Musculocutaneous nerve: histotopographic study and clinical implications

Area of Science:

• Anatomy
• Orthopedic Surgery
• Neuroscience

Background:

• The musculocutaneous nerve (MCN) is vital for elbow flexion and its topography is critical for surgical procedures involving the brachial plexus and shoulder.
• Accurate anatomical knowledge of the MCN's relationship to bony landmarks and surrounding muscles aids in preventing iatrogenic injury during surgery.

Purpose of the Study:

• To precisely map the origin, course, and branching patterns of the MCN.
• To establish the MCN's relationship to key bone landmarks, specifically the coracoid process and acromion.
• To investigate the MCN's intramuscular course within the coracobrachialis muscle (CB) and its histological characteristics.

Main Methods:

• Dissection of 12 unembalmed cadavers to analyze MCN topography and its relation to bone landmarks.
• Histological examination of the MCN and coracobrachialis muscle.
• Validation of key measurements during shoulder surgical approaches in 59 patients.

Main Results:

• Detailed measurements of the MCN's distance from the coracoid process and acromion at various points (origin, entry/exit of CB).
• Quantification of the MCN's length within the coracobrachialis muscle, revealing inverse and positive correlations with distances from the coracoid process.
• Histological findings describe the epineurium's layered structure and fibroadipose tissue arrangement, resembling a "telescope" to accommodate muscle length variations.

Conclusions:

• The study provides precise anatomical data on the musculocutaneous nerve's course, essential for surgical planning in brachial plexus injuries and shoulder instability.
• The unique histological structure of the MCN's epineurium within the coracobrachialis muscle allows for nerve compliance, but alterations may lead to compression syndromes.
• This detailed topographical understanding enhances surgical safety and efficacy by defining critical margins during dissection.