What could cause pain at the back of the knee?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Pain at the back of the knee, also called posterior knee pain, is commonly caused by injuries (such as a hamstring strain, meniscus tear, or ligament sprain), arthritis, or fluid buildup like a Baker's cyst. Symptoms can range from mild stiffness to sharp pain, swelling, or difficulty straightening the leg.

Because the back of the knee contains muscles, tendons, ligaments, nerves, and blood vessels, identifying the exact cause requires evaluating your specific symptoms. Some conditions resolve with rest, while others—like blood clots or ligament tears—need prompt medical attention.

Rather than guessing, the smartest next step is a free, instant, online symptom check. In just a few minutes, you'll receive AI-powered insights based on your unique symptoms, helping you understand possible causes and decide whether to self-care, see a doctor, or seek urgent help.

Reviewed for medical accuracy: 07/14/2026

Important Next Steps

Discover causes of back-of-knee pain Learn if back-knee pain needs care See whether knee pain could be serious Find OTC relief for back-knee pain Find a doctor for knee pain Understand home remedies for back-knee pain Discover likely causes of your knee pain

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Explanation

There are a few common reasons why you might feel pain behind your knee:

Baker's Cyst: This is a fluid-filled lump that forms behind the knee. It happens when the knee joint produces too much fluid, causing swelling and discomfort.
Hamstring Injuries: The hamstrings are the muscles at the back of your thigh. If these muscles get strained or injured, it can lead to pain behind the knee.
Knee Osteoarthritis: This is a condition where the knee joint wears down over time. It can cause pain, stiffness, and swelling, sometimes felt at the back of the knee.
Knee Effusion: Also known as a "water on the knee," this is when excess fluid builds up in or around the knee joint. This swelling can make the knee feel tight and painful.

If you are experiencing pain behind your knee, it's important to see a healthcare professional. You can start by using a free symptom checker to better understand your symptoms and determine the best next steps for treatment.

(References)

English S, Perret D. Posterior knee pain. Curr Rev Musculoskelet Med. 2010 Jun 12;3(1-4):3-10. doi: 10.1007/s12178-010-9057-4. PMID: 21063493; PMCID: PMC2941578.
Updated 2023 Jun 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507884/
Updated 2024 Feb 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532279/

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