Distal Limb

Define the terms:

• Papillae

• Lamellae

• Corium

• Dermis

• Epidermis

Papillae: microscopic, finger-like projections extending from the dermis to the epidermis

Lamellae: folds of tissue which interlock, to suspend the inner coffin bone to the outer hoof wall

Corium: sensitive layer of tissue between the hoof capsule and the internal bones of the foot

Dermis: as above
Epidermis: the outermost protective layer of tissue, forming the hard hoof capsule

Draw out the structure of the equine distal limb

Label the following diagram

Describe the blood supply and venous drainage of the hoof

Supplied by: digital arteries (medial and lateral)

These run within the neurovascular bundles on the palmar/plantar aspects of the distal limb

Venous drainage

• The veins run along with the arteries: they are ‘satellite’

• There are many venous plexuses around the foot (no valves in these plexuses)

• Horses need to be able to move around in order to get the venous blood moving back up the limbs

Draw a diagram to show the blood supply and venous drainage of the hoof

Draw a diagram to show the different structures in a longitudinal cross-section of the hoof

What is the hoof dermis?

Dermis: squidgy, living tissue

• Nerves (it has pain sensation)

• Blood vessels (it can bleed and become inflamed)

• Attached to P3

What is the hoof epidermis?

Epidermis: not squidgy 

• Thin layer of cells that produce and support the horn 

• Mostly dead horn

What can be found between the epidermis and dermis of the hoof?

Between the epidermis and the dermis, there is a basement membrane

Describe laminitis

• Can be caused by a number of issues

• Failure of adhesion of cells to the basement membrane 

• This results in detachment and mechanical deformation of the dermal-epidermal junction

• If this is not managed, this causes rotation of P3

• This is a very painful condition that requires prompt, and in some cases, emergency treatment

Describe how the epidermis of the hoof is formed

• Squames lost

• Gradual keratinization

• Loss of nuclei 

• Division of basal cells

What is the intertubular horn of the hoof made by?

The inter-tubular horn is made by the cells between the bases of the papillae

• The dermal papillae are found in the region of the coronary band

Describe how the hoof wall and sole is formed

• The hoof wall is produced predominantly by the coronary dermis (dermal papillae)

• The perioplic dermis produces a thin, waxy and waterproof cover

• The sole is produced by the sole dermis 

What is the white line?

• The white line is the junction of the sole and the hoof wall

• It is important to be able to identify it: seedy toe, white line disease, subsolar abscesses

What are the following structures?

• Stratum internum

• Stratum medium

• Stratum externum

Stratum internum: the layer with the epidermal lamellae 

Stratum medium: the bulk of the hoof wall with horn tubules and intertubular horn

Stratum externum: a thin, waxy layer of keratin forming the outer coating of the hoof wall

Label the following image

Describe how the distal deals with weight bearing

• P3 is suspended from the hoof wall, rather than bearing weight through the palmar/plantar surface 

• Collagen fibre bundles run between P3 and the inner aspect of the claw capsule

Describe how the distal limb deals with support and shock absorption

• There are internal structures that support the caudal foot:

  • Hoof/collateral cartilages 

  • Digital cushion

List the joints of the distal limb, including their common name in the horse and cow

• Metacarpophalangeal (fetlock in horse and cattle)

• Proximal interphalangeal (pastern in horse and cattle)

• Distal interphalangeal (coffin in horse and cattle)

Draw a diagram of the equine MCP joint

Draw a diagram of the equine PIP joint

Draw a diagram of the equine DIP joint

Describe the extensor tendons of the digits

• Common digital extensor 

• Located on the dorso-lateral aspect

• Receives branches from interosseus 

• Tendon of insertion is split according to the number of functional digits in the species 

• Inserts on the extensor process of P3 (distal phalanx)

Describe the flexor tendons of the digits

• Located on the palmar/plantar aspects 

• Superficial digital flexor tendon

  • Flexes the whole digit and stabilises the fetlock joint

  • Subcutaneous and palpable 

  • At the distal end of P1, it splits and inserts on P2

  • Forms a sleeve around the DDFT at the manica flexoria 

• Deep digital flexor tendon

  • Runs deep to the SDFT

  • Passes through the manica flexoria

  • Inserts on the flexor tuberosity of the distal phalanx of each functional digit

Describe the structure and function of the TIOM

• Also known as the TIOM (third interosseous muscle), middle interosseous muscle or suspensory ligament

• Varies in structure and function according to the species 

  • Muscular in the dog and cat

  • Mostly tendinous in the horse

TIOM forms part of the suspensory apparatus of the horse

This supports the fetlock, preventing excessive extension

Describe the pathway of the TIOM

Arises from the proximal metacarpal between splint bones: deep to the SDFT and DDFT

Divides just above the fetlock, before inserting on the abaxial surface of the proximal sesamoids

Extensor branches run to the extensor tendon

Beyond the sesamoid bones, it continues as sesamoidean ligaments to phalanges

Describe the accessory (check) ligaments of the distal limb

• The accessory ligament of the SDFT connects to the radius (just above the carpus)

• The accessory ligament of the DDFT connects to the carpal region

• Function: limiting movement of the tendon to prevent over-stressing, and to support the MCP joint through anchoring flexor tendons

• These ligaments are weak/absent in the hindlimb

How do bursae protect the distal limb?

• Cushion tendons in areas at risk of damage and distributes pressure

• Navicular bursitis can be inflammatory or infectious

How do digital flexor tendon sheaths protect the distal limb?

• Encompasses flexor tendons of the fore/hind limbs

• Extends from above the fetlock joint to the middle of P2

How do annular ligaments protect the distal limb?

• Local thickenings of fascia 

• Stabilise tendons

List the structures that help to protect the distal limb

• Bursae

• Digital flexor tendon sheaths

• Annular ligaments

• Dorsal elastic ligaments

What are the two types of distal forelimb nerve blocks?

1. Palmar digital nerve block (PDN)

2. Abaxial sesamoid nerve block

Which nerves innervate:

• Forelimb extensors

• Forelimb flexors

• Extensors: radial nerve

• Flexors: median and ulnar nerves

Give the roots, muscles supplied and cutaneous supply of:

• Radial nerve

• Median nerve

• Ulnar nerve

Nerve	Roots	Muscles supplied	Cutaneous supply
Radial	C7, C8, T1	Extensors of the elbow, carpus and digits	Craniolateral surface of the forearm Dorsal surface of the digits
Median	C8, T1	Flexors of the carpus and digits	Palmar surface of the manus
Ulnar	C8, T1, T2	Flexors of the carpus and digits	Caudal surface of forearm and lateral manus

What do the tibial and fibular nerves supply?

Tibial: extensors of hock, flexors of hindlimb digits

Fibular: flexors of hock, extensors of hindlimb digits

In the forelimb, where does the radial nerve terminate?

The carpus

Where does the dorsal nerve supply of the forelimb come from?

Medial and ulnar nerves

Where does the dorsal nerve supply of the hindlimb come from?

Fibular nerve

Draw a diagram to show the nerve distribution in the forelimbs and hindlimbs

Describe the vasculature of the distal hindlimb

• Main supply to the distal hindlimb is the cranial tibial a.

• Continues as dorsal metatarsal a.

Describe the vasculature of the distal forelimb

• Main supply to the distal forelimb is the median a.

• Continues as palmar a.

• There is no dorsal a. in the equine forelimb

What are:

• Nasalconchae

• Ethmoconchae

Nasalchonchae: folds of bone projecting from the side walls of the nasal cavities- towards the midline septum. Has thick mucosa to warm, moisten and protect inspired air

Ethmoconchae: conchae projecting rostrally from the ethmoid bone. Has thick mucosa to warm, moisten and protect inspired air, and are also a site of olfaction

What is the intermandibular symphysis?

Intermandibular symphysis: connection between the two halves of the mandible

What connects the different flat bones of the cranium?

Fibrous joints of the skull

Describe the synovial joints of the skull

Joints in the hyoid apparatus

Temporomandibular joint 

• Between the condylar process of the mandible and the mandibular fossa of the temporal bone

• Contains a joint disc, which divides the joint cavity into two separate chambers

Atlantooccipital joint

• Between the occipital bone condyles and C1 

How does the skull manage weight?

The wall of the outer skull consists of an outer and inner layer of cortical bone

The middle layer has a reduced spongiosum, and is called Diploe 

The surface of all these bones is covered by the periosteum

Major foraminae

• Foramen: hole (e.g round foramen- maxillary division V2)

• Fissure: slit (e.g orbital fissure- ophthalmic division V1)

• Canal: tunnel

What are the ramus and body of the mandible?

Ramus: vertical part of the mandible

Body: horizontal part of the mandible

Draw a diagram to show the (rough) vertebral regions of the dog

Draw a table to show the species variations in the number of cervical, thoracic, lumbar and sacral vertebrae. Include the following species

• Rabbit

• Sheep

• Chicken

• Dog

• Cat

• Pig

• Horse

• Cow

	Cervical	Thoracic	Lumbar	Sacral
Rabbit	7	12	7	4
Sheep	7	13	6	4
Chicken	7	7	14
Dog	7	13	7	3
Cat	7	13	7	3
Pig	7	14	6	4
Horse	7	18	6 (Arabs= 5)	5
Cow	7	13	6	5

Draw a diagram to show the bones of the skull and mandible

Draw a diagram to show the ones of the hyoid apparatus

What is the function of the hyoid apparatus?

Attachment site for the tongue (cranially)

Attachment site for the airways and gut tube (caudally)

Suspends the tongue, airways and gut tube from the skull

What are the components of:

• The tongue

• The gut tube

• The airway

Tongue: 

• Glossa (further forward)

• Lingua (further backward)

Gut tube: 

• Pharynx (throat)

• Oesophagus (gullet)

Airway:

• Larynx (voice box)

• Trachea (windpipe)

Describe the functions of the skull

Cranial part: houses and protects the brain and ear 

Facial part: houses the nasal and oral cavities and supports teeth

Both contribute to the orbit to protect the eyes

Membranous or flat bones form the roof of the cranium, whereas the primordial bones form the base of the skull

Define the different types of skull

Mesaticephalic: equal proportions

Brachycephalic: short head 

Dolichocephalic: long head

What are:

• The vertebral foramen

• The intervertebral foramen

Vertebral foramen: contains the spinal cord

Intervertebral foramen: in between bones

Describe the different types of a vertebra

• Body- mechanical loading

• Arch: lamina (layer), pedicle (column/foot)- protects the spinal cord

• Processes- attachment for muscles and ligaments 

• Joint surfaces (facets)- for synovial joints

What type of vertebrae is this?

Cervical

What type of vertebrae is this?

Thoracic

What type of vertebrae is this?

Lumbar

What types of joints are there in the vertebrae?

• Fibrocartilagenous joints

• Synovial joints

Describe the:

• Synovial atlantooccipital joint

• Synovial atlantoaxial joint

Draw a diagram to show their location

Synovial Atlantooccipital joint:

• Joint between the condyles of the occipital bone, and the cranial articular fovea of the atlas

• Allows upward and downward movement only (dorsal and ventral flexion)

Synovial Atlantoaxial joint:

• Pivot joint, allows movement and rotation around the axis 

• Projection (called the dens/tooth) will locate inside bone C1

What is the fibrocartilagenous IVD? Draw a diagram to show the different parts

• Acts as a shock absorber, and spreads load between bones to avoid overload

• Only present between vertebral bodies: not between arches 

• Parts:

  • Nucleus pulposus: spreads load

  • Annulus fibrosus: under tension

List the long vertebral ligaments, including their locations

1. Nuchal ligament: occipital bone - 3rd/4th thoracic vertebrae 

2. Supraspinous ligament: 3rd thoracic vertebrae - sacrum 

3. Ventral longitudinal ligament: 8th thoracic vertebrae - sacrum

4. Dorsal longitudinal ligament: inside the vertebral canal, from neck - sacrum

Describe the types of short vertebral ligament

Includes an intertransverse ligament (between the transverse processes)

• Must be pierced during paralumbar anaesthesia

Interspinous: between adjacent spinous processes

Interarculate/flavum: inside and between adjacent vertebral arches 

• Must be pierced during epidural anaesthesia

What is the term for:

• Spinal flexion

• Spinal extension

Spinal flexion pathology: kyphosis

Spinal extension pathology: lordosis

Describe the two types of muscle group of the spine

Epaxial muscles: will extend the spine if contracting bilaterally

In the body

• Iliocostalis (ilium to the first rib)

• Longissimus (along the entire back to head)

• Transversospinalis (along the entire back)

In the neck

• Longissimus 

• Semispinalis capitis (under splenius)

Hypaxial muscles: will flex the spine if contracting bilaterally

• None in the sacrum or thorax

• e.g longus colli (in neck)

• eg psoas/quadratus (in lumbar region)

Describe how to investigate a lame horse

Clinical examination and history

• Palpation of the back, neck and limbs: checking for heat, swelling or pain

• Visual evaluation for asymmetry, swelling or abnormal posture

• Inspection of the hoof to look for sensitivity, bruising or abscesses

Gait evaluation

• Walking and trotting in a straight line

• Lunging

• Flexion tests 

Nerve blocks 

Diagnostic imaging 

• Radiography

• Ultrasound 

• MRI/CT

List the indications and contraindications of performing nerve blocks

Indications

• Surgery 

• Trauma and fractures

• Pain management

• Diagnostic purposes

Contra-indications

• Patient refusal 

• Infection 

• Allergies 

• Lack of resources

Describe the common equine nerve blocks

Palmar digital (heel) block

• Targets the caudal third of the foot, including the navicular bone 

• The nerve runs in the neurovascular bundle, about 1cm proximal to the cartilage of the foot 

Abaxial sesamoid block

• Desensitises the entire foot, including the proximal interphalangeal (pastern) joint

• Numbs the palmar and plantar digital nerves

Low four-point block

• Desensitises the fetlock joint and everything below it

What are the issues around nerve blocks?

Injection site: bruising, soreness, bleeding, localised infection

Nerve injury: temporary tingling, numbness or weakness

Inadequate relief: the nerve block may fail to work

What are the most common diseases affecting the ovine foot?

The most important causes of lameness are scald, foot rot and CODD- which are all contagious, and caused by bacteria

Describe the bacteria responsible for causing foot rot in sheep

Dichelobacter nodosus is the essential organism for foot rot

Scald (interdigital dermatitis) is caused by various bacteria that invade the surface layers of the skin between the claws 

• This usually follows damage by moisture, frost and/or mechanical damage 

• One common bacteria associated with scald is Fusobacterium necrophorum

• However, if D.nodosus is present on the farm, foot rot develops in the first stage as scald, and in the second stage characterised by under-running of hoof horn, and a characteristic smell 

F.necrophorum is ubiquitous in the environment, and impossible to eliminate from a farm completely 

Both F.necrophorum and D.nodosus are anaerobic bacteria

Describe the spread of foot rot in sheep

D.nodosus is adapted to live and survive on the feet of sheep

• Can survive on pasture or bedding for up to 14 days

• Can survive in hoof horn clippings for a long time

• Infection can spread between sheep if they walk on the same surface 

• Lame sheep can be treated with a combination of antibiotic injections, and topical antibiotic sprays 

• In a small number of sheep, the infection can be very difficult to treat- they tend to get repeat infections, and are a source of infection to the rest of the flock

Label the following image

Describe the advantages and disadvantages of ultrasonography in investigating joints

Advantages

• No radiation risk

• Real-time imaging 

• Soft tissue detail (cartilage, ligaments, muscles)

Disadvantages

• Operator dependent 

• Can be stressful for the animal

• Harder to interpret

Describe the advantages and disadvantages of radiography in investigating joints

Advantages

• Cost-effective

• Non-invasive

• Good for bone and thoracic imaging

• Easy to send off for referral

Disadvantages

• Radiation exposure

• Limited soft tissue detail

• Patient movement/artefacts

Label the following image

Label the following image

List the equipment used in hoof trimming cattle

• Hoof nippers

• Hoof knives

• Hoof gauge

• Hoof testers

• Arm guards/wrist protectors

How do you ensure correct toe length when trimming the feet of cattle? Draw a diagram to support

• Start with the stabilising claw (medial hind claw or lateral front claw)

• Measure an appropriate length from where the claw horn goes palpably hard below the coronary band

• Use hoof nippers to cut excess toe length that exceeds 85-90

What is ataxia?

Ataxia: a neurological term, meaning "lack of coordination"

This describes poor, uncoordinated muscle control- which causes clumsy or unsteady movements

Describe the three different types of ataxia

Sensory Ataxia

Caused by the loss of sensory feedback (proprioception), which leaves the brain unable to track where body parts are in space

Cerebellar Ataxia

The most common form, caused by damage to the cerebellum: the part of the brain that coordinates movement

Vestibular Ataxia

Involves issues with the inner ear, which ruins the body's sense of balance

What are the causes of ataxia?

Spinal issues: slipped or bulging discs (IVDD), spinal tumors, or trauma

Ear infections: severe inner or middle ear infections, that disrupt the vestibular system

Congenital or genetic conditions: some breeds (such as Jack Russell Terriers) are predisposed to inherited cerebellar ataxia

Toxins: accidental ingestion of certain drugs, toxic plants, or chemicals

Inflammatory/infectious disease: conditions that cause swelling in the brain or spinal cord

How can you diagnose and treat ataxia?

Treating ataxia depends entirely on pinpointing the root cause

You may perform a physical and neurological exam to locate the issue, which is often followed by blood work, X-rays, an MRI, or a spinal tap

Depending on the diagnosis, treatments can range from medications (e.g., antibiotics for ear infections) to surgery or supportive care

Describe how you can differentiate between lameness and ataxia by giving the pattern, cause and presentation?

	Lameness	Ataxia
Pattern	Regularly irregular	Irregularly irregular
Cause	Typically localised to a specific limb, joint or tendon- due to injury or arthritis	Neurological conditions such as spinal cord compression, nerve damage, or vestibular disease
Presentation	The animal usually tries to shorten the stance phase on the painful leg- shifting weight away from the affected area to avoid pain	Often affects multiple limbs, shows general weakness, and becomes drastically worse when the animal is made to walk in tight circles, back up, or walk with its head elevated

How is weakness different to ataxia and lameness?

Weakness: the reduced physical capacity to generate force in a muscle- making tasks feel heavy or impossible

What should you cover when taking a history of the lame horse?

Information about the current lameness issue:

• Duration

• Onset

• Severity

• Signs shown

• Exacerbated by different work/surfaces?

Current management (care, work, farriery)

Previous clinical problems

Concurrent medications

What does the static examination consist of when evaluating lameness of the horse?

Conformation

• Assess stance, symmetry and weight distribution (from the front, back and both sides), with the horse standing square on a hard, level surface

• Consider where the weight is distributed through each limb/joint

• Look at the foot balance, and think about weight distribution and load

Visual evaluation, palpation

• Look for asymmetry in muscles, conformation and feet

• Palpate all limbs, joints and soft tissues to identify: heat, pain, swelling, injuries

• Check the shoes/shoeing 

• Apply hoof testers as an indirect form of palpation

What does the dynamic examination consist of when evaluating lameness of the horse?

Assess the gait in walk and trot in a straight line

Evaluate and grade the lameness:

• Is the animal lame?

• If so, which leg is it lame on?

• How severe is the lameness?

Perform exacerbation tests: lunging, flexion tests

Describe the lameness scoring system

0: No lameness (sound)

1: Mild or inconsistent lameness

2: Moderate, consistent lameness

3: Obvious, marked lameness

4: Severe lameness

5: Severe, non-weight bearing lameness (horse cannot and should not be trotted)

What kind of tests would you carry out to investigate lameness in the horse?

The most commonly used diagnostic tests are regional anaesthesia (nerve and joint blocks) and diagnostic imaging (X-Rays, ultrasound, MRI and CT)

Laboratory testing of blood/synovial samples are used for some cases

Describe the principles of CT image production

• Computed Tomography (CT) image production relies on an X-ray tube rotating around the patient, while detectors opposite the tube measure beam attenuation 

• A computer processes these attenuation measurements from thousands of angles, using complex algorithms to reconstruct a 3D volume made up of pixels and voxels

How does CT differ to normal radiographic imaging?

While a standard X-ray generates a single 2D overlay of all tissues, CT acquires thousands of angles to compute highly detailed 3D views

Describe the radiation dosage of CT

• A single standard radiograph (X-ray) delivers an extremely low patient dose

• By contrast, a Computed Tomography (CT) scan administers a radiation dose equivalent to 10x to 50x that of a standard radiograph

What are CT scans good for viewing?

• Bones (fractures, tumors, eroded joints, bone density)

• Soft tissues (muscles, fat, ligaments, internal organ structure)

• Blood vessels (arteries, veins)

• Lungs

Describe the principles of MRI image production

• An MRI produces images by mapping the water (hydrogen) content of your body

• Protons align with a powerful magnetic field and are momentarily tipped by radio waves

• As protons snap back into alignment, they emit unique radio signals that a computer translates into highly detailed, cross-sectional pictures

In MRI imaging, what is the function of:

• The magnetic field

• Magnetic field gradients

• The RF pulse

Magnetic field: aligns the hydrogen protons naturally present in the body's water and fat molecules

Magnetic field gradients: allow the scanner to localize atomic spins spatially, which is what transforms raw radio signals into detailed anatomical images

RF pulse: temporarily disrupts the protons' natural alignment within the main magnetic field, causing them to absorb energy and emit their own detectable signal as they realign

In MRI imaging, what is the function of:

• Proton density images

• Gadolinium

Proton density images map the concentration of mobile hydrogen nuclei (protons) in tissues

Gadolinium alters the magnetic properties of bodily fluids, significantly improving the clarity and diagnostic value of the images

What are the safety issues surrounding MRI?

Safety issues: projectile hazards, severe thermal burns and physiological stress under prolonged anesthesia