The tailbone, known medically as the coccyx, is the small triangular bone at the very bottom of your spine. It sits just below the sacrum (the broad, flat bone at the base of your back) and is made up of three to five small vertebrae fused together, with four being the most common number. Despite its small size, the tailbone plays a surprisingly active role in everyday movement and stability.
What the Tailbone Looks Like
If you were to look at a skeleton from the side, the coccyx appears as a small, slightly curved structure pointing downward and slightly forward. It’s only about an inch long in most people. The individual vertebrae that make it up are much smaller than the ones in the rest of your spine, and in adults, they’re typically fused into a single piece of bone, though the top segment sometimes remains partially mobile at its joint with the sacrum.
The shape and mobility of the tailbone differ between biological males and females. In people with female anatomy, the coccyx is more flexible and can move, which matters during childbirth because it shifts backward to widen the pelvic opening. In people with male anatomy, the coccyx angles inward and is more rigid.
What the Tailbone Actually Does
People sometimes call the tailbone “useless” or purely leftover from evolution, but it serves several functions in your daily life. When you sit down, your weight is distributed across a tripod formed by the two bony bumps at the bottom of your pelvis (the ischial tuberosities, or “sit bones”) and the coccyx. The tailbone helps steady you and support your weight, especially when you lean back.
The tailbone also serves as an anchor point. Several muscles, tendons, and ligaments of the pelvic floor attach to it. These pelvic floor structures support your bladder, bowel, and reproductive organs, and they play a role in controlling continence. Without the coccyx as an attachment site, those muscles would lose structural support. The gluteus maximus, the large muscle of the buttock, also partially attaches to the coccyx, connecting it to hip movement and walking.
Why Humans Still Have One
The tailbone is what remains of the tail our primate ancestors once had. Those ancestors used tails to grasp branches while moving through trees. Somewhere between 25 million and 20 million years ago, tails disappeared from the fossil record in the lineage that would eventually lead to humans and other great apes. Researchers have identified a specific genetic change, a small piece of DNA that inserted itself into a gene called TBXT, as the likely trigger. That gene normally produces a protein essential for tail development in the embryo. The insertion disrupted the gene’s function just enough to prevent a tail from forming, while leaving the short remnant of fused vertebrae we now call the coccyx.
During early embryonic development, human embryos actually do have a small tail-like structure that is reabsorbed by about the eighth week of pregnancy. The coccyx is what remains after that process. Scientists still aren’t entirely sure what evolutionary pressures drove the loss of the tail. It may have been related to the shift from tree-dwelling to ground-dwelling, or to the biomechanical demands of walking upright.
Tailbone Pain: Causes and Symptoms
Pain centered on the coccyx is called coccydynia, and it’s more common than most people expect. The hallmark symptom is a deep ache right at the base of the spine that gets worse when you sit, especially on hard surfaces, and when you stand up from a seated position. Leaning back in a chair tends to increase pressure on the coccyx and make the pain sharper.
The most common causes include:
- Falls and direct impact: Landing hard on your tailbone, such as slipping on ice, is the classic cause of coccyx injury. This can bruise or fracture the bone.
- Prolonged sitting: Sitting for long stretches on hard or narrow surfaces (like a wooden bench or a bicycle seat) puts sustained pressure on the coccyx.
- Childbirth: Because the coccyx shifts during delivery, it can be bruised, dislocated, or fractured in the process.
- Repetitive strain: Activities like cycling or rowing can irritate the tailbone over time.
- No clear cause: In many cases, coccydynia develops gradually without an obvious injury.
Women are more prone to tailbone pain than men, partly because of the wider female pelvis and the coccyx’s greater mobility, which makes it more exposed to injury.
How Tailbone Pain Is Diagnosed
A physical exam is usually the starting point. Your doctor will press on the area around the coccyx to locate the pain and may perform an internal exam to assess the joint from behind. Standard X-rays can show fractures or obvious misalignment, but they don’t always capture the full picture because the coccyx can shift position depending on whether you’re sitting or lying down. A study of patients with coccyx pain found that nearly a third had a posterior displacement of the tailbone that was only visible on X-rays taken in the sitting position, not while lying on their side. This is why some providers use dynamic imaging, comparing X-rays taken while sitting and standing, to check for instability.
Treatment and Recovery
Most tailbone pain improves with conservative measures over the course of several weeks to a few months. The first-line approach is simple: reduce the pressure on the coccyx. A wedge-shaped or donut-shaped cushion designed to offload the tailbone while sitting is one of the most effective tools. Avoiding prolonged sitting, applying ice to the area in the first few days after an injury, and taking over-the-counter anti-inflammatory pain relievers can all help.
Pelvic floor physical therapy is another well-supported option, particularly for chronic cases. A retrospective study of 79 patients who completed pelvic floor therapy (averaging about nine sessions) found that their average pain ratings dropped from roughly 5 out of 10 to under 2 out of 10, and their highest pain ratings fell from nearly 9 to about 5. Patients reported an average global improvement of about 72%. This approach works by addressing tension and dysfunction in the muscles attached to the coccyx, which often contribute to ongoing pain even after the initial injury has healed.
For pain that doesn’t respond to cushions and physical therapy, injections are an option. Corticosteroid injections into the area around the coccyx can deliver significant relief. In clinical reports, patients have experienced pain reductions of 70% or more after a single guided injection. Nerve block injections targeting the nerves near the coccyx have also shown substantial improvements in both pain and function lasting at least 12 weeks.
Surgical removal of the coccyx (coccygectomy) is rare and reserved for severe, treatment-resistant cases. Recovery from surgery takes months, and even after removal, some patients benefit from continued pelvic floor therapy to manage residual symptoms.