Patrick M. Foye, M.D.
Assistant Professor of Physical Medicine & Rehabilitation, New Jersey Medical School, Newark, New Jersey, USA. tailbonedoctor.com/
The 'ganglion Impar' is a cluster of nerve cells in front of the sacrum/coccyx joint. Over-activity of these nerve cells can cause chronic coccyx pain. Injecting these nerves with a local anesthetic gives immediate temporary relief from coccyx pain. When the anesthetic wears off, the pain usually returns at a lower level than before, presumably because the over-activity of the ganglion Impar has been reduced. Repeating the injections can eliminate or at least very substantially reduce the pain in many patients. Often the degree of relief from these injections is so substantial that patients previously considering surgical treatment for coccydynia no longer feel the need to pursue such options.
The ganglion impar
The ganglion Impar is part of the sympathetic nervous system, and is located just in front of the place where the sacrum and coccyx come together. The sympathetic nervous system is the part of the nervous system involved in the "fight or flight" response. Certain pain syndromes involve prolonged or extreme pain signals, perhaps related to increased irritability or excitability of the sympathetic nervous system. A classic example would be Complex Regional Pain Syndrome (CRPS, which was historically more commonly referred to as Reflex Sympathetic Dystrophy, or RSD). One of the classic and most dramatically helpful treatments for RSD, at least short-term, has been the injection of local anesthetic onto the sympathetic nerves that cover the body region were the patient is having the RSD pain. For example, a stellate ganglion block is done at the neck, on the right or left side, to help with RSD pain in the upper limb (e.g. at the hand or arm), on the right or left, respectively. Similarly, a lumbosacral sympathetic block is done for RSD pain in the lower limb (e.g. down at the leg or foot).
Just as the sympathetic nervous system can be temporarily blocked with local anesthetic injections at the stellate ganglion (for upper limb pain syndromes), or at the lumbosacral sympathetic ganglions (for lower limb pain syndromes), the sympathetic nervous system can also be temporarily blocked with local anesthetic injection at the ganglion Impar (particularly for coccyx pain syndromes).
A nerve "block" means that the physician has injected a medication that will "block" the nerve from carrying the electrical signal that the nerve would otherwise carry. If you were to "block" a nerve that was innervating muscles, then you would cause weakness in that muscle. If you were to "block" a nerve carrying sensation from the skin, then you would cause numbness in that region of the skin. If you were to block a nerve carrying impulses/signals via an overactive/hyper-irritable sympathetic nervous system, then you would dampen or quiet down that over-activity/hyper-irritability.
Treatment of coccydynia
One of the theories is that persistent over-activity/hyper-irritability of the ganglion Impar may be responsible for the persistent and severe course that is unfortunately often seen with coccydynia. Thus, an injection to block the signals of that ganglion Impar can very dramatically decrease the pain. Typically, most of my patients will report 100% initial relief of their coccyx pain within just a couple of minutes of having the injection with a local anesthetic. In fact, for these purposes the injection can be considered somewhat diagnostic (meaning that if in reality the patient had coccyx pain that was due to just referred pain from an internal organ, uterine fibroids, etc. then they would not have received the dramatic/complete relief with nerve blocks directed very specifically at the coccyx). Hence, the diagnostic nature of the injection.
Meanwhile, you can only be fully confident of the exact placement of the medication if you are performing the injection under the guidance of fluoroscopy (or under the guidance of a CT scan, but that is MUCH more cumbersome and takes far longer than fluoroscopy). The reason why the imaging-guidance (fluoroscopy) is needed is that the target area is very small and surface anatomy alone is inadequate at reaching the desired target. Worse yet, "blind" (i.e., without fluoroscopy) attempts at injection of the ganglion Impar could increase the chances of injecting into other structures, which might cause injury to the patient.
Most patients with true coccydynia will receive 100% initial relief via appropriately placed injections (i.e., confirmed via fluoroscopy), with local anesthetic. Most patients with severe coccyx pain are indeed pleasantly shocked at the amount of relief that they can receive. For many, it is emotionally very uplifting and reassuring to have such an immediate relief of pain that they may have been suffering from for many months or years. However, the local anesthetic (usually lidocaine, also called Xylocaine, or lignocaine) will typically wear off within a matter of a few hours. Other local anesthetics (such as bupivacaine, which is also called Marcaine) can last longer than the lidocaine, but may take a little longer for the initial onset of relief. I typically perform the ganglion Impar injection primarily with lidocaine the first time that I do it on any given patient, in order to give me and the patient the immediate feedback of how much relief they can get. If the relief is not long-lasting enough, repeat injections can be performed with the addition of a longer-acting local anesthetic, such as Marcaine.
When the local anesthetic wears off, the coccyx pain usually returns, but usually not as severe as it was prior to the injection. Thus, if someone is rating their pain on a "zero to 10 scale", they might report that their pain was an "8" prior to injection, "zero" immediately after the injection (before the local anesthetic wears off), and 3 or 4 during the days, weeks or months after the local anesthetic has worn off. In my pain management practice, I typically refer to this as "resetting the thermostat", meaning that breaking that vicious cycle of coccyx pain (even for a matter of hours) usually leads to a lower pain level, without rising back up to the pre-injection pain levels. Next, if this same patient wants to further decrease the residual/remaining pain from that level "4" severity, then the injection could be repeated at a subsequent date, to further "reset the thermostat" to an even lower pain level.
Although it is not unheard of in my practice for a patient to have a single injection provide 100% relief that lasts indefinitely (without ANY coccyx pain returning at all), the more typical response is for each injection to give 100% complete relief initially, but only partial relief on a persistent basis. Thus, although most patients with coccydynia are not "cured" long-term by a single injection, most will get significant relief and are extremely appreciative of having done so with such a minimally-invasive procedure (i.e., just a local injection under fluoroscopy, as opposed to coccygectomy, which is of course much more invasive since that is actual surgery to remove all or a portion of the coccyx, which can have variable results).
Nerve "blocks" can block the nerves either temporarily or more permanently. Really it just depends upon what medication/agent is injected onto those nerves. Injecting a local anesthetic will block those nerves just temporarily, until the local anesthetic wears off. For example, your dentist might inject a local anesthetic such as lidocaine in order to be able to perform a dental procedure (such as a root canal) without you barely feeling it while he/she performs the surgery.
To more permanently block a nerve, you would need to inject the nerve with a "destructive" agent, rather than just a local anesthetic. The destructive agent could be phenol or absolute alcohol, or anything else that is outright toxic to the nerve. Essentially, injecting a destructive agent onto the nerve can intentionally "kill" or destroy that nerve, or at least a portion of the nerve. If that nerve was carrying painful signals to the brain, then theoretically the signals should be stopped. One of the problems with destructive agents is that often they are toxic/destructive not only to nerve tissue, but also can cause damage to adjacent soft tissue structures in the body. Thus, they should be used with caution. Another potential problem is that even if you destroy a nerve at one point along its pathways, the more central portions of the nerve are still going up to the brain, and some patients might develop the de-afferentation pain syndromes (similar to the way that someone with an amputated leg might still feel like they are having pain in the amputated foot, even though that foot no longer exists, but indeed the nerves which previously carried those signals from that foot certainly do still exist in the spinal cord and brain).
Radiofrequency ablation (RFA) is another way to destroy nerve tissue, but instead of using a destructive medication, it uses radiofrequency waves at the tip of an injection probe. Radiofrequency ablation is certainly not nearly as well established for pain at the coccyx as it is for pain from spinal facet (zygoapophyseal) joints.
Even after a segment of nerves is "destroyed", the nerve can slowly grow back, and re-innervate the structures that the nerve was connected to before. When that nerve segment has grown back, it is possible for the pain to return, but ideally the patient would have at least gotten some significant duration of relief in the meantime (e.g. several months).
Thus, the main theoretical benefit of "destroying" the nerve (instead of just blocking it with a local anesthetic) would be a longer duration of relief. However, destructive agents carry a substantially higher risk of complications, as compared with injections of simple local anesthetics.