Prepatellar Bursitis (Housemaid's Knee)

What prepatellar bursitis is

Bursae are thin, slippery sacs that let skin and tendons glide over bone. The prepatellar bursa lies just under the skin in front of the kneecap (patella). Normally it is flat and contains only a trace of fluid. Pressure, friction or a blow irritates its lining, which produces fluid, so the bursa swells like a water balloon. Because the bursa sits outside the knee joint, the joint itself is usually unaffected.

Prepatellar bursitis is one of the most common types of bursitis. The bursa over the point of the elbow behaves the same way (elbow bursitis).

Causes and risk factors

• Repeated kneeling: plumbers, carpet and tile layers, roofers, gardeners, cleaners, miners and people who pray kneeling for long periods
• A direct blow or fall onto the kneecap, as in wrestling, football, volleyball or basketball
• Infection: bacteria, usually Staphylococcus aureus, enter through a scrape, cut or insect bite over the knee. Because the bursa is so close to the skin, infection is common here
• Inflammatory conditions: gout, pseudogout and rheumatoid arthritis
• Higher infection risk with diabetes, alcohol use disorder, kidney disease and immune-suppressing medicines

Symptoms

• a soft, rounded swelling directly over the kneecap, sometimes as large as a golf ball or bigger
• tenderness when pressing on it or kneeling
• mild pain when bending the knee fully, as the skin tightens
• normal or near-normal knee movement and walking

Signs it may be infected

Infection cannot always be ruled out by appearance, so a red, warm bursa is usually sampled.

Is it bursitis or fluid in the knee joint?

Prepatellar bursitis swells in front of the kneecap, so you can usually still feel the edges of the kneecap's sides and the knee bends well. Fluid inside the knee joint (an effusion) swells the whole knee, including above and around the kneecap, and makes bending stiff and painful. Joint swelling with heat and fever may be septic arthritis, which is an emergency.

Diagnosis

A doctor examines the knee, checks movement, looks for wounds and asks about kneeling, injury and other conditions. Tests depend on the findings:

• Aspiration: a needle draws fluid from the bursa. The fluid is checked for cells, crystals (gout) and bacteria. This is the key test for infection.
• Blood tests: white cell count, CRP and uric acid.
• X-ray: if there was a fall, to look for a fracture or foreign body.
• Ultrasound: shows fluid in the bursa and helps guide aspiration.

Treatment

Non-infected prepatellar bursitis

• Avoid kneeling and pressure on the knee until the swelling settles.
• Ice wrapped in a cloth for 15 to 20 minutes several times a day in the first days.
• Compression with an elastic knee sleeve or bandage.
• Elevation when resting.
• Anti-inflammatory pain relief such as ibuprofen or naproxen at the label dose, if suitable. Avoid NSAIDs if you have kidney disease, stomach ulcers or take blood thinners.

Most cases improve within 2 to 6 weeks. A large, tense bursa may be drained by a doctor. Steroid injections are sometimes used for persistent non-infected bursitis, but only once infection has been excluded, because they can worsen an infection and thin the skin.

Infected (septic) prepatellar bursitis

• Antibiotics targeting staph and strep, usually by mouth for 10 to 14 days or longer. IV antibiotics in hospital if there is fever, spreading cellulitis or weak immunity.
• Repeated aspiration to remove pus.
• Surgical drainage or removal of the bursa if it does not respond.

Surgery for chronic bursitis

If swelling keeps returning despite treatment, the bursa can be removed (bursectomy) through an open incision or keyhole (arthroscopic or endoscopic) technique. The body usually forms a new, normal bursa afterwards. Wound healing on the front of the knee can be slow, so surgery is reserved for persistent cases.

Prevention

• Wear cushioned kneepads for kneeling work, gardening and sports.
• Use a kneeling mat and take regular breaks to stand and stretch.
• Clean and cover any cut or scrape on the knee promptly.
• Keep gout and other inflammatory conditions under control.

Frequently asked questions

What does prepatellar bursitis look like?

It looks like a soft, rounded, squishy swelling sitting directly on top of the kneecap, sometimes as big as an egg or larger. The skin is normal in non-infected cases. In infected bursitis the swelling is red, warm and very tender, and there may be a scrape or cut nearby.

How long does prepatellar bursitis take to go away?

Non-infected bursitis usually settles in 2 to 6 weeks with rest from kneeling, ice and compression. Infected bursitis improves within days of starting antibiotics but may take a few weeks to resolve fully. Some cases become chronic and need drainage or surgery.

Should I drain prepatellar bursitis myself?

No. Never try to pop or drain it yourself, as this can introduce bacteria and cause a serious infection. A doctor can safely drain it with a sterile needle when needed and test the fluid for infection or gout.

Can I keep working or exercising with housemaid's knee?

You can usually walk and do activities that do not involve kneeling or direct pressure on the knee. Avoid kneeling, crawling and contact sports until the swelling settles, and use padded kneepads when you return. Stop and see a doctor if the swelling becomes red, hot or painful.

How do I know if knee bursitis is infected?

Infection is more likely if the swelling is red, warm and very painful, if it started after a scrape or cut, or if you have a fever or feel unwell. Many infected bursae do not cause fever, so any red, hot swelling over the kneecap should be checked by a doctor.