Some of these are minor and self-limiting — others require prompt treatment.
When to Worry: Red Flags to Watch For
While some swelling goes away on its own, here are signs that mean you should see a doctor as soon as possible :
🔴 Sudden, severe swelling
🔴 Significant pain or warmth around the knee
🔴 Redness or fever-like symptoms
🔴 Difficulty walking or bearing weight
🔴 History of recent injury or infection
🔴 One-sided leg swelling and calf pain – Could indicate DVT
These symptoms don’t always point to something life-threatening — but they shouldn’t be ignored .
7 Most Likely Reasons Your One Knee Is Swollen
1. You Recently Injured It
Even if you don’t remember a direct hit, small injuries from twisting, squatting, or lifting can strain your knee joint.
Common culprits: Meniscus tear, ACL/MCL injury, patellar tendinitis
2. You Have a Baker’s Cyst
A Baker’s cyst forms behind the knee and often develops after inflammation from arthritis or cartilage damage.
It doesn’t always hurt, but it can make your knee feel tight or full at the back , especially when bending.
3. Gout or Pseudogout Flare-Up
Gout typically affects the big toe, but it can also show up in the knees — often in just one.
Pseudogout, caused by calcium pyrophosphate crystals, behaves similarly but tends to strike older adults.
4. Infection in the Joint
Septic arthritis is rare but serious. It causes rapid swelling, redness, warmth, and pain — and can worsen quickly without treatment.
People with diabetes, weakened immune systems, or open wounds near the knee are at higher risk.
5. Bursitis
Repetitive kneeling or pressure on the front of the knee can inflame the bursa — fluid-filled sacs that cushion the joint.
This condition, called prepatellar bursitis , makes the knee look puffy and swollen — but it’s usually not painful unless pressed .
6. Arthritis Starting in One Knee
Both osteoarthritis and rheumatoid arthritis can begin in one joint before spreading.
If your knee feels stiff in the morning, gets worse after activity, and improves with rest — this could be the case.
7. Venous Issues (Like Deep Vein Thrombosis)
If the entire leg below the knee is swollen , warm, and possibly tender, consider deep vein thrombosis (DVT) — a potentially life-threatening condition where a blood clot forms in the leg veins .
⚠️ If you notice calf pain, shortness of breath, or chest discomfort , seek emergency care immediately.
How to Reduce Swelling at Home
If there’s no major pain or red flags , try these at-home remedies to ease swelling and support recovery:
✅ Rest and Elevate the Leg – Helps reduce fluid buildup
✅ Apply Ice – 15–20 minutes several times a day
✅ Compression Wrap – Gentle compression helps control swelling
✅ Over-the-Counter NSAIDs – Ibuprofen or naproxen can reduce inflammation
✅ Avoid Strenuous Activity – Give your knee time to recover
✅ Light Stretching and Movement – Prevents stiffness and promotes circulation
However, if swelling returns or worsens, it’s time to dig deeper.
Frequently Asked Questions (FAQs)
Q: Why is only one knee swollen?
A: Usually because of localized trauma, infection, or early-stage arthritis — not systemic conditions.
Q: Should I go to the doctor for one swollen knee?
A: Yes, if swelling persists beyond a few days, is painful, or comes with redness or heat.
Q: Can sitting too long cause one knee to swell?
A: Possibly — poor circulation can lead to mild swelling, but true knee swelling usually has another cause.
Q: Is one swollen knee a sign of heart failure?
A: Not typically — heart-related swelling usually appears in both legs and feet , not just one knee.
Q: Can gout affect only one knee?
A: Yes — though it’s less common than foot or ankle involvement, gout can appear in one knee.
Final Thoughts
Waking up to a swollen knee when the other feels fine is enough to raise eyebrows — and concerns.
But not all unilateral knee swelling is created equal. Some causes are minor and temporary , while others may need prompt medical attention .
The key is knowing the difference — and acting fast when needed.
So if your knee won’t stop swelling, listen to your body. It’s trying to tell you something important.
Your health — and mobility — depend on it.
