Cervical Spine

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The cervical spine consists of a total of seven vertebrae and is divided into the upper (C1and C2) and lower cervical spine (C3 through C7). The Occiput (CO), also known as the Occipital Bone, is a flat bone that forms the back of the head. Seven vertebrae make up the cervical spine with eight pairs of cervical nerves. The individual cervical vertebrae are abbreviated C1, C2, C3, C4, C5, C6 and C7. The cervical nerves are also abbreviated; C1 through C8.

 

Atlas (C1)
The Atlas is the first cervical vertebra and therefore abbreviated C1. This vertebra supports the skull. Its appearance is different from the other spinal vertebrae. The atlas is a ring of bone made up of two lateral masses joined at the front and back by the anterior arch and the posterior arch.

Axis (C2)
The Axis is the second cervical vertebra or C2. It is a blunt tooth–like process that projects upward. It is also referred to as the ‘dens’ (Latin for ‘tooth’) or odontoid process. The dens provides a type of pivot and collar allowing the head and atlas to rotate around the dens.

A complex system of ligaments, tendons, and muscles help to support and stabilize the cervical spine. The vertebrae are also connected by powerful ligaments, resulting in what is overall a very strong but nonetheless highly mobile functional unit. Ligaments work to prevent excessive movement that could result in serious injury . Muscles also help to provide spinal balance and stability, and enable movement. Muscles contract and relax in response to nerve impulses originating in the brain. Some muscles work in pairs or as antagonists. This means when a muscle contracts, the opposing muscle relaxes. There are different types of muscle: forward flexors, lateral flexors, rotators, and extensors.

There are discs between the vertebral bodies. These act as shock absorbers and are able to distribute shocks evenly across the entire surface of the vertebral body.

Types of cervical spine injury

A distinction is drawn between different types of impact:

  • Type A = Compression mechanisms
  • Type B = Injury resulting from the cervical spine being bent too far in one direction
  • TypeC = Injury or injuries caused by the head and neck being forcefully twisted

 In most cases, it is possible to determine the type of impact from the pattern of injuries. For example, major compression will in most cases cause fractures in the area of the vertebral body, which can even be as severe as fragmenting.

Mechanisms causing the cervical spine to be bent too far in one direction frequently result in torn discs and ligaments. The feared dislocation of the cervical spine will in most cases result from forceful twisting movements

 

 

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Spinal fusion

Spinal fusion and instrumentation were developed and applied as independent techniques for treatment of spinal instability in the first half of the 20th century, before the biomechanical principles surrounding spinal instability were understood.

In current practice, bone grafting and instrumentation are often used concurrently based on the expectation that internal fixation of spine enhances the success of bone fusion while a successful bone fusion eliminates the possibility of hardware failure by reducing the chronic biomechanical stresses on the hardware construct.

Of note, the term "fusion" is used in this article and in spine literature to refer to the concept of internal stabilization of spine, generally accomplished by fusion with instrumentation (instrumented fusion), but also, albeit with decreasing frequency, accomplished by bone grafting alone.

Spinal Facet Joints

The joints in the spinal column are located posterior to the vertebral body (on the backside). Facet joints help the spine to bend, twist, and extend in different directions. Although these joints enable movement, they also restrict excessive movement such as hyperextension and hyperflexion (i.e. whiplash).

Flexion Extension