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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!!!)
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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)
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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
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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!)
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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"
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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
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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
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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
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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)
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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)
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Proximal sesamoids
- Triangular shaped
- distal end MC3
- Either side of sagittal ridge
- embedded in suspensory ligament
- protect SDFT and DDFT
- NO dorsal sesamoid
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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
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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)
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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)
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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
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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
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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
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MCP joint
- function relies on interaction between:
- suspensory ligaments
- proximal sesmoids
- sesamoidean ligaments
- common digital extensor tendon
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Clinical considerations (sesamoids)
- ruptured distal sesamoidean ligament (hyperextention)
- fractured proximal sesamoid bones
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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)
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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
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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)
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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
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Lateral/Ungual cartilages
- Cartilage plates
- palmar processes DP
- medial and Lateral
- project above level of Hoof
- shock absorption
- RADIOGRAPHY:
- cartilage not visible, mieralise as age, sidebone
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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
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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
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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)
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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!!!)
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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
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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
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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
- PREVENTION OF HYPEREXTENSION:
- 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)
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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
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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
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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)
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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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