Prelab Images - Forearm & Wrist

Prelab Images - Forearm & Wrist

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.
Step 1. Review the bony landmarks. (Play movie)
The previously examined features of the humerus are seen in plates N420 or TG2-03 and N421 or TG2-03. The previously examined features of the radius and ulna are seen in plates N436 and N439 or TG2-04. The supinator crest of the ulna is not labeled, but it is where the supinator muscle attaches to the ulna in plates N450 or TG2-21, N451 or TG2-22, and N440. The posterior border of the ulna is not labeled in plate N439 or TG2-04, but it looks similar to the anterior border of the ulna that is labeled in this plate. The interosseous crest of the ulna is where the interosseous membrane attaches to it; this is also unlabeled in plate N439 or TG2-04. The interosseous crest of the radius is also unlabeled in plate N439 or TG2-04. The dorsal radial tubercle and grooves for tendons are labeled on the radius in plate N439 or TG2-04. The metacarpals and proximal, middle, and distal phalanges are seen in plates N452 or TG2-31 and N456 or TG2-32.
Step 2. Remove the superficial fascia from the dorsum of the forearm. (Play movie)
Plate N480 or TG2-02 shows what the forearm might look like at the start of the lab covered with antebrachial fascia that thickens into the extensor retinaculum at the wrist. After removing this fascia your forearm should look similar to plate N444 or TG2-23 and TG2-29.
Step 3. On the extensor side of the forearm, separate and dissect the superficial extensor muscles. (Play movie)
Plates N450 or TG2-21 and N451 or TG2-22 show where the muscles of the forearm have their origin and insertion. Plate N444 or TG2-29 displays the superficial forearm muscles. Each muscle can be separated fairly easily by using a probe and your fingers to gently pull them apart at their proximal tendons. Brachioradialis and extensor carpi radialis longus muscles can be seen in plate N444 or TG2-29 and anteriorly in plate N446 or TG2-23. Extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris are all seen in plate N444 or TG2-29.
Step 4. Examine extensor expansion on dorsum of fingers. (Play movie)
After removing the fascia from the dorsum of the hand, consult plate N470 or TG2-40 to help you find the tendons of extensor digiti minimi and extensor digitorum. Plates N441 and N451 or TG2-41A show the extensor digitorum muscle inserting on middle and distal phalanges. Plate N464 or TG2-41B gives a closer look at this. Plates N470 or TG2-41 and 461 label the extensor expansion (hood). The lumbrical muscles actually begin in the palm of the hand (plate N463 or TG2-34), but their tendons wrap around to attach to the extensor expansion (464 or TG2-45). Plate 465 or TG2-35 shows the dorsal interosseous muscles; plate 464 or TG2-41 shows them attaching to the extensor expansion. Plate N470 or TG2-40 labels tendinous crossbridges as intertendinous connections. Plates N451 or TG2-22, N441, and N470 or TG2-32 indicate the insertions of extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris.
Step 5. Dissect the deep extensor muscles of the forearm. (Play movie)
For this step you need to first separate extensor carpi radialis brevis and extensor digitorum (N444 or TG2-29). Pulling these muscles away from each other will allow you to see the deeper muscles in plate N435 or TG2-30 (supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. Plates N470 or TG2-40, N441, and N451 or TG2-41 show the course of the tendons of these muscles. Plates N445 or TG2-30 and N470 or TG2-40 show the 6 compartments formed by the extensor retinaculum, the tendons contained in each, and the synovial bursae. Plate N439 and N470 or TG2-32 show the grooves in the radius that accommodate each tendon. Plate N462 shows how the bursae reflect to form parietal and visceral layers on the flexor side of the hand. This also occurs with the bursae in plate N470 or TG2-40, but a good view of this is not shown. Plates N447 or TG2-24and N478 or TG2-27 give a good idea of where you will find the radial nerve (underneath brachioradialis) near the elbow. Plate N447 or TG2-24 shows the radial nerve giving off a superficial branch, which will run down the arm, disappear underneath brachioradialis, and then reappear in plate N478 or TG2-50 going to innervate the dorsum of the hand. Plate N447 or TG2-24 shows the radial artery running with the superficial branch of the radial nerve. Plate N447 or TG2-24 shows the deep branch of the radial nerve diving posteriorly. Plate N445 or TG2-30 shows this nerve piercing the supinator and emerging in the extensor compartment of muscles. Plate N478 or TG2-50 gives another view of the course of this nerve as it pierces the supinator, gives off motor branches, and then terminates as the posterior interosseous nerve (N445 or TG2-30, N478 or TG2-50). The posterior interosseous artery can be seen in plate N445 or TG2-30 and it will be described in more detail in step 5. Plate N476 or TG2-27 shows the ulnar nerve in the forearm where it gives off its dorsal cutaneous branch. Plate N444 or TG2-39 shows this branch appearing at the wrist of the posterior hand and plate N468 or TG2-40 shows this nerve giving off dorsal digital branches in the hand. Plate N455 or TG2-39 shows the cutaneous distribution of the dorsal branch of the ulnar nerve. Plate N452 or TG2-31 and N456 or TG2-32 labels the carpal bones and plate N456 or TG2-32 shows the general arrangement of metacarpals and phalanges. The palmar carpal ligament is labeled in plate N459 or TG2-34. Do not confuse this with the transverse carpal ligament (flexor retinaculum), which lies deep to it (plates N460 or TG2-34 and N454 or TG2-35). Plates N454 or TG2-35, N460 or TG2-34 and N461 show the arteries, muscles, and nerves running deep to the transverse carpal ligament.
Step 6. On flexor side of forearm, separate and dissect the various muscular layers and trace the median and ulnar nerves. (Play movie)
Plate N446 or TG2-23 shows the superficial layer of flexor forearm muscles. Plate N450 or TG2-21 and N451 or TG2-22 show the origin and insertions of each muscle. Plate N475 or TG2-27A or TG2-27B shows the median nerve passing between the superficial and deep heads of pronator teres. Plates N446 or TG2-23, N460 or TG2-34, and N461 or TG2-28 show the tendons of flexor carpi radialis, palmaris longus, and flexor carpi ulnaris passing into the wrist. Plate N451 or TG2-22 shows the ulnar and humeral origin of flexor carpi ulnaris and plate N476 or TG2-49 shows how the ulnar nerve will pass between these two heads as it makes its way from behind the medial epicondyle into the forearm. Using the median nerve as a guide, you can cut through and reflect the superficial head of pronator teres to reveal the course of the median nerve and the deep head of pronator teres (N447 or TG2-24). Plate N447 or TG2-24 shows the flexor digitorum superficialis, which will be revealed after pushing the superficial layer of muscles aside. The fibrous arch is visible in plate N447 or TG2-24. Plate N461 shows the arrangement of tendons at the wrist. Plate N450 or TG2-21 shows the origin and insertion of this muscle. Cutting through the radial origin of this muscle beginning at the fibrous arch will allow you to push it medially to expose the deepest layer of muscles, which are seen in plate N448 or TG2-25 (flexor pollicis longus, flexor digitorum profundus, and pronator quadratus). The anterior interosseous nerve is a branch of the median nerve and can be seen in plates N475 or TG2-48 and N448 or TG2-25. The anterior interosseous artery is also shown in plate N448 or TG2-25. Plate N434 or TG2-19 shows the brachial artery dividing into radial and ulnar arteries. The course of the radial artery continues in plate N447 or TG2-24 and it gives off the superficial palmar branch in plate N449 or TG2-37A and TG2-37B. The radial artery then curves around to the dorsum of the hand and runs through the anatomical snuff box in plates N465 or TG2-40 and N445 or TG2-41 before piercing the first dorsal interosseous muscle. The radial pulse point can be observed in plate N446 or TG2-40 and N461, but it is not labeled. Plate N448 or TG2-25 shows the ulnar artery giving off the common interosseous artery. The posterior interosseous artery branches from the common interosseous artery and plunges deep into the arm to appear on the posterior side in plate N445 or TG2-30. The anterior interosseous artery branches from the common interosseous artery; and its course is seen in plate N448 or TG2-25. The ulnar artery continues down the forearm in plate N448 or TG2-25 and its termination in the hand can be seen in plate N464 or TG2-37A and TG2-37B. The pulse point of the ulnar artery can be seen in plate N461 or TG2-37A, but is unlabeled. Plate N434 or TG2-19 shows the collateral circulation of the elbow. Plates N448 or TG2-27 and N475 or TG2-48 should give you a good idea of the path of the median nerve. Plate N461 or TG2-36 shows the location of the median nerve at the wrist and plate N448 or TG2-25 shows the anterior interosseous artery. The ulnar nerve is seen in plates N447 or TG2-24, N448 or TG2-25, and N476 or TG2-49. The dorsal cutaneous branch of the ulnar nerve is shown in plates N476 or TG2-39 and N468 or TG2-40. The ulnar nerve at the wrist is featured in plate N461 or TG2-38. The cross sections of the forearm in plate N449 or TG2-28B and TG2-28C may help you trace these nerves. Plates N472 or TG2-33 and N481 or TG2-51A or TG2-51B show the cutaneous distribution of the nerves.