Thefemur (/ˈfiːmər/;pl.:femurs orfemora/ˈfɛmərə/),^[1][2] orthigh bone, is the onlybone in thethigh — the region of the lower limb between thehip and theknee. In manyfour-legged animals the femur is the upper bone of thehindleg.

Femur
Position of femur (shown in red)
Left femur seen from behind
Details
Origins	Gastrocnemius,vastus lateralis,vastus medialis andvastus intermedius
Insertions	Gluteus maximus,gluteus medius,gluteus minimus,iliopsoas,lateral rotator group,adductors of the hip
Articulations	Hip:acetabulum ofpelvis superiorly knee: with thetibia andpatella inferiorly
Identifiers
Latin	os femoris, os longissimum
MeSH	D005269
TA98	A02.5.04.001
TA2	1360
FMA	9611
Anatomical terms of bone [edit on Wikidata]

Thetop of the femur fits into a socket in the pelvis called the hip joint, and the bottom of the femur connects to the shinbone (tibia) and kneecap (patella) to form the knee. In humans the femur is the largest and thickest bone in the body.

The femur is the only bone in the upperleg. The two femurs convergemedially toward theknees, where they articulate with theproximal ends of thetibiae. The angle at which the femora converge is an important factor in determining thefemoral-tibial angle. In females, thickerpelvic bones cause the femora to converge more than in males.

In the conditiongenu valgum (knock knee), the femurs converge so much that the knees touch. The opposite condition,genu varum (bow-leggedness), occurs when the femurs diverge. In the general population without these conditions, the femoral-tibial angle is about 175 degrees.^[3]

The femur is the largest and thickest bone in the human body. It is considered the strongest bone by some measures, though other studies suggest thetemporal bone may be stronger. On average, the femur length accounts for 26.74% of a person's height,^[4] a ratio found in both men and women across mostethnic groups with minimal variation. This ratio is useful inanthropology, as it provides a reliable estimate of a person's height from an incompleteskeleton.

The femur is classified as along bone, consisting ofdiaphysis (shaft orbody) and twoepiphyses (extremities) that articulate with the hip and knee bones.^[3]

Theupper or proximal extremity (close to thetorso) contains thehead,neck, the twotrochanters and adjacent structures.^[3] The upper extremity is the thinnest femoral extremity, the lower extremity is the thickest femoral extremity.

Thehead of the femur, whicharticulates with theacetabulum of thepelvic bone, comprises two-thirds of asphere. It has a small groove, orfovea, connected through theround ligament to the sides of theacetabular notch. The head of the femur is connected to theshaft through theneck orcollum. The neck is 4–5 cm. long and the diameter is smallest front to back and compressed at its middle. The collum forms an angle with the shaft in about 130 degrees. This angle is highly variant. In theinfant, it is about 150 degrees and inold age reduced to 120 degrees on average. An abnormal increase in the angle is known ascoxa valga and an abnormal reduction is calledcoxa vara. Both the head and neck of the femur is vastly embedded in thehip musculature and can not be directlypalpated. In skinny people with thethigh laterally rotated, the head of the femur can be felt deep as a resistanceprofound (deep) for thefemoral artery.^[3]

The transition area between the head and neck is quite rough due to attachment of muscles and thehip joint capsule. Here the twotrochanters,greater andlesser trochanter, are found. The greater trochanter is almost box-shaped and is the mostlateral prominent of the femur. The highest point of the greater trochanter is located higher than the collum and reaches the midpoint of thehip joint. The greater trochanter can easily be felt. Thetrochanteric fossa is a deep depression bounded posteriorly by the intertrochanteric crest on the medial surface of the greater trochanter.The lesser trochanter is a cone-shaped extension of the lowest part of the femur neck. The two trochanters are joined by theintertrochanteric crest on the back side and by theintertrochanteric line on the front.^[3]

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 thelinea quadrata (or quadrate line).

About the junction of the upper one-third and lower two-thirds on the intertrochanteric crest is thequadrate 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 theepiphyseal line passes directly through the quadrate tubercle.^[5]

Thebody 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, thelinea aspera which diverges proximally and distal as the medial and lateral ridge. Proximally the lateral ridge of the linea aspera becomes thegluteal tuberosity while the medial ridge continues as thepectineal line. Besides the linea aspera the shaft has two other bordes; alateral and medial border. These three bordes separates the shaft into three surfaces: Oneanterior, one medial and one lateral. Due to the vastmusculature of the thigh the shaft can not bepalpated.^[3]

Thethird 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]

Thelower extremity of the femur (or distal extremity) is the thickest femoral extremity, theupper extremity is the shortest femoral extremity. It is somewhat cuboid in form, but its transverse diameter is greater than its antero-posterior (front to back). It consists of two oblong eminences known as thecondyles.^[3]

Anteriorly, the condyles are slightly prominent and are separated by a smooth shallow articular depression called the patellar surface. Posteriorly, they project considerably and a deep notch, theIntercondylar fossa of femur, is present between them. Thelateral condyle is the more prominent and is the broader both in its antero-posterior and transverse diameters. Themedial condyle is the longer and, when the femur is held with its body perpendicular, projects to a lower level. When, however, the femur is in its natural oblique position the lower surfaces of the two condyles lie practically in the same horizontal plane. The condyles are not quite parallel with one another; the long axis of the lateral is almost directly antero-posterior, but that of the medial runs backward and medialward. Their opposed surfaces are small, rough, and concave, and form the walls of theintercondyloid fossa. This fossa is limited above by a ridge, theintercondyloid line, and below by the central part of the posterior margin of the patellar surface. Theposterior cruciate ligament of theknee joint is attached to the lower and front part of the medial wall of the fossa and theanterior cruciate ligament to an impression on the upper and back part of its lateral wall.^[3]

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 thepatella; it presents a median groove which extends downward to theintercondyloid 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, theepicondyle. Themedial epicondyle is a large convex eminence to which thetibial collateral ligament of the knee-joint is attached. At its upper part is theadductor tubercle and behind it is a rough impression which gives origin to the medial head of thegastrocnemius. Thelateral epicondyle which is smaller and less prominent than the medial, gives attachment to thefibular collateral ligament of theknee-joint.^[3]

The femur develops from thelimb buds as a result of interactions between theectoderm and the underlyingmesoderm; formation occurs roughly around the fourth week of development.^[8]

By the sixth week of development, the firsthyaline cartilage model of the femur is formed bychondrocytes.Endochondral ossification begins by the end of theembryonic period and primaryossification centers are present in all long bones of the limbs, including the femur, by the 12th week of development. Thehindlimb development lags behindforelimb development by 1–2 days.

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. Somebiarticular muscles – which cross two joints, like thegastrocnemius andplantaris 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 separatefascial compartments divided byfascia, each containing muscles. These compartments use the femur as an axis, and are separated by toughconnective tissue membranes (orsepta). Each of these compartments has its ownblood andnerve supply, and contains a different group ofmuscles. These compartments are named theanterior,medial andposterior fascial compartments.

Afemoral fracture that involves thefemoral head,femoral neck or theshaft of the femur immediately below the lesser trochanter may be classified as ahip fracture, especially when associated withosteoporosis. Femur fractures can be managed in a pre-hospital setting with the use of atraction splint.

In primitive tetrapods, the main points of muscle attachment along the femur are theinternal trochanter andthird trochanter, and a ridge along the ventral surface of the femoral shaft referred to as theadductor 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 extinctarchosaurs, 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 thethird trochanter are present in mammals, including some primates.^[7]

Some species ofwhales,^[11]snakes, and other non-walking vertebrates havevestigial femurs. In some snakes, the protruding end of apelvic 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 inBasilosauridae, 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 theEusthenopteron, aprehistoriclobe-finned fish from theLate Devonian period.

A recent study has revealed that bone is a significantly richer source of persistentDNA viruses than previously thought. In addition toParvovirus B19 andHepatitis B virus, ten other viruses were discovered, including several members of theherpesvirus andpolyomavirus families, as well as humanpapillomavirus type 31 andtorque teno virus.^[13]

Ininvertebrate zoology the namefemur appears inarthropodology. The usage is not homologous with that of vertebrate anatomy; the term "femur" simply has been adopted by analogy and refers, where applicable, to the most proximal of (usually) the two longest jointed segments of the legs of theArthropoda. The two basal segments preceding the femur are thecoxa andtrochanter. This convention is not followed incarcinology but it applies inarachnology andentomology. Inmyriapodology, another segment, theprefemur, connects the trochanter and femur.

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  3D image
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  Muscles of thigh. Lateral view.
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  Muscles of thigh. Cross section.
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  Distribution forces of the femur
• Femur anatomy

•   Media related toFemur at Wikimedia Commons
•   The dictionary definition ofFemur at Wiktionary
•   The dictionary definition ofthighbone at Wiktionary