Injury to Obliques Attachment to Lowest Rib
This injury is called a "floating rib avulsion fracture" or "costal margin avulsion injury." 1
Anatomical Context
The lowest ribs (11th and 12th) are termed "floating ribs" because they have rudimentary cartilage caps and are not attached to the sternum at all, unlike the true ribs (1-7) or false ribs (8-10). 2
- The external oblique, internal oblique, and transversus abdominis muscles attach to the lower ribs, including the floating ribs. 2
- The 10th rib is often also a "floating" rib in 59% of individuals, not consistently attached to the 9th rib. 3
Mechanism of Injury
Floating rib fractures are uniquely athletic injuries caused by sudden vigorous muscle contractions pulling in different directions—these are avulsion fractures. 1
- Violent muscle contractions of the oblique muscles can avulse their attachment points from the 11th and 12th ribs. 1
- This mechanism differs from typical rib fractures caused by direct blunt trauma. 1
- Nontraumatic rupture of the costal margin can occur from severe coughing fits, particularly in patients with chronic obstructive pulmonary disease, though this typically affects ribs 8-10 rather than the floating ribs. 4
Clinical Significance
Lower ribs (11th and 12th) are floating and not critical to respiration, so surgical repair is rarely indicated unless there is marked displacement causing thoracic or abdominal organ impalement, damage, herniation, or marked chest wall deformity. 5
- The necessary tissue trauma to achieve surgical repair likely does not improve pain levels for isolated floating rib injuries. 5
- These injuries should be distinguished from more serious middle rib fractures (ribs 3-8), which are most critical for respiratory mechanics and contribute significantly to thoracic volumes. 5, 6
Differential Diagnosis
When evaluating lateral lower rib pain, consider:
- Intercostal myofascial injury involving damage to connective tissues between ribs. 6
- Slipping rib syndrome, where ribs sublux from their joint connections—the 10th rib subluxes internally in 33% of anatomic specimens, and those with a hooked tip are particularly prone to subluxation. 3, 7
- Severe rib contusion without fracture. 1
- Costochondral separations affecting the costal margin. 1
Management Approach
Treatment for isolated floating rib avulsion injuries consists of ice, NSAIDs, analgesics, and supportive care with rib belt or tape if needed. 1
- Chest radiography should be obtained to confirm the diagnosis and rule out associated injuries. 1
- Healing should be well underway before return to athletic activities. 1
- Monitor for associated abdominal organ injuries, as lower rib fractures (ribs 7-12) are associated with abdominal organ injury in 67% of patients with multiple injuries. 8