Supernumerary Subclavius Muscle in Thais: Predisposing Cause of Thoracic Outlet Syndrome
Sitha Piyawinijwong PhD*, Nopparatn Sirisathira PhD*
Affiliation : * Department of Anatomy, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
Objective : To demonstrate and classify the variation of the subclavius muscle according to its insertion in the Thais.
Material and Method: One hundred and twenty eight upper limbs were dissected out to expose the scapular region. The
attachments of subclavius muscles were examined and recorded.
Results : The subclavius muscle was categorized into 4 types according to its insertion. There are 64.06% of type I, 17.96%
of type II, 15.62% of type III and 2.34% of type IV. The insertion of subclavius muscle is gradually extended from the shallow
groove on the inferior surface of the clavicle towards the conoid ligament and corocoid process, to the superior transverse
scapular ligament and to the superior border of the scapula adjacent to the insertion of inferior belly of omohyoid muscle.
Conclusion : The present study prevailed 64% normal subclavius muscle and other 36% of varied supernumerary subclavius
muscle. The presence of supernumerary subclavius muscle could be a predisposing causative factor of thoracic outlet
syndrome.
Keywords : Subclavius muscle, Subclavius posticus, Supernumerary, Thoracic outlet syndrome
