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2010-11-16 12:55:01

Horse Forelimb anatomy
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  1. Equine forelimb (general)
    • Uguligrade (hoof/horn)
    • perissodactyla (uneven number of digits)
    • weight bearing distal phalanx of 3rd digit
    • (same bones, joints, muscles as dog)
    • manus expanded (DONT confuse with antebrachium- proportions are different!!!)
  2. Biceps brachii muscle
    • Origin: supraglenoid tubercle (seperate from glenoid cavity)
    • double tendon of origin (humerus- intermediate tubercle, two intertubercular grooves)
    • Bicipital bursa: separate from shoulder joint capsule
    • Transverse ligament
    • Inserts: proximal radius (extend shoulder/flexes elbow)
    • lacertus fibrosis: fibrous extension, joins extensor carpi radialis, inserts proximal MC3, maintains shoulder and carpus in extension (part of STAY APPARATUS)
  3. Elbow joint
    • Radius and ulna fused (no rotation, no annular ligament)
    • Bursa: fluid filled cushion, protection of tendons
    • Subcutaneous burse: between skin and tendon
    • Tricipital bursa: between tendon and olecranon process
    • CLINICAL SIG: capped elbow- poor bedding, deeper swelling- trye bursitis
  4. Carpus
    • Carpal bones: all present except 1st CB (may be vestigial)
    • 3rd carpal bone is the larges
    • Movement:
    • most at antebrachio-carpal joint
    • least carpometacarpal joint
    • collecting joint fluid samples
    • SYNOVIAL JOINT: separate compartments
    • SUPPORT: collateral ligaments, palmar fibrocarilagenous plate (origin of check ligament for DDFT), palmar ligament, retinaculum (bandage like/sleeve)
    • CARPAL CANAL: palmar fibrocartilagenous plate, palmar/flexor retinaculum, ABC
    • (dog: DDFT ONLY) Horse: DDFT and SDFT (design flaw!)
  5. Tendon sheath
    • Protects tendon in confined spaces
    • dorsal aspect: surrounds extensor tendons
    • carpal canal: 1 Sheath for both DDFT and SDFT
    • inflammation- increased pressure
    • thoroughpin- bulges proximally and distally
    • "like a water snake"
  6. Clinical consideration (carpus)
    • "broken knees"
    • skin
    • dorsal/extensor retinaculum
    • tendon sheath
    • extensor tendons
    • joint capsule
    • penetration into joint space most likely if flexed during trauma
  7. Metacarpal bones
    • 3rd MC = cannon bone
    • weight bearing, distal articular surface (sagittal ridge)
    • 2nd and 4th MC bones: splint bones, vestigial (non-weight bearing), button at distal end- palpable
    • between MC's: fibrous joints (syndesmosis) mineralised as age, splints
  8. Phalanges
    • proximal phalanx: long pastern bone, raised 'V' on palmar surface, attachment oblique distal sesamoidean ligament
    • middle phalanx: short pastern bone
    • bony lumps: attachment collateral ligaments, ringbone
  9. distal phalanx
    • "pedal/coffin bone"
    • complex shape
    • estensor process: attachment common digital extensor tendon
    • palmar processes: support lateral cartilages
    • solar surface: attachment deep digital flexor tendon
    • dorsal surface: striations: hoof attachments, blood vessels, vascular channel (versus nutrient foramen)
  10. Manus- bone development
    • (same as dog)
    • MC 3: Body and (2) distal epiphysis
    • MC 2 & 4: proximal ephihysis and (2) body
    • PP: proximal epiphysis and body (2)
    • MP: proximal epiphysis and body (2)
    • DP: body (1)
  11. Proximal sesamoids
    • Triangular shaped
    • distal end MC3
    • Either side of sagittal ridge
    • embedded in suspensory ligament
    • protect SDFT and DDFT
    • NO dorsal sesamoid
  12. Distal sesamoid
    • (NOT in the dog)
    • 2 flat articular surfaces
    • covered w/ hyaline cartilage
    • cancellous centre
    • vascular channels
    • located palmer aspect DIP joint
    • Dorsal surface: articulates wth MP and DP
    • Palmar surface: guides DDFT over DIP joint
    • under large amount of pressure
  13. Clinical consideration (navicular bone)
    • navicular disease syndrome:
    • erodes w/ age
    • bone dissolves- visable on radiographs
    • poor correlation between clinical signs and radiographic changes (black hole/lines show changes on Radiographs)
  14. Metacarpo- phalangeal joint
    • (MCP) "fetlock"
    • MC3 and PP
    • synovial joint
    • extensive joint capsule
    • large dorsal pouch: protects extensor tendons
    • large palmar pouch: incorporates proximal sesamoids
    • NO dorsal sesamoid
    • Natural position = extension
    • limited to flexion and extension (sagittal ridge distal MC3, sagittal grrove proximal PP, collateral ligament: MC-PP)
    • Tendency to collapse into hyperextension (supensory ligament, sesamoidean ligaments)
  15. Suspensory ligament
    • entirely ligamentous
    • origin: proximal palmar MC3, fills area between splint bones
    • Brances:
    • abaxial aspect proximal sesamoids
    • passes to dorsal aspect
    • fuses w/ common digital extensor tendon
    • FUNCTION: prevent collapse of MCP joint during weight bearing, return MCP from hyperextension to normal extended position, relies on stability of proximal sesamoid bones
  16. Sesamoidean ligaments (inter and collateral)
    • Inter-sesamoidean ligamen:
    • reinforced fibrocartilage
    • proximal scutum (sheild)
    • passage of DDFT and SDFT over sesamoids
    • Collateral sesamoidean ligaments:
    • proximal sesamoids- MC and PP
  17. Sesamoidean ligaments (distal)
    • 4 total
    • cruciate and short: (very deep)
    • proximal sesamoids- PP
    • Oblique ligament: (deep)
    • proximal sesamoids- PP, V shaped trough on PP
    • Straight ligaments: proximal sesamoids-MP, inserts w/ SDFT
  18. MCP joint
    • function relies on interaction between:
    • suspensory ligaments
    • proximal sesmoids
    • sesamoidean ligaments
    • common digital extensor tendon
  19. Clinical considerations (sesamoids)
    • ruptured distal sesamoidean ligament (hyperextention)
    • fractured proximal sesamoid bones
  20. Superficial structures (horse)
    • Chestnut:
    • vestigial horn pad- 1st metacarpal bone
    • Ergot:
    • horny lumb in skin
    • palmar aspect MCP joint
    • hidden by "feathers"
    • remnant of metacarpal pad
    • (not clinically relavent)
  21. Proximal interphalangeal joint
    • (PIP) Pastern Joint
    • limited to flexion and extension
    • distal PP- sagittal groove
    • proximal MP- sagittal ridge
    • collateral ligaments: PP- MP
    • extension runs to navicular bone
  22. Distal interphalangeal joint
    • (DIP) Coffin joint- burried w/in hoof
    • components:
    • MP and DP
    • Distal sesamoid and DP
    • distal sesamoid MP
    • extensive joint capsule: forms bursa, protects extensor tendon, accessible for injection
    • Flexion and extension: sagittal ridge and groove (broad so some rotation possible to accomodate uneven groud)
    • collateral ligaments (MP-DP)
    • movement: common digital extensor tendon, deep digital flexor tendon
    • NO dorsal elastic ligament in horse!! (like cats)
  23. Distal sesamoid
    • ligaments of distal sesamoid:
    • collateral ligament: PP-distal sesamoid
    • impar ligament: DP-distal sesamoid
    • Navicular/podotrochlear bursa:
    • fluid filled pocket
    • located between sesamoid and DDFT
    • separated from DIP joint by impar ligament
    • protects DDFT
  24. Lateral/Ungual cartilages
    • Cartilage plates
    • palmar processes DP
    • medial and Lateral
    • project above level of Hoof
    • shock absorption
    • cartilage not visible, mieralise as age, sidebone
  25. Extesor tendons
    • below carpus = fibrous tissue only!!!
    • muscle bellies in antebrachium
    • Common digital extensor:
    • Crosses dorsal aspect carpus
    • joined by 2 branches of suspensor ligament
    • inserts PP, MP, and DP
    • Lateral digital extensor:
    • Inserts PP
    • separate from CDE
  26. Flexor Tendons
    • Superficial digital flexor tendon:
    • Accessory check ligament: originates proximal to carpal canal
    • passes through carpal canal
    • splits to let DDFT pass through
    • inserts MP
    • Deep digital flexor tendon:
    • passes through carpal canal
    • accessory check ligament: originates from fibrocartilage plate on palmar aspect of carpus, fuses with DDFT
    • passes through split in SDFT
    • runs over navicular burse/navicular bone
    • inserts DP
  27. Metacarpal region
    • dorsal aspect = extensor tendons
    • palmar aspect:
    • SKIN
    • SDFT
    • DDFT
    • Check ligament (fuses with DDFT)
    • suspensory ligament (splits into 2 bances)
    • (clinical relavence- trauma, U/S exam)
  28. Ultrasound examination!!
    • Long axis/axial plane/sagittal plane through limb
    • SDFT
    • DDFT
    • Check ligament
    • Suspensory ligament
    • (ultrasound: bone=white, soft tissue=grey, fluid=black)
    • (KNOW ORDER!!!)
  29. Digital region
    • Scutum= cartilage sheild
    • palmar aspect joints
    • MCP joint= intersesamoidean ligament
    • smooth passage for tendons
    • Annular ligaments: hold DDFT and SDFT against bone
    • Tendon Sheath: shared by SDFT and DDFT, extends from annular ligament distally- inflammation= increased pressure
  30. Clinical Consideration (bony swellings)
    • bony swellings: splints
    • soft swellings:
    • articular(joint):
    • located between suspensory ligament and MC3
    • Tendon sheath: located palmar to suspensory ligament and proximal to annular ligament
  31. Stay apparatus
    • most weight borne on forlimb
    • mechanism for passive weight bearing
    • Serratus ventralis: suspends weight of body between forelimbs
    • maintenace of extention/prevention of flexion:
    • shoulder: biceps brachii
    • Elbow: collateral ligaments, alignment of bones
    • carpus: lacertus fibrousis
    • carpus: palmar fibrocartilage joint reinforcement, SDFT and check ligaments, retinculum
    • MCP joint: suspensory ligament (common digital extensor, proximal sesamoids, distal sesamoidean ligaments)
    • MCP, PIP, and DIP joints:
    • prevention of hyperextension (DDFT and SDFT/check ligaments), annular ligaments (bind them to palmar aspect of digit)
  32. Blood supply
    • Arterial supply- similar to dog
    • brachial artery: medial aspect elbow, palpable pulse
    • medial and lateral digital arteries: abaxial aspect proximal sesamoids, palpable pulse
    • venous drainage: similar to dog- no clinical relavance
  33. Nerve supply
    • Brachial plexus:
    • same as dog
    • same motor function as dog
    • different sensory areas
    • Nerve damage uncommon:
    • suprascapular nerve: runs around neck of scapula
    • supplies: supraspinatous, infraspinatous, NO cutaneous sensation
    • damage causes joint instability
  34. Median and Unlar nerves
    • above carpus- separate
    • below carpus- intertwined
    • Branches:
    • 1) palmar metacarpal nerves: medial and lateral, run between MC3 and splint bones, emerge at distal end of splint bones, suppy dorsal aspect of digit
    • 2) palmar nerves: medial and lateral, between suspensory ligament and SDFT, cross abaxial aspect proximal sesamoids
    • become: palmar digital nerves (dorsal and palmar branches, supplies hoof contents)
  35. Clinical considerations (nerve blocks)
    • routinely used in equine practice to help localise area of lameness
    • predictable locations
    • inject local anaesthetic
    • desensitise structures supplied by nerve
    • Palmar digital nerve block: palmar digital nerves, run adjacent to digital arteries, 1cm above coronary and, 2/3 wway back, medial and lateral injections, blocks caudal 1/2 foot (includes navicular bone/distal sesamoids)
    • abaxial sesamoid nerve block: palmar digital nerves and dorsal branches, run adjacent to digital arteries, abaxial aspect sesamoids, medial and lateral injections, blocks entire foot
    • Palmar metacarpal nerve block ('4 point block'): palmar nerves (between suspensory and flexors) palmar metacarpal nerves distal end splint bones (2 cm proximal to sesamoids), medial and lateral injections, blocks entire digit

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