Aetiology
Post-traumatic:
Coccygeal trauma may occur after a fall onto the buttocks, or from natural childbirth.
Repetitive stress injury, such as sitting with poor posture or sitting in a poorly designed chair, can also cause coccygodynia.
Non-traumatic:[6]
Degenerative joint or disc disease
Hyper- or hypomobility of the sacrococcygeal joint
Anatomical coccygeal variants
Infection
Neoplasm- rarely associated with coccygodynia.
Idiopathic:
Although psychosocial factors may be involved in some cases, their importance may have been exaggerated in the past. Depression may play a role in some cases of idiopathic coccygodynia.[9][10]
Tight-fitting clothing (jean-seam coccygodynia, also known as Stoshak-Mortimer syndrome) has been implicated as a cause.[11]
Perineural cysts (Tarlov cysts) are usually an incidental imaging finding but can, rarely, be associated with coccygodynia, lower back pain and symptoms of nerve root compression.[12][13]
Pathophysiology
Acute trauma from a fall onto the buttocks causes anteroflexion of the coccyx, injuring the sacrococcygeal or intercoccygeal articulations, or the surrounding ligamentous structures, resulting in hypermobility or subluxation and pain. Direct trauma can also fracture a sacrococcygeal or intercoccygeal synostosis.
The pathophysiology of idiopathic coccygodynia is less clear. Repetitive posterior stress of the coccyx may injure ligamentous structures. Degeneration of the sacrococcygeal joint is a prominent pathological feature of coccygodynia, and its presence might predict the benefit of coccygectomy.[14][15] Provocative and anaesthetic discography has confirmed a discogenic source of pain in 70% of cases of coccygodynia, underscoring the role of sacrococcygeal joint degeneration in coccygodynia.[16] Spasm of the pelvic floor musculature (coccygeus and levator ani muscles) has classically been implicated in coccygodynia, and attendant piriformis spasm may produce an associated pain down the thigh.[17][18] The coccyx is innervated by the S4, S5, and coccygeal nerves, and sacral pathology can result in referred pain.
Classification
Interdisciplinary guideline of the German Society of Coloproctology[1]
Post-traumatic: patient has a history of trauma to the coccyx (e.g., a fall onto the buttocks) or childbirth.
Idiopathic: no identifiable cause.
Classification based on aetiology[2]
True coccygodynia: pain arising from the coccyx.
Pseudococcygodynia: pain referred to the coccyx from visceral organs, dural irritation, or neurogenic pain originating in a root, plexus, or peripheral nerve.
Clinical classification
Acute coccygodynia: symptoms <2 months.
Chronic coccygodynia: symptoms ≥2 months.
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