Fractures of Bone and Bone Healing

Before we start, let’s recap on what we mean by bone

Function:

The skeletal system is made up of all the bones in our body, 206 (in adults) to be exact, and its functions include:

• Protection of our internal organs and vital structures, such as our brain and spinal cord

• Supporting tissues, such as the mucosa and teeth

• Movement

• Maintaining a balance of minerals – mineral homeostasis

• Storage of triglycerides and minerals

• Production of blood cells by the bone marrow which is within bone, through a process known as haematopoiesis

Constituents:

Bone itself is a type of connective tissue comprising of an extracellular matrix surrounding various cells. The extracellular matrix of bone, also called the osteoid, is made up of about 15% water, 30% collagen and 55% mineral salts; most common being calcium phosphate. Calcium phosphate will in turn combine with calcium hydroxide to form hydroxyapatite, the same mineral that makes up our teeth! It is these hydroxyapatite crystals that calcify the collagen, through the process of calcification, to make the bone hard, and therefore healthy.

Cells:

The cells within bones include osteoblasts, osteoclasts and osteocytes. Osteoblasts lay down the osteoid, whilst osteoclasts breakdown osteoid, therefore facilitating bone resorption. Remember, “Osteoblasts build bone, Osteoclasts carve out bone”. Osteocytes reside in hallow spaces called lacunae, and they help maintain bone.

Types:

There are two types of bone, compact and spongy (also referred to as trabecular or cancellous). Compact bone provides protection and support, and it composed of several osteons (also called Haversian systems), lined up next to each other, with little space in between them. Spongy bone does not contain any osteons, it is instead made up trabeculae. Spongy bone is always covered by compact bone.

The bones in our body can also be classified based on their type of shape; long, short, flat, irregular and sesamoid. The cranium is mainly made up of flat bones. Flat bones consist of a layer of spongy trabecular bone in between layers of compact bone. This is important as it demonstrates that the bones in the cranium are adapted for protection and providing a large surface area for muscle attachments in the head.

What are the types of bone fracture?

A bone fracture is the definition given to a break in the bone. Sometimes, when bones are subject to pressure, they can fracture. The clavicle is the most commonly fractured bone in the body. In a retrospective study of more than 2000 patients presenting with facial bone fractures, the most common isolated fracture site was the nasal bone, followed by the mandible (1)

The type of bone fracture describes the nature in which the bone has been broken. Types of bone fracture include:

Compound: (open) fractures – these type of fractures will have a piece of broken bone protruding through the tissues (e.g. skin). It should be noted that mandibular fractures can be compound fractures as the fracture line will be continuous with the PDL, thus the fracture is exposed to the oral cavity

Simple: (closed) fractures – these fractures describe a simple breakage in the bone, where the bone has been broken into two clean segments

Comminuted: fractures– the bone is splintered/crushed at the site of fracture. They most commonly occur in the elderly, as bones become more brittle with age

Greenstick: fractures – occur in children, where one side of a bone is partially fractured whereas the other side of the same bone bends

Spiral: fractures – often occurs due twisting or rotational force being applied to the bone

Transverse, Linear & Oblique: fractures describe the orientation of the fracture line

If the skull is subject to a blunt force, then the skull may experience a depression fracture, where the portion of the skull which had fracture becomes depressed, and is pushed in closer into the brain. These fractures are associated with higher rates of infection, seizure, neurological deficits, and death (The Neurosurgeon's Handbook. Oxford University Press)

Why do bones break in the head and neck?

Common reasons for bone fractures in the head and neck (2) include:

It should be noted that men (average age=43) are three times more likely to experience maxillofacial trauma compared to women (average age=55) (3)

Some key presenting features of head and neck trauma include:

• Pain and swelling
• Loss of function e.g. trismus, restricted eye movement
• Malocclusion
• Altered sensation

How does bone heal?

If a patient presents with signs and symptoms of a fracture, such as a condylar fracture of mandible, a referral to the Oral and Maxillofacial Department would be most appropriate. There may be situations. There may be situations where patients will attend your practice with a fractured bone in the head and neck due to an emergency incident or possible non-accidental injuries, and you would be expected to make a referral for the patient to be seen in secondary care

Most times, treatment for a fracture will involve bringing the segments of the bone together into close apposition, so that the ends of the bone meet. This is known as reduction. When this has happened, the rest of the healing process is taken care of by the bone and its capacity for healing. If reduction is not properly achieved, the healing process may lead to adverse results, such as delayed union of the bones, incorrect fusion of the bone fragments (malunion) or infection

The process of bone healing is broken down into various phases, and each phase has been described below:

Reactive phase

This phase involves inflammation and formation of a fracture haematoma. Following the fracture, the blood vessels that were passing the fracture line rupture, causing leakage of the blood. This creates a clot around the site of the fracture, this is the fracture haematoma. This clot forms 6-8 hours after the fracture had occurred

Nearby dead osteoblasts and osteoclasts stimulate inflammation to occur, and so phagocytes and other cells cleanse the debris consisting of dead bone and cells

Reparative phase

New blood vessels begin to grow within the fracture haematoma Fibroblasts and chondroblasts from the periosteum begin to lay down collagen and fibrocartilage. This eventually leads to the formation of a fibrocartilaginous callus. This is collection of cartilage and collagen, which unites the two broken ends of the bone. This callus takes up to 6 weeks to form

Once this fibrocartilaginous callus has formed, new osteoblasts lay down spongy trabecular bone, converting the fibrocartilaginous callus into a bony hard callus. The bony hard callus will last up to 4 months

Bone remodelling phase

The callus is altered by osteoblasts and osteoclasts through the process of bone remodelling, until it becomes strong healthy bone once again. The time it takes varies based on the severity of the fracture, but it may take months