The femur is the only bone of the human thigh. It is both the longest and the strongest bone in the human body, extending from the hip to the knee.
Important features of this bone include the head, medial and lateral condyles, patellar surface, medial and lateral epicondyles, and greater and lesser trochanters. The head is where the bone forms the hip joint with the innominate bone. The condyles are the points of articulation with the tibia, which is a lower leg bone. The patellar surface is the groove where the bone articulates with the patella, or knee cap. The epicondyles and trochanters are all important attachment sites for various muscles.
The human femur can resist forces of 1,800 to 2,500 pounds, so it is not easily fractured. A break in this bone can only result from a large amount of force, such as can occur during a car accident or a fall from an extreme height. Such an injury can take three to six months to heal.