Objective: Coccydynia is a disorder that decreases quality of life with significant functional failure. Extra-corporeal shock wave therapy (ESWT) is used to treat several painful musculoskeletal disorders. Subjects and Methods: The medical records of 34 patients (29 females, 5 males) who had been treated with ESWT between 2017 and 2018 for chronic coccydynia were evaluated. Visual analog scale (VAS) scores were noted at the initial consultation, at each session, and during the initial and follow-up (at 6 months) examinations after the treatment. The 36-item short form (SF-36) quality of life scale survey was conducted at the beginning and end of the treatment. MRI was performed before the start of the procedure and 1 month after the end of the treatment. Results: The mean VAS score was 9.6 (9–10) before the treatment and 3.4 (0–2) after the treatment (p < 0.05). The VAS score decreased to ≤3 in 79.4% of patients. Bone marrow edema regressed in 6% of patients. Significant improvement was observed in all of the SF-36 parameters, except for two. Conclusion: In our patient group, ESWT provided effective pain control. In order to evaluate the efficacy of ESWT more accurately and sensitively, prospective randomized studies with longer follow-up periods, in which ESWT is compared with different energy doses and different treatment methods, are needed.
Highlights of the Study
Existing literature does not explain the mechanism of extracorporeal shock wave therapy (ESWT) in reducing coccydynia.
This study shows that ESWT is a convenient, cost-effective method with low complication rates.
ESWT provides effective pain control for chronic coccydynia.
The coccyx is the terminal portion of the spine and consists of four or five segments. It is associated with the fifth sacral and coccygeal nerve roots and the terminal sympathetic plexus. Coccydynia is defined as pain in the coccyx and/or coccygeal joints [1-5]; it is five times more common in women than in men . Pain related to coccydynia is aggravated by sitting or prolonged sitting in the same position and cycling [1, 3, 7].
Coccydynia most commonly occurs after a traumatic event, but it also has less common non-traumatic etiologies. A fall on to the tailbone and subsequent non-union of the fracture is the most common cause [1, 3, 7]. Repetitive microtrauma, like childbirth, can also lead to pain and may help explain the increased incidence in women . Repetitive microtrauma and infant delivery are other common causes [3, 4, 7]. The pain may also be related to lumbar stenosis and disk degeneration [1-3]. Rare etiologies, including chordoma or intradural schwannoma, infection, and idiopathic pain, may lead to coccydynia [1, 8-10].
It is typically treated conservatively with modalities such as anti-inflammatory drugs, rest, use of a seating ring, hot water bath, physical therapy, massage, injection of a local anesthetic, or glucocorticoids to the coccyx, and manipulations [1, 6]. Coccygectomy is rarely recommended for patients who do not benefit from conservative treatment [1, 6, 9, 11].
Extracorporeal shock wave therapy (ESWT) is a convenient, cost-effective treatment method with low complication rates . It has been used successfully in the treatment of various musculoskeletal disorders, from non-union of fractures to chronic tendinopathies, calcific tendinitis of the shoulder, lateral and medial epicondylitis, avascular necrosis of the femoral head, jumper’s knee, achilles tendinopathy, plantar fasciitis, and calcaneal spur. The exact mechanism by which ESWT reduces pain caused by musculoskeletal conditions is unclear at this time [12-14], and only a few studies have investigated ESWT for the treatment of coccydynia. Furthermore, ESWT for coccydynia is not standardized in terms of the dose and number of shots. The aim of this study was to evaluate the efficacy of ESWT in the treatment of coccydynia.
Subjects and Methods
This retrospective study was approved by our institutional review board, and informed consent was obtained from the patients. The medical records of patients who had received ESWT for chronic coccydynia were evaluated. Thirty-four patients (mean age 39 years, range 16–62; 5 men, 29 women) were included in the study. The mean duration of their pain was 26.2 months (range 2–120). The inclusion criteria were as follows: skeletal maturity, ongoing pain in the coccyx and/or coccygeal joints despite conservative treatment, and completion of all required ESWT sessions. Conversely, the exclusion criteria were as follows: injection history in the last 3 months (e.g., corticosteroids, autologous blood, platelet-rich plasma, mesotherapy, and dry needling neural therapy), pregnancy, severe coagulopathy, chronic pain conditions (e.g., fibromyalgia and polymyalgia rheumatica), fracture or severe trauma history, and follow-up loss.
Before the treatment, all of the patients reported the intensity of their pain using a visual analog scale (VAS), with scores ranging from 0 to 10 (0 for no pain and 10 for the worst pain) [15-17]. Their VAS scores were further evaluated at the end of the treatment and during the first and sixth months after treatment.
The 36-item short form (SF-36) quality of life scale survey was employed at the beginning and end of the treatment . The SF-36 survey is a self-reporting survey with 36 questions that assess eight dimensions of health, including physical functioning, social functioning, physical and emotional difficulties, mental health, vitality, pain, and general perception of health. The scale score ranges between 0 and 100 points, with higher scores indicating better health.
Before the treatment, all patients underwent a detailed physical examination. Anteroposterior and lateral radiographs of the lumbar spine, sacrum, and coccyx were obtained to evaluate the position of the coccyx and to exclude major coccygeal dislocations. Magnetic resonance imaging (MRI) scans of the lumbar spine, sacrum, and coccyx were obtained using a 1.5-T magnet (Signa Excite HDx, GE Medical Systems, Waukesha, WI, USA) to exclude lumbar spinal pathologies, such as disc herniation or other causes of medulla spinalis or nerve root compression, neoplastic process, fractures, bone bruises, osteoporotic insufficiency, bursitis, and osteophyte formation. The presence of bone marrow edema was also evaluated by MRI and looking specifically at the sagittal planers of the short TI inversion recovery sequences. The MRI scans were evaluated by one author (M.C.G.), who is a highly experienced radiologist in musculoskeletal disorders. MRI was repeated 1 month after ESWT. Bone marrow and soft-tissue edemas were diagnosed on the basis of hyperintense signals on the short tau inversion recovery images .
Prior to ESWT, all patients were treated with steroid injections, manual manipulation, sitting wheel, physical therapy, or non-steroid medication administration; all treatments were stopped immediately prior to the ESWT sessions. ESWT was performed once a week using the same device (Physiomed Elektromedizin AG, Schnaittach, Germany) and by the same physician (C.G.A.). The patients received ESWT with focused shock wave therapy delivering 3,000 shock waves of 0.2 mJ/mm2 directed to the maximal point of tenderness on the coccyx. The probe was placed in a direct 90-degree contact with the coccyx in the sagittal plane in the intergluteal cleft. During the ESWT sessions, the patients were lying in the lateral position with both hips and knees flexed to the maximum possible degree to achieve good exposure to the sacrococcygeal region. The treatment was terminated when the VAS score decreased to ≤3. The duration of the treatment was individualized depending on the VAS scores of the patients during the course of the treatment.
The patients had their first follow-up session 1 month after treatment. Thereafter, they were evaluated at 6-month intervals. Only the first- and sixth-month follow-up outcomes were evaluated, as not all patients reached a third follow-up session. The VAS scores and the SF-36 quality of life scale scores were recorded at the beginning of the treatment, during each ESWT session, and at the first- and sixth-month follow-ups after the treatment. The patients’ activities were not restricted during and after the treatment. The use of anti-inflammatory drugs was prohibited during the treatment.
Data were evaluated using SPSS for Windows 21.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistics were calculated as frequencies and percentages for categorical variables and as means, standard deviations (SDs), and medians for numerical variables. The distribution of the variables was evaluated using the Kolmogorov-Smirnov test. The Wilcoxon test was performed to analyze the dependent quantitative data and the McNemar test to analyze the dependent qualitative data. The significance level was set at 0.05.
A total of 34 patients (29 women; 5 men) were analyzed. The baseline characteristics of the patients are shown in Table 1. ESWT was terminated in the patients when their VAS scores decreased to ≤3. This occurred after the 4th session in 2 patients, after the 5th for 2 patients, after the 6th for 6 patients, after the 7th for 3 patients, after the 8th for 6 patients, after the 9th for 3 patients, and the 10th for 5 patients. The majority of patients completed their treatment in 6–8 sessions. The number of patients who completed their treatment during each session and their VAS scores are shown in Table 2.
A significant decrease was found in the VAS score when the scores from the second, third, fourth, and last sessions and the first- and sixth-month follow-up sessions were compared with the VAS score before the treatment (p < 0.05). Only the VAS scores noted during the second, third, and fourth sessions were included in the statistical evaluation because only the first four sessions of the treatment were completed in all patients. There were significant decreases in the VAS scores between the second and third sessions (p < 0.05), the third and fourth sessions (p < 0.05), and the fourth and last sessions (p < 0.05). There was no significant difference in the VAS score between the last session and first follow-up session (p > 0.05), nor between the first- and sixth-month follow-up sessions (p > 0.05). The results of the statistical evaluation are shown in Table 3. The decreasing trends of the VAS score during the treatment are shown in Figure 1 (decreasing trend of the mean VAS score). The pain intensity increased in 5 patients during the first two sessions of the treatment. Pain relief was not achieved in 1 of these patients at the end of the treatment; the remaining 4 patients benefited from the treatment in the latter phase.
The post-treatment scores for physical functioning, role limitations owing to physical health, role limitations owing to emotional problems, social functioning, pain, general health, and health changes significantly increased compared with the pretreatment scores (p < 0.05). The scores for energy/fatigue and emotional well-being did not significantly change after the treatment (p > 0.943, p > 0.286; Table 4; Fig. 2: changes in SF-36 scores before and after the treatment).
MRI revealed bone marrow edema in 32.4% of the patients before the treatment and 26.5% of the patients after the treatment, and this did not reach clinical significance (p = 0.5). There was no significant correlation between the duration of pain and number of ESWT sessions (p =0.431, r = 0.139) and between the patients’ age and number of ESWT sessions (p = 0.826, r = 0.039).
The mechanism underlying pain relief after ESWT is not clearly understood, and many theories have been formulated on such. One theory regarding the efficacy of ESWT in tendinopathy is that it promotes increased tissue regeneration through the induction of mechanotransduction on the cytoskeleton and the stimulation of protein synthesis . ESWT facilitates tendon repair through upregulating extracellular matrix biosynthesis and increasing the expression of TGFβ1 and IGF-I. ESWT also decreases the levels of inflammatory mediators (interleukins and matrix metalloproteinases) and promotes vascularization of the injured tendon junction to promote tissue healing. ESWT has an effect on pain transmission by acting on substance P. ESWT can support neovascularization by increasing the expression of factors including vascular endothelial growth factor, endothelial nitric oxide synthase, and proliferating cell nuclear antigen [21-25].
ESWT has been previously suggested as an effective modality in relieving pain in the early phases of refractory chronic coccydynia. Marwan et al.  inducted the first study to investigate the efficacy of ESWT in treating coccydynia and included only 2 patients. They performed ESWT in 2 patients with coccydynia and found that it was effective in relieving the pain caused by this disorder. In their study, ESWT was performed once a week for 3 weeks at 3,000 shock waves of 0.2 mJ/mm2 per session directed to the maximal point of tenderness. Pain relief was achieved, and the pain did not recur within the 1-year follow-up period. In our study, no relapse of pain was observed at the sixth-month follow-up session. There was no significant difference in the VAS score between the first- and sixth-month follow-up sessions. We postulate that the pain intensity increased in these patients owing to the induction of inflammation by ESWT. The induction of inflammation has been suggested as a mechanism attributed to the effect of ESWT .
Another study performed in 23 patients with coccydynia who were followed up for 6 months after ESWT reported that ESWT had provided partial relief of pain and disability (disability was deliberately focused on physical activities and not the psychological consequences of acute or chronic pain) in the majority of the patients . The numerical pain scale and Oswestry disability index were used to evaluate the clinical outcome. In our study, we used the SF-36 survey, which is widely used for quality of life assessment. The energy/fatigue and emotional well-being scores did not change significantly after the treatment. Emotional state and feeling of fatigue are parameters that can change daily and be affected by environmental factors. In general, it is claimed that physical therapy has a placebo effect and creates a pseudo-state of well-being and dependency in patients. As such, we postulate that ESWT does not yield major changes in emotional state and does not cause a false healing effect in patients. Conversely, we found significant differences in the other seven parameters of the SF-36 survey. We also observed significant improvements in the functional parameters of the patients.
In a different study including 10 patients with chronic coccydynia, four sessions of ESWT were performed 1 week apart (3,000 shock waves per session of 2-bar pressure and 21-Hz frequency using a radial probe). The VAS score was assessed at the first, second, third, and fourth weeks after the initiation of the treatment and at 1 and 6 months after the last ESWT session. A significant decrease in the VAS score at 4 weeks (p = 0.007) and 2 months (p = 0.007) was observed; however, no significant decrease was detected at 7 months after the last ESWT session when compared with the baseline (p = 0.011) . In our study, we applied a minimum of four and a maximum of 10 sessions of ESWT until the VAS score decreased to ≤3. The desired VAS score was obtained in 27 patients. Seventy-nine percent of the patients had successful results. There was no change in the VAS scores in 5 patients; these patients exhibited periodic well-being during the 10 sessions. However, their VAS scores still did not decrease to ≤3. We observed that recovery was still in progress at the follow-up session (at 6 months; p = 0.0001).
ESWT has been reported to be useful in chronic coccydynia as it increases blood circulation and tissue regeneration. It has also been emphasized that ESWT should be adjusted according to the dose and duration required by the individual . In previous studies, ESWT was generally performed in three or four sessions. The pain relief started after the fourth session in our study. Therefore, we recommend more ESWT sessions for patients with chronic coccydynia. We consider that this result is important and must be considered while establishing a standard protocol for ESWT.
Maier et al.  evaluated MRI results before and after ESWT in the calcaneus and suggested bone marrow edema as an important determinant in the follow-up after ESWT. In our study, we followed a similar method to classify bone marrow edema according to the signal intensity increase. We did not observe any worsening of bone marrow edema in any patients. Severe regression (decrease of signal intensity) of bone marrow edema was observed in only 2 patients; however, there was no significant difference. Based on our results, ESWT does not worsen bone marrow edema. Thus, bone marrow edema shown on MRI may not be associated with the exact therapeutic effect of ESWT.
Our study has some limitations, including its retrospective, non-blinded, and non-randomized design. The study population was limited because of the low incidence of the disorder. Bone marrow and soft-tissue edemas were diagnosed on the basis of hyperintense signals on the short tau inversion recovery images. No repeatability study was undertaken for scoring the images. In addition, longer follow-up periods are required to determine the long-term results.
ESWT is a cost-effective treatment method with low rates of complication . In our study, ESWT provided effective pain control for chronic coccydynia. To evaluate the efficacy of ESWT more accurately and sensitively, prospective randomized studies with longer follow-up periods are needed; these studies must compare the efficacy of ESWT at different energy doses with those of other treatment methods. Each patient’s response to the treatment may be different at the different stages of the treatment. In addition, an increase in pain intensity may be observed owing to inflammation at the beginning of the treatment. Therefore, in such cases, the treatment should not be terminated, concluding that ESWT is not effective. More sessions may be needed to observe the effect of ESWT. Based on our results, at least four sessions of ESWT should be applied to achieve a successful outcome.
The authors would like to thank Can Tulpar for his assistance with data collection and research.
Statement of Ethics
This study was granted ethical approval by the Institutional Review Board of Metin Sabanci Baltalimani Bone Diseases Education and Research Hospital, Turkey.
The authors have no conflicts of interest to declare.
C.G.A, Y.E.A.: conceptualization, writing – original draft preparation. C.G.A., A.Ö., M.C.G., Y.E.A.: investigation.