The adult body has 206 bones and 360 joints, though these can vary slightly. There are a few bones that are separate thought they solidify over some time. Two examples are the sacrum and coccyx that form the tailbone.
When you are born, the sacrum is composed of 5 bones that become one a few years after we stand and walk. The coccyx is made up of 3-5 bones that calcify over time to leave a single joint between it and the sacrum.
The joint that results is the one that helps you with various activities, especially when you bend down to lift something from the pelvic floor.
Sometimes between ages 70 and 75 years, the joint fuses into one, a natural ageing process.
The Sacral Canal
The sacrum is concave in shape, and each vertebra in the sacrum contains a large central opening that is otherwise called the foramen. The fused foramina create a channel that is called the sacral canal which extends along the length of the bone.
We have spinal nerves which arise from L1 and pass through this canal. The branches of these nerves enter and exit the canal via the anterior and posterior sacral foramina.
You will never think about the tailbone until it starts to hurt. The pain in the tailbone is at the very bottom of the spine, right above the buttocks. This bone is small but it has very important jobs. The area also sees a lot of muscles, tendons and ligaments running through it.
Pain in this area is called coccydynia. The pain from this bone can range from acute to chronic. The pain can get worse when you sit or stand up or when you try to lean back in the chair while sitting.
You might have pain when you use the bathroom or when you have sex. Women experience this pain during their periods. The pain is characteristic and can shoot all the way down to the legs.
The pain eases when you stand or when you walk because of the reduction in pressure on the tailbone.
Why the Tailbone Hurts
The tailbone might hurt after a simple action such as sitting on a hard surface for a very long time. Bruises or trauma to the area can also contribute to the pain. The pain results from a bruise, dislocation or breaking of the tailbone.
Pregnant women are more likely to experience this type of pain because the ligaments that are located around the bones loosen up to make enough room for the baby.
You are also more likely to experience the issues if you are overweight because of the weight that you exert on the bone when you sit down.
Additionally, if you lose the weight fast, you lose any padding that protects the tailbone, which exposes it to injury.
In rare cases, the cause of the injury can be a tumour or an infection.
A direct blow to the tailbone area such as those that happen during contact sports can lead to injury to the coccyx. Moreover, the bones can be fractured or injured during childbirth.
Bicycle riders and rowers can also injure these bones due to friction or straining against the coccyx.
Your tailbone is made of two types of bones – the sacrum and the coccyx. These two are essential for some actions of the body, especially when you lift something from the ground. They can also be a source of back pain in case of trauma or infection.
References and Further Reading
1. Coccydynia: An Overview of the Anatomy, Etiology, and Treatment of Coccyx Pain
2. Sacrum and Coccyx Radiographs Have Limited Clinical Impact in the Emergency Department
3. Clinical anatomy of the coccyx: A systematic review