Three-dimensional evaluation of the coccyx movement between supine and standing positions using conventional and upright computed tomography imaging

Fumiko Yagi,Minoru Yamada,Masahiro Jinzaki,Keiichi Narita,Kiyoko Mukai,Takehiro Nakahara,Yoshitake Yamada,Yoichi Yokoyama

doi:10.1038/s41598-021-86312-0

Fumiko Yagi, Minoru Yamada + Show 6 more

Open Access

https://doi.org/10.1038/s41598-021-86312-0

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Abstract

Currently, no three-dimensional reference data exist for the normal coccyx in the standing position on computed tomography (CT); however, this information could have utility for evaluating patients with coccydynia and pelvic floor dysfunction. Thus, we aimed to compare coccygeal parameters in the standing versus supine positions using upright and supine CT and evaluate the effects of sex, age, and body mass index (BMI) on coccygeal movement. Thirty-two healthy volunteers underwent both upright (standing position) and conventional (supine position) CT examinations. In the standing position, the coccyx became significantly longer and straighter, with the tip of the coccyx moving backward and downward (all p < 0.001). Additionally, the coccygeal straight length (standing/supine, 37.8 ± 7.1/35.7 ± 7.0 mm) and sacrococcygeal straight length (standing/supine, 131.7 ± 11.2/125.0 ± 10.7 mm) were significantly longer in the standing position. The sacrococcygeal angle (standing/supine, 115.0 ± 10.6/105.0 ± 12.5°) was significantly larger, while the lumbosacral angle (standing/supine, 21.1 ± 5.9/25.0 ± 4.9°) was significantly smaller. The migration length of the tip of the coccyx (mean, 7.9 mm) exhibited a moderate correlation with BMI (r = 0.42, p = 0.0163). Our results may provide important clues regarding the pathogenesis of coccydynia and pelvic floor dysfunction.

Highlights

No three-dimensional reference data exist for the normal coccyx in the standing position on computed tomography (CT); this information could have utility for evaluating patients with coccydynia and pelvic floor dysfunction
Since humans spend the majority of their time in the upright position, and the effects of gravity and intrapelvic pressure are reduced in the supine position, understanding the morphology, morphometry, and movement of the coccyx in the standing position likely has clinical utility
The coccygeal straight length and the sacrococcygeal straight length were significantly longer in the standing position than in the supine position

Summary

Introduction

No three-dimensional reference data exist for the normal coccyx in the standing position on computed tomography (CT); this information could have utility for evaluating patients with coccydynia and pelvic floor dysfunction. Previous studies have shown that assessments of coccygeal movement play an important part in evaluations of coccydynia[2] and pelvic floor dysfunction[3]. In previous studies, the coccyx was assessed only by plain radiography in the standing and sitting positions[2,7,8], computed tomography (CT)/magnetic resonance imaging (MRI) in the supine p osition[9,10,11,12,13,14,15,16], or MRI in the sitting p osition[17]. As far as we know, no clinical studies to date have compared coccygeal morphology in the supine versus standing positions. Measured in a straight line from the middle of the upper border of S1 to the middle of the inferior border of S5 (Fig. 1a)

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