The femur is the thigh bone.

The femur from the front.

Key components of the femur within the knee joint.
Anatomy of the femur in the knee joint
Only the lower (distal) end of the femur forms part of the knee joint. Together with the plateau of the tibia, the bony ends are encased by the knee capsule so that the joint is water-tight.
Synonyms:
thighbone
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