The cervical spine is responsible for a variety of spinal movements that are crucial to sport success. The cervical spine is the support mechanism for the skull and is a multidimensional turning and lifting device in combination with the muscles of the neck. The cervical spine is also the bony protection for the spinal cord that runs between the spine and the interior of the body. The cervical spine comprises seven vertebrae, numbered C1 though C7 for identification, with the vertebrae connected by way of flexible ligaments known as facets. The vertebrae are each spaced from one another by disks, which are flexible, fluid-filled membranes that provide considerable cushioning for the spine both as it moves and as forces are applied to it.
What are commonly classified as neck injuries primarily occur at two places in the cervical spine: one is at the C1 vertebrae (the cranial cervicojunction), referred to as the atlas, the bone upon which the skull is supported; the second occurs at C2, which is the axis upon which the C1 atlas and the skull are able to pivot, flex forward, and extend backward. Not every neck and cervical spine injury that occurs in sports is a fracture. The construction of the cervical spine is relatively flexible, given the mobility provided by the vertebrae facets. The muscles of the neck are vulnerable to strains, caused by the same kinds of forces that will produce injury in other muscle groups. Fractures of the cervical vertebrae are the more dangerous injury.
Any bone in the body can be fractured if it receives a force that exceeds its tensile strength (resistance to breaking under tension), or its compressive strength (ability to either bend or to absorb the force). Given the position of the parts of the cervical spine, a fracture resulting from a direct blow to the vertebrae is rare.
The common mechanisms that can result in a cervical fracture include: flexion, the bending of the spine; flexion-rotation, a combination bending and rotating movement of the spine; extension, a stretching movement of the spine; extension-rotation, a combination stretching and rotating movement of the spine; or vertical compression, in which force is applied to the top of the spine, causing damage through its downward pressure.
The forces generated by these mechanisms on the body are commonly present in two distinct kinds of sport: high velocity sports, such as downhill skiing, ski jumping, bobsledding, and auto racing, and contact sports, including American football, rugby, and ice hockey.
In high velocity sports where the athlete can often lose control, the athlete is vulnerable to a high-speed, unprotected collision. An example is a downhill skier who misses a turn on a race course at speeds in excess of 75 mph (120 km/h) and falls, a process bringing the skier into contact with the icy surface of the hill. This movement will often cause the neck to be twisted violently, a flexion-rotation movement that will often fracture the C2 vertebrae. Such accidents are difficult to anticipate and equally impossible to protect against. Violent crashes in auto racing will produce an extension force, a much-magnified form of "whiplash," in which the neck and head continue to move forward on impact and the body endeavors to brace itself by resisting the head and neck motion; such a fracture occurs typically at the C2 vertebrae.
Contact sport has its share of both intended and unintended violent collisions; a large number of the cervical fractures occurring in these sports are a product of poor technique by the athlete. American football is the sport that produces the highest number of cervical fractures of almost any sporting activity. The defensive object of the game is to stop the opposition from advancing the football, which requires the execution of a tackle on every play. The defensive player is exposed to a neck injury and, at worst, a cervical fracture or spinal cord injury, if the tackle is executed when the player intends to make contact with the ball carrier by leading with his head. The head then is at risk of being snapped in a direction opposite to the motion of the tackler's body, causing a force that risks both a spinal fracture as well as a spinal cord injury.
Improper tackling technique, as well as the forces incorrectly applied to the neck of an athlete in a rugby scrum may potentially lead to a cervical spine injury. Diving is another sport in which, as a result of the distance through which the body travels and the corresponding speed developed at entry, the force upon which the body strikes the dense water is significant. The diver's neck and cervical spine become exposed to tremendous forces readily capable of causing a fracture. A severed spinal cord and the potential for paralysis are acute in such circumstances.