Effect of shoulder and elbow position on ulnar nerve conduction

Area of Science:

• Neurology
• Neurophysiology
• Musculoskeletal System

Background:

• Ulnar nerve conduction studies (NCS) are crucial for diagnosing peripheral nerve disorders.
• Variability in NCS results can arise from limb positioning.
• Understanding the ulnar nerve's response to positional changes is essential for accurate electrodiagnostic assessments.

Purpose of the Study:

• To investigate the influence of shoulder and elbow positions on ulnar nerve conduction velocity (NCV).
• To quantify the 'reserve length' of the ulnar nerve in asymptomatic individuals.
• To establish recommendations for standardizing limb positioning during ulnar NCS.

Main Methods:

• Healthy subjects (n=22) participated in the study.
• Ulnar nerve conduction studies were performed in four distinct shoulder abduction and elbow flexion positions.
• Nerve conduction velocities were measured and compared across different positions.

Main Results:

• A significant increase in NCV (mean 2.9 m/s) was observed when moving from a relaxed to a stretched limb position (shoulder abducted, elbow flexed) (P < 0.01).
• This positional change indicated a mean ulnar nerve reserve of 28.3 mm (SD=13.8).
• Shoulder abduction alone increased NCV by 0.8 m/s (P = 0.03), irrespective of elbow flexion.

Conclusions:

• The study identified a significant ulnar nerve reserve that is utilized during shoulder abduction and elbow flexion.
• These findings highlight the importance of standardizing shoulder position in clinical ulnar NCS.
• Consistent positioning protocols are recommended to improve the reliability and accuracy of ulnar nerve conduction studies.