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# Prepatellar bursa

The prepatellar bursa is a thin fluid sac in front of the kneecap, under the skin; kneeling can make it swell (bursitis).

Official name: Subcutaneous prepatellar bursa

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## What it is

A thin fluid sac in front of the kneecap.

## What it does

Reduces friction under the skin; it can swell with frequent kneeling (bursitis).

## Key points

- Swelling here is not a joint effusion: the bursa lies in front of the patella, the knee still bends almost fully and the joint line is not tender
- The bursa around the knee most often infected (septic bursitis), usually through a small skin break from kneeling; Staphylococcus aureus is the usual organism
- Gout and rheumatoid arthritis can also inflame it, without involving the joint

## Key facts

**Where**
Subcutaneous, between skin and front of patella

**Function**
Lets skin glide over patella; inflamed by kneeling (housemaid's knee); does not communicate with joint

## Relations

**Superficial**
[Skin](https://durgical.com/en/anatomy/skin/) and thin subcutaneous fat over the [patella](https://durgical.com/en/anatomy/patella/) and the upper [patellar ligament](https://durgical.com/en/anatomy/patellar-ligament/)

**Deep**
Front of the patella and the fibres of the [quadriceps tendon](https://durgical.com/en/anatomy/tendon-of-quadriceps-femoris-muscle/) that pass over it

**Below**
Patellar ligament; the superficial infrapatellar bursa lies further down, over the tibial tuberosity

## How to find it

A distended bursa is a soft, well-defined dome directly over the patella that can blur the kneecap's outline; when infected the skin over it is warm and red. Pressing the patella down does not produce a patellar tap, because the fluid is in front of the bone, not under it.

## On imaging

Ultrasound shows a fluid collection superficial to the patella and separate from the joint, with thickened walls and increased Doppler flow when inflamed. Radiographs are used mainly to look for a patellar fracture or a foreign body after a fall or wound.

## Clinical notes

- Septic and non-septic bursitis are told apart by fluid drawn from the bursa itself (cell count, Gram stain, culture, crystals); the joint is not entered
- A fall onto the knee can bleed into the bursa (traumatic bursitis), and the same blow can fracture the patella
- Chronic or recurrent bursitis thickens the bursal wall; removal of the bursa (bursectomy) is kept for persistent cases

## Anatomical variants

- Instead of a single sac there may be up to three layers in front of the patella: subcutaneous, subfascial and subtendinous prepatellar bursae

## Related conditions

- [Prepatellar Bursitis](https://durgical.com/en/conditions/prepatellar-bursitis/)

## Test yourself

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

## How is prepatellar bursitis told apart from a knee effusion?

The swelling lies in front of the patella, the knee still bends almost fully, the joint line is not tender and there is no patellar tap.

## Which organism usually causes septic prepatellar bursitis, and how does it enter?

Staphylococcus aureus, usually through a small skin break from kneeling.

## What is the common name for prepatellar bursitis from kneeling?

Housemaid's knee.

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

## Its names

**Official Latin (TA2)**
bursa subcutanea prepatellaris; bursa subfascialis prepatellaris TA2 2735

**Official Spanish (DeCS)**
Bolsas prerrotulianas subcutánea y subfascial DeCS D002061

**English (TA2)**
Subcutaneous prepatellar bursa

**Also called**
bursa prepatellaris subcutanea

## Related

- [Patella](https://durgical.com/en/anatomy/patella/)

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, Knee](https://www.ncbi.nlm.nih.gov/books/NBK500017/).

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Representative model, for educational purposes only.

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