Bone Healing

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Bone Healing

Bone Healing Anatomy

Bone Structure

Bones have an outer cortical layer and an inner cancellous layer. Each structure has a specific purpose, as detailed below:

• Cortical: columnar structure and concentric layers connected by longitudinal Haversian canals (central blood vessel) and transverse Volkmann canals (nutrient vessels).
• Cancellous: loosely woven trabeculae of organic and inorganic bone.

These structures are both used in bone grafting.

Bone Blood Supply

Bone receives more than one type of blood supply depending on its location and origin/insertions. The important vascular vessels are:

• Periosteal
• Apophyseal
• Endosteal (nutrient supply to the medullary cavity)
• Epiphyseal (growth plates)

Types of Bone Healing

Primary Bone Healing

This occurs when absolute stability is provided to a fracture fixation resulting in no callus formation. Normal bone architecture is restored when osteoclasts provide a guide for blood vessels to cross the fracture site. A clinical example is a compression plate.

Key aspects to this type of bone healing are:

• No callus formation
• No inflammatory or proliferative phases of healing
• Haversian remodelling/osteonal bone remodelling

Secondary Bone Healing

This occurs when absolute stability is not provided to a fracture fixation resulting in callus formation. Clinical examples include K-wires, external fixators, and casting/splinting.

Key aspects to this type of bone healing are:

• Callus formation
• Fracture haematoma occurs
• Bone healing via endochondral ossification

This is different to bone graft incorporation seen in bone grafts.

Stages of Bone Healing

Bone healing is reliant upon osteoblasts and osteocytes. They help form new bone and maintain calcium homeostasis.

The 5 phases of bone healing are as follows:

1. Haematoma: a "haematoma" is formed at the fracture site.
2. Inflammation: haematoma granulates & osteoclasts remove necrotic bone.
3. Proliferation of periosteal and endosteal cells at the cortex.
4. Callus formation & transformation from a soft callus (osteoid) to a hard callus.
5. Remodelling of woven bone to lamellar bone

There are some similarities to bone and wound healing - but don't get confused!

Complications of Bone Healing

Successful bone healing requires several factors to work together. Sometimes this doesn't occur for a variety of reasons. This can lead to some of the following complications

1. Malunion
2. Non-union
3. Delayed union

These complications can be treated by bone grafting.

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