Intercostal Space Incision

Anatomy of the Intercostal Space

Each intercostal space contains three muscle layers and a neurovascular bundle:

Layer (outer to inner)	Notes
External intercostal muscle	Fibres run downward and forward
Internal intercostal muscle	Fibres run downward and backward
Innermost intercostal muscle	Deepest layer, runs parallel to internal

The neurovascular bundle (intercostal vein, artery, nerve - arranged VAN from top to bottom) runs in the costal groove along the inferior aspect of each rib.

Anatomy of the intercostal space showing external/internal/innermost muscles and the neurovascular bundle (vein, artery, nerve) in the costal groove

Anatomy of the intercostal space. The neurovascular bundle courses in the costal groove along the inferior aspect of the rib. - Mulholland and Greenfield's Surgery, 7e

The Golden Rule of Intercostal Incision

Always enter the intercostal space just above (superior to) the upper border of the lower rib.

This keeps the instrument/incision away from the neurovascular bundle hugging the underside of the upper rib. Violating this rule risks:

Intercostal artery hemorrhage (can be severe - these communicate with the aorta)
Intercostal nerve injury (persistent post-procedural pain/neuralgia)
Intercostal vein injury

Neurovascular bundle anatomy and the technique of "walking" a needle superiorly over the rib to avoid it

A: The intercostal neurovascular bundle (nerve, artery, vein) lies inferior to the rib. B: The correct approach is to "walk" the needle up and over the rib to avoid these structures. - Roberts and Hedges' Clinical Procedures in Emergency Medicine

Common Clinical Procedures Using Intercostal Incisions

1. Tube Thoracostomy (Chest Tube Insertion)

Site: 4th or 5th intercostal space, midaxillary to anterior axillary line (at the level of the nipple in men, inframammary crease in women).

Chest tube insertion sites: 2nd intercostal space midclavicular line (A) for needle decompression, and 5th intercostal space anterior axillary line (B) for chest tube

Entry sites for tube thoracostomy: (A) 2nd ICS midclavicular line for needle aspiration; (B) 4th-5th ICS anterior axillary line for chest tube. - Roberts and Hedges' Clinical Procedures in Emergency Medicine

Technique:

Make an oblique skin incision 1-2 cm below the intended interspace of tube placement
Use a large clamp to tunnel through subcutaneous tissue and intercostal muscles, entering the next higher interspace just above the rib
Once through the internal intercostal fascia, open the clamp to enlarge the hole to ~2 cm
Insert a finger to confirm intrapleural position and check for lung adhesions
Advance the chest tube until the last side hole is within the pleural space

Tintinalli's Emergency Medicine

The oblique subcutaneous tunnel technique closes naturally after tube removal, reducing recurrent pneumothorax risk.

2. Thoracentesis (Needle Aspiration)

Site: Posterior chest, 1-2 interspaces below the fluid level (confirmed by ultrasound), typically around the 7th-9th intercostal space posteriorly.

Technique:

Insert needle above the superior edge of the lower rib
"Walk" the needle up and over the rib surface until it slips into the intercostal space
Advance until the pleural space is entered (a "pop" may be felt)
Always use ultrasound guidance when available to reduce the risk of pneumothorax and visceral injury
Roberts and Hedges' Clinical Procedures in Emergency Medicine

3. Needle Thoracostomy (Tension Pneumothorax Decompression)

Site: Traditionally 2nd intercostal space, midclavicular line. More recently, the 4th-5th ICS at the anterior axillary line is preferred because it provides the shortest distance from skin to pleura and avoids the thick chest wall (mean thickness ~4.5 cm in the US).

Technique: Insert catheter-over-needle at the selected site, entering just above the lower rib.

Tintinalli's Emergency Medicine

4. Open Thoracotomy / Thoracoscopy (VATS)

For thoracotomy incisions, the intercostal muscles are divided along the lower margin of the interspace, taking care not to injure the neurovascular bundle below the rib above. The pleural cavity is then entered.

For urologic thoracoabdominal approaches, the incision runs along the 8th or 9th intercostal space from the posterior axillary line curving over the costal margin into the abdomen.

Schwartz's Principles of Surgery, 11e; Campbell-Walsh-Wein Urology

Summary: Key Points

Principle	Detail
Safe entry zone	Just above the upper border of the lower rib
Neurovascular bundle location	Inferior groove of each rib (VAN order: vein, artery, nerve)
Chest tube site	4th-5th ICS, anterior-midaxillary line
Needle decompression site	2nd ICS midclavicular line OR 4th-5th ICS anterior axillary line
Thoracentesis site	Upper border of lower rib, posterior chest
Skin incision for chest tube	1-2 cm below the actual interspace entry, then tunnel upward

The fundamental reason all intercostal procedures target the superior aspect of the lower rib is to stay safely away from the neurovascular bundle tucked into the costal groove above.

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