L4 Radiculopathy Caused by Disc Herniation

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Disc Herniation Causing L4 Radiculopathy

Lumbar disc herniation with radiculopathy typically involves displacement of disc material beyond the normal margins of the intervertebral disc space. This results in pain, weakness, or numbness in a myotomal or dermatomal distribution.

The clinical presentation in lumbosacral radiculopathy will vary according to the level of the nerve root involved. Lumbar disc herniation with subsequent radiculopathy most typically involves the L4-L5 and L5-S1 levels. Disc herniation is less common in the upper lumbar region. For example, the incidence of L3-L4 herniation is approximately one-tenth of the incidence of L5-S1 herniation.

A posterolateral disc herniation compresses the nerve root that exits the foramen below the herniated disc. Therefore, a posterolateral disc herniation at L3-L4 typically affects the L4 nerve root, herniation at L4-L5 affects the L5 nerve root, and herniation at L5-S1 affects the S1 nerve root.

Clinical manifestations of radiculopathy involve the motor and sensory systems. With motor dysfunction, muscle weakness is a typical characteristic. However, given that many muscles receive innervation from multiple nerve roots, their weakness may not be apparent on clinical examination. Consequently, when performing a neurological examination, specific muscles are assessed for each nerve root level. Similarly, there is considerable variation and overlap in sensory testing. Therefore, specific key sensory areas are assessed for each nerve root.

Causes of Lumbosacral Radiculopathy

More Common

• Disc herniation
• Spondylosis (a narrowing of the central canal, the lateral recess, or the neural foramen due to degenerative arthritis)

Less Common

• Inflammation
• Neoplasm
• Infection
• Vascular disease

• Acute onset of low back pain
• Pain involving the anterior thigh, knee, and the medial aspect of the lower leg
• Low back pain that eases after 24 hours with lower limb pain becoming predominant
• Numbness and tingling (paraesthesia) in the lower limb
• Lower limb weakness
• Pain aggravated by sitting, coughing, sneezing, or straining

• Weakness in ankle dorsiflexion
• Loss of sensation over the L4 dermatome, particularly at the medial malleolus
• Reduced patellar reflex
• Positive Femoral Nerve Stretch test
• Positive Valsalva test
• Pain that is aggravated by lumbar flexion and reduced by lumbar extension

• Plain radiography assesses for osseous causes of radiculopathy (e.g., osteophytosis).
• MRI has advantages over CT. With MRI, there is no ionizing radiation and it is more sensitive in identifying other pathologies (e.g., inflammation, malignancy, and vascular conditions).
• CT enables better assessment of osseous structures than MRI and plain radiography. However, it is unable to sufficiently demonstrate nerve root involvement.

Normal Disc

A normal disc is composed of a central nucleus pulposus (NP) and peripheral annulus fibrosus (AF).

Disc Desiccation

A very common age-related degenerative change of intervertebral discs is referred to as disc desiccation. This occurs when hydrophilic glycosaminoglycan within the nucleus pulposus is replaced with fibrocartilage. The resultant loss of disk height is due to annular bulging and bowing of the vertebral endplate.

Disc Bulge

A disc bulge refers to the extension of disc tissue beyond the edges of the ring apophyses throughout the circumference of the disc (see the blue lines in the image below). This is caused by tears in the annulus fibrosus. A disc bulge is not considered a form of herniation. Unlike herniations, disc bulges are caused by normal wear and tear to the disc and can be seen in people who are asymptomatic. A disc bulge can be circumferential (involving the entire circumference of the disc) or asymmetrical (not involving the entire circumference of the disc).

Determining a Disc Bulge

The disc is divided into 4 quarters (see Image 1 below). A disc bulge refers to a generalized extension of disc tissue beyond the edges of the apophyses by more than 25% of the circumference of the disc (typically less than 3 mm beyond the edges of the apophyses). Image 2 below shows a disc bulge in which the disc is displaced in 2 quadrants by more than 25% of the normal circumference of the disc.

Disc Herniation

A disc is said to be herniated when a focal displacement of disc material is less than 25% of the disc circumference beyond the limits of the intervertebral disc space.

Herniated discs may be classified as disc protrusions or disc extrusions based on the shape of the displaced material.

Disc Protrusion

A disc protrusion indicates that the distance between the edges of the displaced disc (A) is less than the measure of its base (B).

Disc Extrusion

A disc extrusion is present when the distance between the edges of the displaced disc material is greater than the distance at the base.

Disc Sequestration

The term sequestration is used to indicate that the displaced disc material has lost continuity with the parent disc.

The following are examples of “red flags” for patients presenting with radiculopathy:

• Gradual onset of signs and symptoms of radiculopathy
• Worsening radiculopathy signs and symptoms
• 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.

Golden Yellow

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