: Injury to the upper part of the calf muscle where it meets the back of the knee.
: A fluid-filled sac that forms behind the knee, often causing a bulge and a feeling of tightness. Pain in the back of my knee – Mr Validity
: A sprain or tear of the Posterior Cruciate Ligament, usually caused by a direct blow to the front of the knee. Recommended Recovery Steps Pain Behind Knee (Back of Knee Pain) - Cleveland Clinic : Injury to the upper part of the