The C5-C6 spinal motion segment (located in the lower cervical spine just above the C7 vertebra) provides flexibility and support to much of the neck and the head above. Due to its high load-bearing function, the C5-C6 motion segment is frequently affected by poor posture, degeneration, disc herniation, radicular pain, and trauma.1-5
Anatomy of the C5-C6 Spinal Motion Segment
The C5-C6 spinal motion segment includes the following structures:
- C5 and C6 vertebrae. These vertebrae are each composed of a vertebral body, a vertebral arch, and 2 transverse processes. Together they form paired, synovial facet joints with gliding movements. Articulating cartilages are present on the joint surfaces to provide smooth movements and prevent friction between the facet joint surfaces of C5 and C6 vertebrae at the back. The vertebrae are held together with ligaments that attach one vertebra to the other at various attachment points.
- C5-C6 intervertebral disc. A disc made of a gel-like material (nucleus pulposus) surrounded by a thick fibrous ring (annulus fibrosus) is situated between the vertebral bodies of C5 and C6. This disc provides cushioning and shock-absorbing functions to protect the vertebrae from grinding against each other during neck movements, while also allowing movement in all directions.
See Cervical Discs
- C6 spinal nerve. In between C5-C6, the C6 spinal nerve exits the spinal cord through a small bony opening on the left and right sides of the spinal canal called the intervertebral foramen. This C6 nerve has a sensory root and a motor root.
- The C6 dermatome is an area of skin that receives sensations through the C6 nerve. This dermatome includes the skin over the ‘thumb’ side of the forearm and the thumb.
- The C6 myotome is a group of muscles controlled by the C6 nerve. These muscles include the wrist extensor muscles, which allow the wrist to bend backward; and the biceps and supinator muscles of the upper arm, which serve to bend the elbow and rotate the forearm.
The spinal cord is protected within the spinal canal, with the vertebral bodies in front and vertebral arches at the back. The vertebral arteries are protected by bony tunnels going up either side of the vertebrae.
Common Problems at C5-C6
The C5-C6 motion segment is prone to the following injuries and disorders:
- Disc problems. Herniation of the C5-C6 intervertebral disc is common.4 This condition may result due to the shearing forces that affect the disc when the head drifts forward from poor posture.1 Herniation may also result from injury or aging-related wear and tear. The C5-C6 disc may also be subject to traumatic degeneration following a whiplash injury in some cases.6 Problems to this disc are often a source of C6 radicular nerve pain.3,5
- Spondylosis. Spondylosis (degeneration) of the C5-C6 vertebrae and intervertebral disc occurs at a higher rate compared to other cervical vertebrae.3 Spondylosis usually results in the formation of bone spurs (osteophytes), eventually leading to stenosis or narrowing of the intervertebral foramina or spinal canal.
- Fracture. Research suggests about 20% of traumatic neck fractures occur at the C6 vertebral level and 15% occur at C5.2 Motor vehicle accidents or trauma causing forceful bending of the neck forward or backward, such as in whiplash, may cause these fractures, leading to instability of the neck and injury to the nerve roots or the spinal cord.
- Congenital stenosis. The C5 vertebra is at a greater risk for spinal canal stenosis as an inherited genetic trait compared to other vertebrae lower in the cervical spine.7
Rarely, tumors and infections may affect the C5-C6 vertebrae and spinal segment.
Common Symptoms and Signs Stemming from C5-C6
Vertebral and disc pain from C5-C6 may occur suddenly following an injury or gradually increase over a period of time. Typically, a dull ache or sharp pain may be felt at the back of the neck. The neck’s range of motion may also decrease. There may be crepitus (a snap, crackle, or pop sound) with neck movements.
- Pain in the shoulder, upper arm, forearm, hand, thumb, and index finger; frequently aggravated by arm or neck movements.8,9 Sometimes, the pain may also radiate from the neck into the arm.9
- Numbness in the outer side of the forearm, thumb, and index finger.8
- Weakness in the shoulder, elbow, and wrist, commonly affecting the motion of these joints.8,10
Symptoms may occur on one or both sides of the body.
An injury to the spinal cord at the C5-C6 level may cause pain, weakness, or paralysis in the arms and/or legs. There may be loss of bowel and bladder control or breathing problems in some cases.
Nonsurgical treatments are often tried first for pain that stems from C5-C6. In rare cases, surgery may be considered.