Spine Tests: Use of Diagnostic Injections
(Discography, facet joint injection, selective nerve root block, and sacroiliac joint injection).
X-rays, CT Scans and MRI's provide excellent images of various spinal disorders. However, they cannot show pain. Spinal injections, which are typically used to control pain, are also used diagnostically to locate the pain source. Diagnostic spinal injections including discography (discogram), selective nerve root block (SNRB), sacroiliac joint injection and facet joint injection may be used diagnostically.
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.
A discogram helps to determine if a particular intervertebral disc is the pain generator. This is not a routine test, but 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.
Patient Preparation: At Home
It is important that the patient follow all pre-test instructions so that the results of the diagnostic injection are accurate. Some of these instructions include:
- Stop blood-thinning medication 2 days prior to the test
- Do not take any aspirin product 5 days prior to the test
- Stop anti-inflammatory medication 5 days prior to the test
- Stop pain medication 8 hours prior to the test
- Do not eat or drink 6 hours prior to the test
- Arrange for someone to provide transportation home
Patient Preparation: At the Medical Facility
- The medical staff will review the patient's history, condition, medications taken on a daily basis, food and/or drug allergies, and other information.
- The patient changes into a gown and lies down in a hospital bed.
- An EKG monitor (heart function), automatic blood pressure cuff (blood pressure), and oximeter (measures blood-oxygen levels) are attached to the patient. This equipment enables the medical staff to consistently monitor the patient's vital signs before, during, and after the procedure.
- Medication to relax the patient is administered by injection. In some cases, light intravenous sedation may be given. Diagnostic spinal injections require the patient to be awake to respond to the injection specialist's questions.
What to Expect During the Procedure
- The procedure is performed in a sterile setting similar to an operating room.
- The injection site is cleaned and draped. Skin numbing medication is injected into and around the procedure site.
- Before proceeding, the fluoroscopy C-arm is positioned over the patient. Fluoroscopic guidance is used during the procedure to guide the needle into the proper position.
- After the needle is placed, a contrast dye is injected to enhance visualization of the site. An anesthetic in a steroid solution is injected after the contrast dye. The steroid solution may include an antibiotic.
- The goal of the procedure is to replicate the patient's typical discomfort (symptoms). The patient may reproduce symptoms by bending, twisting, walking or sitting. The patient's feedback helps to identify the cause of pain.
After the Procedure
- The patient is wheeled to the recovery area where the medical staff continues to monitor vital signs.
- Patients are usually discharged home within 30-60 minutes with written instructions.
- The area around the injection site will feel numb. Relief from typical symptoms may last for six hours following the injection.
- Steroids may cause side effects that include blurred vision, frequent urination, increased thirst and change in blood sugar levels, especially in diabetic patients. If these side effects become bothersome or worsen, seek medical attention.
- If fever, chills, increased pain, weakness or loss of bowel/bladder function occurs, seek immediate medical attention.
- Patients should follow-up with the treating physician for test results.
Diagnostic spinal injections, like other medical procedures, have risks. Complications include risk of infection, low blood pressure, headache, and injury to nerve tissue.
For their safety, some patients may not be allowed to undergo diagnostic spinal nerve injections for the following reasons:
- Allergy to the contrast medium and/or drugs to be injected
- Significant asthma
- Bleeding problems
- Kidney disease
- Severe spinal abnormality
Diagnostic injections play a useful role in identifying the source of a patient's pain. However, the procedures are often uncomfortable and painful for the patient.