Structure of the Spine and How Injuries Occur to Individual Parts

The spinal column is one of the most vital parts of the human body, supporting our trunks and making all of our movements possible. In profile the spine is an elongated ‘S’ shape and has four main functions

1 To protect the spinal cord

2 To support the upper body

3 To allow flexibility and movement

4 To serve as a point of attachment for ligaments, tendons and muscles.
The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.

The human spinal cord is protected by the bony spinal column. The spinal column is made up of bones called vertebrae.

The vertebrae are arranged one on top of another in a series of four main curves which make up the spinal column.

The human spinal column is made up of 33 bones:

There are 7 vertebrae in the cervical region. These are generally small and delicate bones that are numbered from top to bottom from C1-C7. Interestingly the first cervical vertebra is also called the atlas. Atlas was one of the Titans in Greek mythology. After a fight with Perseus, Atlas was turned to stone and had to carry the weight of the Earth and heavens on his shoulders. Therefore, the first cervical vertebra was named the atlas because it carries the weight of the head! The atlas (C1) and axis (C2) are the vertebrae that allow the neck so much rotation. The atlas allows the skull to move up and down, while the axis allows the upper neck to twist left and right.

There are 12 vertebrae in the thoracic region. These bones are bigger and their spinous processes have surfaces that articulate with the ribs and their connection with the rib cage prevents much movement.

There are 5 vertebrae in the lumbar region. These vertebrae are large and robust as they must support more weight than other vertebrae. They allow significant forward, backward and sidewards bending and to some degree turning or rotating.

There are 5 vertebrae in the sacral region and 4 in the coccygeal region. However, in adults the bones in the sacral region join to form one bone called the sacrum; the bones in the coccygeal region join to form one bone called the coccyx.

The two dimples in most everyone’s back (known as the “dimples of Venus”) are where the sacrum joins the hipbones, called the sacroiliac joint.

Looking at the diagram of the spine you will note that it looks like a double “S” shape constructed from the cervical, thoracic, lumbar and sacral curves. The thoracic and the sacral curves are known as primary curves and are generally injured less than the cervical and lumbar curves which are known as secondary curves. This is because much more movement takes place in the neck and the lower back.

It has been suggested that the ‘S’ shape of the spine:-

assists energy absorption and protects the spinal structures against impact by increasing its strength

helps to maintain balance in an upright position

absorbs shock when a person walks (or runs)

Principle! One of the main principles of good manual handling practice is to maintain the spinal curves in their natural alignment.

The spinal cord is located in the middle of the vertebra which makes up the spinal column. It is made up of 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. A pair of spinal nerves exit from each segment of the spinal cord.

Spinal Cord

The spinal cord is a thin, tubular structure that is an extension of the central nervous system from the brain i.e. it is an extension of the brain. The spinal cord is a collection of nerve fibres that come from the brain and are protected by the spinal column. Nerve fibres (nerve roots) from the spinal cord come out from between the vertebrae and take and receive messages to and from different parts of the body.
The spinal cord is about 45 cm long in men and 43 cm long in women. The length of the spinal cord is much shorter than the length of the bony spinal column. In fact, the spinal cord extends down to only the last of the thoracic vertebrae.

Nerves that branch from the spinal cord from the lumbar and sacral levels must run in the vertebral canal for a distance before they exit the vertebral column. This collection of nerves in the vertebral canal is called the cauda equina (which means “horse tail”).

Receptors in the body send information to the spinal cord and up to the brain through the spinal nerves.

All of the elements of the spinal column and vertebrae serve the purpose of protecting the spinal cord which provides communication to the brain, mobility and sensation in the body through the complex interaction of bones, ligaments and muscle structures of the back and the nerves that surround it.

The spinal column also supports our trunks and makes movements of our head, arms and legs possible.

Each vertebra has a vertebral body which takes most of the weight and a neural arch which protects the spinal cord. Various processes which are attached to the neural arch act as levers so that the muscles can move the spine about.

Between each of the cervical, thoracic and lumbar vertebrae there is a cushion called “intervertebral disc”. The discs are protective, circular pads of cartilage that lie between the bones of the spine (vertebrae) and cushion the vertebrae as for example when you jump or run.

The intervertebral disc is composed of two parts: the central portion with a jelly-like consistency named “nucleus pulposus” (2) and a tough fibrous outer layer (the ‘annulus fibrosus’).

As time passes the forces on the disc can make its jelly / gelatin portion wear out and lose height. A point of interest is that the force on our discs throughout the day causes us to lose height! Whilst astronauts, in weightless conditions, increase their height since the lack of gravity keeps discs from being compressed; the separation between vertebrae is therefore increased.

There are no nerves in the nucleus; they are located in the most external layers of the fibrous ring. This explains why wear and tear on the discs may not be painful as there are no nerves to receive and transmit pain. The function of the intervertebral disc can be summarised as:

1 To separate the vertebrae

2 To allow for movement of the spine

3 To act as shock absorbers

Vertebrae are linked together by ligaments, muscles and tendons which also insert into or attach onto the spinal processes to allow movement.

Ligaments

Ligaments are fibrous tissue that connects bones to other bones, they:

1 Possess varying amounts of elastic tough fibrous tissue which help support the spine.

2 Pass across the articulating surfaces of the facet joints and between the vertebrae

3 Help to prevent unwanted or excessive movements

As they are elastic, ligaments can be damaged if they are over-stretched. With sudden and excessive movements a ligament can be weakened, torn or snapped.

Muscles

The word muscle comes from the latin meaning little mouse! It is a contractile tissue of the body and its function is to produce force and movement. Muscles:

1 Sit over the ligaments

2 Are attached to the bones by tendons

3 Control body movements

4 Act in pairs, as one muscle tightens (contracts) the other relaxes to allow movement.

· Postural muscles hold up the body against the influence of gravity.

· Other important muscles involved in the function of the spine are the abdominal muscles

· Muscles require energy to work efficiently
Muscle work can be either static or dynamic.
Static muscle work is when a muscle is in constant contraction without producing any movement. This could be, for example, when holding a tray or when maintaining your foot on an accelerator pedal when driving.

When muscles work statically blood flow is restricted, oxygen supply is reduced, leading to a build up of waste products, muscle pain and fatigue then occur. If repeated frequently this can lead to deterioration and degeneration of soft tissues and joints. Static muscle work cannot be maintained for long periods.

Dynamic muscle work involves a muscle alternately contracting and relaxing such as when polishing a surface or waving a hand. This type of work allows a fresh supply of blood and oxygen to reach the muscle and also allows waste products to be removed.

Tendons

A tendon (or sinew) is a tough band of fibrous connective tissue that connects muscle to bone, or muscle to muscle and is designed to withstand tension. Tendons are similar to ligaments except that ligaments join one bone to another. Tendons and muscles work together and can only exert a pulling force.

Facet Joints

Facet joints are:

1 Small, sliding joints at the back of each vertebrae

2 Each vertebrae is joined to the next by facet joints

3 The facet joints are designed to allow for movement of the spine together with the discs

4 Help prevent the spine moving beyond its normal range of movements and so putting too much pressure on the discs

Many spinal experts consider the facet joints to be a common source of back pain and discomfort. Repetitive or excessive motions of the upper body, especially rotation (twisting) or extension (bending backwards), can injure or irritate facet joints or the surrounding structures. Poor postural habits can significantly accelerate the normal wear and tear on the facet joints.

It is mainly the soft tissues of the body that are injured as a result of manual handling. Muscles, ligaments, tendons and cartilage can be overloaded and consequently injured. These injured structures then become inflamed causing pain.

This can result in reduced movement and/or altered mechanics of movement which may result in tissues healing in a shortened position. Tissues are then more vulnerable to pain and further injury.

People with back problems often seem to be faced with this vicious cycle:

Damage to the Vertebral body

If the spine is bent (flexed) as it often is in manual handling, damage of the vertebral body can be caused by the intervertebral disc bulging into the vertebra so that it collapses to cause a wedge fracture often leading to a humpback deformity that you can see in the spines of people who have osteoporosis of the spine.

Slipped (herniated) Disc

A slipped disc is the common name for the medical term ‘prolapsed’ or ‘herniated’ disc. A slipped disc occurs when the outer part of a disc ruptures and allows the gel inside to bulge outwards from between the vertebrae. The damaged disc can put pressure on the whole spinal cord or on a single nerve fibre. This means that a slipped disc can cause pain both around the area of the bulge or anywhere along the area controlled by an affected nerve.

Slipped discs occur most often in the lower back. The main symptoms of a slipped disc in this region are sudden, severe back pain, muscle spasm and sciatica. Sciatica is pain, numbness, weakness, or tingling that extends down the sciatic nerve that runs from your lower spine through each buttock and leg. Usually the pain is only on one side. The pain is often made worse by moving, coughing or straining.

If a slipped disc occurs higher up the spine the symptoms can include a band of pain or numbness around your chest, as well as back pain.

If a slipped disc occurs at neck level the symptoms are pain in the shoulder, neck, arm, or hand, muscle spasm and stiffness of the neck.

If the gel inside the disc escapes directly backwards it may press very firmly on the spinal cord. This can cause sciatica in both legs, numbness in the ‘saddle area’ between your thighs and difficulty in controlling your bladder, bowels and sexual function. This is known as Spinal cord compression. It is a medical emergency and needs urgent treatment to prevent permanent damage to the spinal cord.

Slipped disc usually happens when the back is bent forward and a large amount of pressure is put on a disc. Bending forwards opens up the gap in the vertebrae at the back of the spine and makes it easier for the disc to ‘slip’ if it is squeezed, for example by the strain that is put on your back when you are attempting to lift a weight.

The way you stand, sit or move can also be a factor in whether you damage a disc. However, there are factors that make a slipped disc more likely. You are more likely to suffer a slipped disc if you:

have a job that involves heavy manual labour

are lifting incorrectly, especially while twisting or turning

have a job where you sit for a long time

have a job where you drive for many hours at a time

if you are overweight

The process can be shown:

Principle ! Avoid bending and stooping

Principle ! Avoid twisting the spine

Principle ! Avoid lifting heavy loads

Principle! Change posture frequently