What Might Cause Pain at the Back of the Knee When Bending?

Reviewed by Garrett Kneese, MD, MPH

Family Medicine

Pain at the back of the knee when bending can be due to fluid buildup, inflammation, or issues with the muscles and tendons in that area. Often, overuse or repetitive bending can irritate these structures, leading to discomfort.

Explanation

When you bend your knee, several things inside the knee can cause pain behind it. One common cause is a Baker's cyst. This is when extra fluid builds up in the knee, often because of inflammation, and creates a small lump at the back. Inflammation (or synovitis) might happen from arthritis or from bending the knee repeatedly, which makes the tissues in the knee get swollen and sore. Also, the muscles and tendons around the knee, like the hamstring muscles or the popliteus tendon, can get stretched or strained. This can happen with sudden movements, sports, or everyday activities that put pressure on your knee. These tissues help support the knee, and if they are overworked or injured, you might feel pain when bending. It is a good idea to pay attention to how often it happens and how long it lasts. If the pain does not improve or makes it hard to move, it's important to talk to a doctor so that the best way to manage it can be figured out.

(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.
Morganti CM, McFarland EG, Cosgarea AJ. Saphenous neuritis: a poorly understood cause of medial knee pain. J Am Acad Orthop Surg. 2002 Mar-Apr;10(2):130-7. doi: 10.5435/00124635-200203000-00008. PMID: 11929207.
Van Ginckel A, Wittoek R, De Mits S, Calders P. Repetitive Knee Bending and Synovitis in Individuals at Risk of and With Knee Osteoarthritis: Data From the Foundation for the National Institutes of Health Osteoarthritis Biomarkers Consortium. Arthritis Care Res (Hoboken). 2019 Oct;71(10):1372-1378. doi: 10.1002/acr.23760. PMID: 30221482; PMCID: PMC6421112.
D'Ambrosi R, Meena A, Raj A, Ursino N, Hewett TE. Anterior Knee Pain: State of the Art. Sports Med Open. 2022 Jul 30;8(1):98. doi: 10.1186/s40798-022-00488-x. PMID: 35907139; PMCID: PMC9339054.

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