Selective Nerve Root Block – Indications and Applications

Selective nerve root block is similar in approach to facet joint injections but they address different pathologies.

Both of these might be used in the same patient for the diagnostic purpose [to find if the pain is due to facet joint or nerve root] but as therapeutic measure, they address different issues.

As in epidural injections, and facet joint injections, steroids are used in selective nerve root blocks in an attempt to provide temporary relief from pain.

For example, when selective nerve root block is performed for disc herniation, the goal is to provide pain relief for enough time to allow the extruded disks to shrink.

Nerve root blocks aim to anesthetize the desired nerve for diagnostic purposes, and steroids are used in an attempt to produce long-term relief, primarily in patients with radiculopathy.

Rationale for Selective Nerve Root Blocks

Radiculopathy may occur due to the following reasons

• Autoimmune response due to pressure may result in pain.
• Increase in venous pressure leading to compartment syndrome within the nerve causing ischemia and pain
• Phospholipase A mediated inflammation.

Because steroids have anti-inflammatory actions, injections around the nerve root may reduce the inflammation, decreasing or eliminating the pain.

The basis of selective nerve root block is the same as epidural steroid injections. But whereas epidural is a blanket approach selective nerve root block is a more focused approach.

They are especially useful when 1 or 2 nerve roots are considered to be the likely cause of the patient’s symptoms.

Moreover, they are better in relieving irritation of the perineural tissue and the sinuvertebral nerve, which innervates the annulus.

Indications for Selective Nerve Root Blocks

Nerve root blocks are useful primarily in the following subsets of patients with radiculopathy:

• Recurrent radiculopathy after discectomy. The symptoms are often caused by scar tissue tethering the nerve.
• Patients with disk herniations
  •  70- 90% of disk herniations resolve spontaneously with, given enough time.
  • The pain is believed to result from an inflammation and steroid injection can reduce inflammation and pain in many patients. [The pressure on the nerve root by disc per se causes numbness and not pain]
• When patients have symptoms related to a nerve root but
  • No definite radiologic diagnosis explaining the symptoms
  • Many abnormal MRI findings but the origin of the symptoms is difficult
  • Examples are subcostal pain from thoracic nerve roots
  • The selective nerve root block in pain with uncertain pain etiology is effective and accurate means of diagnosis as well as treatment

Contraindications

• History of allergy to local anesthetics or steroids
• Coagulopathy

Procedure of Selective Nerve Root Block

Nerve root blocks are performed under fluoroscopic guidance or CT or  CT fluoroscopy.

While fluoroscopy offers decreased procedure time and cost, whereas CT has the advantages of

• No contrast medium
• The better precision of needle placement
• Visualization of important vascular structures.

An informed written consent is obtained from the patient before the procedure

For lumbar/thoracic nerve roots the patient is positioned in a prone or slightly oblique position. Sterilize the skin and anesthetize with a local anesthetic

For the nerve root injection, use a 20-, 22-, or 25-gauge spinal needle.

Approach the neural foramen from a posterolateral direction and place the needle in the foramen.

Advance the needle tip slowly until either the patient experiences radicular pain or the needle encounters the posterior surface of the vertebral body.

Confirm the location of the needle tip by injecting 1-4 mL of a nonionic contrast medium. Proper placement of the needle is indicated by the flow of the contrast medium around the nerve root. Radicular pain may occur.

Once appropriate needle placement has been confirmed

• For diagnosis – inject 1% lidocaine with or without bupivacaine
• For treatment – 1-2 mL of an appropriate steroid mixed with a small amount (0.5 mL) of bupivacaine.

Following features are unique to Cervical Nerve Root Block

A cervical selective nerve root block is performed with the patient in the supine position.

To avoid injury to the vertebral artery, direct the needle into the posterior portion of the foramen.

Under  CT or CT fluoroscopic guidance the needle is passed posterior to the jugular and carotid vessels, and maneuver the needle to just outside the neural foramen.

Follow-up Care

Transient weakness may occur in the distribution of the injected nerve root if the motor root also becomes anesthetized. Therefore, observe the patient for at least 15 minutes after the procedure to document pain relief and to monitor the patient for motor weakness and allergic reactions.

Activity restrictions are not necessary.

Mostly, the pain relief would be evident within the first 15 minutes after the injection.

But few patients would have pain resolution over the next few days.

Therefore, the injection should not be labeled unsuccessful until 1 week after the injection.

Complications

Complications are rare during and are usually minor.

Bleeding, infection and allergic reactions are the commonest complications

Persisting paraplegia or paraparesis have been reported.

Spinal anesthesia may occur if a local anesthetic is inadvertently injected into the nerve root sleeve. A high level spinal may arrest the patient’s breathing and prompt recognition of this potentially disastrous complication is vital especially during cervical procedures

Measures involve elevation of head and intubation if needed.

Spinal cord infarcts following selective nerve root blocks are potentially devastating but quite rare.

Insomnia, nightmares, and nervousness can be caused by steroids.