During chest tube insertion in the safe triangle (5th intercostal space, anterior axillary line to midaxillary line), which structure lies at the floor of the safe triangle and marks the inferior limit to avoid diaphragmatic perforation?
- A Nipple level (5th rib) — with the arm elevated, this corresponds to the approximate dome of the diaphragm ✓
- B Inferior border of the 4th rib
- C Level of the 4th intercostal space
- D Inferior border of the 6th rib
Correct answer: A. Nipple level (5th rib) — with the arm elevated, this corresponds to the approximate dome of the diaphragm
Explanation
The 'safe triangle' for chest drain insertion is bounded anteriorly by the lateral border of pectoralis major, posteriorly by the anterior border of latissimus dorsi, inferiorly by the 5th intercostal space (nipple level in men) — because the diaphragm rises to the 4th/5th rib level anteriorly, insertion below the 5th ICS anteriorly risks diaphragmatic or intra-abdominal organ injury. The drain should be inserted in the 4th–5th ICS, midaxillary line, above the upper border of the lower rib to avoid intercostal vessels.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.