Supernumerary subclavius muscle in Thais: predisposing cause of thoracic outlet syndrome.
OBJECTIVE
To demonstrate and classify the variation of the subclavius muscle according to its insertion in the Thais.


METHODS
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.


CONCLUSIONS
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.
Piyawinijwong
Sitha
S
Department of Anatomy, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand. sispw@mahidol.ac.th
Sirisathira
Nopparatn
N
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People; D001917:Brachial Plexus / Q000033:anatomy & histology* / Q000473:pathology; D002102:Cadaver; D002968:Clavicle / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000002:abnormalities*; D009334:Neck Muscles / Q000033:anatomy & histology; D013901:Thoracic Outlet Syndrome / Q000209:etiology* / Q000473:pathology