Bursae (one is a bursa) are fluid-filled sacs that cushion areas of friction between tendon and bone or skin. Like air-filled bubble wrap, these sacs reduce friction between moving parts of the body, such as in the shoulder, elbow, hip, knee, and heel.

The number varies, but most people have about 160 bursae throughout the body. Bursae are lined with special cells called synovial cells, which secrete a fluid rich in collagen and proteins. This synovial fluid acts as a lubricant when parts of the body move. When this fluid becomes infected by bacteria or irritated because of too much movement, the painful condition known as bursitis results.

Bursitis Causes

The most common causes of bursitis are trauma, infection, and crystal deposits.

Trauma

Trauma causes inflammatory bursitis from repetitive injury, which results in widening of the blood vessels. This allows proteins and extracellular fluid into the bursae and the bursae react against these “foreign” substances by becoming swollen.

  • Chronic: The most common cause of chronic bursitis is minor trauma that may occur to the shoulder (subdeltoid) bursa from repetitive motion, for example, throwing a baseball. Another example is prepatellar bursitis (in front of the knee) from prolonged or repetitive kneeling on a hard surface to scrub a floor or lay carpet.
  • Acute: A direct blow (let’s say you accidentally bang your knee into a table) can cause blood to leak into the bursa. This rapid collection usually causes marked pain and swelling, most often in the knee.

Infections

Bursae close to the surface of the skin are the most likely to get infected with common organisms; this is called septic bursitis. These bursitis-causing bacteria are normally found on the skin: Staphylococcus aureus or Staphylococcus epidermis. People with diabetes or alcoholism and those undergoing steroid treatments or with certain kidney conditions, or who may have experienced trauma may be higher risks for this type of bursitis. About 85% of septic bursitis occurs in men.

Crystal deposits

People with certain diseases such as gout, rheumatoid arthritis, or scleroderma, for example, may develop bursitis from crystal deposits. Little is known about how this process happens. Uric acid is a normal byproduct of daily metabolism. People who have gout are unable to properly break down the uric acid, which crystalizes and deposits in joints-a mechanism for causing bursitis.

Bursitis Symptoms

Bursitis causes pain and tenderness around the affected bone or tendon. The bursae sacs may swell, often making movement difficult. The most commonly affected joints are the shoulder, elbow, wrist and hand, knee, and foot.

Shoulder

The subacromial (subdeltoid bursa) separates the major tendon (known as the supraspinatus tendon) from the overlying bone and deltoid muscle. Inflammation of this bursa is usually a result of injury to surrounding structures-most commonly the rotator cuff. This is often referred to as “impingement syndrome.” It is often difficult to tell the difference between this type of bursitis pain and a rotator cuff injury. Both cause pain in the side or front of the shoulder.

  • Overhead lifting or reaching activities are uncomfortable.
  • Pain is often worse at night.
  • The shoulder will usually have decreased range of active motion and be tender at specific spots.

Elbow

Olecranon bursitis is the most common form of bursitis. Goose-egg-like, tender red swelling may appears just behind the elbow. This area is at the top of one of the forearm bones called the ulna and is known as the olecranon process.

  • The pain may increase if the elbow is bent because tension increases over the bursa.
  • This bursa is frequently exposed to direct trauma (bumping your arm) or repeated motions from bending and extending the elbow (while painting, for example).
  • Infection is common in this bursa.

Knee

  • Kneecap (prepatellar) bursitis: Swelling on the front of the kneecap is usually associated with either chronic trauma (from kneeling) or an acute blow to the knee. Swelling may occur as late as 7-10 days after a single blow to the area, usually from a fall.
  • Anserine bursitis: The anserine bursa is fan shaped and lies among 3 of the major tendons at the knee. The name anserine (gooselike) comes from the shape of the swollen bursa. When restrained by the 3 tendons, the bursa looks like a goose’s foot.
    • This type of bursitis is most often seen in people with arthritis, especially overweight middle-aged women with osteoarthritis.
    • The pain is typically produced when the knee is bent and is particularly troublesome at night. People often seek comfort by sleeping with a pillow between their thighs.
    • The pain can radiate to the inner thigh and midcalf and usually increases on climbing stairs and at extremes of bending and extending.
    • The area of tenderness is on the middle part of the knee.
    • Anserine bursitis also occurs as an overuse or traumatic injury among athletes, particularly long-distance runners.

Ankle

Retrocalcaneal bursitis occurs when the bursa near the Achilles tendon in the ankle becomes inflamed. This is commonly caused by local trauma associated with wearing a poorly designed shoe (often high heels) or prolonged walking. It can also occur with Achilles tendonitis.

Bursitis in this part of the body often occurs as an overuse injury in young athletes, ice skaters, and female adolescents transitioning to higher heels. The pain is usually on the back of the heel and increases with passive extension or resisted flexion.

Buttocks

Ischiogluteal bursitis causes inflammation of the ischial bursa, which lies between the bottom of the pelvic bone and the overlying gluteus maximus muscle (one side of the buttocks). Inflammation can come from sitting for a long time on a hard surface or from bicycling.

  • The pain occurs when sitting and walking.
  • There will be tenderness over the pubic bone, which may be made worse by bending and extending the leg.
  • The pain may radiate down the back of the thigh.
  • Direct pressure over the area causes sharp pain.
  • The person may hold the painful buttock elevated when sitting.
  • The pain is worse when person is lying down and the hip is passively bent.
  • The person may have difficulty standing on tiptoe on the affected side.

Hip

The iliopsoas bursa is the largest in the body and lies in front of, and deep to, the hip joint. Bursitis here is usually associated with hip problems such as arthritis or injury (especially from running).

  • The pain of iliopsoas bursitis radiates down the front and middle areas of the thigh to the knee and is increased when the hip is extended and rotated.
  • Extension of the hip during walking causes pain so the person may limit the stride on the affected side and take a shorter step.
  • There may be tenderness in the groin area.
  • Sometimes a mass may be felt resembling a hernia. The person may also feel numbness or tingling if adjacent nerves are compressed by the inflamed bursa.

Thigh

The trochanteric bursa, part of the thigh, can be associated trochanteric bursitis, which occurs most frequently in overweight, middle-aged women.

  • It causes deep, aching hip pain along the side of the hip that may extend into the buttocks or to the side of the knee.
  • Pain is aggravated by activity, local pressure, or stretching.
  • Pain is often worse at night.