Giving birth is one of the most common causes of coccydynia.
The coccyx becomes more flexible towards the end of pregnancy. This allows your coccyx, and the part of your spine above it, to bend and give way when you give birth.
Sometimes childbirth can cause the muscles and ligaments (stretchy tissue that connects bones) around your coccyx to overstretch. This can result in coccydynia.
Injuring your coccyx
You can injure your coccyx if you suffer a hard impact to the base of your spine. For example, from an accidental kick during contact sports.
Falling backwards is another common cause of injury to the coccyx.
In most cases where the coccyx is injured, it will only be badly bruised. But in more severe injuries, it may be dislocated (out of place) or fractured (broken).
Repetitive strain injury (RSI)
You may get coccydynia if you regularly take part in sports such as cycling or rowing. This is due to continually leaning forward and stretching the base of your spine.
If this motion is repeated many times, the muscles and ligaments around your coccyx can become strained and stretched.
Straining your muscles and ligaments can permanently damage them. If this happens, your muscles will no longer be able to hold your coccyx in the correct position, causing pain and discomfort.
Read more about repetitive strain injury (RSI).
Sitting in an awkward position for a long period of time, such as at work or while driving, can put too much pressure on your coccyx. This causes pain and discomfort that will get worse the longer you stay in this position.
Read more information about how to sit correctly.
Being overweight or underweight
Being overweight or obese can place excess pressure on your coccyx when you're sitting down. This can cause coccydynia or make existing coccydynia worse.
You may also develop coccydynia if you are very slim. If this is the case, you may not have enough buttock fat to prevent your coccyx from rubbing against the tissues surrounding it.
You can use the body mass index (BMI) calculator to find out whether you are a healthy weight for your height.
As we grow older the small discs of cartilage (a tough, flexible tissue) that help hold the coccyx in place can wear down. The bones that make up the coccyx can also become more tightly fused together. This can place more stress on the coccyx, leading to pain.
Rarely, an infection can occur in the base of the spine or soft tissue and cause coccydynia, such as a pilonidal abscess (a painful collection of pus that usually develops in the cleft of the buttocks).
A rare cause of coccydynia is cancer. This can be bone cancer or cancer that starts somewhere else in the body and then spreads into the bone (metastatic cancer).