Canine and Ruminant Feet (Week 2, Mod 7)

Describe the distal phalanx of the carnivore… what are the 4 main components?

1) Ungual Process - supports claw

2) Ungual Crest - vascular root of claw

3) Extensor Process - extensor tendon insertion point

4) Palmar Process - flexor tendon insertion point

Describe the digital pads of the canine foot… what do they look like, and how are they placed in relation to the skeleton?

Digital pads (n=4):

• overlies DIP (distal interphalangeal) joint

Metacarpal / metatarsal pad (n=1): 

• heart shaped 

• overlies MCP / MTP  joints

Carpal / stopper pad (n=1):

• Forelimb only 

• Protects accessory carpal bone when hyper-extended during a hard break 

What are some functions of the digital footpad? Think of a few… how do they protect the metocarpo/metatarso joints in particular?

Functions of footpads:

• Allow weightbearing over entire digit 

• Support digit & metacarpo / metatarso-phalangeal joints

• Protect deep structures

• Anti-concussion / shock absorption

• Resistance to trauma / wear & tear

• Traction – prevent slipping

Metacarpo/metatarso - phalangeal joint support

• Interosseus muscle for each digit

  • (cf suspensory ligament in horse) 

• Support from metacarpal / metatarsal foot pad

Describe the epithelium of the foot pad… how is it modified for its function?

Epidermis

• Keratinised stratified squamous epithelium 

  • Thick for protection 

  • Maintained by increased turnover of cells

  • Rough surface (conical papillae) for traction

• Sweat glands

  • heat loss for thermal regulation… can only do that via sweating from paw pads or panting

• Variable amounts pigmentation

NO BLOOD OR NERVE SUPPLY TO THE EPIDERMIS

Describe the contents of the digital cushion… what would happen if this gets cut? 

Contains:

• Fibrous and elastic tissue

• Fat

• Vascular channels

  • Is HIGHLY vascularized; acts as a sponge

• Function: Shock absorption

Clinical significance:

• Would be VERY messy and bloody

• Since its made of elastic tissue, would need some suturing

• Keep in mind when bandaging feet, paw pads have sweat glands, so need extra padding for the sweat and need to change bandage often 

What are the 3 main components of the carnivore claw?  Describe its structure

1) Dermis

• Fused to the PERIOSTEUM of the ungual process

• Sensitive; bleeds

2) Germinative layer

• Active in 2 areas of the claw (red dotted lines on image)

• Recess at ungual crest

  • Forms the dorsal and lateral surfaces of the claw

• Palmar surface of ungual process

  • Forms the UNDERSIDE of claw

• This is how the claw grows

3) Epidermis

• Heavily keratinized (horn ± pigment)

How does the canine claw remain in one stabilized position?

Is a balance of forces between the dorsal elastic ligaments (pink), common digital extensor, and the deep digital flexor tendon

• Allows the tip of the claw to touch the ground, keeping it from either hyperextension or hyperflexion 

How does the feline claw RETRACT? (essentially, what ligaments are at play here?)

To be retracted:

• Has a VERY strong dorsal elastic ligament, keeps the claws in its “neutral position” (= distal interphalangeal joint hyperEXTENSION)

• Distal phalanges rotate dorsally

To be exposed:

• Deep digital flexor tendon FLEXES the DIP

Describe the overall structure of the ruminant foot… How is it different from the carnivore, starting at the metacarpals.

The two metacarpals they have are metacarpals 3 and 4

• Are FUSED TOGETHER; looks like a mega-cannon bone of a horse

• At the distal end, has grooves where the proximal phalanges would fit… are also for 2 pairs of proximal sesamoids

Digits 3 & 4:

• All bones present

• Weight bearing

• 2 x proximal interphangeal joint 

• 2 x distal interphalangeal joint

• 2 x distal sesamoid bones

** Digits 2 and 5…

• Present as dewclaws / little hooves on the palmar aspect of the metacarpo/metatarso-phalangeal joint

• 1st digit is absent

Describe the overall visible components of the ruminant hoof…

Components:

• Cloven hoof

  • Medial and lateral claws

  • Interdigital cleft

• Sole 

• Heel 

• Wall:

  • Lateral - convex 

    • Continuous with heel

  • Medial - vertical 

    • Stops at parapedal groove (about 2/3s down the digit; on the inside)

    • Transition hard to soft horn = prone to damage

• White line - between the hoof wall and the sole 

Describe ruminant hoof growth (may need to look at equine hoof notecards for better explanation)

• Starts from the coronary band

  • Only distal part of dermis covered by laminae

• Sensitive laminae

• Insensitive laminae

• Primary laminae ONLY

• No secondary

What are 4 clinical issues that could occur to the ruminant hoof?

1) Horn overgrowth: 

• Due to soft ground

• FL = inner claw overgrowth

• HL = outer claw overgrowth

2) Solar ulcers: 

• especially at parapedal groove

• Due to abrasive flooring

3) Interdigital dermatitis

4) Secondary infection 

• can track up DDFT sheath