The coracobrachialis muscle arises from the tip of the
coracoid process. The coracobrachialis muscle may have a conjoint tendon with
the short head of the biceps muscle. The
coracobrachialis lies lateral to the pectoralis minor muscle. Close to the
origin of the coracobrachialis is the origin of the coraco-clavicular
ligaments. The conoid ligament is medial and the trapezoid ligament is lateral.
The coracobrachialis muscle inserts into the middle third of the medial border
of the humeral shaft. The innervation of
the coracobrachialis, biceps brachii, and brachialis muscle comes from the
musculocutaneous nerve. The brachialis
has dual innervation. The medial part of the muscle innervation is from the
musculocutaneous nerve and the lateral part of the muscle gets innervation from
the radial nerve. The musculocutaneous nerve will also give the lateral
antebrachial nerve with its anterior and posterior divisions. It is the primary
nerve supply of the muscles of the anterior compartment of the upper arm it
supplies sensation to the lateral half of the forearm. The coracobrachialis
muscle flexes and adducts the arm at the shoulder joint. The coracobrachialis muscle originates from
the coracoid, and the musculocutaneous nerve is close to the muscle. The
musculocutaneous nerve pierces the coracobrachialis about 3-8 cm distal to the
coracoid where it then gives a branch to the coracobrachialis muscle. Some
studies show that the nerve may be 1-5 cm from the coracoid. The nerve runs
between the biceps and the brachialis muscles on the anterior compartment of
the arm. The musculocutaneous nerve is close to approaches of the anterior
shoulder especially with retraction of the conjoint tendon of the
coracobrachialis and short head of the biceps. When the musculocutaneous nerve
is injured, we may not be able to measure the deficit except for decreased
sensation on the area supplied by the lateral antebrachial cutaneous nerve,
which is a terminal branch that will give sensation to the forearm. The lateral
antebrachial cutaneous nerve could be injured during distal biceps repair. Be
careful when retracting the conjoint tendon during anterior shoulder surgery
(avoid injury to the musculocutaneous nerve). Occasional, coracoid osteotomy is
done to enhance exposure to the shoulder joint and the conjoint tendon will be
easily retracted without compromising the musculocutaneous nerve.
