A Rare Anatomical Cariation: Biceps Brachii Muscle Attached to Flexor Carpi Radialis Muscle

Abstract

Variations in biceps brachii are relatively uncommon with sources reporting a range of 7% to 30% of all specimens observed having a variation. These variations are typically the finding a supernumerary head and most occur on the left arm. We report a rare anatomical variation in the distal end of biceps brachii that could contribute to median nerve entrapment or compression of the brachial artery.  

A variation of biceps brachii with an accessory fasciculus attached to the proximal end of the flexor carpi radialis (FCR) was observed on the right forearm of a male cadaver. The biceps brachii long and short heads had normal origins at the proximal end. The distal end of the muscle inserts normally on the radial tuberosity and bicipital aponeurosis. An additional fasciculus extends to incorporate with the FCR muscle on the anterior forearm. The FCR muscle retains its normal proximal and distal attachments. The additional muscle bundle is superficial to the pronator teres muscle as it inserts distally on the radius and several muscle fibers blend with the pronator teres muscle. This unique anatomical variation poses a significant clinical risk as the brachial artery runs deep to this additional muscle bundle while remaining superficial to the biceps insertion on the radial tuberosity. It’s possible that shortening of the biceps brachii or flexor carpi radialis muscle could compress the brachial artery decreasing blood flow to the forearm.