The atlas bone is the uppermost bone of the spine. It plays an important role in supporting the head and creating the pivot joint, allowing the head to turn. It is also known as the first cervical, or C1, vertebra. This bone has a slightly different shape from the other vertebrae, most notably lacking a body and having a distinctive ring shape. It is named for the mythological Atlas, a person who supported the weight of the world on his shoulders.
This bone articulates with the base of the skull and the second cervical vertebra (C2), also known as the axis. Together, the axis and the atlas bone stabilize the head to make sure the weight is fully supported. They also provide a base for the head to tilt and rotate, allowing more flexibility than conventional vertebrae would. People also rely on muscles and tendons along the spine and skull to keep the head upright.
Without the atlas and axis bone along with their supporting ligaments, it would not be possible to keep the head fully upright. This could result in pressure on the spinal cord and might eventually cause death by cutting off signals from the brain. Rarely, patients can experience degeneration of the atlas bone and surrounding tissues that lead to sudden spine instability and severe injuries or death as a result of the deterioration. Usually symptoms like neck pain and severe infections provide ample warning before this occurs.
It is possible to fracture the atlas bone. This usually happens when people fall or experience diving injuries, or sustain a sharp blow to the back of the head. A fracture can pose health risks for the patient, including damage to the nerves and spinal cord. Medical imaging is usually necessary to identify it, and the patient may need surgery. In cases where a neck fracture is suspected, emergency responders are very careful to keep the neck stable and prevent additional damage.
This bone starts to form very early in fetal development, along with the rest of the spine. When a baby is first born, part of the atlas bone still includes cartilage, allowing room for growth. This will ossify, with bone cells replacing the cartilage, by the fourth year of life. Small variations in formation can result in shape differences between atlas bones in different people. The bone may be flatter, broader, or narrower in some than in others.