Radial Nerve Injury — FRCA Primary MCQ

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ModerateAnatomyRadial Nerve InjuryFRCA Primary

An adult is anaesthetised in the lateral decubitus position. The dependent upper arm is inadequately padded, allowing the posterolateral aspect of the mid-shaft of the humerus to bear directly on the hard edge of an arm board. Which nerve is most at risk of compression?

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Correct answer: C — Radial nerve

The correct answer is C, the radial nerve. The nerve passes posteriorly around the humeral shaft within the radial groove and is vulnerable where the posterolateral mid-arm rests against an unpadded hard surface. Compression here may produce weakness of wrist, finger and thumb extension, causing wrist drop; triceps function is usually relatively preserved because most triceps branches arise proximally. The ulnar nerve is principally vulnerable behind the medial epicondyle. The axillary nerve winds around the surgical neck of the humerus, while the median and musculocutaneous nerves lie more anteriorly and are not directly apposed to the posterior humeral shaft. Excessive arm abduction would instead raise concern for brachial plexus stretch and therefore was removed from the original explanation.

Reference: Schwarzman G et al. A Case Report of a Radial Nerve Palsy Following Uncomplicated Total Hip Arthroplasty. Journal of Orthopaedic Case Reports. 2018. https://pubmed.ncbi.nlm.nih.gov/30167427/