The femur is the only bone in the thigh. It is classed as a long bone, and is the longest bone in the body. The main function of the femur is to transmit forces from the tibia to the hip joint.
It acts as the site of origin and attachment of many muscles and ligaments, and can be divided into three areas; proximal, shaft and distal.
In this article, we shall look at the anatomy of the femur – its attachments, bony landmarks and clinical correlations.
The proximal area of the femur forms the hip joint with the pelvis. It consists of a head and neck, and two bony processes called trochanters. There are also two bony ridges connecting the two trochanters.
- Head – Articulates with the acetabulum of the pelvis to form the hip joint. It has a smooth surface with a depression on the medial aspect; for the attachment of the ligament of head of femur.
- Neck – Connects the head of the femur with the shaft. It is cylindrical, projecting in a superior and medial direction – this angle of projection allows for an increased range of movement at the hip joint.
- Greater trochanter – A projection of bone that originates from the anterior aspect, just lateral to the neck. It is angled superiorly and posteriorly, and can be found on both the anterior and posterior sides of the femur.
- Site of attachment for many of the muscles in the gluteal region, such as gluteus medius, gluteus minimus and piriformis.
- Lesser trochanter – Smaller than the greater trochanter. It projects from the posteromedial side of the femur, just inferior to the neck-shaft junction.
- Site of attachment for the psoas major and iliacus muscles.
- Intertrochanteric line – A ridge of bone that runs in an inferomedial direction on the anterior surface of the femur, connecting the two trochanters together. After it passes the lesser trochanter on the posterior surface, it is known as the pectineal line.
- Site of attachment for the iliofemoral ligament (strong ligament of the hip joint).
- Intertrochanteric crest – Similar to the intertrochanteric line, this is a ridge of bone that connects the two trochanters together. It is located on the posterior surface of the femur. There is a rounded tubercle on its superior half, this is called the quadrate tubercle, which is where the quadratus femoris attaches.
Clinical Relevance: Proximal Femur Fractures
Fractures of the proximal femur can broadly be classified into two main groups:
Intracapsular fractures are more common in the elderly, especially women. They are a result of a minor trip or stumble. This fracture occurs within the capsule of the hip joint. It can damage the medial femoral circumflex artery – and cause avascular necrosis of the femoral head.
The distal fragment is pulled upwards and rotated laterally. This manifests clinically as a shorter leg length, with the toes pointing laterally
Extracapsular fractures are more common in young and middle aged people. In these fractures, the blood supply to the head of femur is intact, and so no avascular necrosis can occur. Like the subcapital fracture, the leg is shortened and laterally rotated.
The shaft descends in a slight medial direction. This brings the knees closer to the body’s centre of gravity, increasing stability.
On the posterior surface of the femoral shaft, there are roughened ridges of bone, these are called the linea aspera (Latin for rough line)
Proximally, the medial border of the linea aspera becomes the pectineal line. The lateral border becomes the gluteal tuberosity, where the gluteus maximus attaches.
Distally, the linea aspera widens and forms the floor of the popliteal fossa, the medial and lateral borders form the medial and lateral supracondylar lines. The medial supracondylar line stops at the adductor tubercle, where the adductor magnus attaches.
Clinical Relevance: Fractures of the Femoral Shaft
Fractures of the femoral shaft are relatively uncommon, and require a lot of force. They are usually a consequence of a traumatic injury, such as a vehicular accident.
They can often occur as a spiral fracture, which causes leg shortening. The loss of leg length is due the bony fragments overriding, pulled by their attached muscles.
As the method of injury is typically high energy, the surrounding soft tissues may also be damaged. As in any fracture, it is important to assess the neurovascular supply to the affected limb, as they femoral nerve or artery may have been damaged in the injury.
The distal end is characterised by the presence of the medial and lateral condyles, which articulate with the tibia and patella, forming the knee joint.
- Medial and lateral condyles – Rounded areas at the end of the femur. The posterior and inferior surfaces articulate with the tibia and menisci of the knee, while the anterior surface articulates with the patella.
- Medial and lateral epicondyles – Bony elevations on the non-articular areas of the condyles. They are the area of attachment of some muscles and the collateral ligaments of the knee joint.
- Intercondylar fossa – A depression found on the posterior surface of the femur, it lies in between the two condyles. It contains two facets for attachment of internal knee ligaments.
- Facet for attachment of the posterior cruciate ligament – Found on the medial wall of the intercondylar fossa, it is a large rounded flat face, where the posterior cruciate ligament of the knee attaches.
- Facet for attachment of anterior cruciate ligament – Found on the lateral wall of the intercondylar fossa, it is smaller than the facet on the medial wall, and is where the anterior cruciate ligament of the knee attaches.