Accessory brachialis muscle

Last revised by Dr Joachim Feger on 10 Sep 2021

An accessory brachialis muscle, also known as brachialis accessorius muscle, is a very rare accessory flexor muscle of the elbow and an anatomical variant.

Descriptions of origin and course of accessory brachialis muscles have been quite variable. They seem to originate from the anterior lower diaphysis and either medial or lateral intermuscular septum with some reports describing it coursing medially 1-4 and others lateral to the brachialis muscle 5,6

It might form a fibromuscular tunnel with the intermuscular septum containing the median nerve and the brachial artery 2 continuing into the cubital tunnel together with those neurovascular structures 2-4.

The accessory brachialis muscle might be visualized on imaging studies such as MRI or ultrasound coursing adjacent to the brachialis muscle.

A slip of the brachialis anticus muscle coursing over the brachial vessels and the median nerve had been already described by the British surgeon and anatomist John Wood (1825-1891) in 1867 7,9.

An accessory brachialis muscle might be mistaken for a soft tissue tumor, its knowledge is also helpful in patients undergoing elbow surgery 2.

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