Anatomical Variations of the Lumbrical Muscles of the Hand, Regarding Origin, Insertion, Innervation and its Clinical Significance: A Cadaveric Study

Abstract

The Lumbrical muscles originate in the hand from the tendons of the flexor digitorum profundus muscle and extend to the radial side of the metacarpophalangeal joints. Usually, the median nerve innervates the lumbrical muscles I and II, and the ulnar nerve the lumbrical muscles III and IV. Each lumbrical muscle flexes the metacarpophalangeal joint and extends the interphalangeal joints. Also, it assists in the fine motor movements of the hand.Numerous lumbrical muscle variants have been described, absence, accessory slips, variations in origin, insertion, innervation, between others. The objective of this study is to record the anatomical variations related to the origin, insertion, and innervation of this group of intrinsic muscles of the hand and discuss the clinical significance of these variations.For this study, we used ten hands of formalin embalmed cadavers from the anatomy laboratory of San Juan Bautista School of Medicine in Caguas, Puerto Rico. The hands were identified by number, right or left, and male or female. Recollection of Data of anatomical variations of the lumbrical muscles was done through delicate dissection techniques.ResultsFrom the 76 lumbrical muscles in regards to origin, insertion, and innervation. 64% of the lumbrical muscles were normal in origin, innervation, and insertion. Variations were found in various specimens. 13% of the lumbrical muscles showed a proximal origin inside the carpal tunnel. 11% showed Variations in the insertion site. 8% showed variation in the innervation regarded the third and fourth lumbricals. Also, in 4% of specimens, variations regarding the morphology of the lumbrical muscles were found.Anatomical variations of the lumbrical muscles could be associated with the development of pathologies that affect the mechanical functions of the hand. Carpal tunnel syndrome is the most common hand neuropathy in the United States, accounting for 90% of all neuropathies. One of the contributing pathogenetic factors is median nerve compression due to lumbrical muscles variations inside the carpal tunnel. Also, variant innervation of the lumbrical muscles can lead to a misdiagnosis in the event of nerve injuries at the level of the forearm or the hand.