Hip & Pelvis

Bone pain every time you sit: weaver's bottom and ischial bursitis

Hee Seung Nam, MD, Orthopedic Surgeon · September 10, 2026

Just as the lump on the outer side of the little toe in tailors who worked sitting cross-legged is called “tailor's bunion,” there is a condition in the buttock too that got its name from an occupation. It is weaver's bottom. The exact diagnosis of this condition, common among weavers who sat all day weaving cloth on a hard wooden chair, is ischial bursitis.

The bone that touches the seat when sitting: the ischial tuberosity

The prominent part at the bottom of the pelvic bone that touches the seat when you sit on a chair is called the ischial tuberosity. It is what people commonly call the “sitting bone.” Between this bone and the buttock muscle (gluteus maximus) is a small fluid-filled sac that reduces friction, the bursa.

What is interesting is that this area looks different when standing and when sitting. When standing, the thick gluteus maximus covers the ischial tuberosity, but when you bend the hip and sit, the gluteus maximus slides upward and the ischial tuberosity meets the chair with only fat and the bursa in between. Contrary to what you might think, we sit on bone, not on buttock muscle.

Figure. A simplified drawing of the structures around the ischial tuberosity.

If you sit on a hard surface for a long time, the bursa is pressed repeatedly and minor damage accumulates. Then fluid fills the bursa, the wall thickens and chronic inflammation develops. This is ischial bursitis. Korean radiology research also names prolonged sitting and occupations with repeated irritation of the bursa, like weaving, as causes.

A real patient's MRI

This is the MRI of a patient who came with pain in the left buttock, in the area of the sitting bone. The images show slices in turn, moving from the top of the pelvis downward.

Unlike the right buttock, a well-defined, brightly glowing (high signal intensity) mass of fluid is seen around the left ischial tuberosity. It is an ischial bursa thickened by constant friction and filled with inflammatory fluid. Patients like this complain, from the moment they sit down on the chair in clinic, of pain and stiffness as if a hard lump were under the buttock.

In a Korean study that analyzed the MRI of 17 cases of ischial bursitis, the bursa appeared bright on T2 images in all, and its size averaged about 4.7 × 3.8 cm. In many cases there was bleeding into the bursa, or the wall was irregularly thickened and septated. So it is sometimes mistaken for a tumor, but it can be diagnosed on MRI from its characteristic location and fluid-sac shape.

Who is the modern-day weaver?

Weavers at a loom are hard to find today, but this condition is still common.

• People who sit to work for long hours: office workers who sit in the same position in front of a monitor all day, and people who drive for long periods
• Cyclists: those who put their weight on a narrow, hard saddle
• People with reduced buttock muscle and padding: when the buttock muscle has wasted with age or too little exercise, or the cushion covering the bone has thinned after major weight loss. In the MRI study above, too, the patients were aged 50 to 82 (average 64).
• People with inflammatory disease: with an inflammatory condition such as rheumatoid arthritis, it tends not to heal and to last long.

Why it is easily mistaken for a lumbar disc problem

Close to the ischial bursa pass the sciatic nerve running down the leg and the nerve that supplies sensation to the skin at the back of the thigh. So when pain radiates down the back of the thigh it can feel similar to sciatica from a lumbar disc. Many people dismiss it as simple muscle pain and suffer for a long time.

On examination I press on the sitting bone to see whether the usual pain is reproduced, and if needed use ultrasound or MRI to see whether the bursa is filled with fluid. In a Korean study analyzing 64 patients with ischial bursitis, 92% had pain on pressing the ischial tuberosity.

Treatment starts with reducing pressure

The most important prevention and first treatment is to reduce the pressure on the ischial tuberosity. Most people get better with step 1 below.

1. Step 1 · Reduce pressure and medication

   Use a soft cushion, or one hollowed out at the sitting bone area to spread the pressure. A donut cushion with a hole only in the middle was originally made for tailbone pain, so if the sitting bone rests directly on the ring when you sit, it is not suitable. If you have to sit for long, get up and change position every 30 to 60 minutes, and add anti-inflammatory painkillers or shock wave therapy. In the long run, strengthen the buttock muscles to build the “built-in cushion” that protects the bone.

2. Step 2 · Injection

   If it does not improve, a steroid and local anesthetic are injected into the bursa, or the accumulated fluid is drained. Because a nerve runs close by, it is safer to inject at the exact spot under ultrasound.

3. Step 3 · Surgery

   In the rare case that it keeps recurring despite treatment, surgery to remove the bursa is done.

In the Korean study above, followed for more than a year, 79.7% improved with step 1 conservative treatment, 17.2% needed an injection, and 3.1% (2 patients) went on to surgery. Patients with inflammatory disease tended not to respond well to conservative treatment.

In closing

• If there is pain, and tenderness to pressure, right below the buttock bone that touches the seat when you sit (the ischial tuberosity), suspect ischial bursitis.
• When you sit, the buttock muscle slides upward and the bone and bursa take the weight, so the habit of sitting on a hard chair for a long time is the biggest cause.
• It can resemble a lumbar disc problem or a hamstring tendon problem, so if needed confirm with ultrasound or MRI.
• Most people improve with cushions, changing posture and medication, and injection or surgery is not often needed.

If a sharp pain under the buttock comes every time you sit on a hard chair, it may be the body's “weaver's warning.”

This article is general medical information. The causes of buttock pain are varied, so please confirm an exact diagnosis through an examination.