The Gantzer muscle (GM), an accessory head of the flexor pollicis longus (FPL), is a common anatomical variant with potential clinical relevance, due to its proximity to the median nerve (MN). While cadaveric studies report high prevalence, in vivo functional data remain limited. This study aimed to investigate the prevalence, morphology, and functional role of the GM in relation to median nerve morphology using high-resolution ultrasound.
A cross-sectional study was conducted on 51 healthy adults. Participants underwent standardized clinical screening to exclude pre-existing neuropathies. Bilateral forearm ultrasound examinations were performed at rest and during fist formation. GM thickness and MN cross-sectional area were measured, and associations with sex, ethnicity, and body mass index were analysed. Correlation and regression analyses were applied to assess the relationship between GM and MN morphology. The GM was identified in 62.7% of participants, with slightly higher prevalence in the right forearm (74.5%) compared to the left (70.4%). Prevalence did not differ significantly across sex or ethnicity. No significant differences in GM or MN thickness were observed between rest and contraction. However, on the left side, GM thickness at rest correlated positively with MN thickness (r = 0.29, p = 0.042). A significant inverse correlation was found between changes in GM and MN thickness during contraction (r = –0.46, p < 0.001), suggesting transient compression.
The GM is a frequent anatomical variant that does not alter baseline MN morphology but may influence nerve dimensions dynamically. These findings highlight the clinical importance of dynamic ultrasound in evaluating potential mechanisms of intermittent median nerve compression.
