There are several possible causes of coldness below the knee: first, it could be due to an inadequate blood supply to the arteries in the lower extremities. The tissues below the knee are primarily supplied by a branch of the femoral artery, and an embolism or partial embolism of that artery, or a rupture or partial rupture due to injury can cause coldness below the knee. Secondly, cold below the knee can also be caused by abnormal skin sensations, not really cold skin, but cold sensations in the limbs, due to problems with the pain and temperature sensory nerves. Finally, coldness below the knee may also be caused by environmental factors, such as low outside temperatures and poor protection below the knee, which can lead to coldness below the knee.