The ribs : Typical ribs & Atypical ribs
• Of the 12 pairs of ribs the first seven articulate with the vertebrae posteriorly and with the sternum anteriorly by way of the costal cartilages (true ribs).
• The cartilages of the 8th, 9th and 10th ribs articulate with the cartilages of the ribs above ( false ribs).
• The 11th and 12th ribs are termed ‘floating’ because they do not articulate anteriorly ( false ribs).
Typical ribs (3rd–9th)
These comprise the following features :
• A head which bears two demifacets for articulation with the bodies of: the numerically corresponding vertebra, and the vertebra above.
• A tubercle which comprises a rough non-articulating lateral facet as well as a smooth medial facet. The latter articulates with the transverse process of the corresponding vertebra .
• A subcostal groove: the hollow on the inferior inner aspect of the shaft which accommodates the intercostal neurovascular structures.
Atypical ribs (1st, 2nd, 10th, 11th, 12th)
• The 1st rib is short, flat and sharply curved. The head bears a single facet for articulation. A prominent tubercle (scalene tubercle) on the inner border of the upper surface represents the insertion site for scalenus anterior. The subclavian vein passes over the 1st rib anterior to this tubercle whereas the subclavian artery and lowest trunk of the brachial plexus pass posteriorly.
A cervical rib is a rare ‘extra’ rib which articulates with C7 posteriorly and the 1st rib anteriorly. A neurological deficit as well as vascular insufficiency arise as a result of pressure from the rib on the lowest trunk of the brachial plexus (T1) and subclavian artery, respectively.
• The 2nd rib is less curved and longer than the 1st rib.
• The 10th rib has only one articular facet on the head.
• The 11th and 12th ribs are short and do not articulate anteriorly.
They articulate posteriorly with the vertebrae by way of a single facet on the head. They are devoid of both a tubercle and a subcostal groove.