What is the approach for examining radial, ulnar, and median nerves?

Examination of Radial, Ulnar, and Median Nerves

A systematic examination of the radial, ulnar, and median nerves should include specific positioning of the patient, standardized scanning techniques, and targeted assessment of motor and sensory functions to accurately diagnose peripheral neuropathies.

Patient Positioning

• Sitting position with the hand placed on top of the thigh or on an examining table 1
• For dynamic examination, perform active flexion/extension of the fingers 1
• For elbow examination, use full extension with supination for ventral scans and 90° flexion for dorsal scans 1
• Avoid excessive elbow flexion beyond 90° as this increases risk of ulnar neuropathy 2

Standardized Scanning Approach

Wrist Examination

• Volar transverse scan at the carpal tunnel to visualize the median nerve 1
• Volar longitudinal scan 1
• Dorsal transverse and longitudinal scans (radial and ulnar) 1
• Dorsal longitudinal scan of median nerve 1

Elbow Examination

• Anterior transverse scan at distal humeral epiphysis 1
• Anterior humeroradial longitudinal scan 1
• Posterior transverse scan at distal humeral epiphysis 1
• Avoid pressure on the postcondylar groove of the humerus (ulnar groove) 1, 2

Nerve-Specific Assessment

Median Nerve

• Motor testing: Thumb opposition, abduction, and flexion of the thumb and index finger 1, 3
• Sensory testing: Palmar surface of thumb, index, middle fingers, and radial half of ring finger 3, 4
• Ultrasound assessment: Volar transverse scan at carpal tunnel (sensitivity 77-79%, specificity 94-98%) 1, 2
• Look for nerve enlargement and high signal intensity on imaging 1, 2

Ulnar Nerve

• Motor testing: Finger abduction/adduction, thumb adduction, and flexion of 4th and 5th digits 1, 3
• Sensory testing: Little finger and ulnar half of ring finger 3, 4
• Ultrasound assessment: Cross-sectional area at the elbow 1, 2
• Check for nerve dislocation with dynamic ultrasound 1, 2

Radial Nerve

• Motor testing: Wrist and finger extension 1, 3
• Sensory testing: Dorsal aspect of the hand, especially the first dorsal web space 3, 5
• Ultrasound assessment: Best visualized at the elbow 1, 5

Advanced Diagnostic Techniques

• MRI with T2-weighted neurography is the reference standard for nerve entrapment imaging 1, 2
• Ultrasound has high accuracy for detecting nerve abnormalities (sensitivity 77-79%, specificity 94-98%) 1, 2
• Shear-wave elastography shows 100% specificity and sensitivity for ulnar neuropathy at the elbow 1, 2
• Consider nerve interconnections (Martin-Gruber, Marinacci, Riche-Cannieu, and Berrettini anastomoses) which may affect diagnostic findings 4, 6

Common Pitfalls and Considerations

• Anatomical variations exist - median nerve may occasionally be lateral to brachial artery at the elbow 5
• Nerve interconnections may skew electrodiagnostic findings and lead to misdiagnosis 4, 6
• Multi-focal neuropathy affecting all three nerves can occur simultaneously 7
• Avoid prolonged pressure on the ulnar groove during examination 1, 2
• Maintain neutral forearm position when the arm is at the patient's side 2

Optimal Examination Points

• Median nerve: Mid-forearm offers optimal visualization with minimal risk of vascular injury 5
• Ulnar nerve: Mid-forearm for visualization, elbow for entrapment assessment 2, 5
• Radial nerve: Best examined at the elbow 5