Anterior angulation of the coccyx
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Six types of coccyx have been described:
type I: the coccyx is curved slightly forward, with its apex pointing caudally (~70%)
type II: the coccyx is curved more markedly anteriorly, with its apex pointing straight forward (~15%)
type III: the coccyx is sharply angulated forward between the first and second or the second and third segments (~5%)
type IV: the coccyx is subluxed anteriorly at the level of the sacrococcygeal joint or at the level of the first or second intercoccygeal joints (~10%)
type V: the coccyx is retroverted or has a posterior spicule
type VI: the coccyx is scoliotic (lateral deviation)
The intercoccygeal angle is a useful radiological assessment to evaluate the anterior angulation of the coccyx and its deformity.
Patients with a type II-IV coccyx are more prone to develop idiopathic coccygodynia than those with a type I configuration ref. Partial or total coccygectomy usually provides relief in these cases ref.