A cervical rib is an extra rib, a congenital abnormality located above the normal first rib. This supernumerary rib typically arises from the seventh cervical vertebra (C7). The presence of a cervical rib is uncommon, estimated to occur in about 0.2% to 1% of the general population.
The extra rib often remains silent, meaning most people who have one never experience symptoms. When symptoms do occur, they are related to the rib’s position in the neck and shoulder area. These symptoms can be subtle or severe enough to require specialized medical attention.
Anatomy and Developmental Origin
The human body normally has twelve pairs of ribs originating from the thoracic vertebrae. A cervical rib represents a failure in the embryonic development process, where the costal element of the C7 vertebra fails to re-absorb fully. This vestigial structure persists as an extra rib, an anatomical variation present from birth.
Cervical ribs vary widely in size and shape, ranging from a small bony outgrowth to a complete rib. Often, the rib is incomplete, terminating in a dense, fibrous band. This fibrous band can cause compression of nearby structures, similar to a complete bony rib. The extra rib can occur on the right, left, or both sides of the neck.
Clinical Manifestations and Thoracic Outlet Syndrome
The primary significance of a cervical rib is its potential to narrow the thoracic outlet, the passageway for nerves and blood vessels between the collarbone and the first rib. This narrowing can lead to a condition called Thoracic Outlet Syndrome (TOS), which involves the compression of the neurovascular bundle that travels to the arm. Symptoms depend on whether the nerves, artery, or vein is compressed.
Neurogenic TOS (NTOS)
NTOS is the most common presentation. The cervical rib compresses the brachial plexus, the network of nerves controlling movement and sensation in the arm and hand. Symptoms include numbness, tingling, and pain that radiates down the arm and into the fourth and fifth fingers. This is often accompanied by weakness or wasting of the small muscles in the hand.
Arterial TOS (ATOS)
Compression of the subclavian artery leads to Arterial TOS (ATOS), the rarest but most severe form. Constant pressure can damage the artery wall, potentially leading to an aneurysm or blood clots. Symptoms result from restricted blood flow and include coldness, paleness, a weak pulse in the arm, and pain. Severe cases risk non-healing sores or gangrene in the fingertips.
Venous TOS (VTOS)
VTOS occurs when the subclavian vein is compressed, which can result in a blood clot (Paget-Schroetter syndrome). Symptoms are related to blood backing up in the arm, causing swelling, heaviness, and a bluish discoloration (cyanosis). These symptoms often appear suddenly, typically following strenuous overhead activity.
Diagnosis and Treatment Options
Diagnosing a cervical rib and its associated TOS requires physical examination, imaging, and specialized testing. Initial evaluation often includes provocative maneuvers, such as Adson’s test or the Roos test (Elevated Arm Stress Test). These tests involve positioning the arm or neck to see if symptoms are reproduced or if the radial pulse diminishes. While suggestive, these tests are not definitive, as many asymptomatic people can have a positive result.
Plain X-rays are typically the first imaging step, clearly visualizing a bony cervical rib. If the rib is fibrous or if vascular compression is suspected, other modalities are used. These include ultrasound, which assesses blood flow, and computed tomography (CT) or magnetic resonance imaging (MRI) scans. These scans, often using contrast dye (angiography), provide detailed views of the nerves and blood vessels.
Treatment depends on the type and severity of the Thoracic Outlet Syndrome. For most Neurogenic TOS cases, the initial approach is conservative management focused on physical therapy. Therapy aims to improve posture, strengthen shoulder girdle muscles, and stretch tight muscles like the scalenes to help decompress the neurovascular bundle.
If conservative measures fail, or if vascular compromise exists (Arterial or Venous TOS), surgery is recommended. The procedure, called cervical rib resection, involves removing the extra rib and any associated constricting fibrous bands. This surgical decompression widens the thoracic outlet, relieving pressure on the nerves and blood vessels.