Nerve Root Block

What is a nerve root block?

A nerve root block is a procedure in which a needle was passed through the skin onto vicinity of the nerve root just where it exits the lumbar spine through its foramen and medication usually a steroid along with local anesthetic is injected to numb the nerve root. These are done in patients with radiculopathy. The local anesthetic helps in pain relief for a few hours and has diagnostic value. A steroid helps in relieving long-term pain and the effect of steroid starts in about 2 to 5 days and they last 3 months or more. Sometimes their effect may be short lived because of the pathology.

How does a nerve block work?

While doing the procedure of nerve block, a local anesthetic usually mixed with steroid and injected in the area of the nerve root. The local anesthetic helps to numb the nerve root and take care of the acute pain. Effect of local anesthetic usually ends in 2 to 6 hours following which the effect of steroid starts to act in 2 to 5 days and may lead to long term pain relief associated with the nerve root.

Which nerve root causes foot drop?

Involvement of L5 nerve root may lead to foot drop. Involvement of L4 nerve root may lead to partial foot drop. At the same time, involvement of S1 nerve root may lead to weakness of the planterflexors of the foot (which help in push off during walking) and involvement of the gait cycle. Involvement of L5 and S1 nerve root may lead to a flail ankle which the patient is neither able to pull the foot up or take off during the gait cycle.

Which nerve root is affected by L4-L5?

With the most common form of compression at L4-5 – paracentral compression, L5 nerve root is most commonly involved. In cases of foraminal or far lateral compression L4 nerve root is involved. Central compression at L4-5 can lead to involvement of lower nerve roots too.

What causes nerve root compression?

There are multiple pathologies that can lead to nerve root compression, but it is most commonly seen in the setting of degenerative disk disease. The disk material that may have herniated or extruded out of the disk space may cause a pressure defect on the nerve root. At the same time, degenerative ligament may also lead to compression of the nerve roots in the spinal canal.

Occasionally synovial cyst formation from the adjacent facet joint in spondylosis, or the fibrous tissue of pars healing in spondylolisthesis patient may be the cause of nerve root compression. Rarely, the cause of nerve root compression can be mass effect due to her slow growing tumor or a hematoma.

Which nerve roots innervate the bladder?

The bladder was innervated by sacral nerve roots S2, S3, S4. It is supplied by these sacral nerve roots from both sides. These sacral nerve roots exit the spinal canal through the foramina and the sacrum. These nerve roots can be compressed due to mass effect of the tumor of the sacrum, hematoma in the lumbosacral region or a central lumbar disk, which may impinge on the sacral nerve roots.

What is the surgical treatment to relieve pressure in the nerve roots?

Pressure in the lumbar nerve roots when treated surgically are done with the procedure called decompression with or without diskectomy. Other procedures that can cause decompression are foraminotomy or laminoplasty. These procedures are usually done in a minimal invasive fashion so as to minimize complications and expedite recovery. Procedure is decided according to the pathology and their access to the nerve root.

What are the complications of nerve root block?

Though nerve root block is a safe procedure, it carries its own risks and complications, which include injury to the nerve root leading to temporary or permanent deficit or worsening of pain with or without tingling or numbness or involvement of bowel or bladder. Multiple nerve root blocks done in single sitting can lead to weakness and inability to walk for several hours after the procedure.

Occasionally an injection into the blood vessel can be dangerous for patients general health and well being. Injection in the vicinity of the nerve root may lead to bleeding with hematoma formation and cauda equina syndrome which may need urgent surgery to take care of the compression.

What is the mechanism of radiculopathy in compression of nerve roots?

Though it is not confirmed, but it has been hypothesized that compression of nerve roots lead to decreased blood supply to the nerve roots leading to ischemia and hence causing changes in the nerve root to cause pain with or without tingling or numbness and weakness of the muscles.

What is a diagnostic test to identify a nerve root compression?

MRI is usually the diagnostic test to identify nerve root compression. It defines the anatomy of the spine as well as the level of root compression and the probable cause of decompression. In patients with contraindications for MRI (pacemaker, aneurysmal clips, recent stents), confirmation of the diagnosis can be done with CT scan with or without myelography.

When does a nerve root compression need a fusion surgery?

A nerve root compression is usually treated conservatively with medications with or without nerve root injection. If the relief is incomplete following conservative procedures that a surgical treatment can be advised. Surgery for nerve root compression usually in the form of decompression with or without diskectomy, but in cases where the spine is unstable or the surgery in itself will lead to instability of the spine, a fusion surgery of that level may be needed to be performed. A fusion surgery is performed by use of screws and rods and bone grafting so as to achieve fusion.