What is discogenic pain?
Discogenic pain literally means pain from the intervertebral disc — the strong mobile structure that forms the major connection between each of your vertebrae. Pain originating from the discs is the most common cause of chronic low back pain, with studies showing around 40 per cent of patients attending a spinal pain practice for chronic back pain were suffering from discogenic pain.
Single or repetitive trauma — particularly lifting and twisting— can lead to disc injuries. This may cause weakening of the disc with a possible radial tear along the outer part of the disc. If the internal part of the disc (nucleus) spreads along the tear to the outer part of the disc, it will irritate the small nerves located there, producing low back pain.
What is the purpose of a discogram?
The only valid diagnostic procedure for determining if a disc is the pain generator, is a provocative discogram.
A discogram is an imaging-guided procedure in which a contrast agent is injected into the inner core of the vertebral disc.
Procedure details
An intravenous cannula is inserted, containing a fine needle. This needle is passed into the relevant vertebral discs. A small amount of pain relief medication may be used to ensure minimum discomfort for the patient. However, it is imperative that the patient is able to answer questions clearly and precisely during the procedure.
During the procedure, the needle may brush against the facet joints behind the spine. This often causes a deep, aching pain for a short period of time. Sometimes, the needle may brush against the side of the ‘exiting nerve root’, which causes a sharp, ‘electrical’ or ‘hot’ pain to shoot down the leg. The chance of this happening is small, but it is important you tell the doctor if you experience this sort of pain. They will then manipulate the needle away from the nerve, to avoid nerve damage. The procedure is performed under ‘C-arm’ fluoroscopic guidance. Fluoroscopic guidance is an imaging technique that uses x-rays to enable your doctor to view real-time moving images of an internal structure of the body — in this case, your vertebral discs. The ‘C-arm’ simply refers to the shape of the arm on the x-ray machine.
Once the needles are ideally placed, the doctor injects each disc with a radio-opaque dye so that the inside of the disc can be seen. This will also enable them to see if there are any annular tears (a tear in the tough exterior of your disc). An antibiotic is injected in combination with the dye. This procedure is designed to reproduce the usual ‘pain pattern’. A normal, healthy disc will have no pain whatsoever, or only a slight feeling of ‘pressure’ in the back. This is the most common response.
The next response that may occur is that you’ll experience a small amount of pain that’s unlike your normal symptoms. It is important to identify the amount of pain, and confirm that this type of pain isn’t your normal pain.
The final outcome that may occur is the disc injection reproduces the usual pain. It’s important that this test clearly establishes pain as close to the usual pain, in character, distribution and intensity.
Once the injection pressure is released, the pain usually subsides fairly rapidly. At times the doctor may inject a small dose of anaesthetic into the disc to see if the pain rapidly eases. Following the procedure, it is common to have a transforaminal injection at the most painful level to assist in post procedure pain relief. This injection is a combination of local anaesthetic and long-acting steroid.
You’ll then be observed in the recovery ward and discharged from hospital approximately two hours after the procedure.
Risks
While these are rare, it’s important to understand there’s a small risk of developing a disc infection. The risk of this is markedly reduced by a number of precautions that are routinely taken, including:
- A modified double needle technique is used, along with a stilleted needle (as opposed to a standard needle), which means it’s impossible to carry a tiny piece of skin down into the disc. This used to occur in the past and resulted in a higher risk of infection.
- Antibiotics are usually given via the IV cannula and injected into the disc.
There is a risk of causing damage to other structures around the spine, such as the nerve roots. This risk is minimised using live fluoroscopy, and by keeping the patient awake and in communication. The risk of haemorrhage is minimal.