The C1 and C2 vertebrae are the first two vertebrae at the top of the cervical spine. Together they form the atlantoaxial joint, which is a pivot joint. The C1 sits atop and rotates around C2 below. More of the head’s rotational range of motion comes from C1-C2 than any other cervical joint.1
While C1-C2 is relatively sturdy and resistant to injury, it can become quite painful and problematic due to trauma or degenerative conditions. These problems may also affect the spinal nerves, vertebral artery, and/or the spinal cord at the at the C2 level.
Anatomy of the C1-C2 Vertebrae and Spinal Segment
The C1-C2 vertebrae and spinal segment include the following structures:
- C1 and C2 vertebrae. The C1 vertebra, also called atlas, is shaped like a ring. The C2 vertebra has an upward-facing long bony process called the dens. The dens forms a joint with the C1 vertebra and facilitates its turning motions, thereby allowing the head to turn in different directions.
- The atlantoaxial joint. The joint between the C1 and C2 vertebrae is called the atlantoaxial joint. Unlike other vertebral joints, the atlantoaxial joint does not have an intervertebral disc. This joint is secured by a thick, strong ligament called the transverse ligament.
- C2 spinal nerve. At the atlantoaxial joint, the C2 spinal nerve exits the spinal cord through a small bony hole or foramen above the C2, called the intervertebral foramen. This nerve has a sensory root and a motor root.
- The C2 dermatome is an area of skin that receives sensations through the C2 nerve. This dermatome includes the top and back of the scalp, the skin over the front of the neck, and the ear lobes.
- The C2 myotome is a group of muscles controlled by the C2 nerve. These muscles include those that allow the neck to bend forward.
An injury to this nerve can cause problems in any part of its dermatome and/or myotome.
The spinal cord is protected by the C1-C2 vertebrae in the upper cervical area. These vertebrae have several small and large foramens. The spinal cord passes through the large, centrally placed vertebral foramen. The smaller foramens facilitate the passage of blood vessels around the spine.
Common Problems at C1-C2
Problems at the C1-C2 vertebral levels may affect the vertebrae, the C2 spinal nerve, and/or the spinal cord. A few examples of problems at this cervical level include:
- Arthritis. Arthritis in the C1-C2 joint is common in many of the systemic arthritic syndromes such as rheumatoid arthritis or other spondyloarthropathies (spinal arthritis syndromes). This condition is due to the high levels of motion within the C1-C2 joint. Bone spurs and other degenerative changes may eventually compress a nerve root or the spinal cord.
- Fracture. Fractures of the C1 and C2 vertebrae usually occur together. Fractures may result from diving in shallow water, falling, motor vehicle accidents,1 and/or hitting an obstacle with the forehead or chin.2 Trauma to C1-C2 may also cause whiplash injury, spondylolisthesis, nerve injury, and/or spinal cord injury.
- Vertebral artery injury. Injuries at C1-C2 may affect the vertebral artery at this level while it takes a torturous turn to ascend into the brain. Vertebral artery injuries at this level may lead to serious neurological conditions.
- Occipital neuralgia. Injury to the C2 spinal nerve may result in headaches due to occipital neuralgia.
- Crowned dens syndrome. Calcium from the surrounding ligaments may deposit on the dens of C2. This deposition causes inflammation and reduced mobility of the C1-C2 joint.
Depending on the type of injury, associated symptoms may occur in the upper neck and/or in other areas of the body.
Common Symptoms and Signs Stemming from C1-C2
Vertebral pain at C1-C2 can range anywhere from a dull ache to a sharp, burning pain in the neck. C1-C2 pain may either last for a short while or become chronic.
If a C2 nerve root becomes inflamed or injured, additional symptoms may include:
- Radiating pain up to the back and/or top of the head
- Pain in the temple and/or behind the eyes and/or ears
- Neck-tongue syndrome resulting in neck and/or head pain with numbness or abnormal sensation on one side of the tongue
- Sensitivity to light
Symptoms of C2 nerve injuries are usually aggravated while lying down. There may be increased pain at night, causing disturbed sleep.
If the spinal cord becomes compressed at the C2 level, it can cause pain, tingling, numbness, and/or weakness in the arms or legs, loss of bowel and/or bladder control, and other problems. Severe cases of spinal cord injury at C2 can be fatal because breathing and other critical body functions may be impaired or stop.3 Paralysis of the body below the injured region of the spinal cord may also occur in some cases.
Treatment of the C1-C2 vertebrae and spinal segment includes nonsurgical and surgical methods.