VH Dissector: Upper Limb: Anterior Arm

Look at the transverse section in the MPR window. 

The arm is enclosed in a sheath of deep fascia known as the brachial fascia. Two fascial intermuscular septa extend from the sheath of brachial fascia, and are attached to the medial and lateral supracondylar ridges of the humerus. The medial and lateral intermuscular septa divide the arm into anterior and posterior fascial compartments, each containing compartment) contains three muscles (biceps, brachialis, and coracobrachialis), their nerves and vessels. The posterior fascial compartment (extensor compartment) contains one muscle (triceps), its nerve and vessels.

Locate the medial and lateral intermuscular compartments in the MPR window.

Begin with the bones of the upper extremity.

Add the Coracobrachialis muscle. This muscle is important mainly as a landmark; the musculocutaneous nerve pierces it.

Add the Brachialis muscle. It lies deep to the biceps muscle on the anterior side of the humerus. The brachialis is the main flexor of the forearm at the elbow.

Add the Biceps Brachii muscle. As the name indicates it has two heads of origin. The long head and the short head. You can identify these the short head on the 3D cadaver by using the Highlight Tool.

The Short head originates at the tip of the coracoid process of the scapula. The Long head originates at the supraglenoid tubercle of the scapula. The tendon of the long head crosses the head of the humerus within the capsule of the glenohumeral joint and descends in the intertubercular (bicipital) groove of the humerus.

The muscle inserts onto the radial tuberosity on the radius bone and via the bicipital aponeurosis, a triangular, membranous band which runs from the biceps tendon across the cubital fossa into the deep fascia over the flexor muscles in the medial side of the forearm. The bicipital aponeurosis affords protection for the brachial artery and median nerve in the cubital fossa, as well as lessening the pressure of the biceps tendon on the radial tuberosity during pronation and supination of the forearm.

Add the Axillary, Brachial, Radial and Ulnar arteries. The brachial artery provides the main arterial supply to the arm. The brachial artery begins at the inferior border of the teres major muscle as a continuation of the axillary artery. It runs inferiorly and laterally on the medial side of the biceps brachii muscle and then turns anterior at the cubital fossa, where it ends opposite the neck of the radius. Under cover of the bicipital aponeurosis, the brachial artery divides into the radial and ulnar arteries.

Add the Median nerve. As the artery is passing inferiorly it accompanies the median nerve, which crosses anterior to the artery in the middle of the arm. In the cubital fossa the bicipital aponeurosis covers and protects the median nerve and brachial artery and separates them from the median cubital vein.

Add the Profunda brachii artery. The largest branch of the brachial artery with the most proximal origin. It accompanies the radial nerve in its posterior course in the radial (spiral) groove, then divides into radial and middle collateral branches, which help to form the anastomoses of the elbow.Rotate the cadaver to follow the path of this artery.

Add the Brachial Vein and Axillary Vein. The two deep brachial veins accompany the brachial artery. In the extremities, for every artery there are two deep veins. The two brachial veins begin at the elbow by union of the venae comitantes of the radial and ulnar arteries, and end at the axillary vein.

Add the Basilic Vein. Located on the medial side of the inferior part of the arm. Near the junction of the middle and inferior thirds of the arm, the basilica vein passes deep to the brachial fascia and empties into the brachial vein.

Add the Cephalic Vein. Located along the anterolateral surface of the biceps brachii muscle

Add the Deltoid muscle. Superiorly the Cephalic Vein passes in the deltopectoral groove, piercing the fascia of the deltopectoral triangle and emptying into the axillary vein.

Add the Medial Cubital Vein. The communication between the basilic and cephalic veins in the cubital fossa; it lies anterior to the bicipital aponeurosis. This is the vein typically used to draw blood.

Remove the Deltoid and Veins of the arm.

Observe the Median Nerve. This major nerve is formed in the axilla by the union of a lateral root from the lateral cord and a medial root from the medial cord of the brachial plexus. The nerve runs on the lateral side of the brachial artery until it reaches the middle of the arm, where it crosses to its medial side and contacts the brachialis muscle. The median nerve descends into the cubital fossa. This nerve has no branches in the axilla or in the arm except when the musculocutaneous nerve doesn’t exist. In that case the median nerve will send muscular branches to the muscles of the anterior arm.

Injury to the median nerve proximal to the elbow results in loss of sensation on the lateral portion of the palm, the palmar surface of the thumb, flexion of the wrist and fingers, and important movements of the thumb are lost or severely affected.

Observe the Ulnar Nerve. The larger of the two terminal branches of the medial cord of the brachial plexus. It passes anterior to the triceps on the medial side of the brachial artery; at the middle of the arm it pierces the medial intermuscular septum and descends between it and the medial head of the triceps muscle. The ulnar nerve enters the forearm by passing between the medial epicondyle of the humerus and the olecranon process of the ulna. Posterior to the medial epicondyle of the humerus, the ulnar nerve is superficial and easily palpable (hitting the ulnar nerve here has resulted in the term “funny bone” – ha-ha). The ulnar nerve has no branches in the arm, but supplies one and one-half muscles in the forearm.

Injury to the ulnar nerve in the arm results in impaired flexion and adduction of the wrist and impaired movement of the thumb, ring, and little fingers. Characteristic clinical sign of ulnar nerve damage is inability to adduct or abduct the medial four digits.

Remove the Biceps Brachii muscle and add the Musculocutaneous Nerve. This nerve is one of the terminal branches of the lateral cord of the brachial plexus. It pierces the coracobrachialis muscle and then continues between the biceps brachii and brachialis muscles, supplying all three of them. At the lateral border of the distal biceps tendon it becomes the lateral antebrachial cutaneous nerve (AKA lateral cutaneous nerve of the forearm). Not visualized on this 3D Cadaver.

Injury to the musculocutaneous nerve in the axilla results in flexion of the elbow joint and supination of the forearm being greatly weakened

Add the Radial Nerve. This nerve is one of the terminal branches of the posterior cord of the brachial plexus. It enters the arm posterior to the brachial artery, medial to the humerus, and anterior to the long head of the triceps brachii muscle. The radial nerve passes inferolaterally with the profunda (deep) brachii artery around the body of the humerus in the radial (spiral) groove. At the lateral border of the numerus, the nerve pierces the lateral intermuscular septum and continues between the brachialis and brachioradialis muscles to the lateral epicondyle of the humerus, where it divides into the deep and superficial branches. After the deep branch of the radial nerve emerges from the supinator muscle, it is called the posterior (dorsal) interosseous nerve. The deep branch of the radial nerve is entirely muscular and articular in its distribution, while the superficial branch supplies sensory fibers to the dorsum of the hand and fingers.

Injury to the radial nerve proximal to the origin of the triceps results in paralysis of the triceps brachii, brachioradialis, supinator, and extensors of the wrist, thumb, and fingers, as well as loss of sensation to the skin supplied. Characteristic clinical sign of radial nerve injury is wrist drop, i.e., inability to extend or straighten the wrist.