A cervical rib is an extra rib that most commonly extends from the seventh cervical vertebra of the neck above the first set of ribs. It is a congenital overgrowth of bone that develops abnormally from birth. While it is oftentimes unproblematic and goes unnoticed, it is known to play a contributing role in the development of thoracic outlet syndrome.
The rib cage has 12 sets of ribs. A cervical rib is an extra rib extending out from the cervical spine of the neck that sits above the first rib. A cervical rib forms from the overdevelopment of the transverse process of a cervical vertebra, typically from the seventh cervical vertebra in the neck known as C7.1
The transverse process is a bony prominence that projects laterally off the right and left sides of each vertebra of the cervical, thoracic, and lumbar regions of the spinal column.
There are seven cervical vertebrae in the neck, twelve thoracic vertebrae in the upper-mid back, and five lumbar vertebrae in the low back. Below the lumbar vertebrae is the sacrum, made up of five fused vertebrae, as well as the coccyx, or tailbone, made up of four fused vertebrae, for a total of 33 vertebrae in the entire spine.
The transverse processes on each vertebra serve as attachment sites for ligaments and muscles that help rotate and bend the spine. The transverse processes are typically small in the cervical vertebrae but larger in the thoracic spine where they articulate with each of the 12 ribs. A cervical rib forms from an overgrown transverse process of a cervical vertebra that more closely resembles the longer transverse processes of the thoracic vertebrae.
Cervical ribs are extra bone growths that are congenital abnormalities present from birth and vary in size, shape, and attachment sites, occurring in approximately 0.5-1.0% of the population. They may or may not attach to the first rib and can occur on one or both sides of the neck.
It is more common for a cervical rib to be present unilaterally on one side of the neck rather than bilaterally on both sides, with left-sided cervical ribs being more common than right-sided abnormalities.1
There is no distinct physiological function of a cervical rib. It is an abnormal overdevelopment of the transverse process of a cervical vertebra. The transverse processes of the vertebrae in the spine are connected to each other via the intertransverse ligament.
Certain muscles that control motion of the spine also originate from or attach to the transverse processes of the cervical vertebrae. These muscles include:
Rotatores: The rotatores are the deepest of all the muscles throughout the entire spine and provide stability, rotate the spine, and assist with spinal extension.
Iliocostalis: The iliocostalis is one of three vertically oriented muscles, collectively referred to as the erector spinae muscles, that run up and down the spine throughout the cervical, thoracic, and lumbar regions. The iliocostalis is the most laterally located of the erector spinae muscles and helps extend the head and spine and bend them to the side.
Longissimus: The longissimus is another one of the three vertically oriented muscles, collectively referred to as the erector spinae muscles, that run up and down the spine throughout the cervical, thoracic, and lumbar regions. The longissimus is the largest of the erector spinae muscles and helps extend the head and spine and bend them to the side.
Scalenes: The scalenes are a group of three muscles (anterior, middle, and posterior scalene) that connect the transverse processes of the cervical vertebrae in the neck to the first and second ribs. When contracted, the scalenes cause the first and second ribs to elevate and the neck to bend to the side.2
The most common problem associated with the presence of a cervical rib is compression of nearby blood vessels or nerves which can lead to thoracic outlet syndrome. Thoracic outlet syndrome falls into three different categories:1
Neurogenic thoracic outlet syndrome: Caused by compression of nerves branching off from the brachial plexus and comprises about 90% of all cases of thoracic outlet syndrome.
Arterial thoracic outlet syndrome: Caused by compression of the subclavian artery.
Venous thoracic outlet syndrome: Caused by compression of the subclavian vein.
Arterial and venous forms of thoracic outlet syndrome are sometimes grouped together as vascular thoracic outlet syndrome as they both involve compression of nearby blood vessels.
Neurogenic Thoracic Outlet Syndrome
The brachial plexus is a network of nerves formed by the lower four cervical nerve roots and first thoracic nerve root (C5, C6, C7, C8, and T1) that extends from the neck and branches into the nerves that supply the chest, shoulder, arm, forearm, and hand and fingers. Each nerve root corresponds to a vertebra of the spine.
The cervical nerve roots exit above each corresponding vertebra in the cervical spine with the exception of the C8 nerve root, which exits below the C7 vertebra, as there are only seven cervical vertebrae in the neck. The thoracic nerve roots exit below each corresponding vertebra in the thoracic spine.
These nerve roots come together to form the trunks of the brachial plexus, which subdivide anteriorly and posteriorly to form cords which further branch off into individual nerves including the musculocutaneous, axillary, median, radial, and ulnar nerves.
If nerve compression occurs in thoracic outlet syndrome, symptoms like pain, numbness, weakness, and tingling may be experienced in the arm and hand on the affected side of the body.1
Vascular Thoracic Outlet Syndrome (Arterial and Venous)
If arterial compression occurs in thoracic outlet syndrome, the arm on the affected side of the body may have a weak or absent pulse, discoloration of the arm, and decreased temperature, especially in the hand and fingers due to decreased blood flow.
If there is compression of the subclavian vein, the arm will become swollen and take on a bluish hue as blood will be obstructed from circulating back to the heart.1
Your doctor or physical therapist can perform Adson's test to assess for subclavian artery compression by a cervical rib. Your arm will be extended back behind your body and abducted, or lifted out to the side, by 30 degrees. You will then be asked to extend your neck back and rotate your head toward the arm being tested. A positive test will reveal a significantly diminished or absent radial pulse in the wrist with this position.3
Factors that increase the risk of developing thoracic outlet syndrome include overuse of the surrounding neck and chest musculature and poor posture. These can lead to an unbalanced tightening of the muscles surrounding the neck, especially the scalenes, which can compress surrounding structures against a cervical rib.3
Oftentimes, a cervical rib presents without symptoms and goes unnoticed unless X-rays are taken. If a cervical rib is causing compression of structures between the scalene muscles, physical therapy can help decrease muscle tightness, improve neck mobility, strengthen surrounding muscles for improved neck and shoulder posture, and decrease nerve tension.
Other conservative measures include medications like pain relievers and muscle relaxers, as well as injections of steroids, local anesthesia, or Botox to relax overly tightened scalene and pectoralis muscles.
If symptoms do not subside in four to six months of treatment, surgical options are considered for symptom management, especially in neurogenic cases causing uncontrolled pain and progressively worsening weakness of the hand, arm, and shoulder.3
If these methods fail to relieve symptoms, surgical removal of a cervical rib can be performed to reduce compression. A scalenotomy, where a portion of one of the scalene muscles is removed, or a scalenectomy, where an entire scalene muscle is removed, may also be performed to further reduce compression if needed.
Cervical rib removal for the treatment of thoracic outlet syndrome is generally safe and effective for short-term and long-term elimination of symptoms.