A 45-year-old laborer presents with inability to extend the fingers but intact wrist extension, after a closed injury to the proximal forearm. The most likely structure injured is:

• A Radial nerve in the radial groove
• B Posterior interosseous nerve (PIN) after its entry into the radial tunnel ✓
• C Common extensor origin at the lateral epicondyle
• D Extensor digitorum communis muscle belly avulsion

Explanation

The radial nerve at the spiral groove (Holstein-Lewis fracture site) causes wrist drop with intact brachioradialis (elbow flexion in mid-pronation) and sometimes ECRL (wrist extension). However, if wrist extension is PRESERVED but finger extension is lost, the injury is below the branching of ECRL/ECRB, implicating the posterior interosseous nerve (PIN) after it enters the radial tunnel between the two heads of supinator (Arcade of Frohse). PIN supplies all finger extensors and ECU but NOT ECRL/ECRB, explaining preserved wrist extension.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.