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Bone Chest

Ribs 11-12 (Floating Ribs)

costae fluctuantes

The eleventh and twelfth ribs are floating ribs with no anterior cartilaginous connection, they articulate only with the corresponding vertebral bodies and are the shortest ribs, providing attachment for the quadratus lumborum and diaphragm.

Anatomical Data

Structure & Landmarks

Articulations
  • T11 and T12 vertebrae respectively
Landmarks
  • Head
  • Neck
  • Shaft (relatively short)
  • No costal groove in rib 12
  • Anterior free end
OssificationAs per other ribs but without an anterior costal cartilage development.
Clinical Relevance

Clinical Notes

The floating ribs 11 and 12 have no anterior attachment, ending free in the lateral abdominal wall muscles. They protect the kidney posteriorly and the kidney can be surgically approached through the bed of the 12th rib (retroperitoneal approach). Cervical ribs (from C7) can compress the brachial plexus and are more clinically significant than 12th rib anomalies. Os acromiale, a separate acromion ossification centre, is distinct but a similar concept of a normally-fusing bone failing to unite.

Pathology

Common Injuries & Conditions

Floating Rib Fracture

Fracture of the 11th or 12th rib from a blow to the flank may be associated with kidney, liver, or spleen injury.

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