Lame - Foot pathology

Question 1

What are some diseases that can cause laminitis in horses?

Answer 1

Equine pituitary pars intermedia dysfunction
Equine metabolic syndrome
Endotoxaemia
Colic
Hormonal dysfunction

Question 2

What are the predisposing conditions for laminitis usually associated with?

Answer 2

Systemic inflammation
Vascular compromise
Hormonal imbalance

Question 3

What is the pathogenesis of laminitis?

Answer 3

Unknown
Thought to be to do with reduction in laminar capillary perfusion
Shunting blood increasing hydrostatic pressure and causing laminar oedema
Increase inflammatory cells embolising in laminar vessels
Dermal-epidermal junction breaks down

Question 4

What does break down of the dermal-epidermal junction and inflammation of the laminae cause in laminitis?

Answer 4

Rotation of the third phalanx ventrally towards the sole

Question 5

What is navicular syndrome?

Answer 5

A common degenerative disorder of the distal sesamoid - navicular bone

Question 6

What limbs are most often affected by navicular syndrome?

Answer 6

Forelimbs - usually bilateral

Question 7

What is thought to be contributing factors to navicular disease?

Answer 7

The shape of the navicular bone and the angle of the hoof
The pathogenesis is not completely understood however

Question 8

What is found between the navicular bone and the deep digital flexor tendon?

Answer 8

Navicular bursa - synovial joint-like space lined with synoviocytes

Question 9

What is thought to occur in navicular syndrome?

Answer 9

The deep digital flexor tendon compresses the navicular bone when pushing off the ground
This leads to abnormal wear and tear
Causes loss of cartilage and subchondral bone
Granulation tissue, fibrosis and osteophytes form
Damage to the deep digital flexor tendon

Question 10

What is foul in the foot/foot rot?

Answer 10

Infectious bacterial disease of the interdigital skin of the bovine feet

Question 11

Is foul in the foot contagious? What causes it?

Answer 11

No - more due to poor sanitation and recent calving
Previous injury to the skin allows infiltration of bacteria

Question 12

What is the primary pathogen of foul in the foot/fot rot?

Answer 12

Fusobacterium necrophorum

Question 13

What are two other bacteria that can accompany fusobacterium in foul in the foot/foot rot?

Answer 13

Porphyromonas and prevotella
Other bacteria can also infect too

Question 14

What does each bacteria do to cause foot rot?

Answer 14

Fusobacterium cause tissue necrosis
Porphyromonas delays immune response
Prevotella forms biofilm to protect other bacteria

Question 15

What are the steps of foot rot?

Answer 15

Skin abrasion allows fusobacterium in
Hyperaemia and swelling occur
Tissue necrosis
Fissures form
Secondary invasion and abcess formation
Infection spreads to deeper structures - sepsis

Question 16

What are common complications of foot rot?

Answer 16

Septic arthriitis of distal interphalangeal joint
Navicular bursitis
Osteomyelitis

Question 17

What disease is similar to foot rot?

Answer 17

Digital dermatitis

Question 18

Is digital dermatitis contagious?

Answer 18

Yes

Question 19

Where are digital dermatitis lesions usually found?

Answer 19

On the plantar surface of the hind foot in dairy cows

Question 20

What causes digital dermatitis?

Answer 20

Constant exposure to manure and urine in unhygienic environments

Question 21

What bacteria cause digital dermatitis?

Answer 21

Treponema
Then fusobacterium, dichelobacter

Question 22

What happens in digital dermatitis?

Answer 22

Constant exposure to manure and urine
Structural breakdown and dermatitis at skin-horn junction
Treponema invade
Neutrophils are recruited which cause keratinocytes to proliferate and slough
Skin ulcerates and proliferates with mass like projections along coronary band which easily bleed

Question 23

Where do sole ulcers most commonly affect?

Answer 23

The lateral claw of the rear hoof

Question 24

What are the predisposing causes of sole ulcers?

Answer 24

Housing
Nurtrition
Foot trimming
Genetic conformational problems

Question 25

What tends to cause sole ulcers to occur?

Answer 25

Mechanical injury to the corium secondary to weakened suspensory ligaments
Third phalanx sinking and compressing digital cushion

Question 26

What causes weakened suspensory ligaments?

Answer 26

Pregnancy hormone related - cortisol, relaxin, oestrogen and prolactin

Question 27

What causes heel sole ulcers?

Answer 27

Overgrowth of the outer claws in the hind limbs

Question 28

What are the stages of heel sole ulcer formation?

Answer 28

Accelerated growth at the heel of the lateral claw
Cow puts weight on medial claw
Horn overgrowth at digital space
Concussion of corium
Ulcer forms

Question 29

What predisposes to white line disease?

Answer 29

Diseases that disrupt blood flow to corium
So weakened defective horn is produced
Foreign material can separate white line mroe easily

Question 30

What are the consequences of a foreign object in the white line?

Answer 30

Bacteria colonise the white line horn and destroy it
Infection reaches corium and abcess forms
Abcess might drain out, or may cause infection of deeper structures