Bursitis

What it means

A bursa is a thin, slippery sac that acts as a cushion where a tendon, ligament, or muscle slides over a bone. The body has dozens of them around the shoulders, elbows, hips, knees, and heels, plus many smaller ones elsewhere. When a bursa is irritated, it produces more fluid than usual and the sac becomes distended. On imaging this appears as a fluid pocket in a predictable location, sometimes with thickened walls and surrounding inflammation.

Why it appears on a CT or MRI report

Reports name the specific bursa — subacromial-subdeltoid at the shoulder, olecranon at the elbow, trochanteric at the hip, prepatellar or infrapatellar at the knee, retrocalcaneal at the heel. They describe how much fluid is present, whether the walls look thickened, whether the contents are simple (clear fluid) or complex (debris, septations, blood), and whether the surrounding soft tissue looks inflamed. MRI shows bursal fluid and surrounding oedema clearly; CT may show fluid and any associated bone change.

What it usually means

Most cases are mechanical — caused by repeated friction, pressure, or a single overload episode. Common examples include kneeling for prolonged periods (housemaid's knee), leaning on the elbow (student's elbow), running or new exercise programmes (trochanteric or pes anserine bursitis), and overhead work (subacromial bursitis). Inflammatory conditions such as rheumatoid arthritis, gout, and pseudogout can also flare up in bursae. A smaller number of bursitis cases are infected (septic bursitis), most often at the elbow or knee, usually after a skin break or puncture, and these need antibiotics and sometimes drainage. Septic bursitis tends to be warm, red, very tender, and may come with fever. Most non-infected cases settle within weeks with rest, activity modification, ice, anti-inflammatory medication, and addressing whatever caused the friction. Steroid injection helps stubborn cases, and recurrent or unusually located bursitis may prompt a search for an underlying condition.

When to follow up

Talk to your doctor about the report and your symptoms. Most mechanical bursitis is managed in primary care with rest and rehabilitation. Seek urgent care for warmth, redness, rapidly increasing swelling, fever, or severe pain — these can signal an infected bursa that needs prompt antibiotics or drainage. Persistent bursitis that does not settle, recurs in different locations, or appears alongside joint pain elsewhere is worth investigating for an underlying inflammatory or crystal-related condition.

A plain-language way to picture it

Picture a thin balloon filled with a teaspoon of slippery oil, sitting between a bone and a tendon to stop them rubbing. Most of the time it does its job silently. After a lot of rubbing, the balloon swells up with extra fluid to try to protect the area — helpful in moderation, painful when it overdoes it. Most of the time the swelling settles once the rubbing stops; occasionally something gets into the balloon and it becomes infected.