Plantaris a vestigial muscle, its corelation to muscular evolution and its clinical implications

Abstract

Background: Muscular evolution in human is muscular adaptation from stiff quadrupedal walking to bipedalism. Transforming from pre hominid to hominid bipedals provide insights to mechanics of walking in human. Evolutions of legs in primates are surprising in human locomotion providing stability for walking. Plantaris muscle (PM) is regarded as vestigial muscle due to its weak contribution to calf muscles. Apes and prosimians show plantaris continuing with plantar aponeurosis. The objective of the study was to prevalence of the vestigial muscle plantaris, a corelation to evolution and its clinical implications. Methods: Dissection of plantaris muscle done in foetuses and its existence, nerve supply, and insertion recorded. Result: Of the 20 legs dissected, 6 legs showed absent plantaris muscle. Nerve supply was fom branch supplying deep crural muscles of leg. Conclusion: Review of evolution list shows marsupials which shared common genetic imprint with human had plantaris extending to plantar aponeurosis and with absent soleus muscle. Nerve supply to plantaris indicates that muscle is derived from anlage of the deep posterior crural muscles. Daselar and Anson reports verticalization of human posture lead to receding of insertion of plantaris from plantar aponeurosis to calcaneus. It is also reviewed that LCA of all primates had plantaris inserted to plantar aponeurosis.