The normal cervical spine is a curved structure that is similar to the design of the arch of a bridge. This curve allows it to support the weight of the head. Injury mechanisms that predispose the cervical spine to injury often involve straightening out this curve to a shape that is less able to cope with the sudden forces put upon it.
Sudden bending (forced flexion)
Mechanisms that suddenly force the neck forward can result in overload of the cervical spine and cause the ligaments between the bones to tear and become unstable. The modern Rugby behaviour of ducking into tackles to protect the ball with the head bent forward and the shoulders low would be one such potential mechanism. A collapsed scrum can also cause a sudden bending.
Squashing of the spine (axial compression)
Any force that straightens out the neck and compresses it from top to bottom (known as axial loading) such as a fall from height onto the top of the head, can increase the risk of spinal injury. Examples include players who fall from a height, such as contesting a high ball or who are forced head first towards the ground in a spear tackle or collapsed scrum.
Bending and twisting (flexion with rotation)
Any motion that involves bending the neck forwards or backwards with a twisting action can also cause bone, joint or disc injuries. These are often a scrum related mechanism.
Rugby players who lose consciousness or sustain a potential spinal injury may fall or roll into any position. They may be face up, face down or on their side. They may be able to move the head, or walk around and still have symptoms that are suggestive of a serious neck injury.