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Selective Nerve Root Block – Spinal Stenosis Diagnosis

Selective Nerve Root Blocking: Diagnosing Spinal Stenosis


SNRB Injection

Using selective nerve root block (SNRB) as a diagnostic tool is a fairly recent development in spinal health but has proved very useful at isolating the problematic nerve (or nerves) involved in the pathology of conditions such as spinal stenosis. It is also sometimes known as spinal nerve block and was first described in 1971 by Macnab as a potential tool for diagnosis.

Why Use Selective Nerve Root Block as a Diagnostic Tool?

When symptoms are present, for some patients an MRI scan, or physical assessment, can serve to locate the problematic vertebra and associated nerves involved in the aetiology of their spinal stenosis symptoms (Slipman, 2001). For the majority of patients the diagnosis is not that simple. Those with inconclusive scans and no outward markers of deformity, or distension, may be advised to undergo SNRB so as to work out where the problem lies prior to surgery or further therapy. Some patients may have numerous lesions showing up in MRI scans; SNRB can demonstrate which of these is pathologically/clinically significant.

How SNRB Works

In the procedure a small amount of anti-inflammatory medication, and anaesthetic, is injected onto the sheath around the nerve suspected of being problematic. The procedure is used both for diagnostic purposes and as a spinal stenosis treatment option as it can provide pain relief for some spinal stenosis patients if the nerve has been correctly identified. The optimum amount of injected substance is thought to be 1ml, as any more has higher risks of spreading and interfering with other nerves, thereby undermining the diagnostic value of the procedure (Clark, 1990).

What to Expect After the Procedure

Patients usually feel some numbness in the dermatome (the area of skin supplied by a single nerve), and possibly some muscle weakness. Physical therapy, involving procedures for local pain relief, and reconditioning exercises for the spinal muscle, are usually indicated for a minimum of six weeks after the procedure. As with epidural steroid injections it is advised that patients are driven home rather than driving themselves from the clinic.

The Benefits of the Procedure

If the problematic nerve was correctly identified and the anaesthetic and anti-inflammatory perform correctly then the physician can be reassured of the source of the patient’s pain and take appropriate therapeutic action. If the patient does not feel any relief from the procedure then it may be that the nerve that was treated is not the one at the root of their spinal stenosis symptoms. In these cases another SNRB procedure can be carried out to determine if a different nerve is the problem.

The Difference Between Epidural Steroid Injections and SNRB

In an epidural steroid injection the corticosteroid is injected into the epidural space, a much larger and less specific area than that injected in the SNRB procedure. Epidurals are not (normally) used as diagnostic tools, more as a therapeutic intervention. As the SNRB is more specific, the amount of corticosteroid injected is reduced, with concomitant benefits for reduced complications and side-effects such as hypercorticism, hyperglycemia, and fluid retention.

Disadvantages of Using SNRB for Diagnosis

As with any surgical procedure there is always a risk of infection, and of the needle straying into an unwanted area. If too much anesthetic and anti-inflammatory is used then the procedure may not be effective and the results risk misinterpretation (Clark, 1990). Rarely, misinterpreted results can then lead to inappropriate surgery being conducted on the wrong area and nerve root (this is highly unlikely to happen). Clearly no benefit will be felt from spinal stenosis surgery on the wrong nerve and surrounding area. The procedure should be conducted so as to avoid piercing the nerve root itself with the needle; instead the material should be injected onto the nerve root sheath to avoid damage.

The sensitivity of SNRB has been found to be high in comparison to other diagnostic techniques (Saal, 1990), making it an important tool in the physician’s armory when devising a treatment plan for spinal stenosis patients. It can be a useful procedure to identify the area to target for therapy and surgery, or simply function as a short term break in inflammation allowing spontaneous recovery of an area damaged by previous trauma.

1 reply
  1. cindy
    cindy says:

    I was just recently diagnosed w spinal stenosis as well as a few other things. Your site helped me understand more than all the other sites combined. Thanks


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