What is Shoulder Bursitis?
Shoulder bursitis is inflammation of a small fluid-filled sac (called a bursa) that sits between your shoulder bones and the tendons that move your arm, acting like a cushion to reduce friction during movement.
Understanding the Basics
A bursa is essentially a tiny pillow filled with lubricating fluid that prevents your bones, tendons, and muscles from rubbing directly against each other when you move your shoulder 1. Think of it like the oil in a car engine—it keeps everything moving smoothly without parts grinding together.
The main bursa in your shoulder is called the subacromial-subdeltoid bursa, which sits in the space between:
- The bony roof of your shoulder (acromion) above
- The rotator cuff tendons below
- The deltoid muscle on the outside 1
What Happens When You Have Bursitis
When this bursa becomes inflamed or irritated, it fills with extra fluid and swells up 2. This causes:
- Pain when you lift your arm, especially overhead movements
- Swelling in the shoulder area
- Stiffness that makes it hard to move your arm normally
- Tenderness when you press on the shoulder 3
The inflammation makes the bursa thicker and more sensitive, so every time you move your arm, it hurts because the swollen bursa is being squeezed or pinched 2.
Common Causes
Shoulder bursitis typically develops from:
- Repetitive overhead activities (painting, throwing, swimming)
- Direct trauma or injury to the shoulder
- Wear and tear from aging
- Other shoulder problems like rotator cuff tears or calcium deposits in tendons 3, 2
In some cases, the bursa can become infected (septic bursitis), though this is less common in the shoulder than in other joints 3.
Why It Matters
Research shows that bursa inflammation is frequently found in people with shoulder pain—often appearing alongside other shoulder problems like tendon tears or arthritis 2. The bursa contains blood vessels and nerve endings, which explains why it can be so painful when inflamed 1.
The good news is that most people improve with rest, ice, anti-inflammatory medications, and sometimes a cortisone injection directly into the bursa 3. Surgery is rarely needed unless the problem keeps coming back despite treatment 3.