The coccyx, sometimes known as the tailbone, marks the bottom of the vertebral column in humans as well as in some apes. This area is comprised of three to five very small vertebra and is believed to be the remnant of a tail structure. Although these bones are no longer needed to support a tail, the tailbone helps bear weight and provide balance, especially when sitting or leaning backward.
A normal tailbone is shaped like an upside-down triangle, roughly situated between and below the hip bones. The name, coccyx, is believed to come from the Greek word for "cuckoo," as the shape of the tailbone is similar to that of a cuckoo's beak. Unlike the rest of the vertebra, those in the tailbone are solid and do not contain a space for the spinal cord to run through.
Directly above the tailbone is the sacrum, a wedge shaped bone that fits between the hipbones. The sacrum and coccyx are connected by joints and ligaments that allow some small movement between the two bone sections. However, studies have shown that if the coccyx is surgically removed, it causes little or no effect on overall mobility.
Because of the largely vulnerable position of the tailbone, it is subject to a variety of injuries. Pain when sitting down is often the clearest symptom of bruising or damage to the area. If you are suffering from lower back pain when sitting, you may want to visit a doctor or chiropractor to see if the pain may be related to your tailbone. Tailbone pain is referred to as coccydynia, and damage is often confirmed using X-ray images or MRI scans of the lower back. There are many potential contributing factors to coccydynia, including traumatic falls, childbirth, or activities that require excessive sitting, such as bicycling or horseback riding. If you suffer from coccydynia, the condition may be aggravated by these types of sports, or simply by sitting for very long periods of time.
There are also some tumors associated with the tailbone region. Sacrococcygeal teratoma is a type of tumor often found in newborn babies that forms in the base of the coccyx. Although these tumors are often benign, surgical removal of the tailbone is a common procedure to get rid of the tumor. If the tumor is malignant, leaving the tailbone in place leaves the patient at risk for a recurring tumor. Because of the limited complications associated with removing the coccyx entirely, it is often the safest and most effective way to remove the teratoma and prevent a recurrence.