Equine Limb Anatomy Demonstration
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How is the weight of the horse naturally distributed and how does this influence the roles of the fore and hind limbs in this species?
Naturally the forelimbs are more weight bearing. The hind limbs are used for propulsion.
Which carpal bone is most vulnerable to trauma and why?
The 3rd carpal bone as it is the largest
What is the name given to bumps along the length of the 2nd and 4th metacarpal bones, how are they formed, and are they of clinical relevance to you as a vet?
The bumps are called 'splints'. They form due to inflammation of the ligament running between the splint bones and 3rd metacarpal bone. They are painful when forming but not once formed therefore cease to be of clinical relevance. They are considered a blemish and therefore are undesirable in show horses.
How are the rough bony bumps on the surface of the proximal and middle phalanges formed and are these of clinical relevance to you as a vet?
They are formed by mineralisation of the ligaments attaching these bones. As long as they do not impinge on the joint surface they are clinically irrelevant.
The dorsal surface of the distal phalanx is very rough and there are hollow channels through the bone. What is the function of these features?
The rough surface provides a surface of attachment for the dermis. The hollow channels are where blood vessels travel through to the dermis.
How do you feel the individual flexor tendons in a live horse?
You palpate the limb in flexion, otherwise the tendons will feel solid like bone.
If the pulses in the digital arteries were very pronounced what clinical information does this give you?
This suggests the presence of disease in the hoof
What other structures run with the digital arteries and why is it useful to know their location?
Palmar digital nerves and veins - need to know location for digital nerve block.
Which joint is the ergot associated with?
Where is the carpus does most movement occur?
At the radio-carpal joint
Which aspect of the limb is the accessory carpal bone located on?
What are the boundaries of the carpal canal and what passes through it in the horse?
- Dorsal - fibrocartilaginous reinforcement of palmar aspect of joint capsule
- Lateral - accessory carpal bone
- Palmar - flexor retinaculum
- Contents - DDFT and SDFT
What is the function of the distal sesamoidean ligaments?
- Support the metacarpophalanageal joint
- Counteract the pull of the suspensory ligament on the proximal sesamoids
How is it possible to gain access to the distal interphalangeal joint when it is located within the hoof?
It can be entered via the dorsal pouch of the joint capsule, which extends dorsal to the coronary band and so can be accessed on the dorsal aspect of the limb
What is the function of the podotrochelar/navicular bursa and does it communicate with the rest of the distal interphalangeal joint?
It cushions the DDFT as it runs over the distal sesamoid bone. It is separated from the joint by the impar ligament and so does not communicate with the rest of the joint.
What is the function of the annular ligaments?
The annular ligaments hold the tendons against the palmar aspect of the digit and so provide support to the metacarpi/tarsophalangeal, PIP and DIP joints
Which joints in the distal limb are high motion/low motion? What is the clinical significance of this?
- Metacarpophalangeal - high motion
- PIP - low motion
- DIP - low motion
- Minimal damage in high motion joints can cause lameness whereas low motion joints need more significant changes to cause lameness
What is the function of the stay apparatus in the horse and why does the horse need it?
This is a passive system for preventing the limb collapsing during weight bearing. It allows the horse to sleep standing up, which is useful for avoiding predators.
Where do the accessory check ligaments of the SDFT and DDFT arise from and what is their function?
- SDFT - distal end of caudal aspect of radius
- DDFT - fibrocartilaginous reinforcement of palmar aspect of joint capsule - metacarpal region
- They help prevent the joint from going into hyperflexion
What are the components of the stay apparatus and what are their functions?
Suspensory ligament, common digital extensor tendon, proximal sesamoids, distal sesamoidean ligaments. They form a sling to support the metacarpo/tarsophalangeal joint in extension as part of the stay apparatus. They also limit hyperextension of this joint during locomotion and use elastic recoil to return it to its normal weight bearing position.
How are tendons protected as they run through confined spaces?
Protected by tendon sheaths or bursae
On a radiograph, how can you determine which metacarpal bone is 2nd and which is 4th?
Medial bone is 2nd, lateral bone is 4th
Which joint is responsible for the most movement at the carpal joint and which is responsible for the least?
- Most = radio-carpal joint
- Least = carpo-metacarpal joint
What is the function of the muscles that insert onto the accessory carpal bone?
How would you classify the carpal bones and what is the function of this type of bone?
- Short bones
- Movement and shock absorption
What is the function of the sagittal ridge and groove?
They provide the metacarpal/tarsal pharyngeal joint with more stability. This restricts movement to flexion and extension.
Which structure is the proximal sesamoid bones embedded in and what holds them in place?
They are embedded in the suspensory ligament and held in place by collateral ligaments, intersesamoidean ligament and distal sesamoidean ligaments (short, cruciate, oblique and straight)
Which structure does the dorsal projection of the joint capsule protect in life?
Common digital extensor tendon
What is the function of the digital cushion and why is it not visible on a radiograph?
The digital cushion protects overlying tissues (DDFT, navicular bone, etc) and is also involved in shock absorption. It is made up of soft tissue and so will not be radio-opaque and appear on a radiograph
In what clinical condition might it be important to determine the location of the coronary band and dorsal hoof wall relative to the distal phalanx and why?
Laminitis. As the distal phalanx can sink and rotate within the hoof capsule.
Why are normal horse shoes open at the heel?
To allow the bulbs of the heel to expand during shock absorption
What is the first thing you need to do in order to remove a horse shoe for radiography?
'Raise the clenches' - straighten the nail on the dorsal hoof surface
Which part of the foot is first to hit the ground during normal locomotion and which part is weight bearing?
- Frog hits the ground first.
- Walls of the hoof are weight bearing
Which soft structure should you be careful to avoid when picking out a horses feet? What is the function of this structure?
The frog - shock absorption
What is the hoof capsule composed of and how is it formed?
- Tubules of keratin interspersed with inter tubular horn
- The dermis takes the form of cone shaped papillae, papillae produce tubes of keratin, tubes grow distally (5-6mm a month), inter tubular horn fills the space between tubes
What are laminae and what is their function?
- Laminae are ridges in the hoof dermis and epidermis
- These interdigitate to hold the epidermis onto the dermis. They also transfer the weight of the horse to the hoof capsule when the horse is weight bearing by suspending the distal phalanx within the hoof capsule
Why is it possible to shoe horses without them feeling pain? What useful landmark will the farrier use to achieve this when shoeing a horse?
As the hoof wall/epidermis is insensitive - it has no nerve supply. The nails should be inserted outwith the white line.
How does the shape of the fore and hind hooves in the horse differ and how does this relate to their function?
- Front hoof is round in shape - weight bearing
- Hind hoof is pointed in shape - propulsion
Why are nerve blocks performed in the horse and where is the local anaesthetic injected relative to the nerve?
Nerve blocks are performed during lameness investigations. The local anaesthetic is injected into the tissues surrounding the nerve
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