What could a painful lump below the back of knee be?

A painful lump below the knee can have various possible causes. These are a few conditions to consider:

- Baker's cyst: This is a fluid-filled sac that develops behind the knee due to an underlying joint problem, such as osteoarthritis or a cartilage tear. It can cause swelling, pain, and stiffness in the back of the knee.

- Ganglion cyst: A ganglion cyst is a fluid-filled sac that forms on a tendon or joint, often on the back of the knee. It can be firm or soft to the touch and can move around when pressed.

- Bursitis: Bursitis is the inflammation of fluid-filled sacs called bursae, which provide cushioning between tendons and bones. The most common type of bursitis in the knee is called pes anserine bursitis, which affects the region below the knee.

- Muscle strain or tear: A strained or torn muscle in the back of the knee can cause localized pain and swelling.

- Nerve damage: Compression or irritation of a nerve can cause pain and other symptoms in the affected area.

- Blood vessel problems: A blood clot or other issues with blood vessels can cause pain and swelling in the back of the knee.

It's important to see a healthcare provider for proper evaluation to determine the exact cause of the painful lump and to receive appropriate treatment.