Comparative anatomy of the equine hock and distal hindlimb

What arteries supply the equine hindlimb?

cranial and caudal tibial

What vein is large and palpable in equine?

medial saphenous

red

tibial nerve

blue

deep fibular (peroneal) nerve

Where do the dorsal metatarsal nerves run?

medial & lateral to extensor tendons

What nerve provides the majority of sensory innervation to the distal limb?

tibial nerve

What does the deep fibular (peroneal) nerve branch into?

dorsal metatarsal nerves

What does the tibial nerve branch into?

• plantar nerves

• plantar metatarsal nerves

In the hindlimb, what do muscles caudal to the distal limb tend to do?

• flex stifle

• extend hock

• flex digit

What are the 4 levels of the tarsal joint?

• tarsocrural

• proximal intertarsal 

• distal intertarsal

• tarsometatarsal

What levels of the equine tarsal joint communicate?

capsule for TC & PIT

Which levels of the equine tarsal joint occasionally communicate?

DIT & TMT

What ligaments support the tarsus?

• collateral ligaments

• long plantar ligament

red

medial collateral ligament

green

lateral collateral ligament 

blue

long plantar ligament 

What is the role of the collateral ligaments?

ensure joint doesn’t move side to side

What is the role of the long plantar ligament?

resist hyperextension of foot and digit

Where are the hock flexors located?

cranial to hock joint

What hock flexor do equine species NOT have?

fibularis longus

Name the equine hock flexors

• fibularis (peroneus) tertius

• cranial tibial

• long digital extensors

• lateral digital extensors

green

fibularis (peroneus) tertius

blue

cranial tibial

What does fibularis (peroneus) tertius have a shared origin with?

long digital extensor

What nerve innervates fibularis (peroneus) tertius and cranial tibial?

fibular (peroneal) nerve

1 (red)

long digital extensor

2 (green)

lateral collateral ligament of stifle

3 (purple)

lateral digital extensor

Where do extensor tendons fuse?

mid-metatarsus

What nerve innervates the long and lateral digital extensors?

fibular (peroneal) nerve

1 (blue)

gastrocnemius

2 (purple)

superficial digital flexor

3 (green)

deep digital flexor

Name the 3 hock extensors

• gastrocnemius

• superficial digital flexor

• deep digital flexor

Where is the origin and insertion of gastrocnemius?

origin = femur

insertion = calcaneus

What is the origin and insertion of superficial digital flexor?

origin = femur

insertion = calcaneus & P1&P2

What is the origin & insertion of deep digital flexor?

origin = tibia

insertion = P3

How many bellies does deep digital flexor originate as?

3

1

cranial tibial

2

long digital extensor

3

lateral digital extensor

4

biceps femoris

5

common calcaneal tendon

6

deep digital flexor

What do the hip, stifle & hock all tend to do with weight bearing?

flex

What does the passive stay apparatus do?

prevents the hip, stifle & hock from flexing with weight bearing

What does the hindlimb passive stay apparatus comprise of?

• patella locking mechanism

• reciprocal apparatus proximally

• plantar support structures

How is the SDF involved in the stay apparatus?

flexion of hock limited by proximal portion of SDF when stifle locked

What affect does the SDF rupturing have?

hock can flex even with locked stifle - problem for weightbearing

What happens when the fibularis (peroneus) tertius ruptures?

can extend hock despite stifle remaining flexed (DOES NOT AFFECT WEIGHTBEARING)

What is the role of the long plantar ligament?

resist hyperextension of the foot and digit

1

tarsal flexor sheath

2

DDFT

3

SDFT

4

calcaneal bursa

What is the DDFT in?

tarsal sheath (runs in sustentacular groove of talus)

What can swelling of the DDFT in tarsal sheath be confused with?

tarsocrural compartment (between tibia and tarsus)

What protects the SDFT?

calcaneal bursa

What does the calcaneal bursa do?

protect SDFT as it runs over calcaneus

What is the function of the SDFT attachment to calcaneus?

• reciprocal apparatus function

• some check-ligament-like function

1

CDE/LatDE

2

interosseous (suspensory ligament)

3

extensor branches of interosseous

4

oblique sesamoidean ligaments

5

straight sesamoidean ligament

6

palmar ligaments of the pastern

What are the species differences to consider in the bovine hindlimb?

• less covering over rump (no vertebral heads of hamstrings)

• fibularis (peroneus) tertius more muscular/fleshy than horse

• has fibularis (peroneus) longus

What are the features of the bovine distal limb?

• metapodials III & IV fused

• fetlock joint duplicated

What are the extensor tendons in the bovine distal limb?

• common/long digital extensor (2 bellies - lateral=both digits, medial=medial digit)

• lateral digital extensor (goes to lateral digit)

Why is the bovine foot clinically relevant?

• claw amputation

• salvage surgery

• understanding neurovascular arrangement of foot to apply local anaesthetic for surgery

1

median nerve 

2

palmar common digital

3

ulnar nerve

4

dorsal branch of ulnar

5

palmar branch of ulnar

6

axial palmar digit (IV)

7

dorsal axial digital (IV)

8

superficial branch of radial

9

dorsal common digital

What do the fibular (peroneal) nerves (deep & superficial) supply?

dorsal surface of both claws

What does the tibial nerve supply?

plantar surfaces

What nerves are there once on the digits?

nerves at each of the 4 aspects of the digits (axial, abaxial, plantar & dorsal digital nerves)

What veins drain the bovine foot?

• palmar

• plantar

• lateral saphenous

What do the palmar and plantar veins run with?

flexor tendons

Why is the ovine foot clinically relevant?

digital dermatitis (e.g. scald, footrot)

What does this image show?

porcine foot