• Jason T K Woon, Vivekanandan Perumal, Jean-Yves Maigne, and Mark D Stringer.
• Department of Anatomy, Otago School of Medical Sciences, University of Otago, PO Box 913, Dunedin, New Zealand.
• Eur Spine J. 2013 Apr 1;22(4):863-70.

PurposeLack of data on the in vivo morphology and morphometry of the normal adult coccyx hampers understanding of radiological abnormalities in idiopathic coccydynia. The aim of this study was to investigate normal adult sacrococcygeal morphometry.MethodsRetrospective analysis of 112 adult CT scans (mean age 63 ± 14.6 years, 50 males) evaluated the following: number of coccygeal segments; joint fusion; coccygeal spicules, subluxation, sacralization, and scoliosis; sacrococcygeal straight and curved lengths and curvature indices; sacrococcygeal and intercoccygeal angles; and lateral deviation of the coccyx tip.ResultsFour coccygeal segments were present in 76 % of scans. Sacrococcygeal fusion was present in 57 % and intercoccygeal fusion was increasingly common more caudally; there was no significant association with age or gender. A bony spicule was present in 23 %. Subluxation was rare. Nine of 12 coccyges with a retroverted tip were female. Mean coccygeal curved length was 4.4 ± 0.8 cm in men and 4.0 ± 0.8 cm in women (P < 0.01). Mean angle between first and last coccygeal segments was 138° ± 25° in men and 147° ± 25° in women (P = 0.08). There was no significant correlation between coccygeal length or curvature and stature, age or BMI.ConclusionsIn this first detailed study of the CT morphology and morphometry of the adult coccyx, sacrococcygeal and intercoccygeal joint fusion was common. Female coccyges were shorter, straighter, and may be more prone to retroversion, factors that may be relevant to the markedly higher prevalence of idiopathic coccydynia in women.

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