Magnetic Resonance Imaging Morphology and Morphometry of the Coccyx in Coccydynia

Spine (Philadelphia Pasadena Edition)

2013 Nov 1; 38(23): E1437-45

Woon JT (1), Maigne JY (2), Perumal V, Stringer MD.

(1) Department of Anatomy, Otago School of Medical Sciences, University of Otago, PO Box 913, Dunedin, New Zealand

(2)Service de Médecine Physique, Hôpital Hôtel-Dieu, 75181, Paris cedex 04, France.


Study Design

Retrospective case-control study.


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.


Magnetic resonance scans of the coccyx from 107 adults (mean age 43 ± 12 years; 84 females) with clinically diagnosed coccydynia were retrospectively analysed and compared with 112 CT 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.


Compared to normal, women with coccydynia had a more ventrally curved coccyx (curvature index 85 ± 7 versus 90 ± 5; P<0.01), a lower prevalence of sacrococcygeal joint fusion (27% versus 58%, P<0.01), and a higher frequency of bony spicule formation (44% versus 19%, P<0.01). Men with coccydynia showed a trend towards a more ventrally curved coccyx (curvature index: 86 ± 6 versus 89 ± 5, P<0.08), and a lower prevalence of sacrococcygeal (27% versus 60%, P<0.02) and intercoccygeal (0% versus 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.


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.

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