbar region. For instance, L3-L4 herniations are about one-tenth as common as L5-S1 herniations.

In a posterolateral disc herniation, the nerve root that exits the foramen below the herniated disc is compressed. Therefore, a posterolateral herniation at L3-L4 affects the L4 nerve root, the L4-L5 disc affects the L5 nerve root, and the L5-S1 disc affects the S1 nerve root.

Radiculopathy affects both motor and sensory systems. Motor dysfunction often manifests as muscle weakness, although some muscles, innervated by multiple nerve roots, may not show weakness in a routine clinical exam. To accurately assess motor function, specific muscles associated with each nerve root level are evaluated. Sensory testing also shows variation and overlap; thus, key sensory areas corresponding to each nerve root are examined. For a detailed demonstration of these sensory areas, please refer to the video titled “Screening Neurological Examination for Low Back Pain” presented further down this web page.

Causes of Lumbosacral Radiculopathy

More Common Causes

• Disc herniation (displacement of disc material beyond normal disc space margins, which can compress nearby nerve roots)
• Spondylosis (degenerative arthritis leading to narrowing of the central canal, lateral recess, or neural foramen, potentially compressing nerve roots)

Less Common Causes

• Inflammation (conditions that cause inflammation around the nerve roots)
• Neoplasm (tumours affecting the lumbosacral region)
• Infection (infections that involve the spine or surrounding tissues)
• Vascular disease (conditions affecting blood flow to the spinal structures) 

Normal Disc

A normal intervertebral disc has two main components: a central nucleus pulposus (NP) and a peripheral annulus fibrosus (AF).

Types of Disc Disease

Disc Desiccation

Disc desiccation is a prevalent age-related change affecting the intervertebral discs. This condition occurs when the hydrophilic glycosaminoglycans within the nucleus pulposus are gradually replaced by fibrocartilage. As a result, the disc loses its moisture and elasticity, leading to a reduction in disc height. This loss of disc space is further exacerbated by the bulging of the annulus fibrosus and deformation (bowing) of the vertebral endplates.

Disc Bulge

A disc bulge occurs when disc tissue extends beyond the edges of the ring apophyses around the entire circumference of the disc (as indicated by the blue lines in the image below). This condition results from tears in the annulus fibrosus. Unlike disc herniations, disc bulges are not classified as herniations. Disc bulges are often a result of normal wear and tear and may be present in asymptomatic individuals. They can be classified as either circumferential, affecting the entire circumference of the disc, or asymmetrical, affecting only a portion of the circumference.

Determining the Presence of a Disc Bulge

To assess for a disc bulge, the disc is divided into four quadrants (see Image 1 below). A disc bulge is characterized by a generalized extension of disc tissue beyond the edges of the apophyses, affecting more than 25% of the disc’s circumference, typically protruding less than 3 mm beyond the apophyses. Image 2 below illustrates a disc bulge where the disc tissue is displaced in two quadrants, extending beyond 25% of the normal circumference of the disc.

Disc Herniation

A disc is considered herniated when there is a localized displacement of disc material that extends beyond the confines of the intervertebral disc space by less than 25% of the disc’s circumference.

Herniated discs can be classified into two types based on the shape of the displaced material: disc protrusion and disc extrusion.

Disc Protrusion

A disc protrusion occurs when the distance between the edges of the displaced disc (A) is less than the width of its base (B).

Disc Extrusion

A disc extrusion is characterized by the distance between the edges of the displaced disc material being greater than the width of its base.

Disc Sequestration

The term “sequestration” refers to a condition where the displaced disc material has separated and lost continuity with the remaining disc tissue.

• Acute onset of low back pain
• Pain extending into the posterior thigh and lower leg, potentially radiating to the lateral side of the foot (S1 nerve root pattern)
• Initial low back pain that typically improves within 24 hours, with the pain in the lower limbs becoming more pronounced
• Numbness and tingling (paresthesia) in the lower limb
• Lower limb weakness
• Pain that is aggravated by sitting, coughing, sneezing, or straining

• Weakness in ankle plantar flexion
• Reduced sensation over the S1 dermatome, particularly along the lateral aspect of the heel
• Reduced Achilles reflex
• Positive sciatic nerve tension tests (e.g., Straight Leg Raise and Slump tests)
• Positive Valsalva test
• Pain exacerbated by lumbar flexion and alleviated by lumbar extension, reflecting typical disc herniation patterns

• Plain Radiography: Primarily used to evaluate bone abnormalities such as osteophytes that may contribute to radiculopathy. It does not provide detailed information about soft tissues or nerve roots.
• Magnetic Resonance Imaging (MRI): Preferred over CT for assessing radiculopathy due to its ability to visualize soft tissues without ionizing radiation. MRI is highly sensitive for detecting a range of pathologies, including inflammatory conditions, tumors, and vascular issues. It provides detailed images of both the disc and nerve roots.
• Computed Tomography (CT):  Offers superior visualization of osseous structures compared to MRI and plain radiography. It is particularly effective in identifying bone-related changes but does not provide adequate detail of nerve roots or soft tissues.

The following are examples of red flags for patients presenting with low back pain and lower extremity symptom:

• Gradual onset of signs and symptoms of radiculopathy (e.g., in the case of a slowly growing tumor)
• Worsening radiculopathy signs and symptoms
• A history of significant trauma
• Bilateral lower extremity symptoms
• Pronounced neurological impairment
• Bladder and bowel dysfunction
• Saddle anesthesia
• Severe tenderness on palpation or severe pain with any examination procedure
• Unexplained weight loss

If any red flags are identified during history taking and clinical examination, referral for urgent medical evaluation and further investigation is warranted.

Myofascial Pain Syndrome Causing Buttock and Leg Pain

Myofascial pain syndromes can present as low back and leg pain. A comprehensive clinical examination should include an assessment of the following muscles to assess the presence of myofascial trigger points as the concomitant or primary causes of the patient’s pain. Trigger points in myofascial pain syndrome may develop anywhere within a muscle or its fascia. As a result, it is crucial to conduct a thorough examination of the entire muscle. However, based on our clinical experience, the common locations for trigger points are presented below. The primary muscles to evaluate include the following:

• Gluteus medius
• Piriformis
• Gluteus minimus