What muscles and important structures need to be protected during a posterior approach for a supracondylar humerus fracture?

Muscles and Important Structures to Protect During Posterior Approach for Supracondylar Humerus Fracture

During a posterior approach for supracondylar humerus fracture, the radial nerve must be protected as it lies approximately 7.5-10 cm proximal to the distal articular surface when using an olecranon osteotomy approach, and 13-16 cm when using a triceps-splitting approach. 1

Critical Neurovascular Structures

Radial Nerve

• Located in the spiral groove of the humerus
• Pierces the lateral intermuscular septum at approximately:
  • 10.0 cm from distal articular surface in men
  • 9.4 cm from distal articular surface in women
  • Can be as close as 7.5 cm in some individuals 1
• When using a triceps-splitting approach, the nerve is typically found:
  • 15.8 cm from articular surface in men
  • 15.2 cm from articular surface in women
  • Minimum distance of 13 cm 1

Ulnar Nerve

• Particularly vulnerable during medial pin placement in pediatric cases
• Iatrogenic injury risk is approximately 6% with traditional cross-pinning techniques 2
• Careful identification and protection is essential to prevent postoperative neuropathy

Muscular Structures

Triceps Muscle

• Primary posterior muscle of the arm

• Can be approached via:

  1. Triceps-splitting approach: Divides the muscle in line with its fibers
  2. Triceps-sparing approach: Preserves muscle integrity
  3. Olecranon osteotomy: Reflects the triceps with olecranon attachment

• Triceps-sparing approaches show better functional outcomes with high union rates (compared to olecranon osteotomy) 3, 4

Approach Selection Considerations

Pediatric Cases

• The American Academy of Orthopaedic Surgeons recommends closed reduction with percutaneous pinning for displaced pediatric supracondylar fractures 5, 6
• When using pins:
  • Lateral-entry pins are safer regarding ulnar nerve injury
  • Cross-pinning (medial and lateral pins) provides better stability but increases ulnar nerve injury risk 7
  • Modified cross-pinning techniques can reduce ulnar nerve injury risk to approximately 1.1% 2

Adult Cases

• Posterior approach with plating is commonly used 6
• Patient positioning in lateral decubitus or prone position with arm supported is crucial 6

Surgical Pearls and Pitfalls

Key Safety Considerations

• When dissection extends beyond 7.5 cm laterally or 13.0 cm posteriorly from the distal articular surface, explicitly identify and protect the radial nerve 1
• For pediatric fractures requiring medial fixation, consider modified cross-pinning techniques to minimize ulnar nerve injury 2
• Early mobilization is essential to prevent elbow stiffness 6

Potential Complications

• Ulnar nerve injury (especially with medial pin placement)
• Radial nerve injury (during posterior approach)
• Triceps weakness (particularly with olecranon osteotomy)
• Elbow stiffness
• Hardware prominence
• Infection 6

By understanding these anatomical relationships and employing appropriate surgical techniques, surgeons can minimize complications and optimize outcomes when treating supracondylar humerus fractures via a posterior approach.