Download Innervation of the Thoracoabdominal Wall

THE INNERVATION OF THE THORACO-ABDOMINAL SKIN
The intercostal nerves go under the costal margins and enter in between the transversus
abdominus and the internal oblique muscle. In the mid axillary line they send off a lateral
branch while the anterior branch continues on to only supply muscles UNTIL they
emerge along the midline through the rectus as anterior cutaneous nerves and cover skin
over the rectus sheath
The lateral branches of the intercostal nerves are the ones that cover the skin up to the
lateral border of the rectus sheath. They come out and innervate skin at the axillary line
and descend in a diagonal. So there are really two sets of nerves going diagonally across
the abdomen. The lateral branches come out at the axillary line and cover the innervation
of the skin and the anterior branches course with the ribs and then cross the cartilage and
enter the space between the transversus abdominus and internal oblique and innervate the
musculature of the abdomen and then only become cutaneous as the anterior cutaneous
nerves as the perforate the sheath of the rectus muscles and innervate the skin over the
rectus sheath.
Woodburne page 366 and also parts of page 427 and 428
So the TAP block is really only helping to block the nerves that emerge and become
cutaneous near the midline of the abdomen and probably does not help with any
cutaneous innervation lateral to the rectus sheath.
UNLESS the local were to seep posteriorly and get to the area where the lateral branches
of the intercostal nerves were taking off