• Matthias A König, Joachim Grifka, and Achim Benditz.
• Department of Orthopedic Surgery, Regensburg University Medical Center, Bad Abbach, Germany. matthias.a.koenig@gmail.com.
• Eur Spine J. 2022 Jan 1; 31 (1): 101710-17.

BackgroundTreatment of coccygodynia is still a challenging entity. Clear surgical selection criteria are still lacking. The aim of the investigation was to establish a novel radiological classification for surgical decision-making in coccygodynia cases.Material And MethodsRetrospective analysis of standing and sitting X-rays of coccygodynia patients referred to a single centre from 2018 to 2020. The sacro-coccygeal angle (SCA), the intra-coccygeal angle (ICA) and the difference of the intervertebral disc height (∆IDH) were measured. All coccyges were distributed in subtypes and correlated with the patients' treatment.ResultsIn total, 138 patients (female/male: 103/35) with a mean age of 45.6 ± 15.4 years were included in the study. In total, 49 patients underwent coccygectomy. Four different subtypes of displaced coccyges were identified: Type I with a non-segmented coccyx, anterior pivot, increased SCA and ICA from standing to sitting, ∆IDH = 1.0 ± 1.5 mm. Type II with a multisegmented coccyx, anterior pivot, increased SCA and ICA standing/sitting, ∆IDH = 1.1 ± 1.6 mm. Type III showed a posterior pivoted coccyx, negative SCA and ICA, ∆IDH = 0.6 ± 1.6 mm. Type IV is characterized by an anterior-posterior dissociation of the tail bone with a positive SCA, and the ICA shifted from a posterior to an anterior orientation. ∆IDH was - 0.6 ± 1.8 mm.ConclusionThe presented radiological classification could help to facilitate the surgical decision-making for patients with displaced os coccyx. In addition, lateral and sitting X-rays were easy to perform and did not need unnecessary ionizing radiation like in CT scans and were more cost-effective than MRI investigations. The subtypes III and especially IV were more likely leading to surgery.© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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