Anatomy of the intercostal nerves of ribs in the lower rib cage: A pilot study.

Abstract

Background: Traditional intercostal nerve anatomy teaching describes nerves crossing directly across the costal margin. Significant variability in costal margin bony anatomy has been described. Our cadaveric study evaluated variability, branching, and coursing patterns of intercostal nerves at the costal margin.

Methods: Cadaveric dissections were performed evaluating the branching anatomy and course of intercostal nerves, specifically of ribs 7 to 9, at the costal margin because of the highly variable rib anatomy and neural innervation of abdominal wall musculature in this region. Experienced chest wall surgeons evaluated this anatomy using a standardized dissection and assessment to quantify the location and branches of the nerves.

Results: The intercostal nerves and costal margins of 12 hemithoraces were dissected (n = 12). All seventh, eighth, and ninth nerve gave rise to a diaphragmatic branch. The seventh nerve arborized at the costochondral junction in 25% of hemithoraces. The eighth nerve arborized at the costochondral junction in 42% of hemithoraces and continued arborizing at the ninth rib tip in 33%. The ninth nerve arborized at the costochondral junction in 60% of hemithoraces and continued arborizing at the ninth rib tip in 90%. When the eighth rib directly attached to the sternum (42%), the seventh nerve entered the 7/8 interchondral groove, and the eighth nerve directly crossed then ascended along the costal margin giving off abdominal wall musculature branches. When the seventh rib directly attached to the sternum with the eighth rib joining to form the costal margin (58%), the seventh nerve directly crossed then ascended along the costal margin with similar branching.

Conclusion: The seventh, eighth, and ninth intercostal nerves arborize at the costal margin (costochondral junction) to provide branches into the diaphragm and abdominal wall musculature with additional arborization at the lower rib tips. The seventh and eighth intercostal nerve location is variable based on their associated bony anatomy at the costal margin.

Level of evidence: Diagnostic Test; Level II.