Typology of flexor carpi radialis muscle in human fetuses.

Introduction: The musculus flexor carpi radialis (FCR) is a muscle with an important function for the mechanics and physiology of the hand. Its isolation during intrauterine development occurs relatively late, which may result in the presence of high variability during the fetal period. The aim of this study is to determine the detailed typology of FCR in the fetal period based on the available material.

Material and methods: A total of 114 human fetuses (53 female, 61 male) aged between 117.0 and 197.0 days of fetal life were included in the study. The research material was derived from the collections of the Department of Anatomy, Medical University of Wrocław. Fetuses were stored in typical conservation solvents. The study incorporated the following methods: anthropological, preparational, and image acquisition, which was obtained using an innovative digital microscope. Statistical analysis was performed using R software.

Results: The typology of FCR was determined based on the characteristics of the distal attachment of the investigated muscle. The statistical analysis revealed a predominance of type I in the examined fetal material - the attachment located on metacarpal bone II (about 82% of cases). Type IV (attachment to the 4th metacarpal bone) occurs with a frequency of less than 10% and the remaining types II and III occur with a frequency of 4-6%. The statistical analysis did not reveal bilateral or dimorphic differences in the prevalence of each FCR type. In respect of the collected anthropometric parameters, no statistically significant dimorphic differences were revealed. For a more complete description, the FCR proportionality index was introduced. The mean value of this index was 0.6 and was independent of the side or sex of the analyzed fetus.

Conclusions: FCR in the fetal period is characterized by a stable course in both the proximal and distal attachments.