Subacromial bursitis is inflammation of a small, fluid-filled sac that sits between the bony roof of your shoulder and the rotator cuff tendons beneath it. This bursa normally acts as a cushion, reducing friction every time you move your arm. When it becomes irritated or swollen, the result is shoulder pain that can range from a dull, constant ache to a sharp pinch when you raise your arm overhead. It’s one of the most common causes of shoulder pain in adults.
Where the Bursa Sits and What It Does
The subacromial bursa is sandwiched between the acromion (the bony point at the top of your shoulder blade) and the supraspinatus tendon, one of the four rotator cuff tendons. Think of it as a thin, slippery pad. Normally it’s less than 2 millimeters thick. Its job is to let tendons and bone glide past each other smoothly, especially when you lift your arm out to the side or reach overhead. A companion bursa sits just next to it under the deltoid muscle, and the two often function as a single unit to protect the joint capsule and prevent wear on the rotator cuff.
How It Becomes Inflamed
The space between the acromion and the rotator cuff is already tight. Anything that further narrows this gap or irritates the tissue inside it can trigger bursitis. The most common pathway is repetitive overhead arm movement. Painters, carpenters, warehouse workers, and athletes in sports like swimming, tennis, and baseball repeatedly compress the bursa with each overhead stroke or throw. Over time the bursa thickens, swells with extra fluid, and takes up even more space, which creates a cycle of compression and inflammation.
This overlap with shoulder impingement syndrome is important. Subacromial impingement, the most common type of shoulder impingement, occurs when the bursa or a rotator cuff tendon (or both) gets pinched in that narrow subacromial space. Bursitis is often both a cause and a consequence of impingement: the inflamed bursa swells, which worsens the pinching, which worsens the inflammation.
Less often, a direct blow or a fall onto the shoulder can set things off. Anatomical factors play a role too. Some people have a more hooked or curved acromion shape, which leaves less room for the bursa and makes impingement more likely even with moderate activity.
What It Feels Like
Shoulder bursitis can come on suddenly after an injury or build gradually over weeks. The hallmark symptoms include pain, swelling, stiffness, and a reduced range of motion. Many people describe a dull ache that’s always present in the shoulder, punctuated by a sharper, pinching pain when lifting the arm overhead or reaching behind the back. The outside and front of the shoulder are the most common pain locations.
Night pain is particularly characteristic. Sleeping on the affected shoulder typically makes the pain noticeably worse, often enough to wake you up. During the day, you may also notice tenderness to even a light touch over the top of the shoulder, along with warmth or slight redness in the area. Everyday tasks like putting on a coat, reaching for a high shelf, or fastening a seatbelt become difficult.
Who Is Most at Risk
The biggest risk factor is any activity that involves repetitive overhead arm motion. Occupationally, this includes painters, electricians, plasterers, and anyone who works with their hands above shoulder height for extended periods. In sports, swimmers, volleyball players, tennis players, and baseball pitchers are especially prone. Age also matters: the rotator cuff tendons gradually weaken over time, making the bursa more vulnerable to compression. People who have had a previous shoulder injury, even a minor one, are at higher risk of developing bursitis later.
How It’s Diagnosed
A clinician can often identify subacromial bursitis through a physical exam. One common test involves raising your arm to shoulder height, bending the elbow to 90 degrees, and then rotating the forearm downward. If this reproduces your pain, it suggests the bursa or rotator cuff is being pinched. This particular maneuver has a sensitivity ranging from 62% to 92%, meaning it catches most cases but isn’t perfect on its own. When it’s combined with two other tests (checking for pain in a specific arc of shoulder movement and testing the strength of one of the rotator cuff muscles), the diagnostic accuracy improves substantially.
Ultrasound is a useful imaging tool because it can directly measure bursa thickness. A normal subacromial bursa is thinner than 2 mm on ultrasound. Interestingly, even bursa measurements under that threshold can indicate a problem if the affected side is thicker than the opposite shoulder. MRI may be ordered when the clinician suspects a rotator cuff tear or wants to rule out other causes. X-rays don’t show the bursa itself but can reveal bone spurs or acromion shape that contribute to impingement.
Conservative Treatment
Most cases of subacromial bursitis improve without surgery. The first step is activity modification: temporarily avoiding the overhead movements that provoke pain. This doesn’t mean immobilizing the shoulder entirely, which can lead to stiffness and a frozen shoulder. Instead, the goal is to stay active within a pain-free range while the inflammation settles.
Ice applied for 15 to 20 minutes several times a day can reduce swelling in the early stages. Over-the-counter anti-inflammatory medications help manage both pain and inflammation. Physical therapy is the cornerstone of treatment and typically focuses on two goals: restoring range of motion and strengthening the muscles that stabilize the shoulder blade and rotator cuff. Stretching exercises often start gently. A posterior shoulder stretch, for example, involves pulling the affected arm across the body and holding for 15 to 30 seconds, repeated two to four times. Strengthening exercises are added as pain allows, usually beginning with resistance bands before progressing to weights.
More advanced stretches, like reaching up behind the back, are generally introduced later, once most of the range of motion and strength have returned. The key principle across all exercises is starting slowly and backing off if pain increases.
Steroid Injections
When rest, medication, and physical therapy aren’t enough, a corticosteroid injection into the subacromial space is a common next step. The injection delivers a powerful anti-inflammatory directly to the inflamed bursa. Results from clinical studies are encouraging: about 66% of patients report meaningful pain relief within two weeks. That number climbs to 70% at three months and 78% at six months, suggesting the benefits tend to hold up rather than fade quickly.
Injections aren’t a long-term solution on their own. Most clinicians limit the number of injections to avoid potential weakening of nearby tendons. They work best when paired with a structured physical therapy program that addresses the underlying mechanical problem.
When Surgery Is Considered
Surgery is reserved for cases that don’t respond to several months of conservative treatment. The most common procedure is a subacromial decompression, performed arthroscopically through small incisions. The surgeon shaves away a small amount of bone from the underside of the acromion to create more room for the bursa and rotator cuff. The inflamed bursa itself may be removed; the body typically regenerates a new, healthy one. Recovery from arthroscopic decompression generally involves several weeks in a sling followed by a graduated physical therapy program. Most people return to normal activities within three to six months, though full recovery for overhead athletes can take longer.
What Recovery Looks Like
For mild cases caught early, symptoms often improve within a few weeks of activity modification and anti-inflammatory treatment. Moderate cases treated with physical therapy typically take six to eight weeks to show significant progress, though full resolution can take three months or more. The timeline depends heavily on how long the bursitis has been present before treatment starts and whether there’s an underlying rotator cuff issue complicating things.
Recurrence is common if the factors that caused the bursitis aren’t addressed. For someone whose job involves repetitive overhead work, that might mean adjusting workstation height, taking more frequent breaks, or using tools that reduce shoulder strain. For athletes, it often means correcting throwing or swimming mechanics and maintaining a consistent rotator cuff strengthening program even after the pain resolves.