PROCEDURE

1. PRE-WORK (before lab) review the organization of the bony upper extremity from your atlas or on an articulated skeleton in the lab.
    (Netter429) (Netter442) (Netter446)

a) On the humerus, at the distal end identify the medial and lateral epicondyles with the olecranon fossa between. 

b) On the radius, at the proximal end examine the head and neck.

c) On the ulna, at the proximal end examine the olecranon and coronoid processes. Observe that the olecranon process on the ulna articulates with the humerus. The olecranon fossa on the humerus forms a 'socket' for the olecranon process preventing over-extension of the elbow.

The radius and ulna bones are bound together by a fibrous sheet spanning between them, the interosseous membrane.

d) Review the motions of pronation and supination, noting that the radius and ulna bones cross over each other when the hand is fully pronated.

e) The carpal bones are an assembly of bones that facilitate positioning and range of motion of the hand. The two most important are the larger bones in first row, the scaphoid (close to the thumb) and lunate (beside the scaphoid).

A common mnemonic for the names of these bones is "So Long To Pinky…Here Comes The Thumb" representing the first letters in the two rows of bones read lateral to medial across to the little finger 'pinky' (scaphoid, lunate, triquetrum, pisiform) then back across to the thumb side, read medial to lateral  (trapezium, trapezoid, capitate, hamate).

While all the bones have clinical conditions associated with them, the most important from a hand stability and frequency of problems are the scaphoid and lunate bones.

f) Distal to the carpal bones are the phalanges and metacarpal bones making the digits of the hand.  In describing digits by number, the thumb is number 1 and the little finger is number 5. The medial four digits (the fingers) have proximal, middle, and distal phalanges. Digit one (the thumb) has only a proximal and distal phalanges.

In the anatomic position the thumb side of the forearm is lateral and the little finger side of the forearm is medial.

Also in common usage is 'radial side' for the thumb side indicating the lateral position of the radius and 'ulnar side' for the little finger side indicating the medial position of the ulnar.

2. Beginning proximally where skin was removed from the arm reflect the skin fully from the anterior, medial and lateral sides of the forearm.
    (Figure621) (Netter406) (Photo6001a)

Numerous cutaneous nerves and superficial veins are present in the forearm, but we will not examine these in detail and they can be removed along with the skin.

If it is necessary for the individual donor to abduct the forearm over the edge of the table, remember to place one of the disposable chuck pads on the floor to catch potential drips.

While part of your dissection team continues removing skin across the hand (steps 3-5), which can be time consuming, the other part of your team can continue with separating the anterior forearm muscles (step 6+). 

3. Force open the hand if it is clenched and make a shallow incision through the skin across the palmar surface starting at the point where you had removed skin from the forearm.
    (Figure622)

It may be necessary to have someone hold the hand open if the fingers are rigidly clenched.

4. Extend that cut distally across the palm and digits removing skin but leaving subcutaneous tissue in place.
    (Figure622)

Take care when removing skin from the digits as the subcutaneous tissue over the palmar surface of the digits can be thin, particularly at skin creases.

Not all fingers need to have skin removed, but remove skin from digits 2 to the fingertip.

5. Using scraping motions with a dulled scalpel blade, clean subcutaneous fat from the palmar surface of the hand, exposing the palmar aponeurosis.
    (Figure623) (Netter449) (Photo6027)

This aponeurosis consists of four bands of longitudinal connective tissue extending distally across the palm to each of the digits 2-5, stabilized by transverse fibers close to the base of the digits.

Lateral to the palmar aponeurosis you might observe a thin fascia over the thenar muscles (thumb muscles) and medial to the palmer aponeurosis a thin muscle, the palmaris brevis, over the hypothenar muscles (little finger muscles). We will not examine these specifically.

PROCEDURE - ANTERIOR FOREARM

6. Use scissors to make a longitudinal cut through the antebrachial fascia from the cubital fossa to the wrist.
    (Netter406) (Photo6075)

The anterior forearm compartment (flexor compartment) is sheathed by the antebrachial fascia.

7. Use your fingers and blunt dissection to spread open the antebrachial fascia working laterally over to the radius bone and medially over to the ulna bone. 
    (Photo6075a)

Delicate connective tissue septa extend from the antebrachial fascia to wrap each muscle in the compartment. It may be necessary to tear through these septa as you spread open the antebrachial fascia.

The antebrachial fascia may be removed as needed to clear the dissection area.

8. At the elbow palpate to find the medial epicondyle of the humerus.
    (Netter436) (Photo6076)

9. Blunt dissect distal to the elbow to find a group of muscles that all share a common tendon attached to the medial epicondyle of the humerus.
    (Netter436) (Netter430) (Photo6076)

This is the common flexor tendon to which all five of the superficial layer muscles of the anterior forearm attach.

The bicipital aponeurosis extends over the proximal end of these muscles at the common flexor tendon. You may need to separate and reflect the transected end of the bicipital aponeurosis.

Muscles in the forearm are generally named by their function, i.e. muscles with 'flexor' in their name have flexion function and muscles with 'pronator' have a pronation function. Most of the anterior forearm muscles are flexors and this side of the forearm is commonly called the 'flexor compartment'.

Although brachioradialis is situated on the anterior side of the forearm with flexor function, brachioradialis is classified as a posterior compartment muscle because of its radial nerve innervation. This muscle will be examined with posterior compartment structures. 

10. Blunt dissect along the lateral side of the common flexor tendon for fibers of the pronator teres muscle.
    (Figure624) (Netter436) (Netter430) (Photo6077)

The pronator teres muscle is the most lateral of the superficial group and has a roughly cylindrical shape ('teres' translates as 'round'). It lies immediately distal to the biceps brachii tendon and attaches to the radius halfway down the forearm.

The muscle passes deep to the brachioradialis muscle as it crosses the medial epicondyle to the radius. We will examine the brachioradialis muscle in a later lab.

The ulnar artery/vein and median nerve pass deep to the pronator teres muscle. The radial artery travels along the lateral side of the pronator teres muscle. We will examine these later in the lab.

11. Dissect medially from the pronator teres muscle to isolate the flexor carpi radialis muscle, the next in the superficial muscle group. 
    (Figure624) (Netter436) (Netter432) (Photo6078)

Follow the muscle distally to its tendon. Note that the tendon passes towards the lateral side of the wrist.

The flexor carpi radialis tendon will attach to the 2nd metacarpal, but don't follow it out into the palm.

12. Examine the centerline of the wrist for the tendon of the palmaris longus muscle (if present), which blends directly into the palmar aponeurosis.
    (Figure624) (Figure623) (Netter436) (Netter432)
    (Photo6054)

If present, follow the palmaris longus tendon proximally to isolate the muscle body of the palmaris longus muscle. The palmaris longus muscle belly often blends with the edge of the flexor carpi radialis muscle as part of the high variability of the muscle.

The palmaris longus muscle varies greatly in size of the muscle belly/tendon and is absent in up to 20% of individuals. It can also be asymmetric, present on one arm but not the other.

13. Return to the common flexor tendon at the medial epicondyle of the humerus and examine the most medially located superficial muscle arising from that tendon, the flexor carpi ulnaris muscle.
    (Figure624) (Netter436) (Netter432) (Photo6079)

The flexor carpi ulnaris muscle has a distal tendon passing laterally into the hand to attach to the 5th metacarpal. Don't follow the tendon into the palm at this time.

14. Use a Weitlaner retractor to widely spread the gap between the flexor carpi ulnaris and the flexor carpi radialis muscles to expose the intermediate layer of the forearm (consisting of flexor digitorum superficialis).
    (Photo6080)

If present, include palmaris longus on the flexor carpi radialis side of the retraction, as the palmaris longus muscle most commonly integrates with the edge of the flexor carpi radialis muscle.

15. Examine along the medial edge of the flexor digitorum superficialis muscle for the ulnar neurovascular bundle.
    (Photo6080)

This bundle consists of the ulnar nerve, ulnar artery, and ulnar vein. The vein is usually small in diameter and not easily discernable in comparison to the larger diameter artery and nerve.

16. Use a finger to blunt dissect and isolate the flexor digitorum superficialis muscle and ulnar neurovascular bundle to examine the muscle.
    (Figure624) (Netter437) (Netter433)
    (Photo6081) (Photo6082)

The flexor digitorum superficialis muscle is a broad muscle with several heads. One head is connected proximally primarily to the humerus (common flexor tendon), while the second head is attached to the radius partway along the forearm. 

Distally, the muscle separates into distinct bellies each connected to one of the tendons going to each of the fingers (digits 2-5).  The start of each tendon is somewhat variable, so you may see one tendon starting close to the wrist, while other tendons start more proximally along the forearm.

These tendons attach to the middle phalanges of the fingers, we will examine those attachments later in the lab.

17. Reposition the Weitlaner retractor adding the flexor digitorum superficialis muscle/tendons with the flexor carpi ulnaris muscle in the hook of the instrument (i.e. opening the gap between flexor carpi radialis and both flexor digitorum superficialis, flexor carpi ulnaris, and palmaris muscles).
    (Figure625) (Netter438) (Netter433) (Photo6083)

The median nerve travels through the forearm along the deep surface of the flexor digitorum superficialis, thus it is common for that nerve to be retracted along with the muscle. This will not affect later steps and we will isolate the nerve below.

18. Blunt dissect the loose fascia on the lateral side of the deep forearm to isolate the flexor pollicis longus muscle.
    (Figure625) (Netter438) (Netter433) (Photo6083)

The flexor pollicis longus muscle attaches to the radius bone and extends a tendon to insert into the distal phalanx of the thumb. Don't follow the tendon into the hand at this time.

19. Blunt dissect the loose fascia on the central and medial side of the deep forearm to isolate the flexor digitorum profundus muscle.
    (Figure625) (Netter438) (Netter433) (Photo6083)

The flexor digitorum profundus muscle attaches to the ulna proximally and extends four long tendons that pass into the wrist deep to the four tendons of the flexor digitorum superficialis tendon group.

Flexor digitorum profundus lies deep to flexor digitorum superficialis, but has tendons that attach more distally in the fingers.  Thus, flexor digitorum profundus tendons 'punch through' a slit in the tendons of flexor digitorum superficialis in the fingers. We will examine this later in the dissection session.

20. Use a finger to lift and isolate the flexor digitorum profundus muscle so that it can be retracted in the next step.
    (Photo6084)

21. Close to the wrist, retract the tendons of flexor digitorum profundus medially and flexor pollicis longus laterally to observe the deepest forearm muscle, the pronator quadratus muscle.
    (Figure625) (Netter438) (Netter433) (Netter430)
    (Photo6085)

The fibers of the pronator quadratus muscle run perpendicular to the direction of all the flexor muscles. Pronator quadratus spans from the ulnar across to the radius and has roughly a quadrangular shape giving rise to the name 'quadratus'.

The pronator quadratus muscle is the deepest muscle of the anterior compartment.

22. Return to the cubital fossa and follow the brachial artery distally to where it divides into the radial artery and the ulnar artery.
    (Figure626) (Netter437) (NetterBP101) (Netter463)
    (Photo6086)

The radial and ulnar arteries are accompanied by similarly named veins.

The radial and ulnar vessels give rise to small recurrent branches that supply blood to the elbow joint. The branches are termed recurrent as they arise distal to the joint and then project proximally back into the region of the joint. We will not be dissecting these specifically.

The ulnar artery also gives off additional deep branches supplying musculature on each side of the interosseous membrane (anterior and posterior interosseous vessels). We will also not be dissecting these specifically.

23. Follow the ulnar artery (and nerve) distally as far as the wrist where it will pass into the ulnar tunnel (a.k.a. Guyon's canal) to enter the palm. 
    (Netter438) (NetterBP101) (Photo6087)

The ulnar nerve joins the artery partway along the forearm to travel with the artery. This is usually between the flexor digitorum superficialis muscle and flexor carpi ulnaris muscle.

Note, the ulnar nerve does not pass through the carpal tunnel. Thus, carpal tunnel syndrome symptoms mirror the median nerve distribution (digits 1, 2, 3, and half of 4) and spares the ulnar nerve distribution (digit 5 and half of 4).

24. Follow the radial artery distally where it travels along the medial edge (or just deep to that edge) of the brachioradialis muscle.
    (Figure626) (Netter437) (NetterBP101) (Photo6060)

At the wrist, the radial artery travels parallel to the radius bone and the flexor carpi radialis tendon on the thumb side.

The classical radial wrist pulse is detected by placing the tips of your index and third fingers in this location to feel a pulse on a patient.

25. Return to the arm and follow the ulnar nerve to where it courses posterior to the medial epicondyle of the humerus.
    (Figure626) (Netter438) (Netter467)

The ulnar nerve courses around the medial epicondyle of the humerus in a fascial tunnel that you can palpate upon your own elbow, feeling a small 'rod' like structure that with gentle press will elicit tingling in the 4th and 5th digits. We will not dissect the nerve out of this tunnel.

This tunnel is where the nerve is subject to compression against the bone (i.e. the 'funny bone'). The nerve can also become entrapped in the tunnel and inflamed, necessitating steroids and/or surgery to release the nerve.

Symptoms of ulnar compression at the elbow are weakness of the 4th and 5th digits (from ulnar nerve innervation of flexor carpi ulnaris and half of flexor digitorum profundus) and tingling/pain in the ulnar dermatome (5th digit and medial half of the 4th digit), which can be remembered by thinking "one and a half fingers in the hand, one and a half muscles in the forearm" for the ulnar nerve..

The ulnar nerve emerges into the anterior forearm compartment deep to the flexor carpi ulnaris muscle where it joins the ulnar artery partway distal along the forearm.  (Photo6087)

26. Return to the cubital fossa and follow the median nerve distally as far as the wrist.
    (Figure626) (Netter438) (Netter452) (Netter466)
    (Photo6088)

The median nerve courses approximately in the middle of the forearm along the deep surface of flexor digitorum superficialis, before passing into the hand through the carpel tunnel just lateral to the flexor digitorum superficialis tendons.

If present, the tendon of the palmaris longus muscle lies approximately superficial to the median nerve.

The median nerve gives rise to multiple branches innervating multiple muscles in the anterior forearm.

The ulnar nerve innervates flexor carpi ulnaris and half of flexor digitorum profundus. All the remaining anterior compartment muscles are innervated by the median nerve.

PROCEDURE - ANTERIOR HAND (Palm)

27. Pull gently on the tendon of the palmaris longus muscle to apply tension to the palmar aponeurosis.

If the hand lacks the palmaris longus muscle, grip the proximal end of the palmar aponeurosis with a hemostat (locking forceps) so you can lift/pull the aponeurosis firmly.

28. Pull/lift the palmar aponeurosis and detach the aponeurosis from the underlying structures working distally.
    (Figure627) (Netter449) (Netter450) (Photo6032)

As you lift/detach the aponeurosis take care not to cut too deeply as nerves/arteries are in close proximity to the palmar aponeurosis.

29. At the proximal end (base) of digits 2-3 cut through each band of longitudinal fibers of the palmar aponeurosis where it extends into the digits so you can reflect the palmar aponeurosis from the palm.
    (Figure627)

This leaves the aponeurosis attached to digits 4 and 5 while allowing access to the palm and digits 2 and 3.

30. Return to the ulnar artery in the forearm and using blunt dissection follow the vessel where it passes (along with the ulnar nerve) into the palm.
    (Figure628) (Netter450) (Netter456) (Photo6032)

The ulnar nerve and vessels travel through a short fascial tunnel on the anteromedial carpal region called the ulnar tunnel (also known commonly as Guyon's canal).

31. Continue to follow the ulnar artery onto the palm, observing that it curves laterally to form part of the superficial palmar arch.
    (Figure628) (Netter450) (Netter456) (Photo6032)

The superficial palmar arch can be highly variable in position in the palm (proximal or distal palm) and in some cases is only an incomplete arch missing the center 'span' of the arch.

The ulnar artery gives off a deep branch as it enters the palm. This deep branch will form the deep palmar arch reinforcing blood supply to the deep palm. The deep palmar arch is below to the tendons of flexor digitorum superficialis and flexor digitorum profundus. We will not be dissecting down to the deep arch.

32. Identify one of the digital branches arising from the superficial palmar arch heading towards the fingers.
    (Figure628) (Netter450) (Netter456) (Photo6032)

These vessels are common palmar digital arteries. They are called 'common' as they supply more than one finger with blood.

A common palmar digital artery divides into two proper palmar digital arteries at the base of two adjacent digits. Each of the proper palmer digital arteries continues down the side a digit supplying that digit with blood.

Blood (and nerve) supply to digits is along the sides of the digit. Thus, gripping an object tightly does not compromise blood flow to the fingers by compressing the blood vessels.

34. Follow the ulnar nerve into the hand and observe that it gives rise to branches directed towards digits 4 and 5 (little finger).
    (Figure628) (Photo6045)

The ulnar dermatome of the hand is half of digit 4 and all of digit 5...these are the fingers that tingle when the ulnar nerve is compressed at the elbow in a referred sensation/pain phenomena.

35. Return to the wrist and observe the flexor retinaculum attached to the lateral and medial carpal bones (primarily scaphoid to hamate).
    (Figure628) (Figure632)(Netter452) (Netter453)

The flexor retinaculum (also known as the transverse carpal ligament) together with the carpal bones forms a passageway into the palm, the carpal tunnel.

The long flexor tendons (flexor digitorum profundus to digits 2-5, flexor digitorum superficialis to digits 2-5, and flexor pollicis longus to digit 1) and the median nerve crowd through this tunnel.

Carpel tunnel syndrome is a common injury caused by any condition (e.g. overuse injury) that results in pressure on the median nerve as it travels through the tunnel into the wrist.

The ulnar nerve and the other long tendons pass outside the carpal tunnel. The palmaris longus tendon crosses anterior to the flexor retinaculum, attaches to it, then blends with the palmar aponeurosis. The flexor carpi ulnaris tendon passes on the anteromedial side of the carpal tunnel (i.e. ulnar side). The flexor carpi radialis tendon passes on the anterolateral side of the carpal tunnel (i.e. radial side). The ulnar neurovascular bundles passes through Guyon's canal.

36. Slide a blunt probe below the middle of the flexor retinaculum from proximal to distal.
    (Figure650) (Netter452)

The surface of the flexor digitorum superficialis tendons serves as a guide to placement. Passing the probe along the surface of those tendons passes it deep to the flexor retinaculum.

37. Using that probe as a guide using scissors cut through the flexor retinaculum to open the carpal tunnel.
    (Figure650) (Netter452) (Photo6089)

The flexor retinaculum is a dense connective tissue. This tissue commonly makes a stereotypic 'crunchy' noise while being transected.

A carpal tunnel release is performed to alleviate carpal tunnel syndrome and is performed by transecting the flexor retinaculum. This transection 'spreads' the canal reducing the compression on the median nerve improving pain/function.

38. Return to the median nerve and follow it through the carpal tunnel into the palm to where it gives rise to the recurrent branch of the median nerve
    (Figure629) (Netter456) (Photo6090)  

The terminal part of the recurrent branch of the median nerve passes superficially and this end of the nerve branch may have been damaged when stripping skin and the palmar aponeurosis away. 

The recurrent branch of the median nerve innervates the thenar muscles and is an important nerve for control of the thumb.

The superficial location of this nerve, largely unprotected by the palmar aponeurosis as it enters the thenar muscles, renders it vulnerable to injury from relatively shallow cuts on the palm along the base of the thumb.

39. Clean the fascia off the thenar group of muscles (muscles of the thumb).

If you had an intact recurrent branch of the median nerve, preserve the nerve branch.

40. Examine the superficial thenar muscles, flexor pollicis brevis and abductor pollicis brevis muscles.
    (Figure630) (Netter450) (Photo6033)

Flexor pollicis brevis - this muscle attaches to the proximal thumb and flexes the thumb. It sits just medial to the abductor pollicis brevis.

Abductor pollicis brevis - this muscle attaches to the proximal thumb and abducts the thumb. It sits just lateral to the flexor pollicis brevis.

If intact, the recurrent branch of the median nerve crosses superficial to flexor pollicis brevis muscle and disappears deep to abductor pollicis brevis, serving as a useful landmark for the fascial separation between these muscles.

Deep to the flexor pollicis brevis and abductor pollicis brevis is the opponens pollicis muscle. This muscle causes the thumb to rotate towards the fingers, thus allowing for the 'opposable thumb' of primate species. We won't dissect this muscle.

There is a mirror set of muscles at the little finger (digit 5) called the hypothenar muscles. These are flexor digiti minimi, abductor digiti minimi, and opponens digiti minimi. These are small and provide only modest function to the hand...most of the grip function of the hand is provided by the thenar group controlling the thumb. We will not study the hypothenar group.

PROCEDURE - ANTERIOR HAND (fingers)

43. Return to the wrist and follow the tendons of flexor digitorum superficialis and flexor digitorum profundus through the carpal tunnel into the palm, cleaning away tissue of their synovial sheaths as needed.
    (Figure631) (Netter450) (Photo6033) (Photo6036)

Try to preserve the superficial palmar arch if possible. If you are unable to visualize the tendons with the superficial palmar arch intact, then on only one hand transect the superficial palmar arch.

The tendons extend into the digits within an osseofibrous sheath (or tunnel). 

44. Starting at the base of digit 2, slit open the fibrous sheath so you can follow the tendons into that digit.
    (Figure631) (Netter450) (Photo6033) (Photo6036)

Only digit one needs to be opened to demonstrate the tendon arrangement.

45. Observe that near the proximal interphalangeal joint the tendons of flexor digitorum profundus pass through a separation in the tendon of flexor digitorum superficialis
    (Figure630) (Netter453) (Netter451)
    (Photo6033) (Photo6036)

You may need to trim away elements of the tendon fibrous sheath to clearly observe the passage of the flexor digitorum profundus tendon through the flexor digitorum superficialis tendon.

The split tendons of flexor digitorum superficialis attach on each side of the middle phalanx while the tendon of flexor digitorum profundus passes through the slit to attach to the distal phalanx.

CHECKLIST

Skeletal Structures

Radius

Ulna
    Olecranon process

Carpal bones
    Scaphoid
    Lunate

Metacarpal bones (digits 1-5)

Phalanges
    Digits 2-5 (fingers)
        Proximal
        Middle
        Distal
    Digit 1 (thumb)
        Proximal
        Distal

Soft Structures

Antebrachial fascia

Anterior forearm superficial layer
    Common flexor tendon
    Flexor carpi ulnaris muscle & tendon
    Palmaris longus muscle & tendon
    Flexor carpi radialis muscle & tendon
    Pronator teres muscle

Anterior forearm intermediate layer
    Flexor digitorum superficialis muscle & tendons

Anterior forearm deep layer
    Flexor digitorum profundus muscle & tendons
    Flexor pollicis longus muscle & tendon
    Pronator quadratus muscle

Radial artery

Ulnar artery

Palmar aponeurosis

Superficial palmar arch

Flexor retinaculum
    Carpal tunnel

Ulnar nerve

Median nerve
    Recurrent branch of the median nerve

Thenar muscles
    Flexor pollicis brevis muscle
    Abductor pollicis brevis muscle