Variations and morphometrics of palmaris longus in fetuses: a meta-analysis of cadaveric studies.

The palmaris longus muscle, and its tendon, is one of the most variable muscles in humans. Though it has been extensively researched in the adult population, its variations and development in the fetal period were rarely investigated. The aim of this meta-analysis is to conduct an evidence synthesis on PL variations and the prevalence of its agenesis during intrauterine development. Seven studies met the inclusion criteria comprising 497 fetuses and 1027 fetal limbs. The true and crude weighted prevalence rates were of 81.2% and 77%, respectively. The bilateral and unilateral prevalence estimates were of 62.2% and 15%, respectively. No significant differences were found for side-based and gender-based prevalence values. There were significant frequency differences between the studied populations (p < 0.0001).The Japanese population had the highest prevalence, the Turkish had the lowest and the European value was in between. Out of 494 studied muscles, 67 (13.5%) variations were noted. The weighted proportions of the commonest morphological variations were as follows: (a) bifid tendon in 10 (2%) cases, (b) inverted PL muscle in 9 (1.9%), muscle duplication in 6 (1.36%), and digastric muscle in 25 (5.1%). Prevalence values of the fetal PL were similar to those reported in adults; however, variations seem to be higher than in older populations. The true, crude, and ancestry-based prevalence presence rates of PL in fetuses were found to be similar to those of the adult population.