Coccydynia refers to pain in and among the area of the coccyx. It is characterised by coccygeal pain which is typically provocated by pressure. It may remain unclear in origin owing to the unpredictability of the source of pain ¹. Most of patient presented wth coccydynia had prior history of fall, particularly in sitting position¹².

Epidemiology

No accurate data about the frequency of coccydynia is reported, but one study found that coccydynia accounted for ~3% of all low back pain hospital presentations ⁸. It is ~5x more common in females than males ^ref. 

Risk factors

• obesity ¹⁰

• female sex ¹⁰

• osteoporosis and other degenerative bone diseases ^ref

• osteomyelitis ^ref

• contact sports ^ref

• elderly with risk of fall

Associations

• inflammatory bowel disease ^ref

• obesity ^ref

Clinical presentation

As the name suggests, pain is considered to be the primary symptom of coccydynia. However, pain is extremely varied and may be related to sitting, bowel movements, radiculopathic or generalised coccygeal pain. The coccyx may be tender on examination. 

Pathology 

Aetiology

 Coccydynia can be classified into ^ref:

• idiopathic (most common) ^ref

• secondary coccygeal pain

  • abnormal coccygeal mobility

    • hypermobility ¹⁰

    • rigid coccyx with spicule at the tip ¹⁰

    • intersegmental coccygeal subluxation ¹⁰

  • trauma

    • post falls or trauma to gluteal region ¹⁰

    • childbirth, particularly instrumented or difficult deliveries ¹³

      • both subluxation and uncommonly fractures can occur ¹³

    • partial dislocation of the sacrococcygeal synchondrosis

  • intersegmental degeneration ¹⁰

  • tumour, e.g. chordomas, chondrosarcoma (rare) ¹⁰

  • infection, e.g. tuberculosis (rare) ¹⁰

Radiographic features

Coccydynia is essentially a clinical diagnosis, but imaging modalities are helpful in assessment and possible identification of the aetiology.

Plain radiograph

Considered the first line of imaging of painful coccyx ¹⁰. Two types of radiographs:

• standard radiograph

  • coccyx scoliotic deformity (AP and lateral)

    • number and morphology of coccygeal segments including degenerative change

    • useful radiological assessment to evaluate anterior angulation of the coccyx and its deformity

• dynamic sitting and standing radiographs ¹⁰

  • superior to standard radiograph because it can detect measurement of the sagittal rotation of the pelvis and the coccygeal angle of incidence ^ref

  • allows for assessment of coccygeal mobility by measuring the intercoccygeal angle with the generally accepted values being (although this is not validated/standardised) ¹⁰

    • dynamic posterior intersegmental coccygeal subluxation ¹⁰

    • <5°: immobile/rigid ¹⁰

    • 5° to 25°: normal ¹⁰

    • >25°: hypermobility ^7,10

MRI

Described features include ¹¹:

• rigid coccyx with a spicule or spur at its tip

• bursa along the dorsal surface of the coccyx

• presence of fluid collection within the sacrococcygeal synchondrosis

• large draining vein on the ventral coccyx

• any inflammation or soft tissue abnormalities around the coccyx

Treatment and prognosis

Conservative treatment includes rest, coccygeal cushion, physiotherapy and massage. In traumatic coccydynia the joint may heal spontaneously over weeks or months

Interventions include:

• injections of local anaesthetic and steroid

• radiofrequency ablation of coccygeal discs and ganglion impar

• removal of the coccyx by surgery either partial or total (coccygectomy) in refractory cases

  • limited coccygectomy may to resect a mobile segment ⁵

History and etymology 

The word coccyx originates from the Greek word "cuckoo" (kokkyx), on the basis of resemblance to the structure a cuckoo's beak. The term was used in practice for the first time by Simpson in 1859, although was described as early as 1600s. It is also called the "tailbone" because it is located anatomically at the end of the vertebral column below the sacrum.

Differential diagnosis

Causes of pain in the coccygeal region include:

• pilonidal sinus/abscess

• sciatica

• sacroiliitis

• infection including shingles of the buttocks

• haemorrhoids

• paraganglioma of the coccyx

• piriformis syndrome ⁵