Femur anatomy: the thigh bone labelled from hip to knee

What it is

The thigh bone, the longest, heaviest and strongest bone in the body.

Location

Extends from the hip joint (acetabulum) to the knee, articulating with the tibia and patella.

Function

Bears body weight and provides leverage for walking, running and standing.

Body system

Skeletal · paired (left and right)

FMA ID

FMA24475 (Foundational Model of Anatomy)

Key facts

• Its head fits into the acetabulum; greater and lesser trochanters give muscle attachment.
• The linea aspera runs along the back of the shaft.
• The neck meets the shaft at about 125 degrees in adults; the adductor tubercle above the medial condyle receives the hamstring part of adductor magnus.
• The head is supplied mainly by retinacular branches of the medial circumflex femoral artery; the artery of the ligament of the head adds little in adults.

Clinical relevance

Fractures of the femoral neck are common in older adults and can disrupt blood supply to the head.

The femur is divided into a proximal end (head, neck and trochanters), a shaft and a distal end (condyles and epicondyles). It is roughly one-quarter of a person's height. (OpenStax Anatomy and Physiology 2e, 8.4: Bones of the Lower Limb.)

The shaft is not vertical. It slopes medially as it descends, which brings the knees closer to the body's centre of gravity and makes standing more stable. It is roughly circular in the middle and flattened at the back near each end. (TeachMeAnatomy: The Femur.)

The shaft also has a slight forward (anterior) bow, and a rough ridge, the linea aspera, runs down the back of it for muscle attachments. (OpenStax Anatomy and Physiology 2e, 8.4: Bones of the Lower Limb.)

The femoral head is a smooth ball covered in articular cartilage except at a small pit, the fovea (fovea capitis), where the ligament of the head of the femur (ligamentum teres) attaches. The neck is cylindrical and projects upward and medially from the shaft. (TeachMeAnatomy: The Femur.)

Kenhub gives the angle between the neck and the shaft (the angle of inclination) as about 130 degrees in adults, larger in infants and usually wider in females. The neck is also twisted forward by about 10 to 15 degrees (femoral torsion or anteversion). TeachMeAnatomy gives the neck-shaft angle as roughly 135 degrees, so expect slightly different figures between textbooks. (Kenhub: Femur.)

The greater trochanter is the large lateral projection above the junction of neck and shaft, and it is the most lateral bony point you can feel at the hip. Gluteus medius, gluteus minimus and piriformis attach to it, and vastus lateralis arises from it. The lesser trochanter sits on the back and medial side just below the neck and receives iliopsoas. (TeachMeAnatomy: The Femur.)

On the front of the bone, the intertrochanteric line joins the two trochanters and gives attachment to the iliofemoral ligament, the strongest ligament of the hip, and marks the front attachment of the hip capsule. On the back, the more prominent intertrochanteric crest joins them and carries the quadrate tubercle, where quadratus femoris attaches. (TeachMeAnatomy: The Femur.)

The linea aspera is the rough ridge running down the middle of the back of the femoral shaft. It has medial and lateral lips that come together in the middle third of the shaft and separate below into the medial and lateral supracondylar lines. (Kenhub: Femur.)

Traced upward, the lateral lip becomes the gluteal tuberosity, where gluteus maximus attaches, and the medial lip becomes the pectineal line. Traced downward, the supracondylar lines enclose a flat triangular area, the popliteal surface, which forms part of the floor of the popliteal fossa behind the knee. (TeachMeAnatomy: The Femur.)

The adductors attach along the medial lip of the linea aspera (adductor magnus, adductor brevis and adductor longus), while the short head of biceps femoris and vastus lateralis attach to the lateral lip. Pectineus attaches to the pectineal line, and vastus intermedius arises from the front of the shaft. (Kenhub: Femur.)

The distal femur ends in the medial and lateral condyles, which articulate with the tibia at the knee. In front, the condyles meet at the patellar surface, a groove for the patella, which gives the lower end of the femur a U shape when seen from below. Behind, the condyles are separated by a deep intercondylar fossa. (OpenStax Anatomy and Physiology 2e, 8.4: Bones of the Lower Limb.)

The lateral condyle is more prominent at the front, which helps stop the patella sliding laterally; a flatter lateral condyle makes patellar dislocation more likely. Inside the intercondylar fossa, the anterior cruciate ligament attaches to the inner (medial) side of the lateral condyle and the posterior cruciate ligament to the outer (lateral) side of the medial condyle. (TeachMeAnatomy: The Femur.)

The medial and lateral epicondyles are non-articular bumps above each condyle. The tibial (medial) collateral ligament attaches to the medial epicondyle and the fibular (lateral) collateral ligament to the lateral epicondyle. The adductor tubercle, a small bump on the medial side of the lower femur, receives the hamstring (ischiocondylar) part of adductor magnus. Plantaris, the lateral head of gastrocnemius and popliteus attach at the back of the lateral condyle, and the medial head of gastrocnemius to the medial condyle. (Kenhub: Femur.)

The head and neck are supplied mainly by retinacular arteries. These arise from a ring of vessels around the base of the neck formed mainly by branches of the medial and lateral circumflex femoral arteries, then run up along the neck inside the joint capsule. A small extra supply comes from the obturator artery through the ligament of the head. The shaft is supplied by nutrient arteries from the deep femoral (profunda femoris) artery. (Kenhub: Femur.)

The ligament of the head of the femur (ligamentum teres) lies inside the hip joint capsule. It is normally slack, but it carries an artery that supplies the femoral head. (OpenStax Anatomy and Physiology 2e, 9.6: Anatomy of Selected Synovial Joints.)

The femur forms by endochondral ossification, in which a cartilage model is gradually replaced by bone. Ossification begins in the 5th to 6th week of gestation, several ossification centres appear before birth, and the bone finishes ossifying between about 14 and 18 years of age. (Kenhub: Femur.)

In slipped capital femoral epiphysis, the femoral head (capital epiphysis) slips at its growth plate during the pre-teen and teenage years. It mainly affects adolescent boys and is linked with obesity and hormonal factors. (Kenhub: Femur.)

Fractures of the femoral neck are common in older adults after a low-energy fall, especially with osteoporosis, and are more common in women. The lower fragment is pulled upward and rotated outward, so the leg looks shortened and externally rotated. (TeachMeAnatomy: The Femur.)

An intracapsular neck fracture can tear the retinacular branches of the medial circumflex femoral artery and cause avascular necrosis of the femoral head. An extracapsular fracture leaves the blood supply to the head intact, so avascular necrosis is rare. (TeachMeAnatomy: The Femur.)

Fractures of the shaft usually follow high-energy trauma. Spiral fractures are common, and the pull of the thigh muscles makes the fragments override and shorten the leg. A closed shaft fracture can lose an estimated 1000 to 1500 mL of blood into the thigh. (TeachMeAnatomy: The Femur.)

Strong muscle contraction can pull off a piece of bone (an avulsion fracture): gluteus medius can avulse the greater trochanter and iliopsoas can avulse the lesser trochanter. (TeachMeAnatomy: The Femur.)

To orient a femur, hold it with the head at the top. The head points medially toward the acetabulum, the smooth patellar surface faces forward at the lower end, and the rough linea aspera and deep intercondylar fossa face backward. To tell left from right, hold the bone against your own thigh in that position, with the head pointing toward your midline and the patellar surface facing forward: it matches the leg it fits. (OpenStax Anatomy and Physiology 2e, 8.4: Bones of the Lower Limb.)

A good labelling sequence is: head, fovea, neck, greater trochanter, lesser trochanter, intertrochanteric line (front) and crest (back), gluteal tuberosity, linea aspera, supracondylar lines, popliteal surface, adductor tubercle, medial and lateral epicondyles, medial and lateral condyles, intercondylar fossa and patellar surface.

The nearest named structures in the 3D model, measured from the centre of each part:

• Descending branch of lateral circumflex femoral artery · cardiovascular
• Adductor magnus · muscular
• Sartorius · muscular
• Rectus femoris · muscular
• Vastus intermedius · muscular
• Vastus lateralis · muscular
• Long head of biceps femoris · muscular
• Femoral vein · cardiovascular
• Femoral artery · cardiovascular
• Adductor longus · muscular