Injections for back pain management:
Selective nerve root block
(SNRB) for diagnosis and back pain management
Another common injection, a selective nerve root block
(SNRB), is primarily used to diagnose the specific source
of nerve root pain and, secondarily, for therapeutic
relief of low back pain and/or leg pain (see
Figure
1).
When a nerve root becomes compressed and inflamed,
it can produce back and/or leg pain. Occasionally, an
imaging study (e.g. MRI) may not clearly show which
nerve is causing the pain and an SNRB injection is performed
to assist in isolating the source of pain. In addition
to its diagnostic function, this type of injection for pain management can
also be used as a treatment for a far lateral disc herniation
(a disc that ruptures outside the spinal canal).
In an SNRB, the nerve is approached at the level where
it exits the foramen (the hole between the vertebral
bodies). The injection is done both with a steroid (an
anti-inflammatory medication) and lidocaine (a numbing
agent). Flouroscopy (live x-ray) is used to ensure the
medication is delivered to the correct location. If
the patient’s pain goes away after the injection,
it can be inferred that the back pain generator is the specific
nerve root that has just been injected. Following the
injection, the steroid also helps reduce inflammation
around the nerve root.
Success rates vary depending on the primary diagnosis
and whether or not the injections are being used primarily
for diagnosis. While there is no definitive research
to dictate the frequency of SNRB’s, it is generally
considered reasonable to limit SNRB’s to three
times per year.
Technically, SNRB injections are more difficult to
perform than epidural steroid injections and should be performed by experienced
physicians. Since the injection is outside the spine,
there is no risk of a wet tap (cerebrospinal fluid leak).
However, since the injection is right next to the nerve
root, sometimes an SNRB will temporarily worsen the
patient’s leg pain.
Facet joint block for back pain management
In cases where the facet joint itself is the pain generator,
a facet block injection can be performed to alleviate
the pain. Similar to SNRB’s, facet block injections
are a diagnostic tool used to isolate and confirm the
specific source of back pain for the patient. Additionally,
facet blocks have a therapeutic effect as they numb
the source of pain and soothe the inflammation for the
patient.
The facet joints are paired joints in the back that
have opposing surfaces of cartilage (cushioning tissue
between the bones) and a surrounding capsule. Twisting
injuries can cause damage to one or both facet joints,
and cartilage degeneration associated with aging may
also cause pain.
In a facet block procedure, a physician uses fluoroscopy
(live x-ray) to guide the needle into the facet joint
capsule to inject lidocaine (a numbing agent) and/or
a steroid (an anti-inflammatory medication). If the
patient’s pain goes away after the injection, it
can be inferred that the pain generator is the specific
facet joint capsule that has just been injected.
If the facet block procedure is effective in alleviating
the patient's low back pain, it is often considered
reasonable for the procedure to be done up to three
times per year. There are very few risks associated
with this technique.
|
