A+K Chapter 13

Deep palm

Abductor pollicis brevi Interossei Lumbricals

n review, the extrinsic muscles have their proximal attachment above the wrist and their distal attachment on the hand.

Because they cross the wrist, they could have a function there; however, any wrist function is usually assistive at best. The prime function of the extrinsic muscles is in moving the fingers or thumb. Usually the muscle is strongest at the most distal joint it moves.

Intrinsic Muscles of the Hand Thenar:

Flexor pollicis brevis Abductor pollicis brevi Opponenes pollicis

Joint Nonaxial Joints CMC joints (digits 2 to 5)

Joint Classification: Plane Osteokinematic : Gliding Sliding Movement Plane of Motion: 0

As mentioned, the middle finger is the point of reference for abduction and adduction.

Movement away from the middle finger is abduction, and movement toward it is adduction. Note that the middle finger abducts in two directions and therefore does not adduct.

Any muscle spanning the anterior aspect of the finger

Muscles crossing the posterior aspect of the fingers or the posterolateral aspect of the thumb will cause extension.

The Interphalangeal Joints There are two interphalangeal joints in each finger.

The PIP joint is the articulation between the base of the middle phalanx and the head of the proximal phalanx. The DIP joint is formed by the base of the distal phalanx articulating with the head of the middle phalanx. Both the PIP and DIP joints are uniaxial hinge joints allowing only flexion and extension, which occurs in the sagittal plane. They are all concave-on-convex articulations, with the mechanics of their arthrokinematic movements being identical to that of the IP joint of the thumb.

The counterpart to the thenar muscle group is the hypothenar group.

The flexor digiti minimi muscle serves the same function on the little finger as the flexor pollicis brevis does on the thumb. It is attached proximally to the hook of the hamate and the flexor retinaculum, and distally to the base of the little finger's proximal phalanx (see Fig. 13-22). It flexes the MCP joint of that finger. Remember, although most thumb motion occurs at the CMC joint, most finger motion occurs at the MCP joint. Flexor Digiti Minimi Muscle O: Hamate and flexor retinaculum I: Base of proximal phalanx of the fifth finger A: Flexes MCP and CMC joints of the fifth finger N: Ulnar nerve (C8, T1)

The hand

The hand is the distal end of the upper extremity. It is made up of the thumb and finger metacarpals and phalanges. T

The hand is the key point of function for the upper extremity.

The hand is the key point of function for the upper extremity. The main purpose of the upper extremity's other joints is to place the hand in various positions to accomplish these tasks.

The MCP joints of the fingers

The middle finger is the point of reference for abduction and adduction. Abduction occurs when the second, fourth, and fifth fingers move away from the middle (third) finger. Adduction is the return from abduction and occurs with the second, fourth, and fifth fingers. There is no adduction of the middle finger, only abduction occurring in either direction.

The CMC joint

The saddle shape of the carpometacarpal (CMC) joint of the thumb can be compared with the shape of two Pringles potato chips, one of the top on the other fitting right together. The CMC joint is made up of the trapezium bone, which articulates with the base of the first metacarpal It is most commonly described as a modified biaxial saddle joint. Each surface is concave in one direction and convex in the other.

Although the thumb and fingers have essentially the same bony structure, there is one major difference.

The thumb has two phalanges, whereas the fingers each have three. This feature makes the thumb shorter, allowing opposition to be more functional.

The borders of the anatomical snuffbox

are defined by the tendon of the extensor pollicis longus muscle on one side and the tendons of the abductor pollicis longus and brevis muscles on the other side

Intrinsic muscles have their proximal attachment

at or distal to the carpal bones and have a function on the thumb or fingers. These muscles are responsible for the hand's fine motor control and precision movement. The intrinsic muscles can be further divided into the thenar, hypothenar, and deep palm muscles

The second, third, fourth, and fifth digits, ).

commonly known as the index, middle, ring, and little fingers, respectively, have four joints each. These joints are the CMC joint, MCP joint, proximal interphalangeal (PIP) joint, and distal interphalangeal (DIP) joint (see Fig. 13-1).

It should be noted that the bases of all phalanges are

concave, and the heads of all phalanges and metacarpals are convex.

Ulnar drift results in ulnar

deviation of the fingers at the MCP joints.

Mallet finger is caused by disruption of the

extensor mechanism of the DIP joint, either because the tendon was severed or because the portion of bone where the tendon attached has avulsed from the distal phalanx. In either case, the distal phalanx remains in a flexed position and cannot be extended.

Therefore, the hand, made up of the thumb and four fingers,

has five metacarpals, five proximal phalanges, and five distal phalanges, but only four middle phalanges

The hypothenar muscles, forming the

hypothenar eminence, act primarily on the little finger.

Gamekeeper's thumb

is an old term referring to a stretching injury of this same ligament developed over time by English gamekeepers as they twisted the necks of small game. Most injurie

Dupuytren's contracture

occurs when the palmar aponeurosis undergoes a nodular thickening. It is most common in the area of the palm in line with the ring and little fingers. Often those fingers will develop flexion contractures.

Any muscle spanning the anterior aspect of the finger

or the anteromedial aspect of the thumb will pull the anterior surfaces together, causing flexion.

pollicis means "thumb"

pollicis means "thumb"

Although the CMC joint of the thumb is quite mobile, the MCP and IP joints are not. The MCP joint

the MCP and IP joints are not. The MCP joint is a hinge joint that allows only flexion and extension, and is therefore a uniaxial joint. The IP joint, the only phalangeal joint of the thumb, also allows only flexion and extension. Note that phalanx is singular, and phalanges is plural.

The muscles located in the area between the thenar and hypothenar muscle groups are often called the deep palm group, or the intermediate group.

. The adductor pollicis muscle is sometimes placed in this group because it is located deep within the palm. Other sources place it with the thenar group because of its action on the thumb. It is placed here in the deep palm group for perhaps no other reason than to discuss the intrinsic muscles in groups of three!

The CMC joint of the thumb allows more mobility than the CMC joints of the other four fingers, yet it also provides as much stability.

Abduction and adduction occur in the sagittal plane (a plane perpendicular to the palm). In other words, with the forearm supinated and the palm facing up, the thumb moving side to side across the palm is flexion and extension. The thumb moving up toward the ceiling, away from the palm, is abduction, and its

The extrinsic muscles are as follows: Posterior

Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Extensor digitorum Extensor indicis Extensor digiti minimi

If you extend your thumb, you will notice that a depression is formed between what appears to be two tendons.

Actually, there are three tendons. The abductor pollicis longus and extensor pollicis brevis muscles form the lateral border, and the extensor pollicis longus muscle forms the medial border. This depression is called the anatomical snuffbox

Thumb opposition is perhaps the most important function of the hand.

Because it is a combination of flexion, abduction, and rotation of the thumb, other muscles such as the flexor pollicis brevis and abductor pollicis muscles assist in this function.

Hypothenar

Flexor digiti minimi Abductor digiti minimi Opponens digiti minimi

The extrinsic muscles are as follows: Anterior

Flexor digitorum superficialis Flexor digitorum profundus Flexor pollicis longus

The abductor pollicis brevis muscle lies just lateral to the flexor pollicis brevis muscle.

It attaches proximally to the flexor retinaculum, scaphoid, and trapezium, and distally to the base of the thumb's proximal phalanx (Fig. 13-23). It acts to abduct the CMC joint of the thumb. It also has a secondary role in flexing the thumb at the MCP and CMC joints. Abductor Pollicis Brevis Muscle O: Scaphoid, trapezium, and flexor retinaculum I: Proximal phalanx of the thumb A: Abducts the thumb (CMC joint) N: Median nerve (C6, C7)

The extensor digitorum muscle is a superficial muscle on the posterior forearm and hand

It attaches proximally to the lateral epicondyle of the humerus as part of the common extensor tendon. It passes under the extensor retinaculum to attach distally on the distal phalanx of the second through fifth fingers via the extensor expansion (see Fig. 13-12). In the area of the metacarpals are interconnecting bands joining the four extensor digitorum tendons. These interconnecting bands limit independent finger extension. The extensor digitorum muscle is the only common extensor muscle of the fingers. It extends the DIP, PIP, and MCP joints of the second, third, fourth, and fifth fingers. Extensor Digitorum Muscle O: Lateral epicondyle of the humerus I: Base of distal phalanx of the second through fifth fingers A: Extends all three joints of the fingers (DIP, PIP, and MCP) N: Radial nerve (C6, C7, C8)

The opponens pollicis muscle lies deep to the abductor pollicis brevis muscle.

It attaches proximally to the trapezium and flexor retinaculum and distally to the entire lateral surface of the first metacarpal (Fig. 13-24). Its primary function is to oppose the thumb. Remember, this action occurs at the CMC joint. Loss of thumb opposition is caused by damage to the median nerve and is referred to as "ape hand deformity. Opponens Pollicis Muscle O: Trapezium and flexor retinaculum I: First metacarpal A: Opposes the thumb (CMC joint) N: Median nerve (C6, C7)

The abductor pollicis longus muscle is located deep on the posterior forearm.

It attaches to the radius just distal to the supinator, the interosseus membrane, and the middle portion of the ulna. It becomes superficial just proximal to crossing the wrist and attaches to the base of the first metacarpal on the radial side. Although the abductor pollicis longus crosses the thumb's MCP joint, it only abducts the CMC joint because the MCP joint allows only flexion/extension.The thumb moves as one unit in the direction of abduction and adduction. Similarly, abduction of the thumb's CMC joint adducts the entire thumb. Therefore, in this text, when referring to thumb abduction, adduction, opposition, and reposition, it is implied that the action occurs at the CMC joint. Without the abductor pollicis longus, the thumb cannot be moved away from the palm. It also has a secondary action of extending the thumb. Abductor Pollicis Longus Muscle O: Posterior radius, interosseus membrane, middle ulna I: Base of the first metacarpal A: Abducts thumb (CMC) N: Radial nerve (C6, C7)

The extensor digiti minimi muscle is a long, narrow muscle that is deep to the extensor digitorum and extensor carpi ulnaris muscles near its proximal attachment.

It becomes superficial before crossing the wrist. It comes off the common extensor tendon on the lateral epicondyle of the humerus, crosses the wrist under the extensor retinaculum and attaches to the base of the distal phalanx of the fifth finger via the extensor expansion. It is a prime mover in extending the DIP, PIP, and MCP joints of the fifth finger. It makes possible isolated extension of the fifth finger. Extensor Digiti Minimi Muscle O: Lateral epicondyle of humerus I: Base of distal phalanx of fifth finger A: Extends all three joints of fifth finger (DIP, PIP, MCP) N: Radial nerve (C6, C7, C8)

The extensor indicis muscle is a deep muscle that has its proximal attachment on the posterior surface of the distal ulna .

It crosses the wrist under the extensor retinaculum medial to the extensor digitorum muscle and attaches into the extensor expansion of the second finger along with the extensor digitorum muscle. It extends the DIP, PIP, and MCP joints of the index finger. This allows us to point with our index finger while the other fingers are in a fist Extensor Indicis Muscle O: Distal ulna I: Base of distal phalanx of the second finger A: Extends all three joints of the second finger (DIP, PIP, MCP) N: Radial nerve (C6, C7, C8)

The CMC joint of the thumb allows more mobility than the CMC joints of the other four fingers, yet it also provides as much stability. I

It is unusual to benefit from stability and mobility at the same time. The joint allows flexion and extension, abduction and adduction, and opposition and reposition . Thumb motions differ from the usual way we name joint motions. Flexion and extension occur in the frontal plane (a plane parallel to the palm).

The opponens digiti minimi muscle lies deep to the other hypothenar muscles.

Its proximal attachments, the hook of the hamate and the flexor retinaculum, are similar to the proximal attachments of the flexor digiti minimi muscle. Distally, it attaches to the ulnar border of the fifth metacarpal (see Fig. 13-24). Its primary action is in opposition of the fifth finger. This action occurs at the CMC joint. Opponens Digiti Minimi Muscle O: Hamate and flexor retinaculum I: Fifth metacarpal A: Opposes the fifth finger (CMC joint) N: Ulnar nerve (C8, T1)

Uniaxial Joints MCP joint (digit 1) IP joint (digit 1) PIP joints (digits 2 to 5) DIP ( digits 2 to 5)

Joint Classification: All Hinge Joints Osteokinematic: All Flexion and Extension Movement Plane of Motion: MCP and IP Oblique PIP and DIP Sagittal

Frontal Sagittal MCP joints (digits 2 to 5)

Joint Classification: Condyloid Osteokinematic: All Flexion/extension Abduction/adduction Movement Plane of Motion: Sagittal/ Frontal

Joints CMC joint (digit 1)

Joint Classification: Saddle Osteokinematic: All Flexion/extension Abduction/adduction Movement Plane of Motion: Frontal/ Sagittal

Oblique Line

Located on the anterior surface of the radius from below the tuberosity, running diagonally to approximately midradius

In addition to the wrist muscles previously described, there are several other muscles that span the wrist and cross the joints in the hand.

These muscles are called extrinsic muscles of the hand because their proximal attachment is above, or proximal to, the wrist joint. They have an assistive role in wrist function, but their primary function is at the thumb or finger.

The last muscle group to be discussed is rather unique. The lumbricals, of which there are four, have no bony attachment.

They are located quite deep and attach only to tendons. Proximally, they attach to the tendon of the flexor digitorum profundus muscle, spanning the MCP joint anteriorly (Fig. 13-27). This allows them to flex the MCP joint. They then pass posteriorly at the proximal phalanx to attach to the tendinous expansion of the extensor digitorum muscle (Fig. 13-28). This allows them to extend the PIP and DIP joint. Therefore, their action is to flex the MCP joint and extend the PIP and DIP joints of the second through fifth fingers. This combined motion is referred to as the "tabletop position." Incidentally, the plural of lumbrical can be spelled with an "s" or "es."

There are three palmar interosseus muscles. They attach proximally to the palmar surface of the second, fourth, and fifth metacarpals.

They do not attach to, or have a function on, the middle finger. Distally, they attach to the base of the phalanx of the same finger as the proximal attachment (Fig. 13-26). They pull the digits toward the midline of the hand, creating an adduction motion. These attachments are summarized in Table 13-4. Like the dorsal interosseus muscles, the palmar interosseus muscles are innervated by the ulnar nerve. Both the dorsal and palmar interossei play an important role in such activities as typing and playing the piano Palmar Interosseus Muscles O: 2nd, 4th, and 5th metacarpals I: Base of respective proximal phalanx A: Adduct fingers at MCP joint N: Ulnar nerve (C8, T1)

The thenar muscles are those that function to move the thumb.

They form the thenar eminence, or ball of the thumb. The deep palm muscles are located deep in the palm of the hand between the thenar and hypothenar muscles. They perform some of the more intricate motions that usually involve multiple muscles. These muscles are the adductor pollicis, the interossei (of which there are four dorsal and three palmar), and the lumbricals (of which there are also four muscles).

The adductor pollicis muscle is a thumb muscle, although it is not usually considered part of the thenar group.

This is because it is located deep and does not make up the muscle bulk of the thenar eminence. It actually has two heads. The oblique head has its proximal attachments on the capitate and bases of the second and third metacarpals. The transverse head arises from the distal two-thirds of the palmar surface of the third metacarpal. The fibers of the two heads unite to attach on the ulnar side of the base of the proximal phalanx of the thumb (see Fig. 13-24). As its name implies, its function is to adduct the thumb (at the CMC joint). It gives much power to grasp. Adductor Pollicis Muscle O: Capitate, bases of the second and third metacarpal, and distal two-thirds of the palmar surface of the third metacarpal I: Base of proximal phalanx of thumb A: Adducts thumb (CMC joint) N: Ulnar nerve (C8, T1)

If you look at your thumb in anatomical position, you will notice that the pad is perpendicular to the palm.

When you oppose your thumb, the pad is now facing, or parallel to, the palm. Clearly, rotation has occurred. However, if you try to rotate the thumb without any other joint movement, you will find it impossible to do so. The rotation at the CMC joint is a passive, not voluntary, motion. This rotation occurs as a result of the joint's shape and not by any muscle action. This type of motion is commonly referred to as an accessory movement (a movement that accompanies the active movement and is essential to normal motion).

Skier's thumb,

a common hand injury among athletes, involves an acute tear of the ulnar collateral ligament of the thumb.

The extensor expansion ligament,

also called the extensor hood is a small, triangular, flat aponeurosis covering the dorsum and sides of the proximal phalanx of each finger. The extensor digitorum tendon blends into the expansion. The extensor expansion is wider at its base over the MCP joint, actually wrapping over the sides somewhat. As it approaches the PIP joint, the expansion is joined by tendons of the lumbricals and interosseus muscles. It narrows toward its distal end at the base of the distal phalanx. The extensor digitorum, lumbricals, and interosseus muscles form an attachment to the middle or distal phalanx by way of this expansion. The extensor hood area, formed by the extensor expansion proximally, covers the head of the metacarpal and keeps the extensor tendon in the midline.

There are two sets of interosseus muscles: dorsal

and palmar. There are four dorsal interosseus muscles. They each attach proximally to two adjacent metacarpals and distally to the base of the proximal phalanx .Their action is to abduct the second, third, and fourth fingers at the MCP joint. The third digit has two dorsal interosseus muscles, one on either side of the proximal phalanx. This allows the third digit to abduct in either direction. The fifth finger is abducted by the abductor digiti minimi. The ulnar nerve innervates all dorsal interosseus muscles. Dorsal Interossei O: Adjacent metacarpals I: Base of proximal phalanx A: Abduct fingers at MCP joint N: Ulnar nerve (C8, T1)

The CMC joints of the fingers (digits 2 to 5)

are classified as nonaxial, plane-shaped synovial joints that provide slight gliding motion. Actually, they provide more stability than mobility. The trapezoid articulates with the base of the second metacarpal, the capitate with the base of the third metacarpal, and the hamate with the bases of the fourth and fifth metacarpals The second and third CMC joints have very little mobility. The fourth CMC joint allows slightly more motion. The fifth CMC joint is the most mobile of the fingers because of its more condyloid shape, which allows for a small amount of fifth finger opposition. It does not, however, allow as much opposition as the thumb (the first CMC joint).

The MCP joints of the fingers

are formed by the concave-shaped bases of the proximal phalanges articulating with the convex, rounded heads of the metacarpals These are commonly referred to as the "knuckles." They are biaxial condyloid joints with two degrees of freedom, allowing flexion, extension, and hyperextension, plus abduction and adduction .

The longitudinal arch

begins at the wrist and runs the length of the metacarpal and phalanges for each digit. It is perpendicular to the other two arches. These arches contribute to the function of the various grasps described at the end of this chapter.

The proximal carpal arch is formed

by the proximal end of the metacarpals (base) and carpal bones and is maintained by the flexor retinaculum

Loss of lumbrical function will result in "claw hand," rth and fifth fingers will assume this posture.

characterized by MCP hyperextension and PIP and DIP flexion (opposite positions from the lumbricals' actions). The lumbricals are innervated in part by the median and ulnar nerves. If the median nerve is involved affecting the first and second lumbricals, then only the second and third fingers will be involved. If the ulnar nerve is affected involving the third and fourth lumbricals, then the fourth and fifth fingers will assume this posture. Lumbrical Muscles O: Tendon of the flexor digitorum profundus muscle I: Tendon of the extensor digitorum muscle A: Flex the MCP joint while extending the PIP and DIP joints N: First and second lumbricals: median nerve (C8, T1) Third and fourth lumbricals: ulnar nerve (C8, T1)

Carpal tunnel syndrome is an extremely

common condition caused by compression of the median nerve within the carpal tunnel. Symptoms include numbness and tingling in the hand, which often begins at night. Patients often complain of tingling, pain, and weakness in the hand, particularly in the thumb, index, and middle fingers. Tapping over the carpal tunnel often produces symptoms. Some, but not all, fibers of the transverse carpal ligament are often surgically cut to relieve the symptoms. If all fibers were cut, it would allow bowstringing of the extrinsic tendons on the flexor surface.

Stenosing tenosynovitis,

commonly known as trigger finger, is a problem with the sliding mechanism of a tendon in its sheath. When a nodule or swelling of the sheath lining or the tendon develops, the tendon can no longer slide in and out smoothly. It may pass into the sheath when the finger flexes, but it becomes stuck as the finger attempts to extend. The finger can become locked in that position, and it must be manually extended. The flexor tendons of the middle and ring fingers are most commonly involved.

The extensor pollicis longus muscle is located near the two previously mentioned muscles,

deep on the posterior forearm. Its proximal attachment is on the middle third of the ulna and interosseus membrane. Like the other two muscles, it becomes superficial just before crossing the wrist. Its distal attachment is at the base of the thumb's distal phalanx, on the posterior side. It functions to extend the IP, MCP, and CMC joints of the thumb. We use this muscle to pull the thumb back when a flat and open hand is needed. An example of this is clapping. Extensor Pollicis Longus Muscle O: Middle posterior ulna and interosseus membrane I: Base of distal phalanx of thumb A: Extends all three joints of the thumb (IP, MCP, and CMC) N: Radial nerve (C6, C7, C8)

The flexor digitorum superficialis muscle lies

deep to the wrist flexors and palmaris longus muscle Its broad proximal attachment is part of the common flexor tendon on the medial epicondyle of the humerus. It also has an attachment on the coronoid process of the ulna and the oblique line of the radius. It divides into four tendons and crosses the wrist with one tendon going to each finger. Each distal attachment splits into two parts and attaches on each side of the middle phalanx of each finger . Its primary action is to flex the PIP and then MCP joints of the second through fifth fingers. This is an important muscle in the power grip. Flexor Digitorum Superficialis Muscle O: Common flexor tendon on the medial epicondyle, coronoid process, and radius I: Sides of the middle phalanx of the four fingers A:Flexes the PIP and MCP joints of the fingers N Median nerve (C7, C8, T1)

digitorum means

digits/fingers

The flexor pollicis longus muscle

is a deep muscle that has its proximal attachment on the anterior surface of the radius and interosseus membrane and its distal attachment at the base of the thumb's distal phalanx .It is a prime mover in flexion of the IP joint of the thumb. It is the only muscle to do so. It also flexes the MCP and CMC joints of the thumb. Flexor Pollicis Longus Muscle O: Radius, anterior surface I: Distal phalanx of thumb A: Flexes all three joints of the thumb (IP, MCP, CMC) N: Median nerve (C8, T1)

The flexor retinaculum

is a fibrous band of connective tissue that spans the anterior surface of the wrist in a mediolateral (horizontal) direction. It attaches to the styloid processes of the radius and ulna and crosses over the flexor muscle tendons. Its main function is to hold these tendons close to the wrist, thus preventing the tendons from pulling away from the wrist (bowstringing) when the wrist flexes. It also prevents the two sides of the carpal bones from spreading apart or separating. In the construction world, this horizontal structure is called a "tie beam." Its distal border merges with the transverse carpal ligament.

The extensor pollicis brevis muscle

is also located deep on the posterior forearm and spans the wrist just medial to the abductor pollicis longus muscle. Its proximal attachment is on the posterior radius near the distal end and just below the abductor pollicis longus muscle. Its distal attachment is on the posterior surface at the base of the thumb's proximal phalanx (Fig. 13-16). It functions to extend the MCP and CMC joints of the thumb. Without the function of this muscle, the thumb MCP joint remains in a flexed position. Extensor Pollicis Brevis Muscle O: Posterior distal radius I: Base of the proximal phalanx of thumb A: Extends MCP and CMC joints of thumb N: Radial nerve (C6, C7)

The proximal end of the metacarpals and phalanges

is called the base, and the distal end is called the head

Swan neck deformity Boutonnière deformity,

is characterized by flexion of the MCP joint, (hyper)extension of the PIP joint, and flexion of the DIP joint. With a boutonnière deformity, the deformity is in the opposite direction—extension of the MCP joint, flexion of the PIP joint, and extension of the DIP joint. U

. The shallower distal carpal arch

is made up of the metacarpal heads.

The flexor retinaculum

is made up of the palmar and transverse carpal ligaments (anterior view).

The palmar carpal ligament

is more proximal and superficial than the transverse carpal ligament. It attaches to the styloid processes of the radius and ulna and crosses over the flexor muscle tendons.

keep in mind that a muscle can only move the joints

it crosses. By looking at the specific joints that each hand muscle crosses, we can determine at what joints a muscle will have an action.

if the muscle has "longus" in its name,

it implies that there is a counterpart "brevis" muscle. The "longus" muscle either runs out to the distal phalanges or originates more proximally than its "brevis" counterpart.

The abductor digiti minimi muscle lies superficially,

just medial to the flexor digiti minimi muscle on the ulnar border of the hypothenar eminence. It attaches proximally to the pisiform and to the tendon of the flexor carpi ulnaris muscle and distally to the base of the proximal phalanx of the fifth finger (see Fig. 13-23). It abducts the MCP joint of that finger. By being able to abduct the fifth digit, one is able to increase one's grasp. Abductor Digiti Minimi Muscle O: Pisiform and tendon of flexor carpi ulnaris I: Proximal phalanx of fifth finger A: Abducts the MCP joint of the fifth finger N: Ulnar nerve (C8, T1)

The transverse carpal ligament

lies deeper and more distally. It attaches to the pisiform and hook of the hamate on the medial side and to the scaphoid and trapezium bones laterally. It arches over the carpal bones, forming a tunnel through which the median nerve and nine extrinsic flexor tendons of the fingers and thumb pass (four tendons each of the flexor digitorum superficialis and flexor digitorum profundus, and one tendon for the flexor pollicis longus). The bony floor of the carpal bones and the fibrous ceiling of the transverse carpal ligament. Together they form the tunnel through which the tendons and nerve pass. The figure also shows the area of the hand innervated by the median nerve. The scaphoid, providing some lateral attachment of the ligament, drawing, behind)the trapezium. The scaphoid provides some lateral attachement

When abduction and adduction (sagittal plane motion) . During abduction, the distal end of the metacarpal moves anteriorly while the base of the metacarpal glides posteriorly, whereas adduction causes posterior movement of the distal end of the metacarpal with an anterior glide of the base.

occur, the convex base of the first metacarpal glides on the concave trapezium in the opposite direction from the distal end of the metacarpal (convex-on-concave articulation). moves anteriorly while the base of the metacarpal glides posteriorly, whereas adduction causes posterior movement of the distal end of the metacarpal with an anterior glide of the base.

The CMC joint of the thumb allows more mobility than the CMC joints of the other four fingers, yet it also provides as much stability. Opposition is a combination

of flexion and abduction in which the tips of the first and fifth digits move toward one another, with the "built-in" accessory motion of rotation; reposition, using a combination of extension, adduction and "rotation," is the return to anatomical position.

Arthrokinematics From an arthrokinematic When flexion occurs, the base of the

perspective, during flexion and extension (frontal plane motion), the concave base of the first metacarpal glides in the same direction as the distal end of the metacarpal (concave-on-convex articulation). metacarpal glides medially while the distal end of the metacarpal also glides medially. During extension, the base glides laterally, along with lateral movement of the distal metacarpal.

De Quervain's disease is caused by an inflammation and thickening of the sheath containing the extensor pollicis brevis and abductor pollicis longus,

resulting in pain on the radial side of the wrist. Because it is an inflammation of tendons and their surrounding sheaths, it is called a tenosynovitis. Making a fist with your thumb inside and then moving the wrist into ulnar deviation can elicit pain in those tendons and is considered a positive test. Care should be exercised in doing this test because it often causes some discomfort in a normal wrist.

Arthrokinematics In analyzing arthrokinematic motion,

the MCP joints have a concave-on-convex articulation, in that the concave base of the proximal phalanges will move in the same direction as the distal end of the proximal phalanges during movement. Therefore, the base of the proximal phalanx glides anteriorly during flexion and posteriorly during extension, medially (toward the midline of the hand) during adduction, and laterally (away from the midline of the hand) during abduction, while the distal end of the proximal phalanx moves in the same direction with all of these motions.

Arthrokinematics Given that the hinge joint structure yields a concave-on-convex articulation at the majority of finger and thumb joints

the arthrokinematic movement is the same for all of these joints. The base of the more distal segment must glide anteriorly during flexion, and posteriorly during extension, moving with the distal end of the bony segment. When joint mobilizations are performed to restore motion that is limited, an anterior glide is performed to increase flexion, and a posterior glide is used to increase extension.

The first digit, the thumb, has three joints:

the carpometacarpal (CMC) joint, the metacarpophalangeal (MCP) joint, and the interphalangeal joint

In the thenar group,

the flexor pollicis brevis muscle is a relatively superficial muscle. It attaches proximally to the trapezium and the flexor retinaculum and distally to the base of the proximal phalanx of the thumb . Its primary actions are to flex the MCP and CMC joints of the thumb. Flexor Pollicis Brevis Muscle O: Trapezium and flexor retinaculum I: Proximal phalanx of the thumb A: Flexes the MCP and CMC joints of thumb N: Median nerve (C6, C7)

The scaphoid is

the most frequently injured carpal bone. A scaphoid fracture usually results from a fall on the outstretched hand of a younger person. Because of a poor vascular supply, it has a high incidence of avascular necrosis. Kienböck's disease refers to the necrosis of the lunate, which may develop after trauma.

There is one indistinct landmark on the forearm,

the oblique line which is sometimes referred to when describing muscle attachments.

When the hand is relaxed,

the palm assumes a cupped position. This palmar concavity is due to the arrangement of the bony skeleton reinforced by ligaments. There are three arches that are responsible for this shape

The flexor digitorum profundus muscle lies deep to the flexor digitorum superficialis muscle;

these two muscles traverse the forearm and hand together. The profundus muscle has its proximal attachment on the ulna on the anterior and medial surfaces, from the coronoid process to approximately three-fourths of the way down the ulna. It runs beneath the flexor digitorum superficialis muscle until the superficialis tendon splits into two parts at its distal attachment. The profundus muscle tendon passes through this split and continues distally to attach at the base of the distal phalanx of the second through fifth fingers. Its action is to flex the DIP, then the PIP and MCP joints of the second through fifth fingers. This is the only muscle that flexes the DIP joints. Fexor Digitorum Profundus Muscle O:Upper three-fourths of the ulna I: Distal phalanx of the four fingers A:Flexes all three joints of the fingers (DIP, PIP, and MCP) N: Median and ulnar nerves (C8, T1)

Arthrokinematically, both the MCP and IP joints have a concave-on-convex articulation

where the concave base on the proximal end of the distal segment articulates with the convex head on the distal end of the proximal segment. This causes the concave joint surface to glide in the same direction as the distal end of the bony segment during movement.