What is the anatomical description of the area on the lateral (side) abdomen, inferior (below) to the ribs and in line with the mid axilla (mid armpit)?

From the Guidelines

The area on the lateral abdomen, inferior to the ribs and in line with the mid axilla, is anatomically described as the lateral region of the abdomen, with the exact boundaries not being uniformly defined, but can be approximated by the anterior and posterior axillary lines as described by the CWIS method 1.

The anatomical description of this area is complex due to the lack of a uniform consensus on the definition of the anterior and posterior axillary lines. However, according to the CWIS method, the anterior axillary line can be defined by a vertical line from the intersection of the posterior border of Pectoralis Major and the 2nd rib, while the posterior axillary line can be defined by the posterior border of Pectoralis Major or the anterior border of Latissimus Dorsi 1.

Key points to consider in this anatomical region include:

• The location of the rib fractures and their characterization, including degree of displacement, angulation, and bone loss, which can affect the selection of rib fractures for repair 1
• The importance of adequate rib length on both sides of a fracture line to securely anchor fixation screws and ensure adequate stability, with at least 2.5 cm of healthy rib required in most cases 1
• The challenges of treating posterior fractures that abut the transverse process, as well as very anterior fractures 1
• The need for precise reporting language when describing costal cartilage fractures, including the exact point of fracture and whether it involves the cartilage itself, the costochondral junction, or the chondro-sternal junction 1

Understanding the anatomical location and boundaries of this region is crucial for accurate description of symptoms, physical examination findings, and surgical planning, particularly in the context of rib fractures and costal cartilage injuries 1.

From the Research

Anatomical Description

The area on the lateral (side) abdomen, inferior (below) to the ribs and in line with the mid axilla (mid armpit), is a complex region with various anatomical structures.

• The region is located near the 4th or 5th intercostal space, which is a common site for thoracostomy tube insertion 2.
• A venous vessel, identified as the v. thoracoepigastrica, is present at the lateral wall and drains into the v. subclavia 2.
• The course of the v. thoracoepigastrica varies significantly between the left and right thoracic wall, with a variance of almost 5-12 mm to the lateral or medial side 2.
• The anterior to midaxillary line between the 4th or 5th intercostal space is considered a safe area for the use of thoracostomy tubes in preterm and term infants 2.
• The region is also susceptible to rib fractures, which can occur due to high-energy trauma 3, 4.
• The most common fracture location is in the lateral or anterolateral zone of the rib cage 4.
• The neurovascular anatomy in the fourth, fifth, and sixth intercostal spaces in the mid-axillary line is variable, and the concept of a "Safe Zone" for drain insertion should be reconsidered 5.

Neurovascular Anatomy

• The neurovascular bundles in the mid-axillary line are frequently located away from the subcostal groove 5.
• The "Safe Zone" for drain insertion is narrower than previously thought 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 5.
• Knowledge of the anatomical variations in this region is essential for surgeons operating on the anterior thoracic wall involving ribs and intercostal spaces 6, 5.