Surg Radiol Anat (2007) 29:683–687 DOI 10.1007/s00276-007-0262-9 ME DICAL IMAGING Intercoccygeal angle and type of coccyx in asymptomatic patients Ulku Kerimoglu · Merve Gulbiz Dagoglu · Fatma Bilge Ergen Received: 15 February 2007 / Accepted: 10 September 2007 / Published online: 26 September 2007  Springer-Verlag 2007 Abstract Purpose To assess the intercoccygeal angle of asymptomatic patients (without coccydynia), to study if there is a diVerence of angle between types of coccyx and between genders with the same type of coccyx. Materials and methods Ninety-two patients (42 females, 50 males, range of ages 8–86, mean 50) who underwent computed tomography (CT) angiography and colonoscopy were included in the study. CT images with slice thickness of 1 or 1.5 mm were evaluated with 3D sagittal reformats and intercoccygeal angle, type of coccyx were examined. Results Twenty-one females and 18 males had type 1 coccyx with mean intercoccygeal angle 36.4° § 10.56 (33.29° for females and 40.05° for males) and the diVerence of the angles between genders is statistically signiWcant (P = 0.044). Among 36 patients (14 were females and 22 were males) with type 2 coccyx demonstrated mean intercoccygeal angle of 56.36° § 10.8. 15 patients were shown to have type 3 coccyx and the mean intercoccygeal angle was 72.1° § 31.86. No signiWcant diVerence of angles was seen between genders. Type 4 coccyx was not seen and two coccyx could not be classiWed. There was a signiWcant diVerence of intercoccygeal angle between the groups overall. Conclusion Type 1 is the most common coccyx type in asymptomatic patients. SigniWcant diVerence of intercoccygeal angle was deWned between the types of coccyx. These values may be reference for the patients underwent surgery for the coccydynia and a new classiWcation may be needed since exceptional shape of coccyx exists that could not be deWned according to the known classiWcation. U. Kerimoglu (&) · M. G. Dagoglu · F. B. Ergen Department of Radiology, Hacettepe University, School of Medicine, Sihhiye, 06100 Ankara, Turkey e-mail: ulku09@yahoo.com Keywords Coccyx · Intercoccygeal angle · Coccydynia · Computed tomography · Anatomy Introduction Intercoccygeal angle is deWned as the angle between the Wrst and last segment of the coccyx [12]. Kim et al reported that this angle is a useful radiological measurement, which can accurately assess the increased angular deformity of the coccyx. They also concluded the signiWcant diVerence between the intercoccygeal angles measured in patients suVering from coccydynia and asymptomatic population in their study [12]. Coccydynia Wrst described by Simpson is the painful condition of coccyx [19]. This condition varying in intensity can severely limit the physical activities and therefore does a clinical entity deserve to be studied. Although there are questions regarding clinical importance of intercoccygeal angle arised by the previous studies, there are no further studies done focusing on normal population in order to assess a mean value for the intercoccygeal angle, which can be taken as a reference value. A radiological classiWcation of coccyx has been published by Postacchini et al: grade 1 is slightly forward curved, grade 2 is more markedly curved, with the coccyx pointing straight forward, grade 3 is sharply angled anteriorly and grade 4 shows subluxation of sacrococcygeal or intercoccygeal joints [17]. The study done shows that grade 3 and 4 are more prone to coccydynia [17]. However this is a classiWcation depending on description. There are no measurements taken demonstrating the diVerence between the groups objectively. Previous studies about coccyx mostly focused on pathologic conditions, the etiology and radiologic classiWcation [2, 4, 12, 14, 16, 19]. One of these 123 684 Surg Radiol Anat (2007) 29:683–687 studies demonstrated the diVerence between measurements taken from normal population and patients with coccydynia. In their study, they did not show any relation between the diVerent groups of coccyx in their control group of asymptomatic patient. Also to the best of our knowledge there is no study implying on whether there is a diVerence of intercoccygeal angle or not according to gender. In this study our aim was to evaluate the intercoccygeal angle of asymptomatic people associated with type of coccyx and to determine whether there is a diVerence of the angle between genders. Materials and methods Ninety-two patients (42 males and 50 females) were included. The mean age was 50 years (8–86). The patient who was an 8-year-old was the only one younger than 20 years. No other child patient was included in the study. These patients underwent CT angiography and CT colonoscopy. CT angiography was performed for the patients who were evaluated before vascular surgery or follow-up for the vascular grafts. CT colonoscopy was performed to rule out bowel malignancy. None of the patients had diagnosis of any malignancy and pelvic disease or pelvic surgery. The patients were asked if they had a history of traumatic and idiopathic coccydynia were excluded. Written consent was obtained from each patient. The patients obtained CT scan in the supine position. No radiographs in the standing or sitting position were obtained which avoided additional exposure to X-ray. The images of the asymptomatic 92 patients were assessed on computer (Siemens, Leonardo workstation) with sagittal reformats and all the measurements were taken by one musculoskeletal radiologist. The slice thickness was either 1 or 1.5 mm. First the type of coccyx (Fig. 1, 2, 3, 4) was evaluated for all patients and then intercoccygeal angles (Fig. 5) were measured. The intercoccygeal angle was measured twice at diVerent times by the same musculoskeletal radiologist and the mean value was noted. The intercoccygeal angle was measured using the lines parallel to the Wrst and last segment of coccyx. The midsagital image of the coccyx was identiWed and the lines were drawn accordingly. The intercoccygeal angle was measured with freehand angle toolbar on the workstation (Fig. 1). Images were grouped according to types of coccyx and the mean value of the intercoccygeal angle was obtained for each group. The results in each group were compared by one-way ANOVA method. Besides these were classiWed according to gender within each group and they were compared with each other. In the groups of type 1 and type 2, the results regarding genders were compared by T-Test and 123 Fig. 1 Measurement of intercoccygeal angle on sagittal reformatted CT image Fig. 2 Sagittal CT view demonstrates an example of type 1 coccyx in the group of type 3, and they were compared by Mann– Whitney U test. Results Thirty-nine patients had type 1 coccyx (Fig. 2) and this was the most frequently encountered type in our study; 21 of those were females and 18 were males, 36 of the patients had type 2 (Fig. 3) and the rest (n = 17) had type 3 coccyx (Fig. 4). Type 4 was not seen in our study. There were two patients whose coccyx could not be classiWed in any of the known types (Fig. 5). They were both in a retroverted position relative to the sacrum. Surg Radiol Anat (2007) 29:683–687 685 Fig. 5 Retroverted coccyx which could not be classiWed is seen Table 1 Patients characteristics, types of coccyx and intercocygeal angles according to groups and genders Fig. 3 Sagittal CT view demonstrates an example of type 2 coccyx Groups according to type of coccyx Type 1 Type 2 Type 3 Number of patients 39 36 15 Gender (M/F) 18/21 22/14 8/7 51,4 50.7 45 Age Mean § SD Intercoccygeal angle of group Mean § SD 36.67 § 10.56 56.36 § 10.82 72.13 § 10.86 Intercoccygeal angle of female Mean § SD 33.29 § 10.35 53,31 § 13.70 Median (IQR) 74 (68–85) Intercoccygeal angle of men Mean § SD Median (IQR) Fig. 4 Sagittal CT view demonstrates an example of type 3 coccyx The intercoccygeal angles varied from 17 to 88°. The angles in type 1 varied between 17 and 53° and the mean angle was 36.67° § 10.56. The angles in type 2 varied between 24 and 78° and the mean angle was 56.36° § 10.8. The angles were measured between 50 and 88° in type 3 and the mean angle was 72.13° § 10.8. The overall results from each group were compared by one-way ANOVA and all the groups were found out to be signiWcantly diVerent from each other. (0.000 > P) (Table 1). The mean angle for females in type 1 was 33.29° § 10.35 and it was 40.05° § 9.86 for males. There was signiWcant diVerence within these values (P = 0.044). 40.05 § 9.86 59.41 § 8.12 75 (57.5–78.5) In type 2, the mean angles for females and males were 53.31° § 13.70 and 59.41° § 8.12, respectively and there was no signiWcant diVerence between the groups (P = 0.139). Since the number of patients in group 3 was limited, we took the median values for female and male groups, which were 74 (68–85) and 75° (57.5–78.5), respectively (Table 1). These were not signiWcantly diVerent. Discussion There are studies done on coccygeal pathologies [4, 12, 14, 16, 19]. In a study by Postacchini et al. it was concluded that type 3 and 4 were more common in coccydynia patients and in another study by Kim et al. [12] intercoccygeal angle signiWcantly diVered in patients with idiopathic coccydynia [17]. Kim et al. found that the mean intercoccygeal angle in 123 686 patients with idiopathic coccydynia was statistically higher than the mean angle of patients with traumatic coccydynia. They also found signiWcant diVerence between patients with idiopathic coccydynia and control group in terms of intercoccygeal angle. No signiWcant diVerence of intercoccygeal angle was assessed between the patients with traumatic coccydynia and the control group. In the light of those studies the question whether the anatomical shape of coccyx has some clinical importance has arisen. However none of them has focused on normal features of coccyx. Kim et al. [12] deWned intercoccygeal angle as the angle between the Wrst and the last segment of the coccyx and a mean value for intercoccygeal angle in normal population is given in order to compare it with coccydynia patients. On the other hand this study has taken 20 patients in control group and has given one value as a mean neglecting the diVerence between diVerent types of coccyx. In our study we have not only taken 92 patients with a wide range of ages, but also we grouped them according to coccygeal types and obtained a mean value of intercoccygeal angle for each individual group and compared each of them. The previous study has formulated that an increased intercoccygeal angle was a possible cause of idiopathic coccydynia. In another study by Postacchini et al. it was proposed that types 2, 3 and 4 were prone to coccydynia [17]. In our study there was no type 4 coccyx but although type 1 was the most common, type 2 and 3 were also seen. However, we have seen that there is increasing in the mean values of intercoccygeal angle in type 2 and type 3 compared to type 1 showing that previous two studies are consistent with each other. On the other hand it should not be neglected that the wide range of variation of intercoccygeal angle between these groups in asymptomatic patients makes it hard to use this measurement as a predictor of pathology. Furthermore, it was stated that gender factor was important in coccydynia, females being more prone to coccydynia [8, 9, 20]. However in our study we have seen that there is signiWcant diVerence between measurements taken from males and females in the same group only in type 1, which was mentioned as being less prone to coccydynia in the studies done [12, 17]. We did not see any signiWcant diVerence between females and males in terms of intercoccygeal angle in types 2 or 3. This may reXect that a predisposition of females to coccydynia may not be explained only with intercoccygeal angle and may be due to other reasons like hormonal imbalances or motor disadvantages like those mentioned in the article by Yamashita [20]. Besides these, there are two patients whose intercoccygeal angle was retroverted and could not be measured. They do not belong to any of the groups identiWed. Another case of retroverted intercoccygeal angle was reported by Dennell et al. of a 42-year-old female with coccydynia [3]. On the other hand, two cases we have included in the study 123 Surg Radiol Anat (2007) 29:683–687 were asymptomatic. Both of them were males and one of them was 72 and the other was 8-year-old. This may show that other than four diVerent already known groups of types of coccyx, a diVerent type showing retroverted coccyx should be considered. On the other hand, this also should be noted that this type has been seen both in symptomatic and asymptomatic patients. An additional type of coccyx may be added to the classiWcation and since this type is seen so rarely it may be presented as type 0 in the classiWcation. Hypermobile and immobile coccyx were also found to be associated with coccydynia. The normal coccyx pivots slightly (5–25°) either posteriorly or anteriorly with sitting and returns to its original position with standing. Abnormalities of the coccygeal segments in the seated views have anterior hypermobility >25. Subluxation or posterior displacement of the mobile segment of the coccyx is seen when the patient is seated. A spicule of the distal tip is seen most commonly with an immobile coccyx (<5° of motion with sitting) [5]. In addition to the types, it might be better to include the mobility of coccyx in the classiWcation and the new classiWcation would be like: Type 0: Retroverted coccyx on standing position (A) Hypermobile or (B) Immobile on sitting position Type 1: Curved slightly forward on standing position (A) Hypermobile or (B) Immobile in sitting position Type 2: More markedly curved, with the coccyx pointing straight forward on standing position (A) Hypermobile or (B) Immobile in sitting position Type 3: Sharply angled anteriorly on standing position (A) Hypermobile or (B) Immobile in sitting position Type 4: Subluxation of sacrococcygeal or intercoccygeal joints on standing position (A) Hypermobile or (B) Immobile in sitting position We did not evaluate the instability of coccyx, because CT examination was performed only when the patients were in supine position and since the patents were asymptomatic we avoided patients being exposed to additional X-ray. Dynamic MRI would be helpful to assess the coccygeal movement without X-ray. Grassi et al. reported no correlation between coccygeal movements and age, sex, parity, minor trauma and coccydynia [6]. There are non-surgical conservative and surgical management of coccydynia [1,5]. Non-steroid anti-inXammatory and analgesic medications, rest, hot baths, and a cushion to protect the coccygeal region from repetitive trauma are the options for non-surgical management [5]. Several investigators have reported good or excellent results, ranging from 60–92% of patients after coccygectomy [7, 9, 11, 18]. On the other hand, some advise against surgery [10]. No clear consensus exists over widely Surg Radiol Anat (2007) 29:683–687 accepted conservative forms of treatment, like site for injections or manipulations. Disabling coccydynia with radiographic subluxation; instability; or a spicule, particularly on the tip of an immobile coccyx are the indications for surgery [13, 15]. Surgery, consisting of complete coccygectomy or simply excision of the mobile segment, should be done only after non-surgical management fails [17]. Conclusion Our results showed that intercoccygeal angle increases according to the type of coccyx and are so variable even in asymptomatic patients. The intercoccygeal angle cannot propose for any patient being more prone to coccydynia. This result is consistent with the study of 200 patients carried out by Duncan in which he could not demonstrate any diVerence between symptomatic and asymptomatic patients [4]. However we believe that presenting normative measurements for intercoccygeal angle as seen on CT will help understanding this less known bony structure and therefore will make it easier to evaluate in symptomatic patients and in patients after surgery. References 1. Balain B, Eisenstein SM, Alo GO, Darby AJ, Cassar-Pullicino VN, Roberts Se, JaVray DC (2006) Coccygectomy for coccydynia: case series and review of literature. 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