Prepatellar Bursitis

Introduction

Prepatellar bursitis is the painful inflammation of the bursa, or fluid-filled cushion, that sits in front of the kneecap (patella). Triggered by an injury or infection, prepatellar bursitis can occur suddenly and clear up on its own, or become a chronic problem.

Anatomy

A bursa makes it easier for skin, muscles, or tendons to slide across bones throughout the body, including the knee. The prepatellar bursa sits underneath the skin in front of the patella. This bursa lets the patella glide easily underneath the skin when you bend and straighten your knee. Although the prepatellar bursa normally contains a small amount of fluid, it can fill with more fluid and swell if it becomes inflamed as a result of an injury.

Causes

Prepatellar bursitis can be acute (sudden onset) or chronic (ongoing). In acute bursitis, a direct blow or fall on the knee tears blood vessels in the bursa. The torn vessels bleed into the bursa sac, causing swelling and triggering an inflammation reaction in the walls of the bursa. The walls may thicken, causing tenderness that remains even after the body reabsorbs the blood. Acute bursitis can also be triggered by an infection when bacteria from an injury—such as a skin wound over the kneecap—spread into the bursa, causing it to fill with pus.

In chronic bursitis, previous episodes of acute bursitis or repeated injuries from overuse (having a job where you constantly work on your knees, for example) irritates and thickens the bursa over time. Attacks of chronic bursitis may last a few days to several weeks, and may come back frequently.

Symptoms

During an acute episode, your kneecap (and just below it) is painful and swollen. Long-standing pain and swelling limit your motion, making it difficult to do things like kneel on the floor. If the bursa is infected, the kneecap becomes swollen and warm to the touch. An abscess—a tender, fluid-filled bump—can form on the kneecap. You may also develop a fever and chills.

If you have chronic bursitis, you might feel small, tender lumps "floating" underneath the skin of your kneecap; these are actually thickened pieces of bursa tissue.

Diagnosis

As discussed in Arthritis and other Joint Problems, your doctor will take a history and perform a physical exam. Tenderness and swelling of the kneecap and, in some cases, the presence of lumps inside your knee, confirm the diagnosis.

If your symptoms started after a fall, your doctor may order an x-ray film to make sure your kneecap isn't fractured. If an infection is suspected, the doctor may drain the fluid and send it to the lab to determine if bacteria are present.

Treatment

An acute attack usually gets better on its own, as the body reabsorbs the blood in the bursa. In the end, the bursa returns to its normal size.

However, if lab tests confirm an infection, you'll have to take antibiotics. In addition, your knee may need to be drained periodically over several days. If the infection is slow to heal, a draining tube is placed in the bursa through a small incision and left there for several days.

For chronic bursitis, wearing a knee pad makes it easier to kneel down. Icing the knee and taking aspirin or ibuprofen can ease pain as well as inflammation. If the swelling doesn't go down, fluid may be drained and a small amount of corticosteroid injected into the bursa to control inflammation.

If such treatments don't relieve the pain, the bursa may have to be surgically removed. Your doctor will take out the sac through an incision made over the top of the knee. You'll need to stay off your feet for a few days to let the incision heal. Afterwards, a new bursa may grow to replace the removed sac. If it grows back correctly, it will function as a normal bursa, helping the kneecap move easily underneath the skin.