Coccygodynia (or coccydynia) is defined as the painful and disabling condition of the coccyx (tailbone) located inferior to the sacrum. Although it was known as early as the 18th century, there are still uncertainties in terms of multifactorial pain pathophysiology and effective treatment modalities [1].

Most patients have experienced a prior traumatic event such as a fall on the tailbone, childbirth, or lumbar spine surgery, whereas some cases are idiopathic [2]. Prolonged sitting, defecation, standing up from a sitting position, and leaning back while sitting may worsen the pain [3]. The prevalence of coccygodynia is five times more in females than in males, associated with the fact that the coccyx is more prone to trauma because of childbirth and its more posterior location in females [4]. Initial treatment is typically rest, use of pressure-relieving cushions, leaning forward while sitting, hot or ice pack application based on patients’ preference, as well as oral analgesics such as nonsteroidal anti-inflammatory drugs or paracetamol [5].

Interventional procedures are applied to patients whose pain is not relieved by initial treatment. Ganglion impar block (GIB) under fluoroscopic guidance has recently been frequently used in the treatment of chronic coccygodynia [6,7]. The ganglion impar is the sympathetic ganglion located anterior to the coccyx. The block of this ganglion with a steroid and local anesthetic has been shown to relieve both the somatic and neuropathic pain components of chronic coccygodynia [8]. Another treatment option that is relatively less emphasized in the literature, but frequently used in clinical practice, is the caudal epidural steroid injection (CESI) [9]. Although the mechanism of action has not been determined precisely, limited data on its effectiveness support CESI [3,10].

To our best knowledge, there is no prospectively designed study comparing these two interventional methods in the literature. The aim of this study is to compare the treatment outcomes of GIB and CESI in patients with chronic coccygodynia unresponsive to conservative treatment.

This study was a prospective randomized comparison study conducted between June 2019 and January 2021 (clinical trial registration number: NCT04902742). Ethics committee approval was obtained from the Committee of Ethics of Marmara University (Ethics number: 09.2019.395). Patients who have suffered from coccygeal pain for at least 3 months and been diagnosed with chronic coccygodynia in our pain clinic in the subsequent stage, with a clinical and physical examination, as well as radiologic assessments, were included in the study. Other inclusion criteria were intractable pain over the coccyx despite conservative treatment and being between the ages of 18 and 65. Patients with a history of GIB and/or CESI carried out in the previous 3 months, patients with a history of lumbar surgery, patients with systemic and/or local infections, malignancy, bleeding diathesis, acute fracture, known allergy to contrast material and/or local anesthetic substances, known history of any psychiatric disorder, and patients with a history of pregnancy were excluded from the study. Verbal and written informed consent were obtained from all patients participating in the study.

After the enrollment period, all patients were loaded into the computer program for the randomization process and randomly divided into two groups: a GIB group and a CESI group. The patients did not know which treatment group they were in, however, the clinician who performed the interventional procedure knew which method he was using. In this way, our study was conducted with a single blind design. It was also ensured that the clinician who evaluated the patients during the follow-up periods did not know which group the patients were in, thus assessor blinding was provided.

A total of 73 chronic coccygodynia patients accepted enrollment in the study. Thirty-seven patients were allocated to the GIB group and 36 patients to the CESI group. Five patients were lost during follow-up periods, 3 patients from the GIB group and 2 patients from the CESI group. A total of 34 patients in each group were included in the final analyses (Fig. 2).

Patients’ demographic properties and initial assessments were given in Table 1. There were no significant differences between the two groups in any of the initial parameters. In both groups, all patients had significant pain relief after injection, all showing a decrease of 80% 1 hour after injection. Mean NRS in 1st hour was 1.0 ± 1.6 in the CESI group and 0.7 ± 1.4 in the GIB group and were not significantly different (P = 0.413). When each group was analyzed within itself, both groups showed significant improvements in pain at each checkpoint. Pain scores in the GIB group were significantly better in the 3rd week, but there were no significant differences in the 3rd month. SF-12 physical scores improved at the 3rd week mark in both groups, however this improvement was not seen in the 3rd month. No improvement in SF-12 mental scores was seen in either group. There were no significant differences between the quality-of-life scores at all checkpoints between groups. All findings are summarized in Table 2 and Fig. 3.

When the groups were analyzed for the presence of neuropathic pain, the data demonstrated that both groups also showed significant improvements. The number of patients with neuropathic pain was 16 before the injection and 8 at the 3rd week in the CESI group (P = 0.012). These values were 16 before the injection and 10 at the 3rd week for the GIB group (P = 0.014). However, in the 3rd month, the GIB group had 15 patients with neuropathic pain, while this number was 14 for the CESI group, and was not significantly different from the initial assessment (P = 0.684 for both analyses). There were no significant differences in each checkpoint between the groups (P = 0.204; P = 0.343).

After the interventions, two patients in the GIB group developed hypotension due to vasovagal reactions. After the short-term follow-up, both patients, whose symptoms were relieved and findings improved, were discharged with recommendations. No other side effects or complications were encountered.

In this study, both GIB and CESI were shown to cause pain reduction in coccygodynia. It was also shown that both methods might have short-term beneficial effects on the neuropathic pain component. These results are a crucial contribution to the literature comparing the effectiveness of both interventional treatment methods prospectively for the first time.

As a sympathetic ganglion, the ganglion impar is the endpoint of the paravertebral sympathetic chain, and subtends the nociception and sympathetic innervation of the perineal region [14]. The efficacy of the GIB as a popular treatment option has been previously shown in many studies [6,15,16]. The GIB can be performed with fluoroscopy, computerized tomography, or ultrasound guidance with no well-defined superiority [17]. In the blockage, a mixture of local anesthetic and steroids can be used, as well as an only local anesthetic. It was preferred to add steroids, as the addition of steroids appeared to produce a greater reduction in pain in a previous comparative study [13]. In this study, it was found that the GIB provided a more significant pain reduction in the 3rd week. The ganglion impar is a relay point that has an important role in sympathetically mediated pain transmission and neuropathic pain pathophysiology. As a more definitive target, GIB may be more beneficial in pain reduction than CESI, which acts as a peripheral mechanism through the sacrococcygeal nerves. Although GIB generally provides an adequate clinical response in patients with coccygodynia from to non-malignant causes, ganglion impar neurolysis or radiofrequency ablation procedure can be applied in patients with persistant pain mostly seen in pelvic and perineal cancers [18]. Neurolytic blocks consist of the destruction of nervous tissue usually through the injection of alcohol or phenol.

CESI is a frequently used treatment method in disorders causing low back pain. Although it is frequently used in clinical practice and stated as a method that can be applied in patients who do not respond to conservative treatment [10,19], there is a shortage of high-quality studies on coccydynia. In a recently published retrospective study, the efficacy of the GIB and CESI combined with transrectal manipulation was compared, and the former was found to be more effective in improving pain sensation and painless sitting periods in a 6-month follow-up [10]. One of the striking results of this study was the limited reduction in pain in the CESI with manipulation group. The effect of CESI on pain reduction can be explained by the relief of pain associated with lumbar pathology and blockage of the sacrococcygeal nerves, which is an important source of pain in coccydynia. There is a close relationship between coccydynia and lumbar pathologies such as disc herniation, disc degeneration, and spinal stenosis as an important target of CESI [1,20]. Pulsed radiofrequency and neuromodulation interventions can also be performed via the caudal epidural route for the sacrococcygeal nerves as a peripheral target [21,22]. Further studies are still needed to understand the effectiveness of CESI and other interventions with a caudal approach in coccygodynia more comprehensively.

Another point to be emphasized about CESI is that there is no consensus on the optimal injectable volume for coccygodynia. In lumbar pathologies, a high volume is preferred due to the distance to the targeted area, but it is thought that clinical benefit can be obtained with a lower volume due to the closeness of the sacral roots in coccygodynia. In addition, it has been reported that complications related to compression such as anosmia and hiccup can be seen due to volume effect in CESI [23,24]. We preferred to use a lower injectable volume, but further studies are needed to examine the effect of volume on clinical outcomes of CESI in patients with coccygodynia. Chronic coccygeal pain can have a neuropathic component that should also be evaluated in order to provide effective pain reduction. It has been previously shown that GIB is effective in decreasing the neuropathic component of pain in chronic coccygodynia with a 6-month follow-up period [8]. In this study, while improvement was observed in both groups in the 3rd week, it was found that this improvement did not persist in the 3rd month. To explain these differences in neuropathic pain outcomes, it must also be kept in mind that the LANSS reflects the presence or absence of neuropathic pain without assessing severity. More objective assessments are needed to better understand all aspects of pain mechanisms. With the possible negative contribution of the neuropathic component of pain, assessment of the quality of life has crucial importance on coccydynia. In this study, the SF-12 physical scores were found to be improved at the 3rd week in both groups. This finding can be explained by a reduction in pain and providing pain-free sitting. However, a recent study found that the SF-12 physical score improved significantly in the 3rd month without associated pain-free sitting, while this improvement was not seen in the 6th month [8]. The point to consider when evaluating differences in results is that existing quality of life measurements are not explicitly made for coccygodynia.

Since there are no well-defined guidelines on the treatment of coccygodynia, the treatment options should be decided considering the positive and negative aspects on an individualized basis. It has been reported that some rare complications such as rectal rupture, neuritis, and cauda equina syndrome may be seen [25], although these decrease under the guidance of imaging. The GIB provides greater pain reduction. However, the risk of disc-related infection (discitis) should also be considered. CESI may be preferred in patients with accompanying low back pain under appropriate conditions. It is important to evaluate clinical and pathophysiological factors that cause coccygeal pain in each patient to determine the most beneficial treatment method.

This study has some limitations. Due to the short follow-up time, it is unclear that efficacy continues for both groups over the long term and whether repeated injections would be required. Different results may have been found in the CESI group, as possible pathologies that may cause low back pain had not been evaluated. Functionality could not be evaluated because of the absence of specific scales directed at chronic coccygodynia. Finally, the study did not include a placebo control group for ethical reasons. Nonetheless, because this is the first comparative, prospective study regarding GIB and CESI, the results of this study should arouse interest in more comprehensive studies.

In conclusion, both the GIB and CESI are useful treatment methods in coccygodynia unresponsive to more conservative treatments. The GIB may provide more significant pain reduction in the short term. Further studies with a long follow-up period and more objective assessments for the neuropathic component of pain are warranted to understand the efficacy of both treatment methods more precisely.