What structures need to be identified and preserved during an anterolateral approach to the humerus after skin incision?

Anatomical Structures in the Anterolateral Approach to the Humerus

After skin incision in an anterolateral approach to the humerus, the surgeon must identify and protect several critical neurovascular structures while navigating through specific muscle planes to safely access the humeral shaft.

Superficial Structures

After skin incision, the following structures are encountered:

• Subcutaneous tissue and fascia
• Lateral cutaneous nerve of the arm - must be identified and protected 1
• Cephalic vein - often encountered in the deltopectoral interval proximally 1

Muscle Planes

The anterolateral approach utilizes specific internervous planes:

• Proximally: Between the deltoid (axillary nerve) and triceps (radial nerve) muscles 1
• Distally: Through longitudinally split fibers of the brachialis muscle 1, 2

Key muscles encountered:

• Deltoid muscle - anterior border must be preserved at its insertion 1
• Brachialis muscle - split longitudinally in its distal portion 1, 2
• Triceps muscle - lateral head may need to be elevated from the humerus proximally 1
• Brachioradialis muscle - identified distally 1

Critical Neurovascular Structures

The most important structure to identify and protect:

• Radial nerve - traverses the spiral groove of the humerus 1, 2, 3
  • Proximally: Protected by the triceps muscle
  • Distally: Protected by the retracted lateral portion of the brachialis muscle
  • Can be exposed throughout its entire course in the arm with this approach

Other important neurovascular structures:

• Axillary nerve - limits proximal extension of the approach 1
• Posterior circumflex humeral vessels - encountered proximally 1
• Musculocutaneous nerve - innervates the brachialis muscle, at risk during muscle splitting 2
• Brachial artery and median nerve - located medially, must be protected 4

Surgical Technique Considerations

1. Patient positioning: Supine position allows better access and is advantageous for multiply injured patients 5, 6

2. Incision path:

   • Starts proximally along posterior border of deltoid muscle
   • Extends anteriorly and distally over lateral border of biceps muscle 1

3. Deep dissection:

   • Proximal: Between deltoid and triceps muscles
   • Distal: Through longitudinally split brachialis muscle fibers 1, 2

4. Radial nerve protection:

   • Create a neuromuscular bridge to protect the nerve 6
   • Avoid excessive retraction of the brachialis muscle 2

5. Plate application:

   • Can be applied on anterolateral surface without elevating the firmly attached anterior deltoid insertion 1
   • Limited contact dynamic compression plates are commonly used 3

Advantages and Limitations

Advantages:

• Allows visualization of the radial nerve throughout the extent of the incision 5, 1
• No muscle splitting required in the proximal portion 5
• Can be extended both proximally and distally 3
• Preserves deltoid insertion 1

Limitations:

• More suitable for proximal and mid-shaft fractures than distal third fractures 3
• Requires careful technique to avoid radial nerve injury

Common Pitfalls and Prevention

1. Radial nerve injury:

   • Always identify and protect the nerve throughout the procedure
   • Use gentle retraction and maintain visualization of the nerve
   • Create a neuromuscular bridge for protection 6

2. Axillary nerve injury:

   • Limit proximal extension to avoid damage to the axillary nerve
   • Be aware of its location approximately 5-7 cm from the acromion

3. Brachialis muscle damage:

   • Split the muscle longitudinally along its fibers rather than transversely
   • Avoid excessive retraction that could damage the musculocutaneous nerve

4. Inadequate exposure:

   • Consider extending the approach if necessary for better visualization
   • Use appropriate retractors to maintain the surgical field

By understanding these anatomical relationships and following proper technique, surgeons can safely navigate the anterolateral approach to the humerus while minimizing the risk of neurovascular complications.