Study on the supernumerary heads of biceps brachii muscle in Nepalese.

Biceps brachii is a double headed muscle. In terms of number and morphology of its head, it is one of the most variable muscles in the human body. Most common variation is third head, but four, five or even seven heads have been reported. In this study, 32 arms from 16 Nepalese cadavers were studied; supernumerary heads of biceps brachii were observed in 12.5% of 32 arms. Among these three headed biceps brachii was presented on 6.2% and the four headed was also on the same percentage. All the variations were in the right sided arms of males. Third heads of all cases originated from the medial border and adjoining anteromedial surface of humerus distal to the insertion of coracobrachialis thus have been classified as inferomedial humeral head. Fourth head of the four headed biceps brachii originated from the anterior border of humerus nearby the insertion of deltoid muscle. These supernumerary heads might be significant in producing the strong flexion as well as supination of forearm. They may cause compression of neurovascular structures because of their close relationship to brachial artery and median nerve. Variant biceps brachii may confuse a surgeon who performs procedures on the arm and may lead to iatrogenic injuries. The surgeons and traumatologists have to keep such muscular variations in mind.