Thoracic Wall and Osteology

Twelve vertebrae (T1–T12), distinguished from cervical and lumbar vertebrae by the presence of costal facets for rib articulation.

• Body: Heart-shaped, with facets (or demi-facets) on the posterolateral surfaces for the rib heads, most thoracic vertebrae (T2–T8 typically) have superior and inferior demi-facets, since a rib head usually articulates with the vertebral body of its own number and the one above.
• Transverse processes: Carry a facet for articulation with the corresponding rib's tubercle (costotransverse joint), present on T1–T10, absent on T11–T12 (which lack costotransverse joints, since ribs 11–12 do not articulate with transverse processes).
• Spinous processes: Long and angled sharply downward in the mid-thoracic region (T4–T9 especially), overlapping the vertebra below, relevant to interpreting the level of spinous processes relative to the vertebral body they arise from (a spinous process may sit 1–2 levels below its own vertebral body in the mid-thoracic spine).
• Increasing body size from T1 to T12, transitioning toward lumbar vertebral morphology at the thoracolumbar junction.

Twelve pairs, classified by their sternal attachment and morphology.

Rib classification:

• True ribs (1–7): Attach directly to the sternum via their own costal cartilage.
• False ribs (8–10): Attach indirectly to the sternum, via the costal cartilage of the rib above.
• Floating ribs (11–12): No anterior attachment to the sternum at all; costal cartilages end freely in the abdominal wall musculature.

Typical ribs (3–9): Share a common structural pattern.

Atypical ribs:

• Rib 1: Short, flat, broadest and most sharply curved rib; single facet on the head (articulates only with T1); has scalene tubercle for anterior scalene attachment, and grooves for the subclavian artery and vein crossing its superior surface (vein anterior to scalene tubercle, artery posterior, the nerve roots of the brachial plexus emerge between the artery groove and the tubercle).
• Rib 2: Thinner, less curved than rib 1; has a distinctive tuberosity for serratus anterior origin on its outer surface; single facet on the head is uncommon (usually has a full facet, since it articulates mainly with T2 but can have a small demi-facet relationship with T1).
• Rib 10: Single facet (articulates only with T10, since ribs 11–12 lack a corresponding vertebra above to share a demi-facet with in the typical two-level pattern).
• Ribs 11–12: Short, no neck or tubercle, single facet, no articulation with a transverse process (float freely, no costotransverse joint).

Rib landmarks (typical rib):

• Head: Wedge-shaped, articulates with the vertebral body demi-facets (usually two, of its own numbered vertebra and the one above), the crest of the head divides the two facets and attaches to the intra-articular ligament.
• Neck: Narrow segment between head and tubercle.
• Tubercle: Junction of neck and shaft, bears a facet articulating with the transverse process of its own numbered vertebra (costotransverse joint).
• Angle: Point of greatest curvature, lateral to the tubercle, where the rib turns anterolaterally.
• Shaft (body): Thin, curved, with internal and external surfaces; twists along its length.
• Costal groove: Along the inferior internal surface, near the lower border, houses the intercostal neurovascular bundle (vein, artery, nerve (superior to inferior order)) providing some protection to these structures, though the neurovascular bundle is unprotected at the rib's lower margin, relevant to needle/drain insertion technique.

Flat bone in the midline of the anterior thoracic wall, composed of three parts.

• Manubrium: Broadest, most superior part; has the jugular (suprasternal) notch superiorly, clavicular facets for the sternoclavicular joints (superolaterally), and facets for the 1st costal cartilage and part of the 2nd.
• Body of sternum: Longer, narrower, formed embryologically from four fused sternebrae (fusion lines occasionally visible radiographically); has facets along its lateral borders for costal cartilages 2–7 (2nd cartilage articulates partly with the manubrium, partly with the body, at the manubriosternal joint).
• Xiphoid process: Smallest, most inferior, variably ossified (often cartilaginous into adulthood); no direct rib articulation, but is an attachment point for the linea alba, rectus abdominis (partial), and the diaphragm.
• Manubriosternal joint (sternal angle/Angle of Louis): Secondary cartilaginous joint (symphysis) between manubrium and body; palpable ridge, key surface landmark corresponding to the T4/T5 vertebral level, the single most important surface landmark in thoracic anatomy.
• Xiphisternal joint: Between the body and xiphoid process, typically at the T9 vertebral level; usually ossifies (fuses) with age.

• Hyaline cartilage bars connecting the ribs to the sternum (ribs 1–7 directly, 8–10 indirectly via the cartilage above).
• Provide elasticity to the thoracic wall, permitting the volume changes required for respiration.
• Tend to calcify with age, which can alter their radiographic appearance and slightly reduce chest wall compliance in older individuals.

• Costovertebral joints: Synovial joints between the rib head and the vertebral body demi-facets (typically two vertebrae per rib, T2–T8; single facet for ribs 1, 10, 11, 12); reinforced by the radiate ligament.
• Costotransverse joints: Synovial joints between the rib tubercle and the transverse process of the corresponding vertebra (present T1–T10 only, absent for ribs 11–12); reinforced by costotransverse ligaments.
• Sternocostal joints: Between costal cartilages 1–7 and the sternum; the 1st sternocostal joint is a primary cartilaginous joint (synchondrosis), essentially immobile; joints 2–7 are synovial (plane), permitting some gliding movement important for rib elevation during respiration.
• Interchondral joints: Small synovial joints between adjacent costal cartilages of ribs 6–9 (variable), contributing additional stability to the lower costal margin.
• Manubriosternal joint: Secondary cartilaginous joint (symphysis), may ossify with advancing age.
• Xiphisternal joint: Secondary cartilaginous joint, typically ossifies by middle age.

Rib fractures:

• Most commonly involve the middle ribs (4–9), the region of greatest mechanical exposure and least protection from surrounding structures.
• Direct trauma tends to fracture the rib at the point of impact; indirect (compressive) trauma tends to fracture at the point of maximum curvature (near the angle).
• Lower rib fractures (9–12) raise concern for underlying splenic (left) or hepatic (right) injury, given the proximity of these organs beneath the costal margin.
• Upper rib fractures (1–3) are relatively uncommon given their protection by the clavicle and shoulder girdle, but when present indicate substantial force and raise concern for associated great vessel or brachial plexus injury.

Flail chest anatomy:

• Occurs when three or more consecutive ribs are fractured in two or more places, creating a free-floating segment of chest wall disconnected from the rest of the thoracic cage.
• This segment moves paradoxically: inward during inspiration (rather than outward with the rest of the chest wall) and outward during expiration, due to loss of structural continuity and the effect of intrathoracic pressure changes.
• Impairs effective ventilation and is frequently associated with underlying pulmonary contusion; a significant thoracic trauma emergency.

First rib relations:

• Grooved superiorly by the subclavian vein (anterior to the scalene tubercle) and subclavian artery (posterior to the tubercle, in the same groove as the lowest trunk of the brachial plexus).
• The anterior scalene muscle inserts on the scalene tubercle, separating the vein (anterior) from the artery and brachial plexus (posterior), the anatomical basis for thoracic outlet syndrome, where compression of these structures occurs at this crowded space.

Cervical rib:

• A relatively common congenital anomaly: an extra rib (partial or complete) arising from the C7 vertebra.
• Narrows the thoracic outlet/inlet space, predisposing to compression of the lower trunk of the brachial plexus and/or the subclavian artery, producing neurological symptoms (paraesthesia, weakness in the C8/T1 distribution) and/or vascular symptoms (diminished pulse, ischaemic changes in the hand), a classic cause of thoracic outlet syndrome, tested clinically by symptom reproduction with specific arm positioning manoeuvres.