Overview

Knee bursitis is swelling or inflammation of one of the small fluid-filled sacs (bursae) that cushion tissues around the knee. The knee has several bursae; the ones that most often cause trouble are in front of the kneecap (prepatellar), just below it (infrapatellar), along the inner knee (pes anserine) and behind the knee (Baker's cyst).

Most knee bursitis is not dangerous and settles with simple measures. The main thing to take seriously is the possibility of an infected bursa (septic bursitis), which needs prompt medical care.

Typical Pattern

Where you feel it depends on which bursa is involved:

Prepatellar (front of the kneecap): soft swelling over the kneecap, often after kneeling or a direct knock. It may be surprisingly painless and just feel "full." Repeated kneeling gave this the old name "housemaid's knee."
Infrapatellar (below the kneecap): swelling or discomfort just below the kneecap, often from repetitive kneeling or squatting.
Pes anserine (inner knee): aching pain along the inner knee, worse with stairs, rising from a chair or sitting with the knee bent. It often accompanies knee osteoarthritis.
Baker's cyst (behind the knee): a feeling of tightness or a lump behind the knee, more noticeable when the knee is straight. It usually forms because extra joint fluid from arthritis or a meniscus problem backs up into the back of the knee.

Why It Develops

Repetitive pressure from kneeling, or a direct knock to the area
Underlying knee conditions such as osteoarthritis or a meniscus tear that produce extra joint fluid
Inflammatory conditions such as gout
Infection — more likely if the skin over the bursa is broken, or in people with lowered immunity

How It Is Diagnosed

Bursitis is diagnosed mainly by examination: the swelling's location, feel and the history around it. If the bursa is warm, red or painful, or the cause is unclear, a clinician may aspirate fluid to check for infection or crystals. Imaging is used when another knee problem needs to be ruled out.

Treatment

Reduce the aggravating load — padding or avoiding prolonged kneeling
Ice, compression and simple pain relief as recommended by a clinician
Keep moving within tolerance, including gentle knee strengthening, so the surrounding muscles stay strong
Persistent swelling can be aspirated, sometimes followed by a corticosteroid injection, under a clinician's guidance
If the bursitis is linked to arthritis or a meniscus problem, treating the underlying knee condition matters too

Most cases settle with these measures. Surgery is rarely needed and is reserved for stubborn or infected cases that do not respond to other care.

Red Flags: When to Get Assessed Promptly

A hot, red, painful swollen bursa — especially with fever, chills, a break in the skin or lowered immunity
Sudden severe calf swelling and pain with a lump behind the knee — this can be a ruptured Baker's cyst, but deep vein thrombosis must be ruled out
Rapidly increasing swelling, inability to bend the knee, or swelling after significant trauma

References

Rishor-Olney CR, Taqi M, Pozun A. "Prepatellar Bursitis." StatPearls. 2024. https://www.ncbi.nlm.nih.gov/books/NBK557508/
Mohseni M, Mabrouk A, Li DD, Graham C. "Pes Anserine Bursitis." StatPearls. 2024. https://pubmed.ncbi.nlm.nih.gov/30422536/
Hyland S, Sinkler MA, Varacallo MA. "Baker's Cyst." StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK430774/
Baumbach SF, et al. "Prepatellar and olecranon bursitis: literature review and development of a treatment algorithm." Archives of Orthopaedic and Trauma Surgery. 2014;134(3):359-370. https://pubmed.ncbi.nlm.nih.gov/24305696/

This information is for education only and is not a medical diagnosis. InjuryAtlas does not replace an assessment by a qualified health professional. If you have severe pain, visible deformity, numbness, loss of function, or symptoms that are getting worse, seek medical care promptly.

Knee Bursitis