Topics Anatomy of the Hand • Surface Anatomy • Bony Anatomy Diane Coker, PT, DPT, CHT • Joints & Ligaments • Muscular Anatomy • Tendon Anatomy University of California, Irvine •Flexors Irvine, CA •Extensors February 9-11, 2018 • Neuroanatomy • Thumb Surface Topography P3 • Joint flexion creases P2 • DPC • Thenar crease DIP • Hypothenar crease P1 • Digital creases PIP • Distal wrist creases DPC = MP joint volar crease (prox • Muscle groups & distal palmar • Thenar crease) • Hypothenar IP • Rays • 1 - 5 Bones of the Hand Bony Anatomy Metacarpal Cascade • 19 bones distal to the carpus • Metacarpals (5) . Numbered • Phalanges (12) • Proximal (P1) • Middle (P2) • Distal (P3) • Thumb phalanges (2) 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 Types of Joints Joints and Articulations (condyloid) Joints in the Hand Fixed and Mobile Units • Saddle: Carpometacarpal (CMC) • Ellipsoidal: • “Ulnar” opposition Metacarpophalangeal (MP or MCP) • 20-30° at SF • 10-15° at RF • Hinge: Interphalangeal (IP) • Plane: Hamate and • Less mobility at MCs Triquetrum II & III thought to be a • Not represented: ball and functional adaptation socket to enhance ECRL/B & FCR activity MCP Joints • Condyloid (Ellipsoid)Joints • flexion/extension P1 • abduction/adduction • IF sl rotation • Motion increases radial to ulnar in digits • 0/90‐110⁰ MC • Hyperextension varies Green: Mobile Units among individual Red: Fixed Units MCP Joints Have Increased MetaCarpoPhalangeal Joints Bony Congruity in Flexion • 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 MP/IP Ligament Structure MP Joint Volar Plate Phalanx Metacarpal Loose proximal attachment of the volar plate InterPhalangeal Joints PIP Volar Plates • PIPs are • Bicondylar hinge joint with immobilized in intercondylar ridge extension to avoid • Volar plate P2 joint contracture (palmar fibrocartilagenous via the check rein plate) ligaments • Collateral ligaments have equal (swallowtails) tension in flexion & extension • Proximal condyle head stretches CL at about 15° • Check rein ligaments P1 P2 in PIPs Safety Positioning Safety vs. Functional Positioning • MPs at 70-90° • IPs at 0 - 15° Wrist in 20-35° extension Extrinsic Muscles Originate in Forearm & Insert in Hand Finger Flexors . Flexor Digitorum Superficialis, Flexor Digitorum Profundus Muscles Finger Extensors . Extensor Digitorum, Extensor Indicis, Extensor Digiti of the Hand Minimi Thumb . Extensor Pollicis Longus, Extensor Pollicis Brevis, Abductor Pollicis Longus, Flexor Pollicis Longus Intrinsic Hand Muscles Opponens Pollicis & Opponens Digiti Minimi • Thenar . Abductor Pollicis Brevis . Flexor Pollicis Brevis • OP rotates 1st . Opponens Pollicis metacarpal so that • Hypothenar thumbnail faces the ceiling when hand is . Abductor Digiti Minimi placed palm up . Flexor Digiti Minimi • Slight rotation of 5th . Opponens Digiti Minimi metacarpal with ODM • Adductor pollicis • Palmaris Brevis • Lumbricals • Interossei APB & Abd Digiti Minimi Flexor Digiti Minimi & Flexor Pollicis Brevis • APB works with OP • FPB has 2 during opposition heads with • APB most radial different and superficial innervations • Deep head of FPB occ described as an thenar muscle additional palmar • APB first muscle interosseous muscle to show signs of atrophy in median nerve dysfunction Lumbricals Adductor • Two heads • Travel along radial • Innervation side of each digit • Transverse • Ulnar nerve • Oblique • 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 Volar Interossei • First DI much larger • 3 unipennate than other DI muscles •No DI to SF • Smaller than dorsal • First DI can rotate IF interossei slightly at MCP joint, • Adduct I, R, S Fs and assists adductor towards MF, assist pollicis in thumb lumbricals in MP adduction flexion Palmaris Brevis • Both palmaris longus and brevis serve minimal function in the Tendon Anatomy hand • Brevis serves to tighten the hypothenar Flexor Tendons skin, possibly deepen concavity of palm Extensor Tendons • Innervation • Ulnar • No bony attachments Flexor Tendon Anatomy Flexor Digitorum Superficialis • 2 separate origins • Flexor Digitorum Profundus • Medial compartment—4 separate bundles • Splits into 2 separate bundles in mid-forearm • Often separate slips for IF & M/R/S Fs • ? FDS to little finger • Innervation: AIN I & M, ulnar R & L • Innervation: median Extrinsic Flexors: FDS & FDP Flexor Pollicis Longus Length Tension Issues • Innervation • FDS and FDP are • Median (AIN) dependent on wrist • Unique to humans position to enhance • Rudimentary of absent in other primates function;35°‐40°ext for maximum grip • Occasional connection to FDP • Weakest flexion force is • Linburg‐Comstock syndrome in wrist flexion • Occasional accessory long head • ECRB provides present counterbalance to • Ganzer’s muscle prevent wrist flexion; • Can compress AIN ECRL contributes with power grip Tendon Orientation through Flexor Tendon Zones the Carpal Tunnel • 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 • FDS • Thumb (3) • Volar to FDP Zone T1: from IP entering synovial sheath joint distal • Spiral turn Zone T2: from IP • Now dorsal to FDP joint proximal to • Camper’s Chiasm MP joint • Can insert as far as neck Zone T3: from MP of P2 joint proximal to transverse carpal • FDP ligament • Straight line Camper’s Chiasm • 50% of fibers from FDS cross over • 50% of fibers remain on same side Flexor Sheaths Tendon Nutrition • 2 pathways: • 2 Systems • Synovial diffusion • Synovial sheaths • Vascular perfusion • Provide nutrition to tendons • Diffusion plays a greater role than perfusion • Low-friction gliding • Retinacular sheaths • Provide efficient mechanical function by holding the tendon close to the bone • Annular & cruciate pulleys Retinacular Sheath System Retinacular Sheath System • 2 Part Composition • Fingers • Thumb •5 Annular pulleys • A1, A2, Oblique • A1: over MP joint • A3 over PIP • A5 over DIP •3 Cruciate pulleys Bowstringing AKA: Rock Climbers’ injury Pulley Mechanics Extensor Tendon Anatomy • Compartments • 1: APL, EPB • 2: ECRL, ECRB • 3: EPL • A2 and A4 most • 4: ED(C), EI(P) important to preserve • 5: EDQ(M) • 6: ECU for normal function in • Only pulley is the fingers extensor • Oblique pulley in thumb retinaculum • Synovial sheaths located only at wrist level Extensor Tendon Zones Extensor Tendon Zones • Fingers .Thumb (5) • Zone 1: DIP Zone T1: IP joint • Zone 2: middle phalanx Zone T2: Middle phalanx • Zone 3: PIPs Zone T3: MP joint • Zone 4: proximal phalanx st • Zone 5: MPs Zone T4: 1 metacarpal • Zone 6: dorsum of hand Zone T5: Carpus • Zone 7: retinacular compartment • Extensor tendons Extrinsic Extensors are different from flexor tendons • EIP and EDM add • Anatomy more complex independent function, not • Restraining structures throughout system strength • More superficial, more vulnerable, thinner • ED can produce IP extension • Flexor tendons can if MPs blocked in slight become “stuck” under the flexion pulleys, but extensor tendons often heal with a lag 2° longer excursion pull Extensor Mechanism (Hood) The Extensor Apparatus . 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 Sagittal Bands •ED • Lateral band • Terminal tendon • Interossei/lumbri cal contributions to lateral band • 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 CarpoMetaCarpal Joint of Thumb • Saddle Joints • Thumb & Digit V • AKA basal • Flex/Ext (ll to palm) joint, 1st CMC • Abd/Add ( to palm) • Opposition net effect • Asymmetrical • Complex • Plane Joints ligamentous • Digits II‐IV system • Flexion/Extension MCP Joint of Thumb CMC Joint of the Thumb • A “saddle” joint • Flatter than I-S Fs MP heads • Biconcave sellar joint • Easily dislocated • 7 ligaments for CMC stabilization • 2 sesamoid bones • 16 ligaments for STT and • Greatest variation CMC joint stability in ROM: • Greatest stability in palmar abduction and pronation 30 – 90° • The hand occupies nearly 1/3 of the motor cortex Peripheral Innervation • Thumb approx ¼-1/3 of hand representation Variations in Cervical Dermatomes Cervical Dermatomes • Representation in the hand: •C6 C7 •C7 •C8 Potential Contributors to Sensation in the Thenar Eminence • Palmar cutaneous Peripheral branch of median N • Superficial branch Patterns radial N • LABC • Median