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 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 and thin subcutaneous fat over the patella and the upper patellar ligament
- Deep
- Front of the patella and the fibres of the quadriceps tendon 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
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.
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
Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Skin Bursa; Anatomy, Bony Pelvis and Lower Limb, Knee.
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Representative model, for educational purposes only.
