Transcript Flexor
DISSECTION OF THE ANTERIOR FOREARM Skin Incisions B C A B SKIN INCISIONS • Make the following skin incisions with the cadaver in the supine position. • From the jugular notch A along the clavicle and across the acromion B to a point about 10 cm distal to the acromion. • From A to the xiphisternal junction C. • From C laterally to the table. • At about mid-arm, make a complete circular incision. • At the level of the wrist make another circular incision. • Join these two circular incisions with a longitudinal one on the lateral aspect of the upper limb, that extends to the cut that is distal to the acromion.. Reflect the skin of the arm and forearm and remove it completely. DO NOT damage the superficial veins and cutaneous nerves in the superficial fascia. !!!! IMPORTANT !!!! To identify the structures in the anterior forearm I think it is best to look at structures in the cubital fossa and the anterior carpus and then ‘work towards the middle’. Of course, this requires that you perform a good job of removing the superficial fascia, WHILE TRYING TO LEAVE THE SUPERFICIAL VEINS INTACT. Remember that these superficial veins are somewhat conspicuous in the living individual and are frequently the sites for drawing blood and injecting medications. BUT, in the cadaver, the superficial veins are empty and generally cannot be seen through the skin. It is my opinion that you are most likely to save these veins if you begin the removal of skin and superficial fascia from the most distal site, i.e., the dorsal hand or carpus. The veins in this region drain into the basilic and cephalic veins. So, once these veins are found in this region, it is much easier to simply follow them proximally as you continue dissection. Cephalic vein Cephalic vein in the arm in the forearm Median antebrachial vein Median cubital vein Basilic vein in the arm Cephalic vein in the arm Cephalic vein in the forearm Cephalic vein emptying into the axillary vein Identify and try to save the superficial veins in this region. Cephalic vein usually lateral to the biceps brachii muscle Basilic vein which will ultimately become the axillary vein Median cubital vein which forms a connection between the cephalic and basilic veins It is IMPORTANT you note that the median cubital vein lies ANTERIOR to the bicepital aponeurosis. Before going further, make certain you are familiar with the anatomical borders of the cubital fossa. It is a triangular space with the following borders: 1. lateral border is the brachioradialis muscle 2. medial border is the pronator teres muscle 3. superior border is an imaginary line drawn between the two epicondyles of the humerus At this time in your dissection, the cubital fossa is covered by the bicepital aponeurosis. This structure is said to be the roof of the cubital fossa, and is one of the insertions of the biceps brachii muscle. The other insertion for this muscle is via its tendon to the tuberosity of the radius. Bicepital aponeurosis Biceps brachii muscle Median nerve Tendon of biceps brachii muscle Brachial artery Radial nerve Radial artery Bicepital aponeurosis Cut through the bicepital aponeurosis. This strong triangular band of connective tissue aids in protecting the underlying nerves and vessels. With the bicepital aponeurosis cut, you should now be able to observe the contents of the cubital fossa. From its lateral to its medial borders, the structures passing through the cubital fossa are: 1. the musculocutaneous nerve, which at this point is called the lateral antebrachial cutaneous nerve 2. the tendon of the biceps brachii 3. the brachial artery 4. the median nerve forearm To get a better view of some of the underlying structures, it is best to also cut the distal portion of the biceps brachii muscle, but do NOT do this unless you are specifically asked to do so. forearm arm arm Look at the peripheral nerves in this region, beginning with the median nerve. forearm At the level of the cubital fossa, the median nerve is generally medial to the biceps tendon and brachial artery, and lies directly on the brachialis muscle. It then enters the forearm between the two heads of the pronator teres muscle. Median nerve arm Brachial artery lateral On the medial side of the tendon of the biceps brachii muscle and the brachial artery, you should find the median nerve. medial Now, let’s examine the radial nerve. Recall that this nerve is in the posterior compartment of the arm, but then is found on the anterolateral aspect of the cubital fossa. At about the level of the lateral epicondyle, the radial nerve divides into superficial and deep (posterior interosseous) branches. Superficial branch of the radial nerve forearm arm Deep (posterior interosseous) branch of the radial nerve The superficial branch of the radial nerve is often easiest to find just deep to the brachioradialis muscle. superficial branch of the radial nerve brachioradialis muscle The superficial radial nerve (which is often called the anterior interosseous nerve) travels to the approximate level of the proximal border of the pronator quadratus muscle. The superficial branch supplies sensory fibers to the dorsum of the hand and digits. Superficial branch of the radial nerve The deep branch supplies muscles in the posterior compartment of the forearm (so it is very important to the movements of wrist and finger extension). forearm arm Deep (posterior interosseous) branch of the radial nerve Another peripheral nerve that you need to find is the ulnar nerve. At the level of the elbow, it lies in a groove between the olecranon and the medial epicondyle of the humerus. In this location the nerve is extremely superficial and prone to injury (“funny bone”). And the last peripheral nerve of interest is the musculocutaneous nerve which at this point is called the lateral antebrachial cutaneous nerve. Recall that the musculocutaneous nerve is one of the terminal branches of the brachial plexus. It pierced the coracobrachialis muscle and then continued distally between the biceps brachii and brachialis muscles. At the lateral border of the tendon of the biceps, the musculocutaneous nerve becomes the lateral antebrachial cutaneous nerve. Brachial Plexus . Now take a look at the brachial artery as it ends by branching into the radial and ulnar arteries at the inferior aspect of the cubital fossa. arm forearm forearm Radial artery arm forearm Radial artery Pronator teres muscle The ulnar artery passes deep to the pronator teres muscle and the flexor muscles of the forearm. In this view, the pronator teres muscle has been reflected to better see the ulnar artery. Do NOT cut this muscle unless you are specifically told to do so. Ulnar artery arm Median nerve entering the forearm between the two heads of the pronator teres muscle As the radial artery is cleaned, you may see the radial recurrent artery. This artery participates in the collateral circulation about the elbow. Radial recurrent artery Ulnar artery Brachial artery Common interosseous artery The common interosseous artery is a very short branch of the ulnar artery (approximately one centimeter in length). It divides into the anterior and posterior interosseous arteries. Anterior interosseous artery The anterior interosseous artery is a branch of the common interosseous artery. It travels distally in the anterior compartment on the interosseous membrane to the proximal border of the pronator quadratus. In this region this artery is generally accompanied by the anterior interosseous branch of the median nerve. Posterior interosseous artery The posterior interosseous artery is a branch of the common interosseous artery. It is generally smaller than the anterior interosseous artery. It exits the anterior compartment and enters the posterior compartment by traveling just superior to the proximal border of the interosseous membrane. This is another view of many of these vascular structures. Now examine the structures that are evident on the anterior carpus. Once you have identified some of the tendons at this level, it makes it easier to identify their muscle bellies within the forearm. Radial artery Tendon of the flexor carpi radialis m. Median nerve Tendon of the palmaris longus m. Four tendons of the flexor digitorum superficialis m. Ulnar artery Ulnar nerve Tendon of the flexor carpi ulnaris m. Brachioradialis m. With an understanding of structures in the cubital fossa and the structures at the level of the anterior carpus, identify muscles within the anterior forearm, beginning with the brachioradialis muscle. Note how this is a good muscle to use as a ‘divider’ between the two compartments of the forearm. The muscles of the anterior forearm are described as being in three layers. The superficial and intermediate layers are evident in this slide. Superficial Layer 1. pronator teres muscle 2. flexor carpi radialis muscle 3. palmaris longus muscle (not visible) 4. flexor carpi ulnaris muscle Intermediate Layer 1. flexor digitorum superficialis muscle Note that to get a good view of the flexor digitorum superficialis m., you must reflect the palmaris longus and flexor carpi radialis mm.. Do NOT make these cuts unless you are specifically asked to do so. flexor carpi radialis m. palmaris longus m. flexor digitorum superficialis m. If these cuts are performed, as well as cutting the flexor digitorum superficialis muscle, you will be able to get a good view of the remaining portion of the median nerve in the forearm, and the deep layer of muscles: 1.flexor digitorum profundus muscle 2.flexor pollicis longus muscle 3.pronator quadratus muscle To best see the muscles in the deep layer of the anterior compartment, it is best to retract or cut the flexor digitorum superficialis muscle. Do NOT cut this muscle unless you are specifically directed to do so. Flexor digitorum profundus muscle Flexor pollicis longus muscle Pronator quadratus muscle Revealed deep layer of muscles: 1. flexor digitorum profundus muscle 2. flexor pollicis longus muscle 3. pronator quadratus muscle (not evident) Median nerve Within the forearm, the median nerve travels in a plane between the flexor digitorum superficialis and flexor digitorum profundus muscles after first traveling through the two heads of the pronator teres muscle. You do not need to do as much work to follow the course of the ulnar nerve. It can usually easily be found on the deep surface of the flexor carpi ulnaris muscle. The ulnar artery should be traveling alongside the ulnar nerve. You must look at one more muscle in this region. Identify the supinator muscle which lies very deep within the cubital fossa. deep branch of the radial nerve (also called the posterior interosseous nerve Note that the supinator muscle is pierced by the deep branch of the radial nerve (also called the posterior interosseous nerve) which innervates it. This nerve emerges from the posterior surface of the supinator muscle and is responsible for supplying the extensor muscles in the posterior compartment of the forearm.