The coccyx, sometimes referred to as the 'tailbone', is the bone at the bottom of the spine. The word 'coccyx' is derived from the Greek word for 'cuckoo' as it looks a little like an upside-down bird's beak.
Although considered 'vestigial' (i.e. no longer needed), the coccyx does play an important role in human anatomy – for example when you sit down it shares weight distribution with the hip bones and provides stability and balance, and a number of pelvic floor muscles involved in walking and running (and going to the toilet) connect at the coccyx.
Any persistent pain that is felt in the coccyx is referred to as coccydynia (with 'dynia' meaning 'pain').
The direct anatomical causes of tailbone pain generally fall into three categories…
- Excessive mobility of the coccyx ('hypermobility') which puts additional pressure on the joint connecting the coccyx to the sacrum.
- Limited mobility of the coccyx, which leads to the it sticking out a little when sitting down. This also causes stress to the joint as above.
- Dislocation of this joint (rare).
Generally, these are caused in turn by the following…
- An injury (trauma) to the coccyx – this is the commonest cause and generally occurs in a fall on to the buttocks. Injury in this case is generally bruising to the bone and inflammation of the ligaments and damage to the joint. In rarer cases there may be a fracture in the coccyx or a dislocation.
Injury to the coccyx can also occur…
- During childbirth, as the head of the baby passes very close to the top of the coccyx and this pressure can cause some injury to it.
- Due to other conditions, such as the presence of infection or a tumour close to the coccyx.
- Due to referred pain where the cause is in fact higher up in the spine e.g. low lumbar facet pain or sacroiliac joint pain or other degenerative spinal issues disease.
Risk factors of developing coccydynia include…
- Being female - partially due to the childbirth connection, but also due to differences in the male / female pelvic anatomy.
- Being obese – people who are obese have less movement in the pelvis, which places greater stress on the coccyx.
The primary symptom is pain in the area of the coccyx. The following other symptoms may also be present…
- Tenderness / aching in the area which can severe or mild.
- General discomfort or tightness in the area.
- Pain when moving that part of the body.
- Pain when sitting down, but particularly when moving into or out of a seat.
- Pain when defecating.
- Pain during sexual intercourse.
Where the direct cause of coccydynia is not clear, this is referred to as 'idiopathic coccydynia'.
Tests / Diagnosis
The first way of diagnosing coccydynia is physical examination, where the area around the coccyx is checked for pain or tenderness. Further tests are generally only required where there is no clear indication of the cause of pain. These tests may include diagnostic injections.
Other scans such as CT scan or MRI scan may be recommended – especially where a fracture or tumour is suspected.