The joy of summer sports and yard work has resulted in a number of patients coming to see me complaining of sore shoulders, elbows, hips and knees. Many of these folks have been suffering from bursitis. Most people have heard of bursitis, but what is it really?

Any time a medical term ends in "itis," it indicates inflammation of the tissue or organ involved. In this case, bursitis is an inflammation of a bursa (pleural bursae or bursas). Bursa is Latin for purse, a very good descriptor of what it looks like - a small sac made of connective tissue.

A bursa is lined with a synovial membrane that secretes fluid, filling the sac. This turns the bursa in to a little pillow filled with a slippery liquid that helps cushion structures around it. It also allows these structures to glide more easily over each other. Here's a fun activity for the kids; make your own bursa by putting just a little water in a small balloon. Then put an object like a book on top of it and roll it around on the table to get an idea of how bursae work.

There are many bursae in the body. The ones that cause the most problems are found in the shoulder, elbow, hip, and knee. These joints are fairly complex and have many bones, tendons and ligaments that intersect and move over each other. Without the aid of bursae, these structures would rub together, causing a lot of pain as well as wear and tear.

All cases of bursitis have a common presentation. There is pain around a joint, often with some associated swelling. The area is tender to touch and there is pain with movement of the joint. There can be superficial redness and warmth as well. These are the classic signs of inflammation: redness and swelling with heat and pain.

The most common cause of bursitis is repetitive motion of a joint, especially in people who overdo things. Shoulder bursitis usually follows too much throwing (common in weekend warriors), pulling or pushing (garden work), or overhead activity such as painting a wall with a roller. The subacromial bursa is the one most commonly involved in the shoulder. It is found just under the end of the clavicle (collarbone).

The olecranon bursa in the elbow is also a common location for bursitis. You may have seen someone with swelling over the pointy part of the elbow. The point is formed by a piece of bone called the olecranon that has a bursa over it for the arm tendons to slide over. Bursitis in this location is usually the result of trauma from resting or rubbing the elbow on something or banging the elbow into things. Basketball players posting up in the paint are often afflicted from the constant elbowing that occurs.

Hip bursitis is not as common as that in the shoulder or elbow. It is four times more common in women and can occur at any age. It is usually associated with direct trauma such as a fall and is often found in runners. The bursa involved is called the greater trochanteric bursa and is found over the outside of the upper thigh where a protrusion of bone can be felt. Often these patients describe pain up and down the outside of the thigh and increased pain when lying on the affected side.

Knee bursitis was made famous by the sidelining of Peyton Manning in 2008. The bursa most commonly involved in the knee is the pre-patellar bursa that is positioned between the kneecap (patella) and the skin of the knee. Pre-patellar bursitis results in swelling over or above the kneecap and pain with bending the knee. Since the knee is subject to skin abrasions, and the bursa lies directly under the skin, it can also become infected. This may require surgical drainage, which is what happened to #18.

Pre-patellar bursitis is usually caused by direct trauma and is often seen in those who kneel frequently. It has the nickname "housemaid's knee," for it was frequently seen in women who used to kneel while scrubbing floors. Carpet layers are also at risk.

Treatment for all types of bursitis involves resting, icing and anti-inflammatory medication. Occasionally the fluid has to be drained and the bursa may need to be injected with steroid medication to reduce the inflammation.

Dr. John Roberts is a local physician. His column appears in Monday's edition of the Times, and he has a daily health tip on the front page. Dr. Roberts is one of the owners of Sagamore News Media, parent company of The Times.