Anatomy of the Hand

Diane Coker, PT, DPT, CHT

University of California, IrvineIrvine, CA

February 9-11, 2018

Topics• Surface Anatomy• Bony Anatomy• Joints & Ligaments• Muscular Anatomy• Tendon Anatomy

• Flexors• Extensors

• Neuroanatomy• Thumb

Surface Topography• Joint flexion creases

• DPC• Thenar crease• Hypothenar crease• Digital creases• Distal wrist creases

• Muscle groups• Thenar• Hypothenar

• Rays• 1 - 5

PIP

DIP

DPC = MP joint volar crease (prox & distal palmar crease)

P3

P2

P1

IP

Bones of the Hand

Bony Anatomy• 19 bones distal to the

carpus• Metacarpals (5) Numbered

• Phalanges (12)• Proximal (P1)• Middle (P2)• Distal (P3)

• Thumb phalanges (2)

Metacarpal Cascade

Structural Units

• Fixed Unit• Distal carpal row• Metacarpals 2 & 3

• 3 mobile units• Thumb ray• Index finger ray• Metacarpals 4 & 5, with

long, ring, & little fingers

Green: Mobile Units

Red: Fixed Units

Joints and Articulations

Types of Joints

(condyloid)

Joints in the Hand• Saddle: Carpometacarpal

(CMC)• Ellipsoidal:

Metacarpophalangeal (MP or MCP)

• Hinge: Interphalangeal (IP)• Plane: Hamate and

Triquetrum• Not represented: ball and

socket

Fixed and Mobile Units

• “Ulnar” opposition• 20-30° at SF• 10-15° at RF

• Less mobility at MCs II & III thought to be a functional adaptation to enhance ECRL/B & FCR activity

Green: Mobile Units

Red: Fixed Units

MCP Joints• Condyloid (Ellipsoid)Joints

• flexion/extension• abduction/adduction• IF sl rotation

• Motion increases radial to ulnar in digits

• 0/90‐110⁰

• Hyperextension varies among individual

MC

P1

MetaCarpoPhalangeal Joints

• Condyloid joints, 2 or 3 (IF) planes of motion

• Collaterals loose in extension, taut in flexion

• Prolonged immobilization should be in flexion, with collateral ligaments on stretch

MCP Joints Have Increased Bony Congruity in Flexion

MP/IP Ligament Structure MP Joint Volar Plate

MetacarpalPhalanx

Loose proximal attachment of the volar plate

InterPhalangeal Joints• Bicondylar hinge joint with

intercondylar ridge

• Volar plate

(palmar fibrocartilagenous plate)

• Collateral ligaments have equal tension in flexion & extension

• Proximal condyle head stretches CL at about 15°

• Check rein ligamentsin PIPs

P1 P2

P2

PIP Volar Plates• PIPs are

immobilized in extension to avoid joint contracture via the check rein ligaments (swallowtails)

Safety Positioning• MPs at 70-90°• IPs at 0 - 15°

Wrist in 20-35° extension

Safety vs. Functional Positioning

Muscles of the Hand

Extrinsic MusclesOriginate in Forearm & Insert in Hand

Finger Flexors Flexor Digitorum Superficialis, Flexor Digitorum

Profundus

Finger Extensors Extensor Digitorum, Extensor Indicis, Extensor Digiti

Minimi

Thumb Extensor Pollicis Longus, Extensor Pollicis Brevis,

Abductor Pollicis Longus, Flexor Pollicis Longus

• Thenar Abductor Pollicis Brevis Flexor Pollicis Brevis Opponens Pollicis

• Hypothenar Abductor Digiti Minimi Flexor Digiti Minimi Opponens Digiti Minimi

• Adductor pollicis• Palmaris Brevis

• Lumbricals

• Interossei

Intrinsic Hand Muscles Opponens Pollicis & Opponens Digiti Minimi

• OP rotates 1st

metacarpal so that thumbnail faces the ceiling when hand is placed palm up

• Slight rotation of 5th

metacarpal with ODM

• APB works with OP during opposition

• APB most radial and superficial thenar muscle

• APB first muscle to show signs of atrophy in median nerve dysfunction

APB & Abd Digiti Minimi Flexor Digiti Minimi &Flexor Pollicis Brevis

• FPB has 2 heads with different innervations

• Deep head of FPB occ described as an additional palmar interosseous muscle

Adductor• Innervation

• Ulnar nerve

• Two heads• Transverse

• Oblique

Lumbricals

• Travel along radial side of each digit

• Innervation• I/M: median• R/S: ulnar

• Radial two muscle bellies are unipennate

• Ulnar two are bipennate• Bipennate muscles shorten

less, generate more force than unipennate

Dorsal Interossei

• First DI much larger than other DI

• No DI to SF

• First DI can rotate IF slightly at MCP joint, and assists adductor pollicis in thumb adduction

Volar Interossei

• 3 unipennate muscles

• Smaller than dorsal interossei

• Adduct I, R, S Fs towards MF, assist lumbricals in MP flexion

Palmaris Brevis• Both palmaris longus

and brevis serve minimal function in the hand

• Brevis serves to tighten the hypothenar skin, possibly deepen concavity of palm

• Innervation• Ulnar

• No bony attachments

Tendon Anatomy

Flexor TendonsExtensor Tendons

Flexor Tendon Anatomy

• Flexor Digitorum Profundus• Splits into 2 separate bundles in mid-forearm

• Often separate slips for IF & M/R/S Fs• Innervation: AIN I & M, ulnar R & L

Flexor Digitorum Superficialis• 2 separate origins

• Medial compartment—4 separate bundles

• ? FDS to little finger• Innervation: median

Extrinsic Flexors: FDS & FDPLength Tension Issues

• FDS and FDP are dependent on wrist position to enhance function;35°‐40°ext for maximum grip

• Weakest flexion force is in wrist flexion

• ECRB provides counterbalance to prevent wrist flexion; ECRL contributes  with power grip 

Flexor Pollicis Longus• Innervation

• Median (AIN)

• Unique to humans• Rudimentary of absent in other primates

• Occasional connection to FDP• Linburg‐Comstock syndrome

• Occasional accessory long head present

• Ganzer’s muscle

• Can compress AIN

Tendon Orientation through the Carpal Tunnel

Flexor Tendon Zones• Zone I: distal to

FDS insertion• Zone II: A1 pulley

to FDS insertion• No Man’s Land

• Zone III: distal end of CT to A1

• Zone IV: CT• Zone V: proximal

to CT

Flexor Tendon Zones• Thumb (3)

Zone T1: from IP joint distal

Zone T2: from IP joint proximal to MP joint

Zone T3: from MP joint proximal to transverse carpal ligament

• FDS• Volar to FDPentering synovial sheath• Spiral turn• Now dorsal to FDP• Camper’s Chiasm• Can insert as far as neck

of P2

• FDP• Straight line

Camper’s Chiasm

• 50% of fibers from FDS cross over• 50% of fibers remain on same side

Flexor Sheaths• 2 Systems

• Synovial sheaths• Provide nutrition

to tendons• Low-friction

gliding• Retinacular sheaths

• Provide efficient mechanical function by holding the tendon close to the bone

• Annular & cruciate pulleys

Tendon Nutrition• 2 pathways:

• Synovial diffusion• Vascular perfusion

• Diffusion plays a greater role than perfusion

Retinacular Sheath System

• 2 Part Composition

• Fingers• 5 Annular pulleys

• A1: over MP joint• A3 over PIP• A5 over DIP

• 3 Cruciate pulleys

Retinacular Sheath System

• Thumb• A1, A2, Oblique

BowstringingAKA: Rock Climbers’ injury

Pulley Mechanics

• A2 and A4 most important to preserve for normal function in fingers

• Oblique pulley in thumb

Extensor Tendon Anatomy

• Compartments• 1: APL, EPB• 2: ECRL, ECRB• 3: EPL• 4: ED(C), EI(P)• 5: EDQ(M)• 6: ECU

• Only pulley is the extensor retinaculum

• Synovial sheaths located only at wristlevel

Extensor Tendon Zones

• Fingers• Zone 1: DIP• Zone 2: middle phalanx• Zone 3: PIPs• Zone 4: proximal phalanx• Zone 5: MPs• Zone 6: dorsum of hand• Zone 7: retinacular

compartment

Extensor Tendon Zones

Thumb (5)Zone T1: IP jointZone T2: Middle phalanxZone T3: MP jointZone T4: 1st metacarpalZone T5: Carpus

• Extensor tendons are different from flexor tendons

• Anatomy more complex• Restraining structures

throughout system• More superficial, more

vulnerable, thinner• Flexor tendons can

become “stuck” under the pulleys, but extensor tendons often heal with a lag 2° longer excursion pull

Extrinsic Extensors

• EIP and EDM add independent function, not strength

• ED can produce IP extension if MPs blocked in slight flexion

Extensor Mechanism (Hood) Complex system covering dorsal aspect of digits

Creates cable system • Extends MPs & IPs • Allows lumbricals to assist in MP flexion

• Components Extensor digitorum Juncturae tendinae Central slip/band Sagittal bands Lateral bands Transverse retinacular

ligament Oblique retinacular

ligament Terminal tendon

The Extensor Apparatus

• ED• Lateral band

• Terminal tendon• Interossei/lumbri

cal contributions to lateral band

Sagittal Bands

• Insert into & stabilize ED at dorsum of MP joint• Ruptures common, often with a trivial incident• Often lax• ED will eventually function as a flexor as it falls below the joint axis of

motion

Juncturae Tendinae

• Link EDC to prevent independent function

• Maintain dorsal placement of extensors tendons over MPs during flexion The Thumb

Thumb Mechanics The Thumb

• CMC joint is not in sagittal, coronal, or transverse planes of the digits

• Difficult to categorize as being in flexion/extension planes or abduction/adduction planes

• Thumb “scaption”

CMC Joints • Saddle Joints

• Thumb & Digit V

• Flex/Ext (ll to palm)

• Abd/Add ( to palm)

• Opposition net effect

• Plane Joints• Digits II‐IV

• Flexion/Extension

CarpoMetaCarpal Joint of Thumb

• AKA basal joint, 1st CMC

• Asymmetrical

• Complex ligamentous system

CMC Joint of the Thumb

• A “saddle” joint

• Biconcave sellar joint

• 7 ligaments for CMC stabilization

• 16 ligaments for STT and CMC joint stability

• Greatest stability in palmar abduction and pronation

MCP Joint of Thumb

• Flatter than I-S Fs MP heads

• Easily dislocated

• 2 sesamoid bones• Greatest variation

in ROM:

30 – 90°

Peripheral Innervation

• The hand occupies nearly 1/3 of the motor cortex

• Thumb approx ¼-1/3 of hand representation

• Representation in the hand:

• C6• C7• C8

Cervical DermatomesVariations in Cervical Dermatomes

C7

Peripheral Patterns

Potential Contributors to Sensation in the Thenar Eminence

• Palmar cutaneous branch of median N

• Superficial branch radial N

• LABC

• Median N proper

• MABC

Entrapment Sites• Include

compression, tension, combination

• All 3 major peripheral nerves pass through a 2 headed muscle near the elbow

• Median: Pronator Teres

• Ulnar: FCU• Radial: Supinator

Median Nerve• 2 main branches

distal to elbow• Main branch continuing

on to innervate the hand• AIN = PQ, FPL, & radial

½ FDP

• Palmar cutaneous branch

Median Nerve

• Entrapment sites• Ligament of Struthers• Lacertus fibrosus

• AKA bicipital aponeurosis• Pronator teres• FDS arch• Carpal tunnel• Ganzer’s muscle

Ligament of Struthers

A rare occurrence

• Compression with elbow flexion

Arch of FDS

Entire Median Nerve Involved 

• Sublimus (superficialis) arch

• Irritation of fascial edge of FDS

Lacertus Fibrosus Pronator Syndrome

• Median nerve penetrates pronator teres between its 2 heads

• PT spared in Pronator Syndrome

• PT weak if median nerve compressed under ligament of Struthers

AnteriorInterosseous Branch• Pure motor branch

bifurcating slightly proximal to FDS arch

• Innervates FPL, PQ, FDP to I & M

Martin-Gruber Anastomosis• Median nerve sends

fibers to ulnar nerve in forearm

• Rare: ulnar to median anastomosis

• Incidence ranges from 8-30%

Carpal Tunnel Compression

• Motor to IF,MF lumbricals

• Recurrent motor branch

• Branches distal to CT• Motor to thenar muscles• The “million dollar” nerve

• Sensation to ends of thumb, IF, MF, ½ RF

(usually!)

Anatomical Variations of Recurrent Motor branch

Palmar Sensation• Thenar eminence

sensation supplied mainly by palmar cutaneous branch

• Fingernails & dorsum of fingertips supplied by median nerve terminal endings

Palmar cutaneous nerve does not enter carpal tunnel

Ulnar Nerve

• Entrapment Sites• Arcade of Struthers• Cubital tunnel• FCU• Guyon’s canal

Arcade vs. Ligament of Struthers

• Arcade of Struthers• Fascial band• Usually present• Potential compression

site for ulnar nerve

• Ligament of Struthers• Rare• Potential site of

compression for median nerve

Cubital Tunnel

(Fascial arch between)

• Ulnar nerve passes between 2 heads of FCU

• Fascial arch

• A potential site of compression

Guyon’s Canal• Dorsal ulnar

sensory branch bifurcates proximal to Guyon’s canal

• First dorsal interosseous muscle receives terminal innervation fibers from deep motor branch

Intrinsic Insertions of Palmar Branch Ulnar N

• Motor to • interossei, • ulnar 2 lumbricals • adductor pollicis • deep head of FPB

• Palmar sensation to SF, RF

Froment’s sign

Overuse of FPL 2°loss of stabilization of pinch from adductor pollicis

Froment’s sign on right

Teardrop sign on R: AIN(Reverse Froment’s sign)

Froment’s sign on R

Froment’s sign: ulnar paresis

Tear drop sign: AIN paresis

Radial Nerve

• Entrapment sites:• Spiral groove

(Saturday night palsy)• Mid-humeral trauma• Arcade of Frohse/supinator

arch/radial tunnel• Wartenburg syndrome

• Main nerve innervates mobile wad of Henry (muscles originating from supracondylar ridge + ECRB)

• Bifurcates at level of radiocapitellar joint

• PIN (motor branch)• Superficial sensory branch

Posterior Interosseous Nerve (PIN)

• Motor branch• Arcade of Frohse

(supinator arch)• Radial Tunnel vs

Supinator syndrome

Wartenburg Syndrome (Distal radial sensory nerve compression)

DRSN is “scissored” between the brachioradialis and 2nd

compartment tendons 2-3 fingertips above

radial styloid, sl medial “Watchband” or

“handcuff” syndrome

Thank You!

• dacoker@cox.net