Bursitis develops when one of the small, fluid-filled sacs (bursae) that cushion your joints becomes inflamed. The most common cause is repetitive motion or prolonged pressure on a joint, but it can also result from a sudden injury, an infection, or an underlying condition like gout or rheumatoid arthritis. Your body has more than 150 bursae, and any of them can become irritated, though the shoulders, elbows, hips, and knees are the most frequent trouble spots.
Repetitive Motion and Prolonged Pressure
The single most common path to bursitis is doing the same movement over and over. Each repetition creates a small amount of friction against the bursa. Over time, that friction triggers the blood vessels in the area to widen and become more permeable. Fluid and protein leak into the bursa, the lining cells multiply, and the sac swells with excess liquid. You don’t feel much at first, but eventually the inflammation reaches a tipping point and the joint becomes painful, stiff, or visibly swollen.
Sustained pressure works the same way. Kneeling on a hard floor for hours compresses the bursa at the front of the kneecap. Leaning on your elbows at a desk irritates the bursa at the tip of the elbow. The tissue doesn’t get a chance to recover between bouts of pressure, so inflammation builds gradually over days or weeks.
Jobs That Put You at Risk
Any occupation involving repetitive motion or awkward positioning raises the odds. The Canadian Centre for Occupational Health and Safety identifies several high-risk pairings:
- Knee bursitis: carpet layers, floor installers, gardeners, carpenters, and plumbers, all of whom spend long stretches kneeling or squatting
- Elbow bursitis: plumbers, HVAC technicians, and musicians who lean on or repeatedly flex their elbows
- Hip bursitis: warehouse laborers and others who do heavy lifting, repetitive bending, or prolonged cycling
- Shoulder bursitis: painters, construction workers, and anyone who reaches overhead repeatedly throughout the day
Sports and Overhead Activities
Athletes who repeat the same forceful motion are especially vulnerable. Throwing a baseball, rowing, swinging a tennis racket, and swimming all involve powerful overhead shoulder movements that can pinch the bursa between the bones of the shoulder joint. The more force behind each repetition, the faster irritation develops. Weekend warriors who suddenly ramp up activity after a long break often trigger bursitis because the tissue hasn’t been conditioned to handle the load.
Runners face a different version of the problem. The repeated contraction of muscles and connective tissue along the outside of the hip during each stride can irritate the bursa at the bony prominence of the hip. Running on banked or sloped surfaces makes things worse because it creates an uneven stride, essentially forcing one leg to function as though it were shorter than the other.
Direct Injury or Trauma
A single hard blow can cause bursitis almost immediately. Falling onto your knee, banging your elbow against a hard surface, or taking a hit during a contact sport can damage the bursa wall and fill the sac with blood or inflammatory fluid. This type of bursitis tends to come on faster and hurt more intensely than the slow-building kind from repetitive use. The swelling is often visible within hours.
Infection (Septic Bursitis)
Bursae that sit just beneath the skin, like the ones at the elbow and kneecap, are vulnerable to bacterial infection. A cut, scrape, insect bite, or even a small puncture wound near the joint can allow bacteria to enter the bursa directly. The bacterium most commonly responsible is Staphylococcus aureus. Once inside, it multiplies quickly in the warm, fluid-rich environment.
Septic bursitis is more serious than the non-infectious kind. The joint typically becomes red, warm, and very tender, sometimes with fever. The fluid inside an infected bursa can contain dramatically elevated white blood cell counts, sometimes exceeding 70,000 cells per microliter compared to fewer than 2,000 in a non-infected bursa. It requires antibiotic treatment and occasionally surgical drainage if the infection doesn’t respond.
Gout, Arthritis, and Other Conditions
Several systemic diseases can trigger bursitis even without repetitive motion or injury. Gout deposits sharp uric acid crystals in and around joints, and these crystals can irritate nearby bursae, particularly at the elbow and knee. Rheumatoid arthritis creates widespread joint inflammation that frequently extends to the bursae. Psoriatic arthritis and thyroid disease are also associated with bursitis, though less commonly.
Calcium deposits that form in or near a bursa, especially in the shoulder, can act like internal grit, creating friction and inflammation even during normal movement. These deposits sometimes appear without any obvious underlying disease.
How Aging Changes Your Risk
Your bursae become more vulnerable as you age, largely because the fluid that lubricates your joints changes in composition. Production of hyaluronic acid, the molecule responsible for making that fluid slippery and viscous, declines over time. Levels of lubricin, a protein that minimizes friction between joint surfaces, also drop. The result is thinner, less protective fluid that allows more mechanical stress to reach the bursa.
At the same time, the balance of inflammatory signals inside your joints shifts. Older joints tend to produce more pro-inflammatory molecules and fewer anti-inflammatory ones, creating a low-grade chronic inflammation that makes it easier for bursitis to take hold from even mild triggers. Enzymes that break down structural tissue become more active, further weakening the joint’s natural defenses. This is why a motion you performed without trouble at 30 might cause a flare-up at 60.
Biomechanical Factors
The way you walk, stand, and move can set you up for bursitis even if you don’t have a physically demanding job or hobby. A leg-length discrepancy, even a small one, shifts your gait enough to create extra friction on the hip bursa with every step. Spinal problems and issues with the sacroiliac joint (where your spine meets your pelvis) can alter your movement patterns in ways that overload specific bursae. Prior hip surgery can also change the mechanics of the joint enough to provoke inflammation on the outer side of the hip.
Poor posture plays a role too. Rounded shoulders compress the space where the shoulder bursa sits, increasing the chance of impingement during overhead movement. Tight muscles around the hip, particularly the iliotibial band running along the outside of the thigh, pull repeatedly across the hip bursa during walking and running.
Multiple Causes Often Overlap
In practice, bursitis rarely comes from a single factor acting alone. A 55-year-old gardener who develops knee bursitis is dealing with both the repetitive kneeling and the age-related decline in joint lubrication. A runner with hip bursitis may have a slight leg-length difference compounded by tight connective tissue and training on uneven terrain. Understanding which factors apply to your situation helps explain why the problem developed and what changes are most likely to prevent it from coming back.