Femur

The femur is categorised as a long bone and comprises a diaphysis (shaft or body) and two epiphyses (extremities) that articulate with adjacent bones in the hip and knee.^[3]

Upper part

A slight ridge is sometimes seen commencing about the middle of the intertrochanteric crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the

About the junction of the upper one-third and lower two-thirds on the intertrochanteric crest is the quadrate tubercle located. The size of the tubercle varies and it is not always located on the intertrochanteric crest and that also adjacent areas can be part of the quadrate tubercle, such as the posterior surface of the greater trochanter or the neck of the femur. In a small anatomical study it was shown that the epiphyseal line passes directly through the quadrate tubercle.^[5]

Body

The body of the femur (or shaft) is large, thick and almost cylindrical in form. It is a little broader above than in the center, broadest and somewhat flattened from before backward below. It is slightly arched, so as to be convex in front, and concave behind, where it is strengthened by a prominent longitudinal ridge, the linea aspera which diverges proximally and distal as the medial and lateral ridge. Proximally the lateral ridge of the linea aspera becomes the gluteal tuberosity while the medial ridge continues as the pectineal line. Besides the linea aspera the shaft has two other bordes; a lateral and medial border. These three bordes separates the shaft into three surfaces: One anterior, one medial and one lateral. Due to the vast musculature of the thigh the shaft can not be palpated.^[3]

The third trochanter is a bony projection occasionally present on the proximal femur near the superior border of the gluteal tuberosity. When present, it is oblong, rounded, or conical in shape and sometimes continuous with the gluteal ridge.^[6] A structure of minor importance in humans, the incidence of the third trochanter varies from 17–72% between ethnic groups and it is frequently reported as more common in females than in males.^[7]

Lower part

The

The articular surface of the lower end of the femur occupies the anterior, inferior, and posterior surfaces of the condyles. Its front part is named the patellar surface and articulates with the patella; it presents a median groove which extends downward to the intercondyloid fossa and two convexities, the lateral of which is broader, more prominent, and extends farther upward than the medial.^[3]

Each condyle is surmounted by an elevation, the

The femur develops from the limb buds as a result of interactions between the ectoderm and the underlying mesoderm; formation occurs roughly around the fourth week of development.^[8]

By the sixth week of development, the first

development by 1–2 days.

Function

As the femur is the only bone in the thigh, it serves as an attachment point for all the muscles that exert their force over the hip and knee joints. Some

plantaris

muscles – also originate from the femur. In all, 23 individual muscles either originate from or insert onto the femur.

In cross-section, the thigh is divided up into three separate

posterior fascial compartments

.

Muscle attachments

Muscle	Direction	Attachment[9]
Iliacus muscle	Insertion	Lesser trochanter
Psoas major muscle	Insertion	Lesser trochanter
Gluteus maximus muscle	Insertion	Gluteal tuberosity
Gluteus medius muscle	Insertion	Lateral surface of greater trochanter
Gluteus minimus muscle	Insertion	Forefront of greater trochanter
Piriformis muscle	Insertion	Superior boundary of greater trochanter
Gemellus superior muscle	Insertion	Upper edge of Obturator internus's tendon (indirectly greater trochanter )
Obturator internus muscle	Insertion	Medial surface of greater trochanter
Gemellus inferior muscle	Insertion	Lower edge of Obturator internus's tendon (indirectly greater trochanter )
Quadratus femoris muscle	Insertion	Intertrochanteric crest
Obturator externus muscle	Insertion	Trochanteric fossa
Pectineus muscle	Insertion	Pectineal line
Adductor longus muscle	Insertion	Medial ridge of linea aspera
Adductor brevis muscle	Insertion	Medial ridge of linea aspera
Adductor magnus muscle	Insertion	Medial ridge of linea aspera and the adductor tubercle
Vastus lateralis muscle	Origin	Greater trochanter and lateral ridge of linea aspera
Vastus intermedius muscle	Origin	Front and lateral surface of femur
Vastus medialis muscle	Origin	Distal part of intertrochanteric line and medial ridge of linea aspera
Short head of biceps femoris	Origin	Lateral ridge of linea aspera
Popliteus muscle	Origin	Under the lateral epicondyle
Articularis genu muscle	Origin	Lower 1/4 of anterior femur deep to vastus intermedius
Gastrocnemius muscle	Origin	Behind the adductor tubercle, over the lateral epicondyle and the popliteal facies
Plantaris muscle	Origin	Over the lateral condyle

Clinical significance

Fractures

A

In primitive tetrapods, the main points of muscle attachment along the femur are the internal trochanter and third trochanter, and a ridge along the ventral surface of the femoral shaft referred to as the adductor crest. The neck of the femur is generally minimal or absent in the most primitive forms, reflecting a simple attachment to the acetabulum. The greater trochanter was present in the extinct archosaurs, as well as in modern birds and mammals, being associated with the loss of the primitive sprawling gait. The lesser trochanter is a unique development of mammals, which lack both the internal and fourth trochanters. The adductor crest is also often absent in mammals or alternatively reduced to a series of creases along the surface of the bone.^[10] Structures analogous to the third trochanter are present in mammals, including some primates.^[7]

Some species of whales,^[11] snakes, and other non-walking vertebrates have vestigial femurs. In some snakes the protruding end of a pelvic spur, a vestigial pelvis and femur remnant which is not connected to the rest of the skeleton, plays a role in mating. This role in mating is hypothesized to have possibly occurred in Basilosauridae, an extinct family of whales with well-defined femurs, lower legs and feet. Occasionally, the genes that code for longer extremities cause a modern whale to develop miniature legs (atavism).^[12]

One of the earliest known vertebrates to have a femur is the