Home🦵 Why Is One Knee Swollen But Not the Other? A Doctor’s Guide to Sudden, Unilateral Knee Swelling
🦵 Why Is One Knee Swollen But Not the Other? A Doctor’s Guide to Sudden, Unilateral Knee Swelling
Waking up to a puffy, stiff, or painful knee — while the other feels perfectly fine — can be confusing and concerning.
You didn’t recall a major injury.
You haven’t overdone it at the gym.
So why is only one knee swollen?
Sudden swelling in a single knee (called unilateral knee swelling) is more common than you think — and while it’s not always serious, it can be a sign that your body needs attention.
Let’s explore the most common causes, when to worry, and what you can do — straight from a medical perspective.
đź©ş What Is Unilateral Knee Swelling?
Unilateral knee swelling means fluid buildup (effusion) in one knee joint, leading to:
Visible puffiness or puffball-like appearance
Stiffness or tightness
Pain or warmth
Reduced range of motion
