The knee capsule
Knee joint capsule · capsula articularis genus
The fluid-filled sleeve that wraps the knee joint.
What it does
A fibrous capsule surrounds the knee joint, lined with a membrane that makes slippery synovial fluid. The fluid lubricates the joint and feeds its cartilage. A pad of fat below the kneecap fills the space at the front.
Surprising fact
The knee is the largest joint in the body, and its lining extends up under the thigh muscles in a pouch above the kneecap.
Why it matters
After injury or in arthritis, the lining can produce too much fluid, causing "water on the knee", a visible swelling around the kneecap.
Nearby
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Sources
Drafted with AI help; awaiting a human fact-check against these sources.
Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.