Femur

Femur

Also known as: thigh bone, femoral head, femoral neck, greater trochanter

The longest, strongest and heaviest bone of the body (≈26% of stature), forming the skeleton of the thigh between the hip and the knee.

Show on body map Long Bone — Structure Muscles — Posterior View

Overview

Length≈45–48 cm (≈26% of height)

Angle of inclination≈125° (adult), ≈150° (newborn)

Angle of anteversion≈10–15°

Blood loss in shaft fracture≈1–1.5 L

Proximal end: the spherical head (≈2/3 of a sphere) points medially, upward and slightly forward into the acetabulum; its small central pit, the fovea capitis, anchors the ligament of the head of the femur. The neck joins the head to the shaft at an angle of inclination of ≈125° in adults (≈150° at birth; coxa vara < 120°, coxa valga > 135°) and is twisted forward relative to the knee axis (anteversion ≈10–15°). At the neck–shaft junction lie the greater trochanter (gluteus medius and minimus, piriformis, obturator internus and gemelli) and the lesser trochanter (iliopsoas), joined anteriorly by the intertrochanteric line (iliofemoral ligament, capsule) and posteriorly by the prominent intertrochanteric crest with its quadrate tubercle.

Shaft: bowed forward and inclined medially toward the knee, bringing the knees beneath the body's centre of gravity (the Q-angle, wider in females). Posteriorly, the rough ridge of the linea aspera receives the adductors, the short head of biceps femoris and the vasti, diverging above into the gluteal tuberosity and pectineal line, and below into the medial and lateral supracondylar lines enclosing the popliteal surface.

Distal end: two large condyles separated posteriorly by the intercondylar fossa (cruciate ligament attachments) and united anteriorly by the patellar surface. Above them lie the medial and lateral epicondyles (collateral ligaments) and the adductor tubercle (adductor magnus, hamstring part). The medial condyle extends further distally, so that the condyles rest on a horizontal tibial plateau despite the oblique shaft.

Location: Thigh, from the hip joint to the knee joint.

Parts & subdivisions

Head and fovea capitis
Articulates with the acetabulum; ligament of the head (carries a small branch of the obturator artery).
Neck
Angle of inclination ≈125°; anteversion ≈10–15°; commonest fracture site in the elderly.
Greater trochanter
Gluteus medius and minimus, piriformis, obturator internus, gemelli.
Lesser trochanter
Insertion of iliopsoas.
Intertrochanteric line and crest
Anterior line: iliofemoral ligament and capsule; posterior crest: quadratus femoris.
Linea aspera
Posterior ridge for the adductors, vasti and short head of biceps femoris.
Gluteal tuberosity
Insertion of part of gluteus maximus.
Medial and lateral condyles
Articulate with the tibia; medial is larger and projects further distally.
Patellar surface
Articulates with the patella; lateral lip higher, resisting lateral dislocation.
Intercondylar fossa
Attachments of the ACL (lateral wall) and PCL (medial wall).
Adductor tubercle
Insertion of the hamstring part of adductor magnus.

Anatomy

Arterial supply: Femoral head: chiefly the medial circumflex femoral artery via retinacular arteries running up the neck beneath the synovium (lateral circumflex contributes less); the artery of the ligament of the head (obturator) is small in adults. Shaft: perforating branches of the profunda femoris (nutrient arteries).
Articulations: Acetabulum of the hip bone (hip joint), tibia (tibiofemoral joint), patella (patellofemoral joint).
Ossification: Primary centre in the shaft ≈week 7. Secondary centres: distal end ≈36 weeks’ gestation (present at term — a forensic sign of maturity), head ≈6 months–1 year, greater trochanter ≈4 years, lesser trochanter ≈12–14 years. The distal epiphysis is the growing end and fuses last (≈18–20 years).

Function

Supports body weight in standing and walking
Lever for powerful hip and knee muscles
Forms the hip and knee joints
Houses red marrow in the proximal end (adult)

Clinical significance

Hip (proximal femoral) fracture

A hallmark osteoporotic fracture in older adults after a fall: the leg is shortened and externally rotated. Intracapsular (femoral neck) fractures disrupt the retinacular vessels → risk of avascular necrosis and non-union, so displaced fractures are usually treated by hemiarthroplasty or total hip replacement (Garden III–IV). Extracapsular (intertrochanteric, subtrochanteric) fractures have a good blood supply and are fixed (e.g. dynamic hip screw, intramedullary nail). One-year mortality ≈20–30%.

Femoral shaft fracture

High-energy injury in young adults; large blood loss, fat embolism risk; the proximal fragment is flexed (iliopsoas) and abducted (gluteals); treated with intramedullary nailing.

Paediatric hip disorders

Developmental dysplasia of the hip (newborn), Perthes disease (idiopathic AVN of the femoral head, 4–8 years) and slipped capital femoral epiphysis (obese adolescents).

Test yourself

An elderly woman falls and her right leg is shortened and externally rotated. A displaced intracapsular femoral neck fracture is seen. Damage to which artery explains the high risk of avascular necrosis?

Artery of the ligament of the head of the femur
First perforating artery
Superior gluteal artery
Medial circumflex femoral artery (retinacular branches)

Answer: Medial circumflex femoral artery (retinacular branches)

The femoral head is supplied mainly by retinacular branches of the medial circumflex femoral artery, which run along the neck beneath the synovium and are torn in displaced intracapsular fractures. The artery of the ligament of the head (obturator) is insignificant in most adults.