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Magnetic Resonance Imaging Morphology and Morphometry of the Coccyx in Coccydynia

Woon, Jason T. K., BBioMedSc(Hons)*; Maigne, Jean-Yves, MD; Perumal, Vivekanandan, BPT, MSc (Med Anat)*; Stringer, Mark D., MS, FRCS*

doi: 10.1097/BRS.0b013e3182a45e07

Study Design. Retrospective case-control study.

Objective. To determine if differences exists between the bony anatomy of the coccyx in patients with coccydynia and that in subjects with no known coccygeal pathology.

Summary of Background Data. Numerous bony characteristics of the coccyx have been described in patients with coccydynia but their significance is uncertain. This study aimed to evaluate these in patients with coccydynia and compare them with normal coccyges.

Methods. Magnetic resonance scans of the coccyx from 107 adults (mean age, 43 ± 12 yr; 84 females) with clinically diagnosed coccydynia were retrospectively analyzed and compared with 112 computed tomographic scans from sex-matched adults with normal coccyges. The following were assessed: coccygeal segmentation; sacrococcygeal and intercoccygeal joint fusion, angles, and curvature; bony spicule formation; and subluxation.

Results. Compared with normal, females with coccydynia had a more ventrally curved coccyx (curvature index, 85 ± 7 vs. 90 ± 5; P< 0.01), a lower prevalence of sacrococcygeal joint fusion (27% vs. 58%, P< 0.01), and a higher frequency of bony spicule formation (44% vs. 19%, P< 0.01). Males with coccydynia showed a trend toward a more ventrally curved coccyx (curvature index: 86 ± 6 vs. 89 ± 5, P< 0.08), and a lower prevalence of sacrococcygeal (27% vs. 60%, P< 0.02) and intercoccygeal (0% vs. 22%, P< 0.02) joint fusion. Combining statistically significant coccygeal parameters in a logistic regression model yielded sensitivity, specificity, and positive predictive values of 72%, 71%, and 73%, respectively in females and 52%, 92%, and 73%, respectively in males.

Conclusion. This is the most detailed comparison of coccygeal morphology and morphometry in adults with and without coccydynia investigated using cross-sectional imaging. Anatomical differences in joint fusion and coccygeal curvature may either predispose to the development of coccydynia or arise as a result of this condition.

Level of Evidence: N/A

Magnetic resonance imaging scans from patients with coccydynia (n = 107) were compared with computed tomographic scans from normal subjects (n = 112) to determine differences in coccygeal bony anatomy. Significant differences were noted in coccygeal curvature, sacrococcygeal joint fusion, and bony spicule formation. These static differences may predispose to or occur as a result of coccydynia.

*Department of Anatomy, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand

Service de Médecine Physique, Hôpital Hôtel-Dieu, Paris Cedex, France.

Address correspondence and reprint requests to Mark D. Stringer, MS, FRCS, Department of Anatomy, Otago School of Medical Sciences, University of Otago, Box 913, Dunedin, New Zealand; E-mail:

Acknowledgment date: January 23, 2013. Revision date: May 30, 2013. Acceptance date: July 8, 2013.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

© 2013 by Lippincott Williams & Wilkins