Extremities Lab 4.2

Lab 4.2: Forearm and Hand

Learning objectives:

Understand the flow of blood both from and to the upper extremity
Identify the muscles and neurovasculature in the anterior and posterior compartments of the forearm
Identify the muscles and neurovasculature in the hand

Short List of Structures - 4.2

Pronator teres muscle
Supinator muscle
Flexor digitorum profundus tendon at distal phalange
Opponens pollicis muscle
Ulnar nerve at the palm

Before you Begin...

Dissecting the forearm and hand will, in essence, be a continuation of the dissection of the arm; there is a support system of bones, surrounded by muscles that move those bones, and supplied by vessels that bring blood to the muscles, and nerves that cause the muscles to contract and supply sensory innervation to the overlying skin.

From your point of view, one of the important differences between the arm and the forearm is that there are a much greater number of muscles in the forearm than in the arm. but there is a pattern to how they’re named, so keep that in mind as you work your way through.

Naming Conventions

Many (but not all) of the muscles in the forearm follow this naming convention:

Flexor or extensor - flexors are in the anterior compartment, extensors in the posterior compartment.
Carpi or digitorum - muscles that insert in the wrist are carpi, those that insert in the digits are digitorum.
Ulnaris or radialis - carpi muscles are either on the lateral (radial, or thumb) side of the forearm, or the medial (ulnar, or pinky) side of the forearm.

So the flexor carpi ulnaris is a muscle in the anterior compartment that attaches to the wrist on the pinky (medial) side of the forearm. The extensor carpi radialis is in the posterior compartment (so it’s an extensor), it attaches to the wrist, or the radial (thumb) side. Further, there are 2 extensor carpi radialis muscles, and one is longer than the other, so theres the extensor carpi radialis longus, and the extensor carpi radialis brevis. Similarly, there are two flexor digitorum muscles, one is superficial and one is deep, so there’s the flexor digitorum superficialis and the flexor digitorum profundus.

Other muscles are named according to their attachments (brachioradialis) or their actions (pronator teres). There’s not a single rule for naming all these muscles, but all the names make sense when you break them down.

Anterior (flexor) compartment of the forearm

Just as the anterior compartment of the arm was the flexor compartment (muscles there produced flexion at the shoulder and the elbow), the anterior compartment of the forearm is a flexor compartment. The majority of the anterior muscles of the forearm originate from the medial epicondyle of the humerus, and while technically they cross the elbow joint, they have a trivial effect on elbow flexion. The anterior forearm muscles flex the wrist and the digits. Muscles that attach at the wrist will have no effect on the digits. Muscles that attach to the digits, since they cross the wrist joint on the way to the digits, will have some flexion action on the wrist as well.

Begin your dissection of the forearms by removing the skin, at least down beyond the wrist. To most accurately identify the forearm muscles, it’s best to see their distal attachments. You’ll be able to see that with the muscles that attach to the wrist, but with the muscles that pass through the wrist and attach to the digits, you won’t be able to see those attachments until you dissect the hand.

As with the muscles in the arm, the muscles in the forearm are covered in a heavy connective tissue sheath. You’ll have to remove most of that sheath to identify the individual forearm muscles, but proximally (near the elbow) that connective tissue sheath also forms part of the origin of many of the muscles, and you don’t want to shred those muscles during your dissection.

The best way to reflect the deep connective tissue sheath around the forearm muscles is to start at the wrist. There you’ll find the sheath is not as tightly applied to the underlying muscles. Pull up a fold of the sheath at the wrist and cut it open, and then open it broadly. Around the wrist the forearm muscles are mostly shiny white tendons. To begin, grab a tendon and work your way proximally to the muscle belly (the fleshy part of the muscle). No tools are necessary, so use your hands to separate the muscle from adjacent muscles and from connective tissue. As you do this with each tendon you’ll separate the forearm muscles from one another, and you’ll be able to start to identify them.

As you separate the muscles of the forearm you’ll come across blood vessels and nerves. Safeguard those for now, and we’ll identify them as we work our way through the muscles.

Figure 2.1 The forearm muscles are covered by a deep connective tissue sheath that will have to be opened to see the muscles

Removing the Skin

Removing the Skin of the Palm

There are a lot more important fragile structures on this side of the hand.

Flippinghte hand over, below the skin, the palm of the hand is covered by a thick, fibrous palmar aponeurosis. Below this aponeurosis are the important neurovasculature structures that we want to preserve. To begin:

Cut into the skin near the bottom of the palm and find the plane between the skin and the palmar aponeurosis, stay above it when removing the skin and keep it intact.
Find the tendon of the palmaris longus m. , it directly attaches to palmar aponeurosis, and free both structures up with scissor spreading.
Take a scalpel and run it underneath the palmaris longus tendon and palmar aponeurosis, being very careful not to cut structures deep to the palmar palmar aponeurosis.
You can now reflect the palmar aponeurosis and begin working on scissor spreading in the hand.

Cutting the Transverse Carpal Ligament

Once the skin is removed, to visualize the path of the tendons and to make the dissection of the palm easier, it will be helpful at this time to cut through the flexor retinaculum (transverse carpal ligament)

This will allow you to pull the tendons of the flexor digitorum superficialis and profundus out of the carpal tunnel.

To do this...

Work a blunt probe or a scalpel handle (no blade) through the carpal tunnel, just deep to the transverse carpal ligament, making sure you are above the median nerve.
Then cut the ligament by cutting down onto the probe or handle. This will help ensure you don’t cut into the median n. or any of the muscle tendons.
Once the ligament is cut you should be able to pull the muscle tendons out of the carpal tunnel and “bowstring” them to give yourself more room to work in the palm.

Superficial Muscles

Start with the most lateral (radial side) muscle of the anterior compartment, the brachioradialis m. The brachioradialis has the most proximal attachment of all the forearm muscles, attaching proximal to the lateral epicondyle of the humerus (brachio-), and inserting into the distal end of the radius (-radialis). It’s a good muscle to use as a reference, because it defines the lateral edge of the flexor compartment. Any muscles posterior to the brachioradialis are extensors.

Moving medially (toward the pinky, or ulnar side), the next muscle you’ll see that has a large distal tendon is the flexor carpi radialis m. In addition to flexing the wrist, this muscles also contributes to radial deviation at the wrist.

In the elongate triangular interval between the brachioradialis m. and the flexor carpi radialis m., up toward the elbow, you’ll find another forearm muscle that does not extend into the wrist or digits. This is the pronator teres m., which originates on the medial aspect of the humerus and ulna, crosses the forearm at an angle to the long axis, and inserts into the radius. The action of the pronator teres m. is to pronate the forearm, which is the action that rotates the forearm such that the wrist faces posteriorly (assuming anatomical position).

Medial to the flexor carpi radialis is a very small muscle belly with a very long tendon that extends into the palm of the hand. This is the palmaris longus m. Some individuals do not have a palmaris longus m., and some have the muscle only on one side of the body. You can check yourself for palmaris longus by flexing the wrist and looking for the broad, flat, superficial tendon just proximal to the wrist.

The last of the superficial muscles in the anterior forearm is the flexor carpi ulnaris m., which originates close to the flexor carpi radialis, but inserts on the pinky (ulnar) aspect of the wrist. In addition to flexion of the wrist, the flexor carpi ulnaris m. also produces ulnar deviation of the wrist.

Blood Vessels and Nerves

You’ll need to mobilize the superficial muscles to see the deeper muscles of the anterior compartment. If the space seems really tight you can cut the superficial muscles to see the deeper ones, but you do not need to do this. If you do, first find blood vessels and nerves so you can safeguard them.

In the cubital fossa, find the brachial a. and the median n. Follow the brachial a. into the forearm and you’ll see that it splits to form the radial a. and the ulnar a. Usually this split is just distal to the elbow, but sometimes the split is much more proximal in the arm.

The radial a. runs along the radial aspect of the forearm, on the deep surface of the brachioradialis m. Soon after the split into radial and ulnar aa. the radial a. gives off a recurrent radial a. that contributes to the anastomosis around the elbow. Close to the wrist the radial a. emerges from beneath the brachioradialis m., and this is where you take the radial pulse. We’ll return to the radial a. when we dissect the hand.

Near the origin of the brachioradialis m., on its deep surface, look for the two branches of the radial n. The superficial branch of the radial n. runs with the radial a. The deep branch of the radial n. runs into the posterior compartment of the arm, we’ll pick it back up when we get there. The superficial branch of the radial n. can be seen in the distal forearm, running out onto the skin of the thumb.

The ulnar a. is usually the larger of the two branches of the brachial. Close to the split between radial and ulnar aa. look for ulnar recurrent aa., which are part of the anastomosis around the elbow.

The ulnar a. gives off a large branch that travels deep and lateral, the common interosseous a. The common interosseous a. then divides to form an anterior interosseous a. and a posterior interosseous a. These travel anterior and posterior to the interosseous membrane that runs between the radius and ulna.

Figure 2.4 Arteries of the arm and proximal forearm.

The main trunk of the ulnar a. runs inferiorly, deep to the superfical muscles, and emerges again at the wrist. Running with the ulnar a. is the ulnar n.

Intermediate muscles in the anterior compartment:

You may be able to view the intermediate muscles by pulling the superficial muscles out of the way, but you may also transect the more superficial muscles.

In the middle part of the anterior compartment you’ll see the flexor digitorum superficialis m. This is a broad muscle with 4 tendons that run through the carpal tunnel, though the palm of the hand, and insert into the middle phalanges of digits 2 - 5.

Also intermediate in position is the flexor pollicis longus m., which originates from the mid-shaft of the radius, passes through the carpal tunnel, and inserts into the distal phalanx of the first digit (thumb, = pollex).

Deep Muscles

Pull the tendons of the flexor digitorum superficialis anteriorly to view the flexor digitorum profundus m., which sits on the interosseous membrane. Again, for a clearer view you may choose to transect the flexor digitorum superficialis m., but first find the median n., which runs between the two flexor digitorum mm. The median n. runs through the carpal tunnel, along with the tendons of the flexor digitorum superficialis and profundus and the flexor pollicis longus. The tendons of the flexor digitorum profundus pass through the carpal tunnel, through the palm of the hand, and insert into the distal phalanges of digits 2 - 5.

Close to the wrist, and deep to the flexor digitorum mm., look for the pronator quadratus m. The fascicles of this small muscle run transversely between the ulna and radius, and assist the pronator teres in pronating the forearm.

When you dissect into the hand you’ll see the tendons of the flexor digitorum and flexor policis mm, and eventually you’ll cut through the transverse carpal ligament to open up the carpal tunnel.

Summary - Muscles of the Anterior Forearm:

Superficial layer (lateral to medial):

Brachioradialis
Pronator teres (proximal forearm only)
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris

Intermediate layer (lateral to medial):

Flexor pollicis longus
Flexor digitorum superficialis x

Deep layer:

Flexor digitorum profundus x4

Deepest layer:

Pronator quadratus (distal forearm only)

Posterior (extensor) compartment of the forearm

Just as the posterior compartment of the arm was the extensor compartment (mainly of the elbow, less so of the shoulder), the posterior compartment of the forearm is also an extensor compartment. And similar to the organization of the anterior compartment of the forearm, the muscles in the posterior compartment of the forearm may insert in the wrist or the digits, and thereby cause extension of the wrist, or of the digits and (indirectly) the wrist. There are fewer extensor muscles in the forearm, likely because extension of the wrist need not be as powerful as flexion, as flexion is used for grasping. Conveniently, the extensor compartment of the forearm is innervated by the radial n., as is the extensor compartment of the arm. Many of the extensor muscles of the forearm originate from the lateral epicondyle of the humerus.

As with the anterior compartment of the forearm, there will be some heavy connective tissue that you’ll need to work through to isolate the muscles and tendons of the posterior compartment of the forearm. And as with the anterior compartment the best way to go about this part of the dissection is to find the distal tendons of the posterior compartment muscles around the wrist, isolate those tendons, and then follow them proximally to define the muscle bellies. There is a heavy band of transverse connective tissue on the posterior wrist, the extensor retinaculum.

In the middle of the posterior compartment look for the tendons of the extensor digitorum m. You can easily see these muscle tendons in the back of your hand by flexing and extending your digits at the metacarpophalagneal joints. Typically you’ll find 4 tendons, one going to each of the digits 2-5. There is only one extensor digitorum, so there’s no superficialis or profundus distinction.

Just medial (on the ulnar side) of the extensor digitorum m. look for a small muscle belly that leads to a second tendon that goes to digit 5, the extensor digiti minimi m.

Continuing medially, look for the extensor carpi ulnaris m., which inserts into the 5th metacarpal and so both extends and medially deviates the wrist.

The most medial muscle of the forearm is the anconeus m., a small triangular muscle that does not extend much beyond the elbow. The anconeus is said to assist in extending the elbow, but given its size that contribution must be minor.

Now go back to the extensor digitorum m., and re-identify the brachioradialis m. Sitting between these two muscles are the extensor carpi radialis longus m. and the extensor carpi radialis brevis m. The longus is the more superficial of the muscles, as it inserts more proximal (higher) on the humerus, just distal to the insertion of the brachioradialis m. The brevis is just deep to the longus. Sometimes the two muscles are difficult to differentiate. If that’s the case find the tendon of the longus and follow it proximally to the muscle belly.

There are several deep muscles in the posterior compartment. You can probably see them by mobilizing the superficial muscle and moving them around out of the way, but if you need or want to cut any of the superficial muscles, that’s fine.

Just distal to the anconeus, deep to the proximal attachments of the extensor carpi radialis mm., is the supinator m.. You should have seen the supinator in the deep space of the anterior compartment of the elbow, but check out the posterior view as well.

Distal to the supinator m. are 3 muscles that are referred to collectively as the outcropping muscles. All three muscles insert into and move the thumb, and their names describe their actions (1 abductor and 2 extensors). The muscle bellies of these three can be hard to separate, especially the abductor pollicis longus m. and the extensor pollicis brevis m., but again isolate their tendons and then work proximally toward the muscle bellies. There is a space between the extensor pollicis brevis m. and the extensor pollicis longus m., you can palpate that space on your own wrist.

The last of the deep muscles of the posterior compartment of the forearm is the extensor indicis m. Just like the pinky (5th digit), the pointer finger (second digit) has an additional muscle (besides the extensor digitorum) that extends it.

Summary - Muscles of the Posterior Forearm:

Superficial layer (lateral to medial):

Extensor carpi radialis longus
Extensor digitorum x4
Extensor digiti minimi
Extensor carpi ulnaris
Anconeus (proximal forearm only)

Deep layer (lateral to medial):

Supinator (proximal forearm only)
Extensor carpi radialis brevis
Abductor pollicis longus
Extensor pollicis brevis
Extensor pollicis longus
Extensor indicis (distal forearm only)

Arteries and Nerves:

Most of the arteries and nerves in the forearm are in the anterior compartment, and have already been seen; the median and ulnar nn., and the radial and ulnar aa.

As it enters the forearm, the radial n. splits into a superficial and a deep branch. The superficial branch runs deep to the brachioradialis m., and crosses the wrist to innervate the lateral (radial) aspect of the hand. The deep branch of the radial n. runs through the substance of the supinator m. and then emerges to supply motor innervation to the muscles of the posterior compartment of the forearm and sensory innervation to the overlying skin.

You may be able to separate the deep muscles of the posterior forearm to see the posterior interosseous a. running along the posterior surface of the interosseous membrane.

Hand

The Dorsal side of the Hand

Begin by removing the skin, you will quickly realize there are many tendons, like those of the extensor digitorum m. right below it, try not to cut these.

Just beyond the tendons you will start to see the dorsal interossei musculature. Innervated by the ulnar nerve, these muscle produce digit abduction.

You may cut through the thick connective tissue sheath, the extensor retinaculum, if you wish to see the full extent of the tendons.

But you will need to be sure to spend some time working on visualizing the tendons of the extrinsic muscles that move the thumb. Identify all of them:

Note that these muscles will sometimes have more than one tendon associated with them, for example, the abductor pollicis longus mm. very often has 2-3 tendonous slips. You will be able to differentiate muscles by following them to see where they are going, this will take some additional dissection through connecitve tissue sheaths.

The flexor digitorum mm. tendons

You will only need to remove the skin and dissect deep into one of the digits.

But once you get deep enough and cut through the connective tissue sheaths, you will see the tendon of the flexor digitorum superficialis m. split and then the tendon of the flexor digitorum porfundus m. running through it, as in the image to the right.

This means that the flexor digitorum porfundus m. is the only muscle that causes flexion between the middle and distal phalanx.

Many of the forearm muscles, both the radial and ulnar aa., and the ulnar and medial nn. pass into the hand to move the digits, and supply blood and motor innervation to the intrinsic mm. of the hand. The forearm muscles that have tendons going into the hand (those that pass through the carpal tunnel) to move the digits are extrinsic mm. of the hand. There are several small muscles within the hand that produce fine movements of the fingers, these are the intrinsic mm. of the hand.

The radial and ulnar aa. cross the wrist and form two main anastomotic networks in the palm of the hand, the superficial and deep palmar arches. Palmar and digital arteries branch from those arches to supply the palm of the hand and the digits.

The intrinsic mm. of the hand are innervated by terminal branches of the median and ulnar nn. The radial nerve has no motor innervation in the hand.

Palmar and digital arteries:

As you dissect through the palmar aponeurosis, you’re looking for the superficial palmar arch, an arterial arch that forms an anastomosis between the radial and ulnar aa. Later in your dissection, deep in the palm of the hand, you may also find the deep palmar arch, which is also an arterial anastomosis between the radial and ulnar aa. Branches from the superficial palmar arch that radiate into the palm of the hand are the common palmar digital aa. Branches from the deep palmar arch that radiate into the palm of the hand are the palmar metacarpal aa. The common palmar and palmar metacarpal aa. join in the distal palm, forming the common palmar digital aa. Those arteries bifurcate and send arteries up either side of the digits, the proper palmar digital aa.

Palmar and digital nerves:

Accompanying the palmar and digital aa. are palmar and digital nn. that supply motor and cutaneous innervation to the hand. The ulnar n. is the main motor nerve in the hand, but the median nerve also has important motor function in the hand. For now just be aware that you will find nerves running along with the arteries. Do your best to expose and safeguard them, and we’ll consider which nerves innervate which muscles as we work through the muscles.

The Thenar Eminence:

The thenar eminence is the mound of muscle at the base of the thumb. It is made of three muscles, and all three of those muscles are innervated by the recurrent median n., which branches from the median n. as it exits the carpal tunnel.

The most superficial muscle of the thenar eminence is the abductor pollicis brevis m., and the next muscle as you move towards the middle of the palm is the flexor pollicis brevis m. Deep to these two muscles is the opponens policis m. As you consider the names and actions of these 3 muscles, recall that the thumb is rotated 90 degrees relative to digits 2-5. So while abducting digits 2-5 spreads them apart from one another, abducting the thumb actually swings it anteriorly, perpendicularly away from the palm. Opposition is the movement in which the thumb and pinky swing toward one another such that the the tips of digits 1 and 5 meet over the surface of the palm.

The Hypothenear Eminence:

The hypothenar eminence is the mound of muscle at the base of the pinky. The names and positions of the three muscles of the hypothenar eminence are similar to those of the thenar eminence, except where the thenar muscles are “pollicis” (thumb), the hypothenar are “digiti minimi” (pinky), so that the three muscles of the hypothenar eminence are the abductor digiti minimi m. (sometimes with “brevis” added), flexor digiti minimi m., and opponens digiti minimi m.. the hypothenar muscles are all innervated by the ulnar n. Again, recall that the movements of digits 2-5 are oriented 90 degrees different than the movements of digit 1.

The middle compartment of the hand:

We’ll work from superficial to deep as we consider the muscles of the middle compartment of the hand.

The lumbrical mm. are the first muscles you’ll come to in the center of the palm of the hand. They are small and cylindrical (lumbricalis is the scientific name for the earthworm). The lumbrical mm. do not attach to bone, but originate from the tendons of the flexor digitorum profundus m., and insert into the tendons of the extensor digitorum m. at a site called the extensor expansion. Because they run from the flexor side of the palm to the extensor region of the digits the action of these muscles is to both flex the metacarpophalangeal joints, and extend the interphalangeal joints. The first and second lumbricals are innervated by the median n., and the third and fourth lumbricals are innervated by the ulnar n.

Interosseus muscles:

There are two sets of muscles left to identify in the palm, the palmar interosseus mm., and the dorsal interosseus mm. All interossei are innervated by the ulnar n.

You will first come to the palmar interosseus mm., of which there are three. They attach to digits 2, 4, and 5. The palmar interosseus attaching to digit 2 may be mostly covered by the adductor pollicis m. Abduction and adduction of digits 2-5 are movements relative to digit 3 (known locally as the welcome to Rhode Island finger). So adduction of digits 2-5 involves digits 1, 4, and 5 moving toward digit 3.

The dorsal interossei were most easily seen on the posterior (dorsal) dissection of the hand you did earlier. Where the palmar interossei are adductors, the dorsal interossei are abductors (they spread the fingers). Recall that the thumb (digit 1) and the pinky (digit 5) have their own abductors as part of the thenar and hypothenar muscle groups. That leaves only digits 2, 3 and 4, but still there are 4 dorsal interossei. Digit 3, which again is designated as the midline of the hand as concerns abduction and adduction of the fingers, has a dorsal interosseus on either side, so that it can move toward the radial (thumb) or ulnar (pinky) side of the hand. This movement of the 3rd digit is termed radial or ulnar (lateral or medial) deviation of the finger.

So...

Palmar interossei ADduct - PAD
Dorsal interossei ABduct - DAB

Figure 2.22 Adductor pollicis and palmar interosseus muscles

Figure 2.23 Muscles of the palm.

Sensory innervation of the hand

Sensory innervation of the hand fairly closely follows the pattern of motor innervation, except that while the radial n. has no motor input in the hand it does carry sensory output from the hand. As with sensory innervation anywhere in the body you will find maps that show slight differences, which are no doubt reflective of the reality of variation in sensory innervation between individuals.

Figure 2.24 Sensory innervation of the hand.

Clinical Correlations

Boxer’s Fracture

Introduction – Metacarpal fractures represent approximately 40% of all injuries to the hand. When these fractures occur over the neck of the 4th or 5th metacarpals, they are said to be “Boxer’s Fractures.” The metacarpal neck is the most common metacarpal segment to be fractured. The 5th metacarpal is the most commonly fractured. Mechanism of fracture is most commonly due to direct blow (axial load) to a clenched fist (punching a wall or fixed object).

Epidemiology – Most common among males, ages 10-29

Anatomy – The metacarpals are concave over the palmar surface and have several distinct regions: a head that articulates with the phalanges at the MCP joint, and narrower neck that connects the head to the shaft, and a base that articulates with the carpals (CMC joint). The 2nd and 3rd metacarpals are slightly more rigid with regard to bony and ligamentous attachments, making it less likely for these to be fractured.

Diagnosis – Physical exam will demonstrate swelling and pain on palpation over the affected metacarpal. There may be a palpable “bump” over the dorsum of the affected hand, representing fractured bone tenting the skin. There may be a laceration over the fracture if the fracture protruded through the skin – an open fracture. If there is rotation of the fracture segments, there may be overlapping of fingers when the patient is asked to partially and/or fully flex the fingers (see diagram, showing overlapping 4th and 5th digits).

X-ray is used to characterize the injury. Three views are obtained—standard AP, lateral, and oblique.

Treatment – If the fracture is open (protruded through the skin), immediate surgery is indicated to wash the wound and repair the fracture. If not open, patient’s are typically splint-immobilized. Reduction (manual pushing/movement by physician) may be attempted if there is significant angulation in the AP or radio-ulnar planes; this may be difficult if there is rotation of the bones. Once swelling has subsided (1-2 weeks post-injury), the patient may be casted for 4 weeks, or may need surgery if the splint or attempted reduction failed to align the fracture to acceptable angulation and/or shortening of the bone segments. Surgery includes pinning the fracture using small Kirschner wires (K-wires) or screws.

Carpal Tunnel Syndrome

Introduction – Carpal tunnel syndrome is a compression neuropathy of the median nerve as it traverses through the carpal tunnel of the volar aspect (flexor surface) of the wrist, and causes pain, paresthesias (tingling), numbness, and motor deficits over the median nerve distribution of the hand. It typically presents with frequent nighttime awakening with hand pain, numbness, and tingling. It appears to have both genetic and environmental causes and is often seen in chronically ill patients, and those who perform repetitive, manual labor.

Epidemiology – Women are more affected than men. Associated conditions include obesity, diabetes, hypothyroid, rheumatoid arthritis, pregnancy, and amyloidosis.

Anatomy – The median nerve travels along the flexor (volar) surface of the wrist and provides motor innervation to the Thenar eminence at the base of the thumb (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis) and sensory innervation to the volar thumb, index, middle and radial half of the ring fingers. The median nerve travels through the carpal tunnel alongside the eight flexor digitorum superficialis/profundus tendons and the flexor pollicis longus. The borders of the carpal tunnel include the scaphoid tubercle and trapezium radially, the hook of the hamate and pisiform ulnarly, the transverse carpal ligament palmarly (roof), and the proximal carpal row dorsally (floor).

Diagnosis – Several physical exam tests may be performed:

Carpal Tunnel compression test (Durkan’s Test) – most sensitive; physician uses thumbs to compress the median nerve for 30 seconds. Positive if elicits pain/paresthesias/numbness.
Phalen’s Test – less sensitive; patient flexes wrist and extends elbow for 60 seconds.
Tinnel’s Test – less sensitive, more specific; physician taps the volar wrist overlying the Carpal Tunnel.

Physicians may also order an electromyography (EMG) to assess the conduction speed of the median nerve. Slower conduction times suggest compression and CTS.

Treatment – Performed step-wise in an algorithmic approach:

Nighttime wrist splints, NSAIDs, activity modification – immobilize affected wrist(s) during sleep, when symptoms are most active. NSAIDs are helpful to reduce inflammation. Activity modification may reduce repetitive stress/compression
Corticosteroid injection of the carpal tunnel – second-line treatment. 80% have transient improvement, but nearly all will have return of symptoms within 1 year.
Carpal Tunnel Release surgery – Incision and release of the transverse carpal ligament, with care to incise the most ulnar aspect of the ligament (so as to avoid transection of the recurrent motor branch of the median nerve).

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