The strongest, longest, and largest bone in the human body is the femur, or thigh bone, which is a bone in the leg that runs from the knee to the hip. All weight from the upper part of the human body rests on the leg bones when walking or standing, and therefore these bones must be long and strong. The human leg contains four bones: the tibia, femur, fibula, and patella (kneecap).
The top end of the femur fits into the hip socket, while its lowermost end connects to the knee. Below the knee are the tibia and the fibula, which are connected to the upper leg by a hinge joint. Leg bones have rough patches that hold muscles on their surfaces. The contraction of muscles pull bones, which initiate movement of the legs.
Parts of the femur include the upper part, the body, and the lower part. The upper part is called the proximal extremity and contains the head, neck, two trochanters, and neighboring structures. The head of the femur has a minor groove that joins to the sides of the acetabular notch through round ligaments. It connects the shaft to the neck, which is four to five centimeters long. The head and the neck are firmly embedded in the hip musculature to prevent direct palpation. The lower and the greater trochanter are located in the shift area, in the middle of the neck and the head of the femur. The greater trochanter is box-shaped, while the lesser trochanter is cone-shaped.
Beneath the neck of the femur is its cylindrical, long, and slender shaft (body). It is concave from behind and convex in front, enhancing its strength alongside the prominent longitudinal ridge. The shaft is also free from palpation since it has enormous musculature of the thigh close to it. In some cases, a third trochanter is present on the proximal femur, and it is rounded, oblong, and conical in shape. However, it is a structure of less importance in human beings.
The lower part of the femur (distal extremity) is larger than the upper part of the bone. It takes the shape of a cube, but it has a large transverse diameter compared to its anteroposterior diameter. The distal extremity is made up of two eminences called the condyles (lateral and medial condyle) which are separated by patellar surface from the front, and by the intercondylar fossa from the back.
The only bone in the thigh is the femur, and therefore it serves as the core socket of connection for all muscles that exert force over the knee and hip joints. Some muscles such as the plantaris muscles come from the femur. In fact, 22 distinct muscles insert onto the femur or originate from it. In addition, the femur acts as an axis for the three fascial compartments of the thigh (posterior, medial and anterior).