Shoulder anatomy · plain english

Shoulder bursitis, explained

A tiny fluid-filled cushion in your shoulder got angry. Here's what's actually going on and what to do about it.

What's the bursa?

Acromion (bone) Bursa 🔥 Rotator cuff Humerus (arm)

The subacromial bursa is a slippery little sac of fluid that sits between the top of your arm bone and the bony roof of your shoulder (the acromion).

Its job: let your rotator cuff tendons glide smoothly under that bony roof when you lift your arm.

When it gets irritated, it swells up. Now the space is tighter, so every time you move, it gets pinched — which irritates it more. Welcome to the pain cycle.

Feels like

  • • Dull ache on the outside/top of the shoulder
  • • Sharp pain lifting your arm overhead or out to the side
  • • Can't sleep on that side
  • • Reaching behind you (seatbelt, back pocket) sucks
  • • Worse after activity, better with rest

Usually caused by

  • • Repetitive overhead motion (painting, swimming, lifting)
  • • A sudden increase in activity
  • • Poor posture (rounded shoulders → less space up there)
  • • Falling on the shoulder
  • • Age (tendons/bursa get crankier over time)
  • • Rarely: infection or gout (that's septic bursitis — needs a doctor now)

How to fix it — the escalation ladder

Start at the top. Give each stage real time before escalating.

1️⃣

Calm it down

Days 1–7

Relative rest (not total rest — don't freeze it up). Stop the aggravating motion. Ice 15 min a few times a day. NSAIDs like ibuprofen if your stomach/kidneys tolerate them. Sleep with a pillow under the arm.

2️⃣

Restore motion

Week 1–3

Gentle range-of-motion: pendulum swings, wall walks, doorway stretches. Pain-free range only. Do this daily so the shoulder doesn't stiffen into a bigger problem (frozen shoulder is way worse).

3️⃣

Rebuild strength

Week 2–6+

This is the actual fix. Strengthen the rotator cuff and the muscles that pull your shoulder blades back and down. Stronger cuff = better tracking = more space for the bursa. Bands are your friend.

4️⃣

See a professional

If no progress in 2–4 weeks

Physical therapist first — they'll find why it happened (posture, weakness, technique). Doctor can consider a corticosteroid injection into the bursa. Ultrasound or MRI if they suspect a rotator cuff tear.

5️⃣

Surgery (rare)

Last resort

Arthroscopic bursectomy or subacromial decompression — only if months of conservative treatment fail. Most people never get here.

🚨 See a doctor now if…

  • • The shoulder is red, hot, and swollen (possible infection)
  • • You have a fever with it
  • • You can't lift your arm at all after an injury (possible tear)
  • • Numbness, tingling, or weakness down the arm
  • • Pain is severe and not improving after a week of sensible care

Pull on a thread

Educational, not medical advice. If it's bad or persistent, see a clinician.