Lecture 1: Equine Musculoskeletal Anatomy and Conformation

what plane is this?

sagittal

ideal conformation and posture

• supports optimal limb loading and movement patterns

• reduces the risk for musculoskeletal injuries

conformational faults

• are not synchronous with lameness but often contribute to altered limb loading and movement

• increased risk for musculoskeletal injuries

altered posture

• often a sign of musculoskeletal pain (antalgic stance)

• or neurologic disease → ataxia, weakness

conformational features include

size, shape, height, angles, contours, transitions, relative proportions, left-right symmetry, muscle development, breed standards

ideal conformation provides

• a broad base of support

• equal weight bearing across all limbs

why is conformation important?

form affects function

function affects form due to

changes in structure → left-right hoof asymmetries, heel height asymmetries, hoof landing, medial-lateral hoof wall imbalance

what is conformation?

• the symmetry, size, and shape of various body regions relative to each other or in general appearance

• structure is not easily changed

what is posture?

• the position in which someone holds their body when standing or sitting

• function can be modified or trained

altered posture is often due to

pain, weakness, neurologic deficits

altered posture includes

laminitic stance, unweighted limb, ataxia, severe weakness

conformational faults of the forelimb

• induces altered limb loading

• fetlock osteoarthritis, splint bone disease

what are these pictures showing?

conformational faults of the forelimb

conformational faults of the forelimb associated with splint bone disease

fetlock osteoarthritis

what are these showing?

fetlock osteoarthritis

is this conformational or posture?

conformational

is this conformational or posture?

conformational

is this conformational or posture?

posture

is this conformational or posture?

conformational

is this conformational or posture?

conformational

toed in limb conformation =

paddling

toed out limb conformation =

interference with contralateral limb

what are these showing?

conformational flaws of the hind limb

conformational faults of the digit are due to

hoof-pastern angle

ideal hoof-pastern angle

• supports limb loading

• proper movement

upright pastern angle

• short stride length

• prone to navicular disease and pastern osteoarthritis

sloping pastern angle

• longer stride length

• prone to soft tissue injuries → suspensory ligament injury

the equine limb primarily bears weight on

a single functional digit

long- lightweight distal segments of the equine limb reduce

limb inertia and the muscular effort required during locomotion

long flexor tendons function as

elastic springs

digital tendon sheaths and synovial bursae reduce

friction where tendons pass over joints and bony prominences

stay apparatus allows

prolonged standing with minimal muscular effort

fetlock is supported by

the proximal sesamoid bones and the suspensory apparatus

the carpus includes

radiocarpal joint, midcarpal joint, and carpometacarpal joint

what is D?

radiocarpal joint

what is E?

midcarpal joint

what is F?

carpometacarpal joint

fetlock joint =

metacarpophalangeal joint

what is G?

fetlock aka metacarpophalangeal joint

pastern joint =

proximal interphalangeal joint

what is H?

pastern aka proximal interphalangeal joint

coffin joint =

distal interphalangeal joint

what is I?

coffin aka distal interphalangeal joint

carpal articulations

• distal radius → radiocarpal joint

• proximal row of carpal bones → midcarpal joint

• distal row of carpal bones → carpometacarpal joint

• metacarpus

distal forelimb

• third metacarpal bone → 2nd and 4th metacarpal bones (splint bones)

• fetlock joint → proximal sesamoid bones

• pastern joint

• coffin joint → distal sesamoid bone (navicular bone)

what is 1?

proximal phalanx

what is 2?

middle phalanx

what is 3?

distal phalanx (coffin bone)

what tendon is light blue?

common digital extensor tendon (long digital extensor tendon in pelvic limb)

what is in yellow?

suspensory ligament → body, medial and lateral branches, extensor branches

what tendon is in red?

deep digital flexor tendon

what is in green?

distal accessory (check) ligament

what is in dark blue?

superficial digital flexor tendon

what is A?

common digital extensor tendon

what is B?

lateral digital extensor tendon

what is 4?

interosseus (suspensory) ligament

what is 4’?

medial and lateral branches of interosseus ligament

what is 1?

superficial digital flexor tendon

what is 2?

deep digital flexor tendon

what is 3?

distal accessory (check) ligament

what is D?

interosseus ligament

what is G?

SDFT

what is F?

DDFT

what is F’?

check ligament

what is 4?

digital tendon sheath

what is 1 and 1’?

dorsal and palmar pouches of fetlock joint

what is 2 and 2’?

dorsal and palmar pouches of the pastern joint

what is 3 and 3’?

dorsal and palmar pouches of the coffin joint

what is 5?

navicular bursa

digital annular ligaments

• palmar annular ligament

• proximal annular ligament

• distal digital annular ligament

digital tendon sheath

• surrounds the SDFT and DDFT

• extends from mid-cannon to mid-P2

what is A?

palmar annular ligament

what is B?

proximal digital annular ligament

what is C?

distal digital annular ligament

what is 9?

SDFT

what is 11?

DDFT

what is 13?

interosseus ligament

what is 15?

extensor branches of interosseus ligament

what is 12?

common digital extensor tendon of interosseus ligament

what is 18?

straight distal sesamoidean ligaments

what is 17?

oblique distal sesamoidean ligaments

what is 16?

cruciate distal sesamoidean ligaments

what is C?

patellofemoral joint of stifle

what is D?

femorotibial joint of stifle

what is E?

tibiotarsal joint of tarsus

what is F?

proximal intertarsal joint of tarsus

what is G?

distal intertarsal joint of tarsus

what is H?

tarsometatarsal joint of tarsus

patellar ligaments of stifle

• medial → patellar fibrocartilage, medial trochlear ridge

• intermediate (middle)

• lateral

stifle joint

• patellar ligaments

• patellofemoral ligaments

• collateral ligaments

• cruciate ligaments

• menisci

tarsal articulations

• distal tibia → tarsocrural (tibiotarsal) joint → cochlea of distal tibia, trochlea of talus

• proximal row of tarsal bones → proximal intertarsal joint

• intermediate row of tarsal bones → distal intertarsal joint

• distal row of tarsal bones → tarsometatarsal joint

• metatarsus

forelimb arteries

• axillary → subscapular

• brachial → transverse cubital, collateral ulnar, common interosseus

• median

• medial palmar

• palmar digital

thoracic limb innervation

• subscapular

• idk