X-rays, CT Scans and MRI's provide excellent images of various spinal disorders. However, they cannot show pain. Spinal injections, typically used to control pain, are also used diagnostically to locate the pain source. Diagnostic spinal injections include discography (discogram), selective nerve root block (SNRB), sacroiliac joint injection and facet joint injection.
In the spine, nerve roots and intervertebral discs are the usual sources of pain. For example, a lumbar herniated disc may entrap a nearby nerve causing buttock and leg pain. A pinched cervical nerve root may cause shoulder and arm pain. The type of diagnostic spinal injection chosen is determined by the patient's medical history, physical and neurological examination, and findings from other studies such as CT Scan.
A discogram helps to determine if a particular intervertebral disc is the pain generator. This is not a routine test, and may be used when surgery is considered.
A contrast dye is injected into the suspect disc (or discs) under fluoroscopy (a technique that allows for real-time imaging of the patient’s internal anatomy). The dye enhances the anatomical characteristics of the disc. The disc may appear normal or the disc lining may show tears (fissures).
Discography can be an uncomfortable test. As the dye is injected, the patient's typical symptoms may be reproduced. This is called a positive discogram. The patient's pain response is important to help diagnose the exact source of the pain. If the injection does not replicate the patient's pain, then the test is a negative discogram.
The procedures take 30 to 45 minutes depending on the number of discs (spinal levels) injected. Infection is a possible risk, although it is rare. Antibiotics are injected before the procedure or with the dye to avoid infection.
Selective Nerve Root Block (SNRB)
SNRB is performed to determine if a specific spinal nerve is the source of pain. It can help to diagnose cervical or lumbar radiculopathy (irritation and inflammation of a nerve root serving a particular body part).
Under fluoroscopic guidance, the specialist injects steroid medication at a specific nerve root. The steroid is a strong anti-inflammatory. If the injection reduces or alleviates the patient's symptoms, then the source of pain is located. The test takes 15-30 minutes per spinal level.
Facet and Medial Blocks
Joint inflammation between the spinal bones can cause back pain. Facet and medial blocks involve the injection of steroid medication into joint areas to determine if that joint is a pain generator. Steroids reduce inflammation and alleviate pain.
A facet joint block is an injection of local anesthetic and steroid medication into the joint. A medial block uses similar medication injected outside the joint space near the nerve that feeds that joint. These injections are performed under fluoroscopy.
If pain is relieved, it could mean that the suspect joint or medial nerve is the pain generator.
Sacroiliac Joint Injection
The sacroiliac joint is the largest joint in the spine. It is located in the lower spine above the tailbone. Inflammation of the sacroiliac joint can cause low back and buttock pain.
Using fluoroscopy, local anesthetic and steroid medication is injected into the sacroiliac joint. If pain is relieved, it could mean that the suspect joint is the pain generator.