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# Deep hip bursae

The deep hip bursae are small fluid sacs under the deep buttock and hip muscles, including one over the sitting bone; they reduce friction.

Official name: Bursa of piriformis muscle

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## What it is

Several small fluid sacs deep in the buttock and around the hip: under the piriformis, obturator internus, gluteus maximus and [iliacus](https://durgical.com/en/anatomy/iliacus-muscle/) tendons, between the gluteal muscles, and at the top of the biceps femoris near the sitting bone.

## What it does

Reduce friction where muscles and tendons slide over bone or over each other.

## Key points

- Ischial (ischiogluteal) bursitis is the classic weaver's bottom: when sitting, gluteus maximus slides off the ischial tuberosity and the bursa takes the pressure
- The obturator internus bursa lies where the tendon turns sharply round the lesser sciatic notch, over cartilage-covered bone
- The sciatic nerve passes close to the ischial tuberosity, so a large ischial bursa can mimic sciatica

## Key facts

**Where**
Under piriformis, obturator internus (at lesser sciatic notch) and gluteus maximus over ischial tuberosity

**Function**
Reduce friction of deep hip muscles on bone; ischial bursa inflamed by prolonged sitting

## Relations

**Superficial**
[Gluteus maximus](https://durgical.com/en/anatomy/gluteus-maximus-muscle/) covers all of them

**Deep**
Ischial tuberosity (ischial bursa), lesser sciatic notch ([obturator internus](https://durgical.com/en/anatomy/obturator-internus/) bursa), and the greater trochanter and [hip capsule](https://durgical.com/en/anatomy/articular-capsule-of-hip-joint/) ([piriformis](https://durgical.com/en/anatomy/piriformis-muscle/) bursa)

**Lateral**
[Sciatic nerve](https://durgical.com/en/anatomy/sciatic-nerve/), running down over obturator internus and the gemelli, lateral to the ischial tuberosity

**Below**
Hamstring origin on the ischial tuberosity, next to the ischial bursa

## How to find it

Lying on the side with the hips bent, the ischial tuberosity is felt deep in the lower buttock as the sitting bone; tenderness directly over it suggests ischial bursitis or a problem at the hamstring origin. The other bursae are too deep to feel and are met in the posterior approach to the hip.

## On imaging

Ultrasound or MRI shows a fluid collection over the ischial tuberosity or around the [obturator internus tendon](https://durgical.com/en/anatomy/tendon-of-obturator-internus/); MRI also separates bursitis from a hamstring tendon tear and from a soft-tissue tumour.

## Common problems

- They can become irritated and sore (bursitis), for example near the sitting bone after long sitting.

## Clinical notes

- Ischial bursitis and proximal hamstring tendinopathy both hurt on sitting; tendon pain also comes with stretching the hamstrings and resisted knee flexion
- The posterior approach to the hip detaches the piriformis and obturator internus tendons and opens the bursae beneath them
- A chronically enlarged ischial bursa can be mistaken for a soft-tissue tumour

## Test yourself

Think of the answer, then tap the question to see it.

## Which deep hip bursa causes «weaver's bottom», and why?

The ischial (ischiogluteal) bursa: when sitting, the gluteus maximus slides off the ischial tuberosity and the bursa takes the pressure.

## Why can a large ischial bursa mimic sciatica?

The sciatic nerve passes close to the ischial tuberosity.

## How is proximal hamstring tendinopathy told apart from ischial bursitis?

Both hurt on sitting, but tendon pain also comes with hamstring stretching and resisted knee flexion.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
bursa musculi piriformis; bursa ischiadica obturatoris interni TA2 2727

**Official Spanish (DeCS)**
Bolsas del piriforme y del obturador interno DeCS D002061

**English (TA2)**
Bursa of piriformis muscle

**Also called**
isciatic bursa of obturator internus · sciatic bursa of obturator internus muscle

## Related

- [Piriformis](https://durgical.com/en/anatomy/piriformis-muscle/)
- [Obturator internus tendon](https://durgical.com/en/anatomy/tendon-of-obturator-internus/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=2094&filter=ths_termall&q=Bolsa%20Sinovial); [Anatomy, Skin Bursa](https://www.ncbi.nlm.nih.gov/books/NBK554438/); [Anatomy, Bony Pelvis and Lower Limb, Hip](https://www.ncbi.nlm.nih.gov/books/NBK526019/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/bursa-of-piriformis-muscle/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/bursa-of-piriformis-muscle/