A 35-year-old presents with wrist drop, inability to extend fingers, and loss of sensation over the first dorsal web space. Radial nerve palsy at the spiral groove (Saturday night palsy) typically spares which muscle, distinguishing it from a higher radial nerve lesion?

• A Brachioradialis
• B Triceps ✓
• C Extensor carpi radialis longus
• D Extensor digitorum

Explanation

The radial nerve enters the spiral groove of the humerus after giving off the branch to triceps (long, medial and lateral heads) and the lower lateral cutaneous nerve of the arm. Therefore, in a spiral groove radial nerve lesion (e.g., Saturday night palsy, humeral shaft fracture at the spiral groove), triceps is typically spared — allowing elbow extension. In contrast, a radial nerve lesion in the axilla (e.g., axillary crutch palsy) causes triceps weakness in addition to wrist drop. Distinguishing triceps involvement helps localize the level of injury. Brachioradialis and ECRL are also typically spared or only partially affected in mid-spiral groove lesions.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.