What is the lump on the outside of my knee?

Common causes

• Meniscal cyst: a firm, tender swelling on the outer joint line, more prominent when the knee is slightly bent and often smaller when fully bent; it usually sits over a horizontal tear of the lateral meniscus
• Ganglion cyst: a smooth, fluid-filled lump that can arise near the tibiofibular joint just below the outer knee
• Bursitis: a soft, squashy swelling over a bony point, sometimes after kneeling, pressure or a knock
• Bony prominence: the head of the fibula, which many people notice for the first time when the knee is sore
• After an injury: bruising or a swelling over a sprained ligament

What you can do meanwhile

Note when you first saw the lump, whether it changes size with activity or knee position, and whether it hurts. Avoid pressing or kneeling on it, use ice if it is sore, and do not try to drain it. Photos over a few weeks can help your doctor see whether it is changing.

When a lump needs prompt review

Arrange an assessment soon if the lump is growing, feels hard and fixed, aches at night or at rest, or if you have fever, weight loss or a red, hot swelling. Numbness or weakness in the foot with a lump below the outer knee can mean a cyst is pressing on the peroneal nerve. These features are uncommon, but they mean the lump should not be watched at home.

Diagnosis at Aman Hospital in Doha

Dr. Gelber examines the lump and the knee together, because the cause is often inside the joint. Ultrasound shows whether it is fluid-filled, and an MRI is used when a meniscal tear or a cyst near the nerve is suspected. Treatment depends on the cause: many cysts are simply monitored, while a symptomatic meniscal cyst is usually treated by addressing the meniscus tear arthroscopically, since draining the cyst alone often lets it return.