I have a soft lump behind my knee that gets bigger when I stand. What is it?

Why it changes through the day

Standing and walking pump joint fluid backwards through a small natural opening into a sac behind the knee. During the day, especially after long periods on your feet, the sac fills and the lump looks bigger and feels tighter. Lying down overnight lets some fluid drain back, so it often looks smaller in the morning.

The lump is usually slightly to the inner side of the back of the knee and is easier to see with the leg straight. It often feels tight when you bend fully or squat.

What usually lies behind it

• Osteoarthritis, the most common cause in adults from middle age
• A degenerative meniscus tear, often with pain on the inner joint line
• Inflammatory arthritis or gout, which make the knee produce extra fluid
• A cartilage injury or loose body
• In children, often no joint problem at all

What you can do now

• Reduce long periods of standing where you can, and sit with the leg supported when possible
• Ice the back of the knee for 15 to 20 minutes after a long day
• A simple compression sleeve may make it feel more comfortable
• Keep the knee moving with gentle bending and straightening, cycling or swimming
• Avoid deep squats and long sessions sitting on your heels while it is tight

When to see a knee surgeon in Doha

Book an assessment if the lump is growing, painful or limiting bending, or if you also have knee pain, catching or swelling. Go urgently if the calf suddenly becomes swollen, tight and painful, because a leaking cyst and a blood clot can look alike and need different treatment. A lump that is hard, fixed, not in the usual place, or growing without knee symptoms should also be checked promptly. At Aman Hospital, Dr. Gelber examines the lump and the joint, and an ultrasound or MRI confirms the cyst and its cause.