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The femur is the longest, heaviest, and strongest human bone. At the proximal end, the pyramid-shaped neck attaches the spherical head at the apex and the cylindrical shaft at the base. There are also two prominent bony protrusions, the greater and lesser trochanter, that attach to muscles that move the hip and knee. The angle between the neck and shaft, also known as the inclination angle, is about 128 degrees in the average adult. However, the inclination angle decreases with age.[1][2] The adductor tubercle for the attachment of the posterior half of the adductor magnus and the linea aspera are other important features. The hip is a ball-in-socket joint composed of the acetabulum of the pelvis encompassing the femoral head. The head is pointed in a medial, superior, and slightly anterior direction. The ligamentum teres femoris connects the acetabulum to the fovea capitis femoris, which is a pit on the head. The shaft has a mild anterior arch. At the distal femur, the shaft flares out in a cone shape onto a cuboidal base of the medial and lateral condyle. The medial and lateral condyles join the femur to the tibia, forming the knee joint. Both the hip and the knee joints are synovial joints covered by cartilage to reduce friction and optimize the range of motion. The bony features serve as landmarks for measuring the axis along the femur.[3][4]