A patient cannot extend the wrist or fingers but has intact brachioradialis and normal elbow flexion. Sensation is lost over the dorsum of the hand in the first web space. The radial nerve injury is most likely located at:

• A Posterior interosseous nerve (deep branch) in the radial tunnel, distal to the branching of brachioradialis and ECRL ✓
• B Radial nerve in the spiral groove of the humerus (Saturday night palsy)
• C Radial nerve at the level of the lateral epicondyle, distal to the brachioradialis branch
• D Posterior cord of the brachial plexus

Explanation

Brachioradialis and extensor carpi radialis longus (ECRL) are innervated by the radial nerve proximal to its bifurcation in the radial tunnel. When these are preserved but wrist and finger extension are lost, the lesion is distal to these branches — affecting the posterior interosseous nerve (deep motor branch) in the radial tunnel/arcade of Frohse. The superficial sensory branch is spared (intact first web space sensation in purely motor PIN palsy). Saturday night palsy (spiral groove) affects all radial nerve branches distal to that point including brachioradialis. Posterior cord lesion would also affect axillary nerve and show deltoid weakness.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.