The main bundle lies in the costal groove above, but a collateral branch runs along the rib below
Mnemonic
VAN, from superior to inferior in the costal groove:
- V - Vein, uppermost
- A - Artery
- N - Nerve, lowest
“Insert just above the rib below, never below the rib above.” Because the bundle hugs the inferior border of each rib, a needle passed immediately above the lower rib avoids it.
The collateral branch running along the upper border of the rib below is why the “safe” zone is relative rather than absolute, and why the mid-axillary approach with the needle walked onto the top of the rib remains standard.
This governs chest drains, thoracocentesis, intercostal nerve blocks and rib fixation.
The same VAN order applies in reverse for the neurovascular bundle of the anterior abdominal wall, and remembering it as “the vein is closest to the rib above” avoids confusion.
Expansion
The classic teaching is that the vein, artery and nerve lie in the costal groove on the underside of the rib above, so a needle should pass close to the rib below.
That is only half the picture. Each intercostal nerve and artery also gives a collateral branch which runs forwards along the upper border of the rib below. So both borders of the space carry neurovascular structures.
The safest point is therefore the middle of the intercostal space, in the mid-axillary line or within the triangle of safety. The bundle is also most exposed posteriorly, before it settles into the costal groove, another reason to avoid paravertebral puncture sites.