The femur (also thigh bone, Latin: os femoris) is the only bone in the thigh, and it articulates at the hip and knee joints. It is the longest bone in the human body.

The femur belongs to long bones, and it has three parts: a proximal extremity, a shaft in the middle of the bone, and a distal extremity.

Proximal extremity of femur

The proximal extremity (or proximal end, or epiphysis) is the upper end of the femur, which articulates with the acetabulum, forming the hip joint. It presents several landmarks, including:

    • head of the femur, featuring a fovea of the femur
    • neck of the femur,
    • greater trochanter, with the trochanteric fossa
    • lesser trochanter,
    • intertrochanteric line, and
    • intertrochanteric crest.

The head of the femur is the most upper part of the thigh bone. It is directed upward, medialward, and a little forward, and is globular-shaped. The neck of the femur supports the femoral head. It is the portion of the bone between the femoral head and the greater trochanter. The femoral head presents with a depression called the fovea of the head of the femur. It serves for the attachment of the ligament of the head of the femur.

The greater trochanter is a large prominence on the superolateral aspect of the proximal femur for the attachment of the gluteus mediusgluteus minimus, and piriformis muscles.

The trochanteric fossa is a depression medial to the root of the greater trochanter of the femur. It serves as the origin site for the obturator internusgemellus superior, and gemellus inferior muscles.

The lesser trochanter is a small prominence on the posteromedial aspect of the proximal part of the femur. It serves for the attachment of the iliopsoas muscle.

The intertrochanteric line is a rough anterior line between the femoral shaft and the neck of the femur, extending from the greater trochanter to lesser trochanter.

The intertrochanteric crest is a posterior bony ridge between the shaft and the neck of the femur, running from the greater trochanter to lesser trochanter.

Shaft of femur

The shaft (also diaphysis or body) of the femur is the extended middle portion of the bone, and it features the following landmarks:

    • linea aspera, with
      • lateral ridge,
      • medial ridge,
    • pectineal line,
    • gluteal tuberosity,
    • popliteal surface.

The linea aspera (from Latin meaning "rough line") is a rough double line on the posterior aspect of the shaft of the femur. It serves for the attachment of the two vasti muscles (vastus medialisvastus lateralis) and the short head of the biceps femorisThe linea aspera is also the insertion site of the adductors of the thighgluteus maximus, and pectineus.

Superiorly, the linea aspera is continuous with three ridges: the lateral ridge, the intermedial ridge (also called the pectineal line), and the medial ridge. The pectineal line is a bony ridge on the shaft of the femur that extends downward from the lesser trochanter, nearly reaching the linea aspera. The pectineal line gives attachment to the pectineus muscle.

The gluteal tuberosity is a rough, oblong area on the shaft of the femur continuous with the linea aspera superolaterally. The gluteal tuberosity serves as the insertion site for the gluteus maximus muscle.

The popliteal surface is a triangular field on the posterior aspect of the femur. It is found on the distal part of the femoral shaft between the intercondylar line and the diverging lips of the linea aspera. The popliteal artery lies upon the popliteal surface.

Distal extremity of femur

The distal extremity (or end, or epiphysis) of the femur is the lower end of the bone, which articulates at the knee joint. It features the following landmarks:

    • medial condyle, with
      • articular surface of medial condyle,
      • medial epicondyle,
    • lateral condyle, with
      • articular surface of the lateral condyle,
      • lateral epicondyle,
    • patellar surface,
    • intercondylar fossa.

The medial condyle is the medial knee joint surface of the femur, which has an articular surface and a medial epicondyle. The medial epicondyle is a bony elevation on the medial aspect of the medial condyle.

The lateral condyle is the lateral knee joint surface of the femur, which also features an articular surface and an epicondyle. The lateral epicondyle is a bony elevation on the lateral aspect of the lateral condyle.

The patellar surface is the aspect of the distal end of the femur that articulates with the articular surface of the patella.

The intercondylar fossa is a deep notch between the rear surfaces of the lateral and medial epicondyle of the femur.