Guyon's Canal Anatomical Variations and Ulnar Nerve Compression: A Systematic Review

Guyon's canal was first described in 1861 as a narrow fibro-osseous tunnel at the wrist. While ulnar tunnel syndrome is a well-recognized compression neuropathy, detailed anatomical data regarding the structure of the Guyon's canal remain unclearly described. This systematic review provides a comprehensive overview of normal Guyon's canal anatomy and variations associated with ulnar nerve entrapment. A systematic search of literature using PubMed, Embase, and CINAHLNAHL databases according to the PRISMA guidelines was performed. Only original anatomical articles and case reports in English or German language were included. For the quality assessment of the anatomical studies the Anatomical Quality Assessment (AQUA) tool was used. Of the 1,051 articles identified and only 14 (5 original studies and 9 case reports; 198 hands total) were included in the review. Guyon's canal roof is its most complex boundary as it comprises the palmar carpal ligament, palmaris brevis, and hypothenar fascia; the floor is the flexor retinaculum, and the pisiform is the medial boundary. Anatomical studies typically exclude the hook of hamate as a true wall. Anatomical variations that can cause ulnar nerve compression at this site include aberrant muscles (more often an accessory abductor digiti minimi [ADM], and rarely aberrant flexor carpi ulnaris [FCU] or palmaris longus) or neurovascular anomalies like ulnar artery vascular leashes, or atypical nerve branching. Guyon's canal is more of a complex neurovascular space than a fixed fibro-osseus tunnel. More cadaveric studies including a histological examination of the sample are needed to further refine the understanding of the complex architecture of Guyon's canal.