I have a lump behind my knee. What is it?

Why Baker's cysts form

The knee joint makes lubricating fluid. When something inside the knee is irritated, such as a meniscus tear, cartilage wear or inflammatory arthritis, extra fluid is produced and can be pushed into a small sac at the back of the knee, forming a cyst. It often feels bigger or tighter after activity and on straightening the leg, and softer when the knee is bent.

Many Baker's cysts cause only a feeling of fullness or tightness. Large ones can ache, limit bending, or occasionally leak or burst into the calf, causing sudden calf pain and swelling.

Lumps that are not a Baker's cyst

• A lump that pulses with your heartbeat can be a popliteal artery aneurysm, a widened artery that needs vascular assessment
• A hard, fixed or steadily growing lump, especially if it aches at rest or at night, should be imaged to exclude a soft-tissue or bone tumour, which is rare
• A red, hot, tender lump with fever may be infection
• A swollen calf with the lump, particularly after a flight or surgery, needs same-day emergency assessment to rule out a blood clot

Looking after it at home

Reduce the activities that make the knee swell, use ice after exercise, and keep the knee moving gently. Simple painkillers can help if they are safe for you. Avoid squeezing or massaging the lump.

When to see a knee surgeon in Doha

Book an assessment if the lump is painful, getting larger, limits bending, or if you have other knee symptoms such as catching or swelling. Dr. Gelber examines the knee to find the underlying cause, and an ultrasound or MRI confirms the diagnosis. Treatment focuses on the problem inside the joint; draining the cyst alone often lets it return, and surgery on the cyst itself is rarely the first step.