Chapter 7 Structure and Function of the Hand

Chapter 7 Structure and Function of the Hand Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Osteology: Metacarpals are designated numerically as 1 through 5, beginning on the radial side Each metacarpal has a base, shaft, head, and neck First (thumb) metacarpal is shortest and thickest Second is usually longest Remaining three bones’ bone lengths decrease from the radial to ulnar (medial) direction Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 2

Osteology: Metacarpals – cont’d With hand in anatomic position, the thumb's metacarpal is rotated almost 90 degrees medially, relative to other digits Second through fifth metacarpals are aligned generally side by side, with palmar surfaces facing anteriorly Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 3

Osteology: Metacarpals – cont’d Terminology describing surfaces of carpal bones and finger bones (except thumb) is standard: palmar surfaces anteriorly, radial surfaces laterally, etc. Dorsal surface of thumb faces laterally Palmar surfaces medially Radial surfaces anteriorly Ulnar surfaces posteriorly Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 4

Osteology: Phalanges The hand has 14 phalanges Phalanges within each finger referred to as proximal, middle, and distal Thumb has only proximal and distal phalanx Except for differences in sizes, all phalanges within a particular digit have similar morphology Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 5

Osteology: Arches of the Hand Proximal transverse arch Formed by distal row of carpal bones Ø Static, rigid arch that forms carpal tunnel Ø Capitate bone is keystone of this arch Ø Longitudinal arch Follows general shape of second and third rays Ø Articulations provide longitudinal stability to hand Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 6

Osteology: Arches of the Hand – cont’d Distal transverse arch Ø Ø Passes through MCP joints Sides of distal arch are mobile Transverse flexibility occurs as peripheral metacarpals "fold" around central metacarpals Keystone formed by MCP joints of these central metacarpals Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 7

Arthrology: Hand Terminology Finger movements using cardinal planes Flexion and extension occur in sagittal plane Ø Abduction and adduction occur in frontal plane Ø Abduction and adduction of fingers is described as motion toward (adduction) or away (abduction) from middle finger Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 8

Arthrology: Terminology for Thumb Flexion is movement of palmar surface of thumb in frontal plane across and parallel with palm Extension returns thumb back to anatomic position Abduction is forward movement of thumb away from palm in a sagittal plane Adduction returns thumb to plane of hand Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 9

Arthrology: Terminology for Thumb – cont’d Opposition describes movement of thumb across palm, making direct contact with tips of any fingers Terminology serves as basis for naming of thumb muscles Ø e. g. , opponens pollicis, extensor pollicis longus Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 10

Arthrology: Carpometacarpal Joints Form articulation between distal row of carpal bones and bases of metacarpal bones Positioned at proximal region of hand Basis for all hand movements starts at CMC joints, at most proximal region of each ray Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 11

Arthrology: Carpometacarpal Joints – cont’d First CMC joint is most mobile Fourth and fifth CMC joints are next-most-mobile CMC joints Increased mobility of fourth and fifth CMC joints improves grasp effectiveness and functional interaction with opposing thumb Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 12

Arthrology: Carpometacarpal Joint of Thumb – cont’d CMC joint of thumb located at base of first ray, between metacarpal and trapezium Most complex of CMC joints, enabling extensive thumb movements Saddle shape allows thumb to fully oppose and encircle objects held within palm Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 13

Arthrology: Carpometacarpal Joint of Thumb – cont’d Capsule surrounding joint is naturally loose, allowing a large range of motion Capsule is strengthened by stronger ligaments and forces produced by overriding musculature Ligament rupture often causes joint dislocation, forming a “hump” at base of thumb Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 14

Arthrology: Carpometacarpal Joint of the Thumb – cont’d CMC joint of thumb is saddle joint Each articular surface is convex in one dimension and concave in other—like saddle on horse This shape allows a maximum of combined mobility and stability Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 15

Kinematics: Carpometacarpal Joint of the Thumb – cont’d Motions occur primarily in 2 degrees of freedom Abduction and adduction generally occur in sagittal plane Flexion and extension generally occur in frontal plane Opposition and reposition of thumb incorporate two primary planes of motion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 16

Kinematics: Abduction and Adduction In neutral adduction position, thumb lies within plane of hand Maximum abduction positions thumb metacarpal about 45 degrees anterior to plane of palm Full abduction forms wide concave curvature, useful for grasping objects Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 17

Kinematics: Flexion and Extension Performing flexion and extension of CMC thumb joint is associated with varying amounts of metacarpal spinning During flexion, metacarpal rotates slightly medially During extension, metacarpal rotates slightly laterally Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 18

Kinematics: Flexion and Extension – cont’d Axial rotation is evident by watching change in orientation of thumbnail between full extension and full flexion In anatomic position, CMC joint can be extended an additional 10 -15 degrees From full extension, thumb metacarpal flexes across palm about 45 -50 degrees Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 19

Kinematics: Opposition First, thumb metacarpal abducts Next, abducted metacarpal flexes and medially rotates across palm toward small finger Muscle force helps guide and rotate metacarpal to extreme medial side of articular surface of trapezium Small finger contributes indirectly to opposition, allowing tip of thumb to more easily contact tip of small (little) finger Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 20

Metacarpophalangeal Joints: Fingers “Knuckles” of fingers are articulations formed between convex heads of metacarpals and shallow concave proximal surfaces of proximal phalanges Motion at MCP joint occurs predominantly in two planes: flexion and extension in sagittal plane, and abduction and adduction in frontal plane Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 21

Metacarpophalangeal Joints: Supporting Structures Capsule Ø Radial and ulnar collateral ligaments Ø Connective tissue that surrounds and stabilizes MCP joint Cross MCP joints in an oblique palmar direction; limit abduction and adduction; become taut on flexion Fibrous digital sheaths Ø Form tunnels or pulleys for extrinsic finger flexor tendons; Contain synovial sheaths to help lubrication Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 22

Metacarpophalangeal Joints: Supporting Structures – cont’d Palmar (or volar) plates Thick fibrocartilage ligaments crossing palmar side of each MCP joint Ø Limit hyperextension of MCP joints Ø Deep transverse metacarpal ligaments Ø Merge into wide, flat structure that interconnects and loosely binds second through fifth metacarpals Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 23

Finger Kinematics: Flexion Controlled by flexor digitorum superficialis and flexor digitorum profundus Stretches and increases tension in dorsal part of capsule and collateral ligaments, stabilizing joint in flexion, useful during grasp Kinematics of extension occurs in reverse Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 24

Finger Kinematics: Abduction Proximal phalanx rolls and slides in radial direction Kinematics of adduction of MCP joints occurs in reverse fashion Radial collateral ligament becomes taut Ø Ulnar collateral ligament slackens Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 25

Thumb Kinematics Active and passive motions at MCP joint of thumb are significantly less than fingers’ MCP joint of thumb allows only 1 degree of freedom: flexion and extension within frontal plane Active abduction and adduction of thumb MCP joint is limited and considered an accessory motion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 26

Interphalangeal Joints Proximal interphalangeal (PIP) joints Ø Formed by articulation between heads of proximal phalanges and bases of middle phalanges Distal interphalangeal (DIP) joints Ø Formed through articulation between heads of middle phalanges and bases of distal phalanges Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 27

Interphalangeal Joints – cont’d Articular surface appears as tongue-in-groove articulation Articulation helps limit motion at PIP and DIP joints to flexion and extension only Same ligaments that surround MCP joints also surround PIP and DIP joints Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 28

Interphalangeal Joints: Kinematics Flexion at PIP and DIP joints is greater in more ulnar digits Similarities in joint structure cause similar roll-andslide arthrokinematics at PIP and DIP joints Passive tension in collateral ligaments remains constant throughout range of motion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 29

Interphalangeal Joint: Thumb Kinematics Motion is limited primarily to 1 degree of freedom, allowing active flexion to about 70 degrees IP thumb joint can be passively hyperextended beyond neutral to about 20 degrees This motion is often employed to apply force between pad of thumb and object Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 30

Innervation to Hand Radial, median, and ulnar nerves innervate skin, joints, and muscles of hand Normal sensory innervation is essential for protection of hand against mechanical and thermal injury Persons with peripheral neuropathy are thus vulnerable to injury Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 31

Extrinsic Flexors of Digits Extrinsic flexor muscles of digits are flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus These muscles originate primarily from medial epicondyle of humerus and palmar surfaces of radius and ulna Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 32

Extrinsic Flexors of Digits: Flexor Digitorum Superficialis Proximal attachments Ø Distal attachment Ø Four tendons, each to the sides of middle finger phalanges Innervation Ø Common flexor tendon on medial epicondyle of humerus, coronoid process of ulna, and radius Median nerve Actions MCP and PIP joint flexion Ø Wrist flexion Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 33

Extrinsic Flexors of Digits: Flexor Digitorum Profundus Proximal attachments Ø Distal attachment Ø By four tendons, each to the base of the distal phalanx of digits 2 -5 Innervation Ø Anterior ulna and interosseous membrane Medial half: ulnar nerve; lateral half: median nerve Actions Ø MCP, PIP, and DIP joint flexion, wrist flexion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 34

Extrinsic Flexors of Digits: Flexor Pollicis Longus Proximal attachments Ø Distal attachment Ø Base of distal phalanx of thumb Innervation Ø Middle anterior portion of radius and interosseous membrane Median nerve Actions Ø CMC, MCP, and IP joint flexion, wrist flexion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 35

Flexor Pulleys Embedded within each fibrous digital sheath Surround flexor tendons, providing them with nutrition and lubrication Following tendon injury, adhesions may develop between tendon and adjacent digital sheath or between adjacent tendons Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 36

Passive Finger Flexion via “Tenodesis Action” Extrinsic flexors of digits cross over anterior side of wrist, and wrist position alters amount of stretch placed on these muscles Stretching multi-articular muscle at one joint creates passive movement at another joint and is referred to as tenodesis action of muscle Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 37

Extrinsic Extensors of Fingers Extensor tendons do not attach directly to phalanges but blend with extensor mechanism Proximal end of extensor mechanism is the dorsal hood, which wraps completely around MCP joint Extensor mechanism serves as primary distal attachment for both extensor muscle tendons and intrinsic muscles of fingers Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 38

Extrinsic Extensors of Fingers: Extensor Digitorum Proximal attachments Ø Distal attachment Ø Four tendons, each to base of extensor mechanism and base of proximal phalanx of all four fingers Innervation Ø Lateral epicondyle of humerus—common extensor tendon Radial nerve Actions Ø Extension of MCP, PIP, and DIP joints Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 39

Extrinsic Extensors of Digits: Extensor Indicis Proximal attachments Ø Distal attachment Ø Blends with index tendon of extensor digitorum Innervation Ø Posterior surface of distal ulna and interosseous membrane Radial nerve Actions Ø Extension of MCP, PIP, and DIP joints of index finger Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 40

Extrinsic Extensors of Fingers: Extensor Digiti Minimi Proximal attachments Ø Distal attachment Ø Joins tendon of extensor digitorum to little finger Innervation Ø Ulnar side of belly of extensor digitorum Radial nerve Actions Ø Extension of MCP, PIP, and DIP joints of little finger Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 41

Extrinsic Extensors of Thumb Extrinsic extensors of thumb are extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus Tendons of these muscles make up “anatomic snuffbox” on radial side of wrist Tendons attach to different regions of dorsal side of thumb; may have secondary actions Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 42

Extrinsic Extensors of Thumb: Extensor Pollicis Longus Proximal attachments Ø Distal attachment Ø Dorsal base of distal phalanx of thumb Innervation Ø Posterior surface of mid-ulna and interosseous membrane Radial nerve Actions Ø Extension of IP, MCP and CMC joints of thumb Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 43

Extrinsic Extensors of Thumb: Extensor Pollicis Brevis Proximal attachments Ø Distal attachment Ø Dorsal base of proximal phalanx of thumb Innervation Ø Posterior aspect of distal radius and interosseous membrane Radial nerve Actions Ø Extension of MCP and CMC joints of thumb Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 44

Extrinsic Extensors of Thumb: Abductor Pollicis Longus Proximal attachments Ø Distal Attachment Ø Base of the metacarpal of the thumb—dorsal-radial aspect Innervation Ø Posterior surface of mid-radius, ulna, and interosseous membrane Radial nerve Actions Ø Abduction and extension of CMC joint of thumb Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 45

Intrinsic Muscles of Hand Muscles of thenar eminence Abductor pollicis brevis Ø Flexor pollicis brevis Ø Opponens pollicis Ø Muscles of hypothenar eminence Flexor digiti minimi Ø Abductor digiti minimi Ø Opponens digiti minimi Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 46

Intrinsic Muscles of Hand – cont’d Adductor pollicis Lumbricals and interossei (intrinsic muscles of fingers) Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 47

Intrinsic Muscles of Hand: Muscles of Thenar Eminence All three muscles are proximally attached on transverse carpal ligament and adjacent carpal bones Short abductor and flexor attach to base of proximal phalanx of thumb Deeper opponens muscle attaches along radial border of first metacarpal Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 48

Intrinsic Muscles of Hand: Muscles of Thenar Eminence – cont’d Primary responsibility of muscles of thenar eminence is to position thumb in varying amounts of opposition Each muscle within thenar eminence is prime mover for at least one component of opposition Opponens pollicis is especially important in its ability to medially rotate thumb toward fingers Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 49

Intrinsic Muscles of Hand: Muscles of Hypothenar Eminence Flexor digiti minimi, abductor digiti minimi, and opponens digiti minimi Proximal attachments on transverse carpal ligament and adjacent carpal bones Short abductor and flexor attach distally on base of proximal phalanx of small finger Opponens digiti minimi has its distal attachment along ulnar border of fifth metacarpal Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 50

Intrinsic Muscles of Hand: Muscles of Hypothenar Eminence – cont’d Common function of hypothenar muscles: raise and curl ulnar border of hand This action deepens distal transverse arch and enhances contact with held objects Injury to ulnar nerve can completely paralyze hypothenar muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 51

Intrinsic Muscles of the Hand: Adductor Pollicis Two-headed muscle lying in the web space of the thumb Proximal attachments Ø Distal attachment Ø The capitate bone, second and third metacarpals Base of the proximal phalanx of the thumb Important for activities involving pinching objects between the thumb and index finger, and for actions used to close a pair of scissors Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 52

Intrinsic Muscles of Hand: Lumbricals Four very slender muscles originating from tendons of flexor digitorum profundus Distally, lumbricals do not attach to bone but to lateral bands of extensor mechanism These muscles flex MCP joints and extend PIP and DIP joints Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 53

Intrinsic Muscles of Hand: Interossei Named according to their location between metacarpal bones Include palmar and dorsal sets Both sets contain four individual muscles, originating on medial or lateral shafts of metacarpals Dorsal interossei are larger and responsible for fullness of shape of dorsal side of hand Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 54

Intrinsic Muscles of Hand: Interossei – cont’d All eight are innervated by ulnar nerve Primary function is to abduct or adduct fingers Dorsal interossei abduct fingers at MCP joint away from an imaginary reference line through middle digit Middle digit has two dorsal interosseous muscles: one that radial deviates and one that ulnar deviates Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 55

Intrinsic Muscles of Hand: Interossei – cont’d Palmar interossei adduct fingers at MCP joints toward middle digit Palmar and dorsal interossei have line of force that passes palmar to MCP joints They flex MCP joints and extend PIP and DIP joints Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 56

Opening Hand: Finger Extension Extensor digitorum exerts force on extensor mechanism, pulling MCP joint toward extension Flexion torque is produced at MCP joint This flexion torque prevents extensor digitorum from hyperextending MCP joint Ø Only with MCP joint blocked from being hyperextended can extensor digitorum effectively tense bands of extensor mechanism Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 57

Closing Hand: Finger Flexion Flexing fingers against resistance or at high speed requires activation of flexor digitorum profundus, flexor digitorum superficialis, and, to a lesser extent, interossei muscles Force produced by flexor digitorum profundus and superficialis flex all three joints of fingers Lumbricals may exert a passive flexion torque at MCP joint Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 58

Functional Consideration: Wrist Extensors during Finger Flexion Making a strong fist requires equally strong synergistic activation from wrist extensor muscles Wrist extensor activity can be verified by palpating dorsum of forearm while making fist If wrist extensors are paralyzed, attempts at making fist result in posture of wrist flexion and finger flexion —a weak and ineffective action Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 59

Common Deformities Deformity of hand is often caused by disease or trauma that disrupts balance of forces around joints Three types of deformities are typical in hand with severe rheumatoid arthritis Ulnar drift Ø Swan-neck deformity Ø Boutonniere deformity Ø Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 60

Summary Joints of hand are organized into three sets of articulations: carpometacarpal, metacarpophalangeal, and interphalangeal MCP joints form base of each digit IP joints flex and extend only; other potential planes of motion are blocked by bony fit of joint and by periarticular connective tissues Simultaneous extension of all three joints of fingers requires coordinated interplay among muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 61