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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
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