Anatomy

What structures are most commonly injured?

The neck is the flexible connection between the head and the body. The head is controlled by muscles that start from the neck or shoulder girdle and attach to the skull. The cervical spine is made up of seven bones called vertebrae. Between each vertebra are two joints. These joints allow a little movement between each vertebra forwards and backwards called flexion and extension, side to side movement, and rotation. Because there are seven segments, the small movement between each bone is multiplied. The neck as a whole can flex forward 45 degrees until the chin almost touches the chest and backward 50 degrees, until the chin is level with the ears.

Normally, you can bend your neck from side to side about 40 degrees. This means that you can put your ear halfway to the shoulder. Most people can rotate their head about 70 degrees, placing the chin on the shoulder. Injuries to the neck occur most often when the neck is forced beyond its normal range of movement - over rotation for example. The momentum of the head is important in the mechanism of injury. Neck injuries very often result from sudden changes in acceleration as in falls, motor vehicle accidents (particularly motorcycles), sports injuries, or diving into shallow water. The head wants to go one way and the body another. The neck in between becomes strained and is damaged.

The anatomical structure of the neck helps to explain how injuries occur. Each vertebra has a drum-like vertebral body in front. This is where the weight is transferred. The vertebral body can be injured when the compression forces on the neck are excessive. This may occur with little force when the bone itself is weakened by aging processes like osteoporosis.

Between one vertebral body and the next are ligaments. The ligaments prevent excessive movement. The intervertebral disc is a special type of ligament that sits between each vertebra. The disc provides some shock absorption and allows some rocking front to back and side to side movement. Too much compression may rupture the disc. Too much rocking can tear off the ligaments and cause instability between vertebrae.

Behind the vertebral body is an arch of bone called the lamina which protects the spinal cord, an extension of the brain that passes down to the level of the waist. At the back of the arch the spinous process projects backward. You can feel the tips of the spinous processes by pressing on the back of the neck. The lateral masses and the transverse processes project outwards from the arch. All these processes act as points of attachment for muscles of the neck. The lateral masses also act as support for joints with the next vertebra. Pull-off, or avulsion injuries occur where the muscles and ligaments attach to the spinous process, the transverse processes, and even sometimes the vertebral bodies.

The vertebrae stack on one another with facet joints between the lateral masses. The joints allow some movement of the neck. Too much movement can dislocate the joints, tear the ligaments and fracture the lateral masses and the laminae. These injuries are dangerous because the spinal cord and the spinal nerves are so close.

Spinal Cord Injury

With certain patterns of neck injury, damage to the spinal cord can cause quadriplegia (also called tetraplegia). Spinal cord injury affects the legs as well as the arms and usually both sides of the body are involved. This condition results in partial or complete paralysis below the neck. There may be no sensation or movement of the arms and legs (complete quadriplegia) or there may be movement and sensation in some areas left unchanged (incomplete quadriplegia). Both complete and incomplete quadriplegia may partly recover if the pressure from the bone fragments is relieved before the spinal cord tissue dies. Spinal cord tissue does not re-grow so any recovery may be partial. A great deal of attention in the management of neck fractures is paid to preventing spinal cord injuries from occurring or getting worse.

Spinal Nerve Injury

The nerves that leave the spinal cord in the neck pass into the arm and supply sensation and the control of movement in the arm and hand. The spinal nerves as they leave the spine are sometimes referred to as the "nerve roots". These spinal nerves travel very close to the bone of the vertebrae and to the intervertebral disc. As a result, they may be damaged or compressed by injury to these structures. Injury to the spinal nerves causes loss of sensation or weakness, often on one side only. The pattern of nerve function loss gives a clue as to which nerve root is injured.