Excursion and strain of the median nerve

Area of Science:

• Biomechanics
• Neuroanatomy
• Orthopedics

Background:

• The median nerve (MN) is susceptible to injury and dysfunction, particularly neuropathies like carpal tunnel syndrome.
• Understanding the biomechanical behavior of the MN during various movements is essential for elucidating its role in nerve pathologies.
• Previous studies have not comprehensively quantified MN excursion and strain across multiple joints.

Purpose of the Study:

• To measure the excursion and strain of the median nerve (MN) at the wrist and elbow.
• To correlate MN biomechanics with different positions of the shoulder, elbow, wrist, and fingers.
• To determine the relationships between joint motions and MN excursion/strain.

Main Methods:

• Dissection of five fresh-frozen transthoracic cadaver specimens (ten upper extremities).
• Measurement of median nerve excursion and strain at the wrist and elbow.
• Systematic assessment across various shoulder, elbow, wrist, and finger positions.

Main Results:

• Wrist flexion/extension caused significant MN excursion (19.6 mm) at the wrist; finger motion caused 9.7 mm excursion and 19.0% strain.
• Shoulder abduction/adduction resulted in 9.1 mm MN excursion and 13.3% strain at the elbow; elbow flexion caused 12.3 mm excursion.
• Combined joint movements amplified MN excursion and strain, with potential adverse effects on nerve function if excursion is limited (e.g., by scarring).

Conclusions:

• Limb and joint positioning profoundly impacts median nerve (MN) excursion and strain at the wrist and elbow.
• These biomechanical findings offer insights into the pathophysiology of median nerve neuropathy.
• Factors limiting normal MN excursion may contribute to nerve strain and dysfunction.