Femur

At a glance

English

Femur

Latin (TA2)

Os femoris

System

Bone

Region

Lower limb

Side

Paired, left and right

About the femur

The femur, the thigh bone, is the longest and strongest bone in the body and the only bone of the thigh. It reaches from the hip, where its head sits in the acetabulum of the pelvis, down to the knee, where it rests on the tibia and is faced in front by the patella. Its shaft slopes inwards as it descends, which brings the knees closer to the midline of the body and under its centre of gravity.

The upper end has a rounded head covered in cartilage except for a small central pit, the fovea, where the ligament of the head attaches. A long neck carries the head upwards, inwards and forwards at an angle to the shaft. Where neck meets shaft are two large projections: the greater trochanter on the lateral side, which can be felt at the side of the hip, and the lesser trochanter on the back and medial side. They are joined behind by the intertrochanteric crest and in front by the intertrochanteric line.

The shaft is smooth and rounded in front. Along its back runs the linea aspera, a raised double ridge that anchors the adductors, the vastus muscles and the short head of biceps femoris. Near the knee the ridge divides to enclose the flat popliteal surface. The lower end widens into the medial and lateral condyles, which bear on the tibia and are separated behind by the deep intercondylar fossa. In front they join in a smooth groove for the patella. The medial and lateral epicondyles above them anchor the collateral ligaments of the knee, and the small adductor tubercle receives part of adductor magnus.

As the single bone of the thigh, the femur gives attachment to the muscles working across the hip and knee, and also to gastrocnemius and plantaris which cross the knee to the ankle. Fascial septa attached to it divide the thigh into anterior, medial and posterior compartments, each with its own muscles, nerve and vessels. Breaks of the head, neck or the region just below the lesser trochanter count as hip fractures and are common in older people with osteoporosis; neck fractures can cut off blood to the head. A shaft fracture can be splinted with traction before reaching hospital.

Function and supply

Function

Carries the body's weight from the pelvis to the tibia and acts as the lever for walking, running, climbing and standing up.

Nerve supply

No muscle-style supply; the femoral, obturator and sciatic nerves run alongside it in the three thigh compartments.

Blood supply

Nutrient arteries from the perforating branches of the profunda femoris; the head and neck are supplied mainly by the medial and lateral circumflex femoral arteries, with a small contribution through the ligament of the head.