What Are Posterior Superior Iliac Spine Blocks And Ablations?

Nerve blocks are performed to provide relief from chronic pain. Nerve blocks may be used as a therapeutic tool by providing pain relief or as a diagnostic tool by confirming the nerve carrying pain signals. When this pain occurs in or originates on the back of the pelvis, the type of nerve block that may be used is referred to as a posterior superior iliac spine block. Following a nerve block, ablation may be performed to destroy the sensory nerve and prevent it from sending the pain signals to the brain.

The posterior superior iliac spine is the lower part of the spine above the tailbone. The sacrum is the triangular region at the back of the pelvis that is situated between the lumbar spine and the coccyx, or tailbone. This triangular bone begins as a set of vertebrae that fuse within the first few decades of life. The place where the sacrum joins with the iliac bones of the pelvis is referred to as the sacroiliac joint. The posterior superior iliac spine is the uppermost region of this juncture.

Once the physician is confident that the posterior superior iliac spine is the region where the pain is originating or being transmitted through, a nerve block may be performed. The success of a posterior superior iliac spine block will confirm that this is the region to target in order to provide pain relief to the patient. Once this has been established, ablation of the target nerve may be performed to eliminate the nerves that are carrying the pain signal.

How Are Posterior Superior Iliac Spine Blocks Performed?

A posterior superior iliac spine block is performed after careful analysis by a physician to determine the likely source of lower-body or lower back pain. If the doctor suspects that the pain is originating from the region where the sacrum of the lower spine sits between the iliac of the posterior pelvis, then a posterior superior iliac spine block may be recommended to relieve swelling and inflammation, provide pain relief, and confirm the location of the affected nerve.

A posterior superior iliac spine block is performed as an outpatient procedure taking approximately 30 minutes with additional time for monitoring the patient for side effects and comfort before leaving the office. The area to receive the injection is cleaned, sterilized, and treated with a local anesthetic. Some form of imaging may be used to help the physician accurately guide the needle during this procedure. Sonogram or a fluorescent dye coupled with X-ray imaging are used for targeting assistance. MRI has also been explored as a novel imaging option for this procedure.

Once the needle is at the desired location, a local anesthetic and a powerful steroid are injected into the site. The steroid helps reduce inflammation and swelling that may be contributing to the pain. In some cases, this is effective as a treatment, but it may also be used as a diagnostic tool prior to doing a more permanent procedure.

How Are Ablations Performed?

Generally, a nerve block will be performed as a diagnostic test prior to exploring nerve ablation. A successful nerve ablation procedure will destroy the target nerve. The targeted nerves are sensory nerves, so they are not involved in movement and should not have any adverse effect on the patient.

A nerve ablation procedure is very similar to a nerve block procedure, though it utilizes a heat probe instead of a needle. A patient is prepared for the procedure by cleaning and sterilizing the surrounding skin. A local anesthetic is also administered.  In order to ensure accurate probe placement, a fluorescent dye may be injected and monitored by X-ray imaging. Alternatively, the probe placement can be monitored by sonogram.

Once the probe has been carefully inserted alongside the target nerve, radiofrequency is used to heat the tissue immediately adjacent to the probe. This treatment kills the nerve and prevents it from sending any more pain signals to the brain. In some cases, the nerve may regrow, in which case the physician will decide if a second ablation is necessary.

Conditions Related To Posterior Superior Iliac Spine Blocks And Ablations

Posterior superior iliac spine blocks and ablations are performed when self-administered anti-inflammatory medications and pain relievers are insufficient for pain relief. Several conditions can lead to pain originating from the nerves in this region, including age-related wear and tear, acute injury, local tissue damage, pregnancy, or changes in gait. It is currently being investigated whether these procedures are effective for the treatment of discogenic pain in this region.

As mentioned above, the sacroiliac joint is part of the pelvis, so anything that alters the shape of the pelvis, pressure on the pelvis, or leg and hip motion can lead to problems in this region of the lower back. For instance, the pressure on the pelvis from a growing fetus during pregnancy, along with the additional weight on the pelvis, can lead to complications of the lower spine. Leg injuries or anything that affects a person’s gait can also lead to changes in the hips and pelvic region, leading to tissue damage and chronic pain.


Posterior superior iliac spine blocks and ablation treatments are viable options for patients suffering from back pain originating from the posterior pelvic region. These treatments target the upper region of the rear of the pelvis, where it meets the lower vertebrae. The nerve block contains a powerful steroid and is often used as a diagnostic tool prior to undergoing nerve ablation in which the target nerve is destroyed. These treatments are each performed as outpatient procedures requiring about 30 minutes of procedure time with about 45 minutes of post-treatment monitoring.

If you are suffering from chronic pain, consult your physician. These procedures, and others, provide both temporary and lasting relief with very few side effects, allowing most patients to experience an increased quality of life with very few complications.


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