A CT-based study of coccyx morphology in adult Chinese without symptoms of coccydynia

English Keywords:Asymptomatic  Coccygeal morphology  Radiographic

English Abstract:

  【Abstract】 Objectives: To investigate the coccygeal morphology in adult Chinese without coccydynia using CT scans, and to provide a morphological reference for assessing the risk of coccydynia in Chinese population. Methods: A retrospective analysis was conducted on 113 patients without coccydynia who underwent pelvic three-dimensional CT scans at the Second Affiliated Hospital of Wenzhou Medical University between August 2018 and August 2023. There were 67 males and 46 females, with a mean age of 53.5±19.1 years(range: 18-93 years). The morphological characteristics of the sacrococcygeal anatomical structures, including coccyx number, coccyx type(modified Nathan classification), sacrococcygeal joint fusion, intercoccygeal joint subluxation, coccygeal sacralization, lateral deviation of coccygeal tip, ventral angulation of S5, and coccygeal bony spicule, were analyzed on the three-dimensional reconstructed CT images; And relevant morphological parameters were measured, such as the coccygeal straight length, sacral straight length, sacrococcygeal straight length, sacrolumbar angle, sacrococcygeal angle, sacrococcygeal joint angle, intercoccygeal angle, and first intercoccygeal joint angle, with consistency tests conducted for the measurements. The differences in morphological parameters were compared between different genders and age groups(<50 years and ≥50 years). Results: Among the 113 asymptomatic adult Chinese subjects, 88 cases(77.9%) had a 4-segment coccyx, and type Ⅰ coccyx(modified Nathan classification) was the most common type(53 cases), accounting for approximately 46.9%. The incidence of sacrococcygeal joint fusion, intercoccygeal joint subluxation, coccygeal sacralization, lateral deviation of the coccygeal tip, ventral angulation of S5, and coccygeal bony spicule were 52.2%(59 cases), 25.7%(29 cases), 20.4%(23 cases), 53.1%(60 cases), 7.1%(8 cases), and 15.0%(17 cases), respectively. The consistency test showed that the consistency of the measurement data among observers was good. In Chinese population, the coccygeal straight length was 3.59±0.72cm, sacral straight length was 10.97±0.92cm, and sacrococcygeal straight length was 12.68(11.99, 13.69)cm. The lumbosacral angle, sacrococcygeal angle, intercoccygeal angle, and first intercoccygeal joint angle were 38.0°±7.3°, 110.6°±10.6°, 173.1°(164.2°, 178.2°), 131.5°±21.5°, and 152.8°±17.1°, respectively. Gender comparisons showed that males had greater sacrococcygeal straight length and sacrococcygeal angle than females(P<0.05). Age group comparisons revealed that subjects <50 years had shorter coccygeal straight length, smaller lumbosacral angle, sacrococcygeal joint angle, and first intercoccygeal joint angle than those ≥50 years(P<0.05), while the sacral straight length was longer in the <50 years group(P<0.01). Conclusions: Among the adult Chinese without coccydynia, 4 coccygeal segments and type Ⅰ(modified Nathan classification) are the most common. Sacrococcygeal joint fusion, coccygeal bony spicules, intercoccygeal joint subluxation, and coccygeal sacralization have relatively high incidences. Males have longer and straighter sacrococcygeal structures than females. Compared with those ≥50 years, subjects <50 years have shorter coccyxes, longer sacra, and smaller lumbosacral angles.