Neurovascular anatomy and variation in the fourth, fifth, and sixth intercostal spaces in the mid-axillary line: a cadaveric study in respect of chest drain insertion.

Chest drains are normally inserted in the fifth intercostal space in the mid-axillary line. The classical technique for chest drain insertion involves locating the drain in an interspace just superior to the inferior rib, so as to avoid the neurovascular bundle. While teaching thoracic wall anatomy on cadavers, considerable variation was noted in the position of the neurovascular bundles, frequently lying well away from the generally accepted subcostal groove. We endeavoured to perform a comprehensive cadaveric study of the neurovascular relationships in the mid-axillary line in the fifth and adjacent spaces to try to describe a 'Safe Zone' for drain insertion to minimise damage to associated structures. The idea that the neurovascular bundle is safely protected in the subcostal groove should be dispelled, as should the concept that there is nothing to damage in the zone immediately superior to the inferior rib. Clinicians should be aware that the Safe Zone is narrower than hitherto appreciated and should be between 50-70% of the way down an interspace to avoid the variably positioned superior intercostal neurovascular bundle and the inferior collateral artery.