Sacrococcygeal Morphologic and Morphometric Risk Factors for Idiopathic Coccydynia: A Magnetic Resonance Imaging Study

STUDY DESIGN: Retrospective case-control study. OBJECTIVES: To evaluate the sacrococcygeal morphologic and morphometric features in idiopathic coccydynia using magnetic resonance imaging (MRI). METHODS: MRI scans from 60 patients with idiopathic coccydynia were compared with scans of 60 controls. Assessment of coccygeal morphology included coccygeal segmentation, coccygeal types, bony spicules, sacrococcygeal joint fusion, and intercoccygeal joint fusion and subluxation. Morphometric parameters included coccygeal straight and curved lengths, coccygeal curvature index, sacrococcygeal and intercoccygeal joint angles, sacral straight and curved lengths, sacral curvature index, sacral angle, sacrococcygeal straight and curved lengths, sacrococcygeal curvature index, and sacrococcygeal angle. RESULTS: The coccydynia group included 28 males and 32 females, with a mean age of 36.1 years. Type II coccyx and bony spicules were more common in coccydynia, P = 0.003 and 0.01, respectively. Sacrococcygeal joints were fused less commonly in coccydynia, P = 0.02. Intercoccygeal joint subluxation was more common in coccydynia, P = 0.007. The sacral angle was lower in coccydynia, P = 0.01. The sacrococcygeal curved length was higher in coccydynia, P < 0.001. The sacrococcygeal curvature index was lower coccydynia, P < 0.001. In females only, the coccygeal curvature index was lower in coccydynia patients, P = 0.04. In males only, the intercoccygeal angle was lower in coccydynia patients, P = 0.02. CONCLUSIONS: Type II coccyx, bony spicules, intercoccygeal joint subluxation were more common, and sacrococcygeal joint fusion was less common in coccydynia patients. Sacral angle and sacrococcygeal curvature index were lower, while sacrococcygeal curved length was higher in coccydynia patients. LEVEL OF EVIDENCE: Level 3. Case-control study.