lecture 8 - equine hoof

AAEP 56th Annual Convention: Baltimore, Maryland 2010

The Equine Hoof

Dr.KathrynCarmalt,DVM,MSc,BA,AS;SlidescourtesyofDr.Anderson

UNIVERSITY OF SASKATCHEWAN Saskatoon, Saskatchewan, Canada. www.usask.ca

Hoof Function •  Traction

•  Frog, shape of hoof (concave), wall •  Shock absorption

•  Digital cushion, ability to expand at heels •  Support of skeletal column

•  Weight of horse transmitted via lamina to hoof wall •  Suspends P3

•  Protection of inner structures •  Periople protects from evaporation •  Hoof wall protects lamina

•  Venous return (peripheral pump) •  Frog, digital cushion, collateral cartilages

The Hoof as a Pump •  Muscle normally required to achieve effective

venous drainage in periphery •  No muscle in digit

•  Digital cushion functions as “pump” •  When horse bears weight digital cushion expands

and veins compressed → blood pools in venous plexus and digital cushion

•  Diastolic phase

•  When horse lifts hoof digital cushion contracts and veins open → blood forced out

•  Systolic phase

DigitalCushion DigitalCushion

P3 P3

P2 P2

Venousbloodpools Venousbloodforcedupleg

StancePhase(diastolic)

FlightPhase(systolic)

Frog

digital cushion is just a fatty blob.

digital cushion is just a fatty blob.

Outer Parts of the Hoof

Periople

Periople

Protective layer to prevent desiccationAnalogous to a cuticle

At same level as the coronary band - is the waxy layer that prevents H2O loss.

At same level as the coronary band - is the waxy layer that prevents H2O loss.

Wall

Wall

Primary weight-bearing structureProtection, force dissipation, traction

Keratinized, tubular epidermis

Toe Quarter

Wall

Bar

BarsExtension of wall

Provides additional weight bearing surfacePrevents excessive expansion � buttress

Heel

Quarter

Toehttp://www.theintellectualdevotional.com/blog/2010/02/21/the-flying-buttresses-of-notre-dame/

Heel Shock absorption → Distributes of forces

White Line

White Line

Junction between solar and laminar epidermisArea where nails are driven in on a shod horse

solar dermis = sole dermis

where you put the nails when your putting on a horse shoe.

Sole

Angle of Sole

Protects bottom of P3Bears minimal weight compared to wall (bottom of hoof is concave)

Provides traction 1/3 of sole is water

Sole

In severe laminitus the toe will break through the sole

Frog

Frog Central Sulcus

Collateral Sulci

Lies over the digital cushion → Peripheral pumpProvides traction

When walking the frog is kinda elastic - it pushes on the digital pad which then expands and allows blood to flow (downwards) and pool.

Coronary Band

CoronaryBand

Hoof wall (coronary epidermis) overlying coronary dermis

the area where the hoof is growing from - damage may f up growth of the hoof later on.

the area where the hoof is growing from - damage may f up growth of the hoof later on.

Where the hoof wall grows from

Coronet

Coronet

Junction between hoof wall (coronary epidermis) and skin (epidermis)

Hoof Growth Growth: 6-9 mm per month

May slow in winter (~3 mm per month)

1.  Keratinized coronary epidermis formed by basal epidermal cells at coronary band**TUBULAR

2.  Continuous with keratinized laminar epidermis

3.  Desmosomes detach between epidermal and dermal lamina to let coronary and laminar epidermis “ratchet” or move down

Hoof Wall Growth

Sole Growth •  Horn tubules orientated vertically •  Growth limited by curling of tubules at ground

•  Slower than wall growth

Inner Parts of the Hoof

Collateral Cartilages •  Attach to P3 •  Structural support for

heel bulbs •  Shock absorption

•  Dissipates force through their expansion

•  Involved in blood pumping action of foot

The Navicular Apparatus

Navicular disease also called caudal heel syndrome.

Navicular disease also called caudal heel syndrome.

The Navicular Bone (Aka Distal sesamoidean bone)

•  Same function as any other sesamoidean bone •  Acts as pulley

–  ↓ strain on DDFT as it changes direction to cross coffin joint –  ↓ work of DDFT to act on P3 (↑ its mechanical effect)

P3

P2

P1

NB

Collateral sesamoidean (suspensory)

ligament of the navicular bone

Impar ligament

Flexor tendon sheath

Navicular Apparatus

Navicular bursa

Navicular disease effects more than just the navicular bone - may also see changes in the soft tissue structures.

Navicular disease effects more than just the navicular bone - may also see changes in the soft tissue structures.

P1

P3

P2

Navicular bursa

Collateral sesamoidean (suspensory)

ligament of the navicular bone

Navicular bone

Impar ligament

P1

P3

P2Deep digital flexor tendon

Deep digital flexor tendonP3 insertion

Flexor tendon sheath

Coffin joint

Frog

Digital cushion

The Navicular Apparatus

P1 P1

P2 P2

P3 P3NB

NB

Impar ligament

Collateral sesamoidean (suspensory) ligament of navicular bone

Navicular bursa

Deep digital flexor tendon

FlexortendonsheathDIPjoint

Navicularbursa

Deepdigitalflexortendon

P3

P2

P1

NB

Implica(onsforwounds...

SynovialStructuresoftheFoot

Penetrating wounds

P3

Navicular bursa

Tendon sheath

P3

Navicular bursa

Tendon sheath

A

E

D

C

B

Adam’s Lameness in Horses, 6 ed

The Inner Hoof Perioplic dermis (microscopic) supplies

•  Periople epidermis = Stratum externum

Periople

waxiness protects from water los

waxiness protects from water los

Coronary dermisSupplies keratinized coronary epidermis that forms tubule and intertubule horn

Laminar dermisSupplies laminar epidermis

Dermal Layers

Laminar epidermis(Stratum internum)

Coronary epidermis(Stratum medium)

Coronary groove (sulcus)Coronary band Epidermal Layers

inner hoof detached from P3

inner hoof detached from P3

Suspension of P3

Suspension of P3 •  Laminar dermis interdigitates & supplies laminar epidermis

P3

Frog

Hoof Wall

AKA stratum internum

The Suspensory Apparatus of the Distal Phalanx

Vet Clin North Am Equine Pract. 2010 Apr;26(1):29-49.

Lamellar Structure & Function

•  The lamellar junction is comprised of an interlocking dermis & epidermis •  Provides nutrition •  Energy transfer • ñ Surface area

Epidermal lamellae lock together - in laminitis the normal morphology is lost and lose connection b/w P3 and the hoof.

Epidermal lamellae lock together - in laminitis the normal morphology is lost and lose connection b/w P3 and the hoof.

Disease

•  Loss of normal morphology has a number of negative outcomes •  Loss of structural

stability è increases risk of further future dissolution of support apparatus

What happens if the suspensory apparatus fails?

DDFT

If you pinch the toe and theres pain there might be laminitis. If you do palmar digital flexor it blocks the caudal part, but not the toe and there is pain it might be laminitis.No more connection to hoofwall = the P3 may sink down, or rotate or both and can come out of the bottom of the foot (through the sole). DDFT pulls on P3 causes it to rotate downwards and increase the angle between P3 and the hoof wall.


DDFT

Rotating


Sinking

Blood & Nerve Supply •  Medial/Lateral Palmar/Plantar Digital

•  Vein, Artery, Nerve

•  Vessels enter on palmar/plantar aspect of P3 •  Arteries though foramen in P3 •  Venous drainage primarily along dorsal border of P3

•  Extensive branching •  Venous plexuses

Arterial supply to the hoof

Venous supply to the hoof

Inject dye into vessel and see how extensive the branching to the hoof is.

Inject dye into vessel and see how extensive the branching to the hoof is.

Palmar/PlantarView DorsalView

TerminalArch

Vesselstodigitalcushion

Solarvenousplexus

Arteriessupplying

lamina&P3

Coronaryvessels

DorsalvenousplexusCircumflexartery

Coronaryvenousplexus

Will show up on radiographs

Will show up on radiographs

lecture 8 - equine hoof

Health & Medicine