European Spine Journal https://doi.org/10.1007/s00586-021-06911-3

ORIGINAL ARTICLE

Conservative treatment for chronic coccydynia: a 36‑month prospective observational study of 115 patients

Solène Charrière1 · Jean‑Yves Maigne1 · Emmanuel Couzi1 · Marie‑Martine Lefèvre‑Colau1,2,3,4 · François Rannou1,2,5 · Christelle Nguyen1,2,5

Received: 20 February 2021 / Revised: 1 May 2021 / Accepted: 24 June 2021 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021

Abstract Purpose To describe long-term outcomes of conservative treatment for chronic coccydynia. Methods We conducted a 36-month prospective observational study. Adults with chronic coccydynia (> 2 months) were included. The frst-line treatment was coccygeal corticosteroid injection. The second-line treatment was either manual therapy or coccygectomy. The primary endpoint was the mean variation from baseline of coccydynia intensity at 6 and 36 months, using a numeric rating scale (0, no pain; 10, maximal pain). Evolution was considered unfavorable when coccydynia intensity was > 3 of 10 points at 36 months or coccygectomy had been performed. We carried out bivariate and multivariate analyses to identify variables associated with an unfavorable evolution. Results We included 115 participants. Mean (SD) age was 43.5 (12.3) years, duration of coccydynia 18.4 (21.6) months and coccydynia intensity 6.5 (2.0) of 10 points. Mean variations for coccydynia intensity were − 1.5 (3.0) at 6 months and − 2.8 (3.2) at 36 months. At 36 months, 59/115 (51%) participants had an unfavorable evolution. In bivariate analysis, posterior coccyx dislocations were numerically more frequent in participants with an unfavorable evolution compared to others (29/59 (48%) versus 17/56 (30%), p = 0.057). In multivariate analysis, longer duration of coccydynia was associated with an unfavorable evolution (OR = 1.04, 95% CI from 1.01 to 1.07, p = 0.023). Conclusion In adults with chronic coccydynia receiving conservative treatment, symptoms decrease overtime, but signif- cantly persist at 36 months in more than half of them. For patients with posterior coccyx dislocation, coccygectomy may be considered rapidly.

Keywords Chronic back pain · Coccydynia · Prospective observational study

Introduction

* Christelle Nguyen [email protected] Coccydynia is defned as a pain localized to the coccygeal area without signifcant radiation, occurring in the sitting 1 Hôpital Cochin, Service de Rééducation Et de Réadaptation position or when standing up [1]. The surgical treatment has de L’Appareil Locomoteur et des Pathologies du Rachis, AP-HP. Centre-Université de Paris, 27, Rue du Faubourg been evaluated in numerous studies [2–5] and provides good Saint‑Jacques, 75014 Paris, France results in selected cases. Its major criterion of selection is 2 Faculté de Santé, UFR de Médecine, Université de Paris, the failure of conservative treatments. 75006 Paris, France Several conservative treatments have been described, 3 Toxicité Environnementale, Cibles Thérapeutiques, including sitting aids, corticosteroid pericoccygeal [6], Signalisation Cellulaire Et Biomarqueurs (T3S), INSERM intradiscal [7] or spicule injections [8], manual therapy [9], UMR-S 1124, Campus Saint‑Germain‑des‑Prés, 75006 Paris, platelet-rich plasma injections, radiofrequency denervation, France shock wave therapy, capsaicin patches, etc. However, out- 4 Institut Fédératif de Recherche Sur Le Handicap, comes of these treatments have not been fully reported [10]. 75013 Paris, France We aimed to describe long-term outcomes of conserva- 5 Centre de Recherche Épidémiologie Et Statistique Paris tive treatment for chronic coccydynia and to identify vari- (CRESS), ECaMO Team, INSERM UMR-S 1153, ables associated with an unfavorable evolution. 75004 Paris, France

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Methods

Study design

We conducted a 36-month prospective observational study. Endpoints and analyses were prespecifed in the protocol. No changes were made to the methods after the study com- mencement. Our study is reported in accordance with the STROBE statement [11] (Appendix 1). Prospective studies in rare conditions may take a long time to complete through a single-center study. However, considering our expected capacities of recruiting participants and because retrospec- tive research is generally considered methodologically infe- rior to prospective research [12], we decided to design a Fig. 1 Dynamic coccyx X-rays. Left panel: lateral standing flm. prospective study. Right panel: lateral sitting flm taken in the painful position showing a posterior coccyx dislocation (luxation) Participants

Adults (≥ 21 years old) were recruited consecutively from the spicule was absent. The coccygeal corticosteroid injec- January to August, 2015. Inclusion criteria were chronic tion could be repeated twice a year, and sometimes three coccydynia (> 2 months) diagnosed by the same investigator during the frst year. In case of persisting pain (VAS > 3), (xxx) and prospective follow-up data available at 36 months. the second-line treatment was either manual therapy or coc- The diagnostic criteria were localized, midline pain covering cygectomy. The choice of a second-line treatment was not the coccyx area, without signifcant radiation, occurring in based on patient’s decision but on the pathology evidenced the sitting position or when standing up. A rectal examina- by the dynamic flms. Coccygectomy was indicated in case tion was systematic. A coccygeal or pelvic MRI was pre- of persisting pain attributed to posterior coccyx dislocation, scribed in case of diagnostic doubt or of failure of the coc- hypermobility or spicule, and this was considered a failure cygeal injection in patients with normal mobility. Exclusion of the conservative cares. Manual therapy (with a minimum criteria were fractures, pregnancy and non-coccygeal pain. of 2 sessions) was ofered in other cases. All participants Dynamic X-rays (lateral sitting flm taken in the painful received sitting aids and usual care, as prescribed by their position compared to a lateral standing flm) were obtained treating physician. for all participants. X-ray fndings were classifed into four groups: (1) posterior coccyx dislocation (luxation) (Fig. 1), Endpoints (2) hypermobility (fexion > 30°), (3) rigid coccyx (absence of movement; frequently associated with a spicule) and (4) Participants were prospectively followed up for 36 months. normal mobility (fexion < 30°). Participants’ characteristics Primary endpoints were mean variations from baseline of collected at baseline included body mass index and history coccydynia intensity at 6 and 36 months. Secondary end- of provocative factor (i.e., history of traumatism, child deliv- points were mean variations from baseline of coccydynia- ery or rapid weight loss) prior the onset of coccydynia. related symptoms at 6 months. Coccydynia intensity was recorded at baseline, 6 and 36 months using a self-adminis- Interventions tered numeric rating scale (NRS) ranging from 0 (no pain) to 10 (maximum pain). Coccydynia-related symptoms were The frst-line treatment was coccygeal corticosteroid injec- recorded at baseline and 6 months using the self-admin- tion (prednisolone acetate, 2–50 mg) under fuoroscopic istered Paris questionnaire (Appendix 2), ranging from 0 guidance. The anatomical target was determined from the (no symptoms) to 10 (maximum symptoms), and the self- dynamic X-rays. In case of posterior coccyx dislocation or administered modifed Dallas questionnaire (Appendix 3), hypermobility, the target was the unstable disk. In case of ranging from 0 (no symptoms) to 30 (maximum symptoms). normal mobility, the target was the most mobile disk or the This evaluation was not conducted in operated patients. Evo- disk exhibiting a complete pinching in the sitting position. lution was prespecifed as unfavorable when coccydynia In case of a rigid coccyx, the target was the extremity of intensity was > 3 of 10 points at 36 months or coccygec- the coccyx: The injection targeted either the spicule itself tomy was either indicated or performed previously during when present, or around the extremity of the coccyx when the follow-up period. The patient acceptable symptom state for coccydynia intensity is unknown. However, in a previous

1 3 European Spine Journal work, our patient acceptable symptom state estimates were Table 1 Characteristics of adults with chronic coccydynia (n = 115) 47.5 (95% CI 40.0–50.0) of 100 points for lumbar pain and Age (years), mean (SD) 43.5 (12.3)a 30.5 (30.0–40.0) of 100 points for radicular pain [13]. Con- Women, n/N (%) 89/115 (77) sistently, Tubach and colleagues reported in a study of 186 Body mass index (kg/m2), mean (SD) 25.4 (4.7)a patients with back pain that the patient acceptable symptom Duration of coccydynia (months), mean (SD) 18.4 (21.6)a state estimate was 39 (95% CI 38–41) of 100 points for pain Coccydynia when getting up (yes), n/N (%) 76/112 (68) [14]. Based on values previously reported in back pain stud- History of provocative factor (yes), n/N (%) 50/115 (44) ies, and in order to best capture what was most likely a clini- Anatomical fndings, n/N (%) cally acceptable pain in patients with chronic coccydynia, Posterior coccyx dislocation 46/115 (40) we prespecifed our cutof for coccydynia intensity at > 3 of Rigid coccyx (including 21 spicules) 28/115 (24) 10 points to consider an evolution as unfavorable. Hypermobile coccyx 26/115 (23) Statistical methods Normal coccyx mobility 15/115 (13) Symptoms, mean (SD) Coccydynia intensity (0 to 10)‡ 6.5 (2.0)b Statistical analyses were performed using the SYSTAT13 for Paris score (0 to 10)§ 7.0 (1.7)b Windows® software. Quantitative variables were described Modifed Dallas score (0 to 30)§ 14.3 (5.6)b by their means and standard deviations (SD) and qualitative variables by their absolute (n/N) and relative (%) frequen- SD standard deviation cies. For comparative analyses between participants who ‡ Higher scores indicate greater pain had an unfavorable evolution and others, normally distrib- § Higher scores indicate more severe coccydynia-associated symptoms uted quantitative variables were compared using a Student a n = 114; bn = 113 t test, non-normally distributed quantitative variables using a Mann–Whitney test and frequencies using a Fisher exact test. After Bonferroni correction for multiple comparisons Table 2 Number of injections received per patient (N = 112) (20 comparisons), a p-value < 0.05 was considered statis- Number of injections received 1 2 3 4–6 tically signifcant. To identify variables associated with Number of patients, n (%) 30 (27) 55 (49) 17 (15) 10 (9) an unfavorable evolution, we conducted a binary logistic regression. Five baseline variables were selected based on our refective practice: (1) Paris score, (2) modifed Dallas score, (3) duration of coccydynia, (4) coccydynia intensity 28/115 (24%), including 21/115 (18%) with spicule, hyper- and (5) history of provocative factor. We presented the com- mobile coccyx in 26/115 (23%) and normally mobile coccyx plete logistic model. in 15/115 (13%) (Table 1). Each participant received an aver- age of 2.1 (1.0) coccygeal corticosteroid injections (Table 2). Ethical consideration Primary and secondary endpoints All participants in the study provided informed consent. Our study protocol was approved by our ethics committee (xxx). Mean variations for coccydynia intensity were − 1.5 (3.0) of 10 points at 6 months and − 2.8 (3.2) of 10 points at 36 months, and − 1.6 (2.9) of 10 points for Paris score Results and − 2.8 (5.8) of 30 points for modifed Dallas score at 6 months (Table 3). Overall, 33/115 (30%) and 56/115 (49%) Participants participants had coccydynia intensity ≤ 3 of 10 points at 6 and 36 months, respectively. Among participants who had Overall, 141 patients were enrolled: 115/141 (82%) had coccydynia intensity ≤ 3 of 10 points at 6 months, 18/33 prospective follow-up data available at 36 months and were had at least one recurrence of coccydynia during follow- included in analyses (Appendix 4). At baseline, mean age up. Among participants who had coccydynia intensity ≤ 3 was 43.5 (12.3) years, duration of coccydynia 18.4 (21.6) of 10 points at 36 months, 34/56 reported that the thera- months and coccydynia intensity 6.5 (2.0) of 10 points. peutic modality that helped them the most was coccygeal Overall, 89/115 (77%) participants were female and 50/115 corticosteroid injections, 11/56 manual therapy and 11/56 (44%) had a history of provocative factor: 33/115 (29%) had the natural evolution of symptoms. Among 59/115 (51%) a traumatism, 10/115 (9%) a child delivery and 7/115 (6%) other participants with a poor evolution under conservative a rapid weight loss. X-ray fndings were posterior coccyx management, 25/59 had a coccygectomy and 11/59 had a dislocation in 46/115 (40%) participants, rigid coccyx in

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Table 3 Thirty-six-month Symptoms, mean (SD) M6 ΔM6–M0 M36 ΔM36–M0 evolution of symptoms in adults with chronic coccydynia who Coccydynia intensity (0–10)‡ 4.8 (2.8)a − 1.5 (3.0)b 3.4 (2.7)c − 2.8 (3.2)d received conservative treatment Paris score (0–10)§ 5.1 (2.9)e − 1.6 (2.9)f – – Modifed Dallas score (0–30)§ 10.2 (6.8)e − 2.8 (5.8)f – –

Δ mean variation; M month; SD standard deviation ‡ Higher scores indicate greater pain § Higher scores indicate more severe coccydynia-associated symptoms a n = 101; bn = 100; cn = 92; dn = 90; en = 76; fn = 75 pending coccygectomy, leaving 23/59 patients with lasting 10 points versus 6.4 (1.6) of 10 points, p < 0.001 and 16.1 chronic coccyx pain. (5.6) of 30 points versus 12.4 (5.0) of 30 points, p < 0.001, respectively). The percentage of posterior coccyx disloca- Variables associated with an unfavorable tions was higher in participants with an unfavorable evo- evolution (i.e., coccydynia intensity > 3 of 10 points lution at 36 months compared to others (29/59 (48%) ver- at 36 months or coccygectomy) sus 17/56 (30%), p = 0.057) (Table 4). In the multivariate analysis, longer duration of coccydynia was associated with In the bivariate analysis, baseline Paris and modifed Dal- an unfavorable evolution (OR = 1.04, 95% CI from 1.01 las scores were higher in participants with an unfavorable to 1.07, p = 0.023) (Table 5). Descriptive analyses in four evolution at 36 months compared to others (7.6 (1.5) of groups, according to the phenotypes observed on dynamic

Table 4 Variables associated Favorable Unfavorable P-value with evolution at 36 months: ­evolutiona n = 56 ­evolutionb n = 59 bivariate analysis Age (years), mean (SD) 43.7 (13.2)a 42.9 (11.9) 0.690* Women, n/N (%) 44/56 (78.6) 44/58 (75.9) 0.824$ Body mass index (kg/m2), mean (SD) 24.9 (4.4) 25.9 (5.0)b 0.420* Duration of coccygodynia (months), mean (SD) 12.9 (12.1) 23.6 (27.0)b 0.009$ Coccydynia when getting up, n/N (%) 36/56 (64) 40/57 (70) 0.686$ History of provocative factor, n/N (%) 18/56 (32) 32/59 (54) 0.023$ Manual therapy (yes) 15/56 (27) 11/59 (19) 0.374$ Anatomical fndings, n/N (%) Posterior coccyx dislocation 17/56 (30) 29/59 (48) 0.057$ Rigid coccyx (including 21 spicules) 20/56 (25) 8/56 (9) 0.009$ Hypermobile coccyx 14/56 (25) 12/59 (20) 0.657$ Normal coccyx mobility 5/56 (9) 10/59 (14) 0.271$ Symptoms, mean (SD) Coccydynia intensity (0–10)‡ 6.0 (1.9) 7.0 (2) 0.010* Paris score (0–10)§ 6.4 (1.6) 7.6 (2) < 0.001* Modifed Dallas score (0–30)§ 12.4 (5.0) 16.1 (6) < 0.001**

SD standard deviation a Evolution was prespecifed as favorable when coccydynia intensity was ≤ 3 of 10 points at 36 months; bEvolution was prespecifed as unfavorable when coccydynia intensity was > 3 of 10 points at 36 months or coccygectomy was needed * Comparisons between the 2 groups by the Mann–Whitney test ** Comparison between the 2 groups by the Student t test $ Comparisons between the 2 groups by the Fisher’s exact test After Bonferroni correction for multiple comparisons (20 comparisons), the p-value was considered signif- cant when < 0.0025 ‡ Higher scores indicate greater pain § Higher scores indicate more severe coccydynia-associated symptoms a n = 55; bn = 58

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Table 5 Variables associated with coccydynia intensity > 3/10 points injected either the sacrococcygeal disk or the pericoccygeal at 36 months or coccygectomy: multivariate analysis (binary logistic atmosphere [6, 16]. In the absence of a control group, the regression) efects we observed cannot be univocally attributed to the Odds ratio 95% CI P-value treatments received. However, in a randomized controlled trial on coccygeal manipulation, improvement was observed Paris score 1.39 0.96–1.99 0.078 in only 12% of the patients in the placebo group [10], indi- Modifed Dallas score 1.06 0.97–1.17 0.205 cating that the magnitude of the placebo efect in chronic Duration of coccydynia 1.04 1.01–1.07 0.023 coccydynia may be limited. Another limitation is that we did Coccydynia intensity 1.02 0.77–1.34 0.907 not collect data regarding medicolegal litigation or employ- History of provocative factor 0.48 0.20–1.16 0.103 ment status, which could have had an impact on long-term CI confdence interval evolution. A p-value < 0.05 was considered statistically signifcant We observed a global improvement in coccydynia inten- sity (i.e., pain ≤ 3 of 10 points) in 30% of the participants at 6 months and in 49% at 36 months. Our fndings are consist- X-rays, show that the percentages of unfavorable evolution at ent with those of Kleimeyer and colleagues who reported 36 months were 29/46 (63%) in those with posterior coccyx an improvement in 43% of patients at 2 years [5]. With a dislocation (p = 0.057), 12/26 (47%) in those with hypermo- less stringent defnition of favorable evolution (“asympto- bile coccyx (p = 0.657), 8/28 (29%) in participants with rigid matic patient at the 3-month review”), Wray and colleagues coccyx (p = 0.009) and 10/15 (66%) in those with normally reported a favorable evolution in 85% of patients under con- mobile coccyx (p = 0.271). Thus, the patients with a rigid servative treatment [6]. Conservative treatment is a long pro- coccyx had the best results and those with a dislocation or cess, due to frequent recurrences of symptoms, requiring a normal coccyx the worse. In the 50 participants with a repeated coccygeal corticosteroid injections or repeated ses- history of provocative factor, the percentage of unfavorable sions of manual therapy. However, it should be considered evolution at 36 months was 32/50 (64%) (p = 0.023). before coccygectomy, as it helps almost half of the patients. Both conservative and surgical approaches are not in concur- rence, but are complementary. In our study, among 59/115 Discussion (51%) participants who had an unfavorable evolution, 25/59 had a coccygectomy (including 20 for posterior coccyx dis- In the present study, we found that symptoms decreased location) and 11/59 had a pending coccygectomy. In light of overtime, but that the conservative management had sig- surgical studies, their prognosis is good. Remaining 23/59 nifcantly failed at 36 months in more than half of adults patients were in failure of conservative treatment and had no with chronic coccydynia. A longer duration of coccydynia surgical indication, because dynamic X-rays were normal before enrollment was associated with an unfavorable evolu- and/or the pain was too difuse. Ten of them were ofered a tion at 36 months. blockade of the ganglion impar. Our primary purpose was to determine the long-term Our secondary purpose was to identify prognostic factors. clinical outcomes of adults with chronic coccydynia treated In bivariate analysis, we found that higher Paris and modi- conservatively. In a review of diferent modalities of con- fed Dallas scores were associated with an unfavorable evo- servative treatment, Howard and colleagues found 7 studies lution under conservative treatment at 36 months. Posterior with a follow-up ranging from 10 days to 9 months [10]. Our coccyx dislocations, when managed conservatively, were follow-up of 36 months was longer than those previously more frequently associated with an unfavorable evolution at reported and may allow a more comprehensive characteriza- 36 months, supporting to consider coccygectomy earlier in tion of the evolution of symptoms under conservative treat- this situation. Conversely, rigid and hypermobile were more ment, especially since the recurrence of symptoms is fre- frequently associated with favorable evolution, supporting quent [6, 15]. Wray and colleagues reported that recurrence to consider conservative treatments in these situations. In occurred during the frst year in 21% of patients who had a multivariate analysis, longer duration of coccydynia was successful coccygeal corticosteroid injection and in 28% of associated with an unfavorable evolution at 36 months. This patients who had a successful manipulation [6]. The rate of fnding is in line with other studies [9, 15]. recurrence we found (55%) was worse than those previously Our study has some limitations including no control reported, but it seems to us that recurrence became rarer over group, no external evaluators, no MRI studies ruling out time. Less intense symptoms at 36 months than at 6 support other diagnosis and lack of minimal important clinical dif- our hypothesis. ference assessment. Our coccygeal corticosteroid injection techniques were In summary, for the frst time, a study on conservative diferent from those reported by others, who systematically treatment for chronic coccydynia, combining systematic

1 3 European Spine Journal coccygeal corticosteroid injections and manual therapy predictive factor of an unfavorable evolution at long-term only when indicated, is presented with an extended follow- is the longer duration of coccydynia. The overall progno- up of 36 months. Recurrences of symptoms are frequent sis is good, since only 23/115 (20%) patients in our study but decrease over time, supporting the value of a long-term were in failure of conservative treatment and had no surgical follow-up and of repeated coccygeal corticosteroid injec- indication. tions or sessions of manual therapy, when needed. The main

Appendix 1 Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement

Item No Recommendation Page No

Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or 1 the abstract (b) Provide in the abstract an informative and balanced summary of 3 what was done and what was found Introduction Background/rationale 2 Explain the scientifc background and rationale for the investigation 4 being reported Objectives 3 State specifc objectives, including any prespecifed hypotheses 4 Methods Study design 4 Present key elements of study design early in the paper 4 Setting 5 Describe the setting, locations, and relevant dates, including periods of 4 recruitment, exposure, follow-up, and data collection Participants 6 (a) Cohort study—Give the eligibility criteria, and the sources and 4, 5 methods of selection of participants. Describe methods of follow-up Case–control study—Give the eligibility criteria, and the sources and methods of case ascertainment and control selection. Give the ration- ale for the choice of cases and controls Cross-sectional study—Give the eligibility criteria, and the sources and methods of selection of participants (b) Cohort study—For matched studies, give matching criteria and num- NA ber of exposed and unexposed Case–control study—For matched studies, give matching criteria and the number of controls per case Variables 7 Clearly defne all outcomes, exposures, predictors, potential confound- 5, 6 ers, and efect modifers. Give diagnostic criteria, if applicable Data sources/measurement 8* For each variable of interest, give sources of data and details of methods 5–6 of assessment (measurement). Describe comparability of assessment methods if there is more than one group Bias 9 Describe any eforts to address potential sources of bias NA Study size 10 Explain how the study size was arrived at NA Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If 6 applicable, describe which groupings were chosen and why Statistical methods 12 (a) Describe all statistical methods, including those used to control for 6 confounding (b) Describe any methods used to examine subgroups and interactions NA (c) Explain how missing data were addressed NA (d) Cohort study—If applicable, explain how loss to follow-up was NA addressed Case–control study—If applicable, explain how matching of cases and controls was addressed Cross-sectional study—If applicable, describe analytical methods taking account of sampling strategy (e) Describe any sensitivity analyses NA

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Item No Recommendation Page No Participants 13* (a) Report numbers of individuals at each stage of study—eg num- 6, Appendix 4 bers potentially eligible, examined for eligibility, confrmed eligible, included in the study, completing follow-up, and analysed (b) Give reasons for non-participation at each stage 6, Appendix 4 (c) Consider use of a fow diagram 6, Appendix 4 Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, 6, Table 1 social) and information on exposures and potential confounders (b) Indicate number of participants with missing data for each variable Tables 1, 2 and 3 of interest (c) Cohort study—Summarise follow-up time (eg, average and total NA amount) Outcome data 15* Cohort study—Report numbers of outcome events or summary meas- Table 2 ures over time Case–control study—Report numbers in each exposure category, or NA summary measures of exposure Cross-sectional study—Report numbers of outcome events or summary NA measures Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted Table 2 estimates and their precision (eg, 95% confdence interval). Make clear which confounders were adjusted for and why they were included (b) Report category boundaries when continuous variables were catego- NA rized (c) If relevant, consider translating estimates of relative risk into abso- NA lute risk for a meaningful time period Other analyses 17 Report other analyses done—e.g. analyses of subgroups and interactions, NA and sensitivity analyses Key results 18 Summarise key results with reference to study objectives 8 Limitations 19 Discuss limitations of the study, taking into account sources of potential 8, 9 bias or imprecision. Discuss both direction and magnitude of any potential bias Interpretation 20 Give a cautious overall interpretation of results considering objectives, 8, 9, 10 limitations, multiplicity of analyses, results from similar studies, and other relevant evidence Generalisability 21 Discuss the generalisability (external validity) of the study results 8, 9 Other information Funding 22 Give the source of funding and the role of the funders for the present 13 study and, if applicable, for the original study on which the present article is based

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Appendix 2 Paris self‑administered 2) Professional activities. How much does your pain inter- questionnaire. Score ranging from 0 (no fere with your work? symptoms) to 10 (maximal symptoms) • Not at all (0) Circle the number which best describes your response. To • A little (1) ensure that your questionnaire will count, please answer all • Moderately (2) 6 questions. • A lot (3)

1) When Iamsitting: 3) Self-control. How well are you in control of your emo- Ihavenopain (0) tional reactions? Ihaveslight discomfort (1) I can onlysit in certain positions (2) • Totally (0) • Often (1) 2) When Iamsitting: • I’m having trouble (2) Ihavenopain (0) • I can’t do it (3) Ifeelpainafter 30 minutes or more (1) Ifeelpainvery quickly,wellbefore30minutes (2) 4) Anxiety/morale. How well do you feel you are dealing with what is required of you? 3) Traveling by car: Travelingis not uncomfortable (0) • Totally (0) The pain is bearable (1) • Often (1) The pain quickly becomes unbearable (2) • I’m having trouble (2) • I can’t do it (3) 4) When standing up from sitting: Ido not feel anyworse than when Iamsitting (0) 5) Worry. How worried are you about your tailbone pain? Standing up from sittingispainful (1) Standing up from sittingisextremely painful (2) • Not at all (0) • A little (1) 5) Standing stillorwalking: • Moderately (2) Ihavenopaininmycoccyx (0) • A lot (3) Iaminpain (1) 6) Stress. How stressed do you feel you are about your 6) At night: Ihavenopainduringthe night (0) tailbone pain? I can getwoken by pain during the night(1) • Not at all (0) • A little (1) • Moderately (2) • A lot (3) Appendix 3 Modifed Dallas self‑administered questionnaire. Score 7) Depression. How depressed have you been since the ranging from 0 (no symptoms) to 30 pain? (maximal symptoms) • Not at all (0) • A little (1) For each question, tick the answer that best suits you. • Moderately (2) 1) Social activity. How much does your pain interfere • A lot (3) with your social life (dancing, games and entertainment, meals or parties with friends, going out, etc.)? 8) Relationships with others. How much do you think your pain has changed your relationship with others? • Not at all (0) • A little (1) • Not at all (0) • Moderately (2) • A little (1) • A lot (3) • Moderately (2)

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• A lot (3) 10) Adverse reactions of relatives. How do you feel that your pain causes irritation, annoyance, anger towards you 9) Support from others. How much support do you need in those around you? from others since your pain (housekeeping, meal prepara- tion, etc.)? • Not at all (0) • A little (1) • Not at all (0) • Moderately (2) • A little (1) • A lot (3) • Moderately (2) • A lot (3)

Appendix 4 Flow diagram

Author contributions SC, JYM, CN contributed to conception and Funding None. design of the study. JYM and CN contributed to drafting of the original protocol. CN contributed to design of the statistical analysis plan. JYM Declarations contributed to coordination of the study. JYM contributed to acquisi- tion of data. SC, JYM and CN contributed to drafting of the present Conflict of interest The authors declare that they do not have any con- manuscript. EC, MMLC and FR contributed to reviewing and provid- fict of interest. ing comments on the manuscript. SC, JYM, EC, MMLC, FR and CN contributed to fnal approval.

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Ethics approval (include appropriate approvals or waivers). Our study discography. Spine 19:930–934. https://​doi.​org/​10.​1097/​00007​ protocol was approved by our ethics committee (CERAP-HP.5). 632-​19940​4150-​00011 8. Maigne JY, Doursounian L, Chatellier G (2000) Causes and Consent to participate (include appropriate statements) All partici- mechanisms of common coccydynia: role of body mass index pants in the study provided informed consent. and coccygeal trauma. Spine 25:3072–3079. https://​doi.​org/​10.​ 1097/​00007​632-​20001​2010-​00015 Consent for publication (include appropriate statements) All authors 9. Maigne JY, Chatellier G, Faou ML, Archambeau M (2006) The listed provided fnal written approval of the version to be published and treatment of chronic coccydynia with intrarectal manipulation: a agreement to be accountable for all aspects of the work in ensuring that randomized controlled study. Spine 31:E621-627. https://doi.​ org/​ ​ questions related to the accuracy or integrity of any part of the work 10.​1097/​01.​brs.​00002​31895.​72380.​64 are appropriately investigated and resolved. 10. Howard PD, Dolan AN, Falco AN, Holland BM, Wilkinson CF, Zink AM (2013) A comparison of conservative interventions and Availability of data and material (data transparency) Academic their efectiveness for coccydynia: a systematic review. J Man researchers can request access to data and material by contacting Manip Ther 21:213–219. https://​doi.​org/​10.​1179/​20426​18613y.​ Associate Professor Christelle Nguyen at [email protected]. 00000​00040 11. von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Van- denbroucke JP (2007) The strengthening the reporting of obser- vational studies in epidemiology (STROBE) statement: guide- References lines for reporting observational studies. Lancet 370:1453–1457. https://​doi.​org/​10.​1016/​s0140-​6736(07)​61602-x 12. Koop PM, Strang V (2002) Prospective and retrospective research: 1. Maigne JY, Tamalet B (1996) Standardized radiologic proto- considerations and questions. Can Oncol Nurs J 12:142–145 col for the study of common coccygodynia and characteristics 13. Daste C, Abdoul H, Foissac F, Lefèvre-Colau MM, Poiraudeau of the lesions observed in the sitting position. Clinical elements S, Rannou F, Nguyen C (2020) Patient acceptable symptom state diferentiating luxation, hypermobility, and normal mobility. for patient-reported outcomes in people with non-specifc chronic Spine 21:2588–2593. https://​doi.​org/​10.​1097/​00007​632-​19961​ low back pain. Ann Phys Rehabil Med. https://​doi.​org/​10.​1016/j.​ 1150-​00008 rehab.​2020.​10.​005 2. Doursounian L, Maigne JY, Faure F, Chatellier G (2004) Coc- 14. Tubach F, Ravaud P, Martin-Mola E, Awada H, Bellamy N, Bom- cygectomy for instability of the coccyx. Int Orthop 28:176–179. bardier C, Felson DT, Hajjaj-Hassouni N, Hochberg M, Logeart I, https://​doi.​org/​10.​1007/​s00264-​004-​0544-3 Matucci-Cerinic M, van de Laar M, van der Heijde D, Dougados 3. Hofstetter CP, Brecker C, Wang MY (2015) Coccygectomy: cur- M (2012) Minimum clinically important improvement and patient rent views and controversies. Contemp Spine Surgery 16:1–5. acceptable symptom state in pain and function in rheumatoid https://​doi.​org/​10.​1097/​01.​css.​00004​62791.​73066.​41 arthritis, ankylosing spondylitis, chronic back pain, hand osteoar- 4. Kerr EE, Benson D, Schrot RJ (2011) Coccygectomy for chronic thritis, and hip and knee osteoarthritis: Results from a prospective refractory coccygodynia: clinical case series and literature review. multinational study. Arthritis Care Res (Hoboken) 64:1699–1707. J Neurosurg Spine 14:654–663. https://​doi.​org/​10.​3171/​2010.​12.​ https://​doi.​org/​10.​1002/​acr.​21747 spine​10262 15. Hodges SD, Eck JC, Humphreys SC (2004) A treatment and out- 5. Kleimeyer JP, Wood KB, Lønne G, Herzog T, Ju K, Beyer L, Park comes analysis of patients with coccydynia. Spine J 4:138–140. C (2017) Surgery for refractory coccygodynia: operative versus https://​doi.​org/​10.​1016/j.​spinee.​2003.​07.​011 nonoperative treatment. Spine 42:1214–1219. https://​doi.​org/​10.​ 16. Mitra R, Cheung L, Perry P (2007) Efcacy of fuoroscopically 1097/​brs.​00000​00000​002053 guided steroid injections in the management of coccydynia. Pain 6. Wray CC, Easom S, Hoskinson J (1991) Coccydynia. Aetiology Physician 10:775–778 and treatment. J Bone Joint Surg Br 73:335–338. https://​doi.​org/​ 10.​1302/​0301-​620x.​73b2.​20051​68 Publisher’s Note Springer Nature remains neutral with regard to 7. Maigne JY, Guedj S, Straus C (1994) Idiopathic coccygodynia. jurisdictional claims in published maps and institutional afliations. Lateral roentgenograms in the sitting position and coccygeal

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