Bones of the Lower Limb

1. Introduction
2. Femur
3. Patella
4. Tibia
5. Fibula
6. Quiz

• There are several bones in the lower limb, including the femur, patella, tibia and fibula. The patella is a sesamoid bone (a bone that develops inside a tendon).

Introduction

The lower limb is composed of many bones, which provide structural support and allow for the attachment of muscles. In this chapter we shall discuss four of these bones:

• Femur
• Patella
• Tibia
• Fibula

Femur

The femur is the only bone that is present in the thigh, and it is the longest bone in the body! It is vital in providing sites of attachment for key muscles of the thigh and therefore aiding movement. It is also one of the strongest bones in the body, so a healthy femoral shaft usually needs a high-energy injury to break. The neck of the femur is more vulnerable, especially in older people with osteoporosis (fragile, thinned bones), and can break after a low-energy fall. 

These are the key proximal landmarks (those nearer the hip) of the femur. Most are attachment sites for muscles and ligaments, or places where fractures matter clinically:

• The Head of Femur - a smooth surface that is covered with articular cartilage (the smooth lining of a joint surface). It articulates (forms a joint) with the acetabulum (the socket of the pelvis) to form the hip joint.
• The Neck of Femur - a cylindrical projection that connects the head of the femur to the shaft. Its angle to the shaft allows a wider range of movement at the hip joint. Fractures inside the capsule of the hip joint (intracapsular fractures) can damage the medial femoral circumflex artery (an artery that supplies blood to the femoral head), leading to avascular necrosis (death of bone tissue because its blood supply is lost) of the femoral head. If the fracture is outside the capsule (extracapsular), the blood supply to the head is intact and avascular necrosis is rare.
• Greater Trochanter - the most lateral projection of the femur. It is a key site of attachment for multiple muscles (e.g. gluteus medius and minimus, the smaller gluteal muscles that move the hip out to the side). This is the easiest part of the proximal femur to palpate - it is the bony lump that is located laterally on the hip. 
• Lesser Trochanter - a smaller projection of the femur, found more medially. It is the key site of attachment for the iliopsoas (the main hip flexor muscle).
• Intertrochanteric Line - a prominent ridge that passes along the anterior surface of the femur between the two trochanters. This is the site of attachment for the hip joint capsule (anteriorly).
• Intertrochanteric Crest - a prominent ridge that passes between the two trochanters posteriorly.

On the shaft of the femur, there are three key bony landmarks. These act as sites of attachment for key muscles of the thigh:

• Pectineal Line - found medially on the posterior surface of the femoral shaft, and extends distally to become the medial aspect of the linea aspera (a roughened ridge down the back of the shaft).
• Gluteal Tuberosity (a tuberosity is a rough, raised area of bone) - found laterally on the posterior surface of the femoral shaft, and extends distally to become the lateral aspect of the linea aspera.
• Linea Aspera - found on the posterior aspect of the shaft. Moving inferiorly, it branches to form the medial and lateral supracondylar lines.

Distally, the femur articulates with the tibia and patella to form the knee joint. There are a few key landmarks to know. The condyles form the knee joint and the epicondyles anchor the collateral ligaments:

• Medial and Lateral Condyles (the rounded, knuckle-like ends of the bone) - articulate with the tibia to form the tibiofemoral (tibia and femur) part of the knee joint. They are covered in articular cartilage.
• Medial and Lateral Epicondyles - found superior to the condyles and act as attachment for the medial and lateral collateral ligaments, which stabilise the knee joint.
• Intercondylar Fossa - a region found on the posterior aspect of the femur, between the two condyles.

Diagram - Posterior aspect of the proximal femur

Creative commons source by Henry Gray Anatomy of the Human Body (1918), edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Diagram - Posterior aspect of the femur

Creative commons source by Henry Gray Anatomy of the Human Body (1918), edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Patella

The patella is a sesamoid bone (a bone that develops inside a tendon) that is located anterior to the knee joint. It protects the anterior knee and aids knee extension by increasing the leverage of the quadriceps tendon.

There are two important landmarks found on the posterior surface of the patella:

• Medial Facet (a facet is a small, smooth, flat area on a bone) - articulates with the medial condyle of the femur to aid movement.
• Lateral Facet - articulates with the lateral condyle of the femur to aid movement.

Diagram - Posterior aspect of the right patella. The most superior aspect of the patella is the ‘base’ whilst the most inferior aspect is called the ‘apex’

Creative commons source by Henry Gray Anatomy of the Human Body (1918), edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

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