Medial Branch Blocks

The Diagnosis of Facet Joint Pain

Medial branch blocks are used to diagnose and/or treat facet joint pain.

Are the Facet Joints the Cause of Pain?

Facet joint pain typically presents with low back pain with, or without referred pain into the leg. Studies have shown that facet joints can be damaged in accidents (e.g. motor vehicle accidents), and that these changes in the facet joints may not show up on x-ray, CT scan or MRI scanning.


The only way to determine whether the facet joints are the cause of pain is to inject the joint or its nerve supply with local anaesthetic. If pain is substantially eliminated while the anaesthetic is acting, it is assumed that the facet joint is the source of pain. This injection process is known as a block (the aim is to block out the pain). The nerve supply to the facet joint is via the medial branches of the adjacent dorsal rami (branches of nerves), which originate from the spinal nerve. Thus, blocks of the nerve supply to the facet joints are called medial branch blocks.


Studies show that a successful block means that there is a 70 per cent chance that the diagnosis is facet joint pain. That means, false positive blocks (blocks that incorrectly diagnose the facet joints to be causing the patient’s symptoms) do occur. A second positive block using other anaesthetic agents increases the diagnostic confidence to 90 per cent.


Medial branch blocks are used for stubborn chronic pain if specific treatment to the facet joint is required. This treatment is known as radiofrequency neurotomy (RFN), or radiofrequency denervation. This treatment applies heat lesions to the nerve and can lead to prolonged pain relief.

Injection Protocol

The major reason for the injection is to determine whether or not pain is altered in the six hours after the injection. Therefore, it’s important to have a method for recording the pain score.


A commonly-used pain scale rates pain from 0 to 10. When represented in a linear fashion on a chart, it’s called a Visual Analog Scale (VAS).


Zero (0/10) indicates no pain while 10/10 indicates pain that is almost unattainable. At 10/10 a person can’t think, move or function at all. Each person needs to know what their VAS is, and apply it to each area of pain. As the aim of the block is to see if pain is altered, it’s essential that pain measures at least a 4/10 on the day of the procedure. Thus, patients shouldn’t take pain medication on the day of the injection.


It’s normal to feel anxious about the injection. However, the injections are very safe, generally not too painful, and can be done quickly.

The Procedure

The injection itself consists of placing a needle through the skin under an x-ray machine. The needle is placed directly on to bone. A thin needle (not much thicker than an acupuncture needle), is used. Generally, only one or two facet joint levels are investigated at a time to ensure the diagnosis is specific to a level in the lumbar spine.

What To Do Afterwards

You should be driven home after the procedure. Repeat confirmatory
injections are performed one to two weeks later if the first injections successfully block the pain. If good relief is obtained at the first session, and this is confirmed at the next session, then it’s assumed the facet joints are the main cause of pain, and the radiofrequency neurotomy (RFN) procedure should benefit you.


If there is no relief following the first session then it may be necessary to investigate other levels, which may require two sets of injections. Your doctor will determine if other injections should be done. If there is still no relief then the conclusion is the facet joints are not the cause of the pain.

More On The Pain Chart

As mentioned above, you must rate your pain between 0 and 10, with 0 equaling no pain, and 10 equaling worst pain imaginable. You should rate your pre-injection pain both in terms of your movements and how you feel doing the things that most aggravate the pain, and then over the next six hours, you should record your pain levels on the pain chart, at the intervals initially of half an hour, and then hourly.


You may need to describe separately different pains that you experience. For example, you may have low back pain and leg pain, and these two pains should be described separately. For instance, the injection may totally relieve the low back pain, but may not help the leg pain. This is important information for your doctor to assess when making recommendations regarding further treatment.



Before injection: back pain = 5 (moderate) left leg pain = 8 (severe)
1 hour after: back pain = 0 (nil) left leg pain = 8

In this example, the back pain has been relieved, but the leg pain is the same. This indicates the back pain may be related to the facet joint, but the leg pain is not. Your doctor will interpret the pain charts and discuss them with you. Please feel free to ask your practitioner questions if any clarification is required.

Downloadable PDF

Please note the contents contained in this Patient Fact Sheet are not intended as a substitute for your own independent health professional’s advice, diagnosis or treatment. At Metro Pain Group, we assess every patient’s condition individually. As leaders in pain intervention, we aim to provide advanced, innovative, and evidence-based treatments tailored to suit each patient. As such, recommended treatments and their outcomes will vary from patient to patient. If you would like to find out whether our treatments are suitable for your specific condition, please speak to one of our doctors at the time of your consultation.

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