Bones and Joints of the Distal Limb
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What type of bones are carpal bones?
What components make up the full complement proximal and distal row of the carpus?
- Proximal row: radial carpal bone, intermediate carpal bone, ulnar carpal bone, accessory carpal bone
- Distal row: 1st, 2nd, 3rd, 4th carpal bones
Which carpal bones are on the medial/lateral aspect of the limb?
- Medial: radial carpal bone, 1st carpal bone
- Lateral: ulnar carpal bone, 4th carpal bone
Which carpal bone has more than one centre of ossification?
Accessory carpal bone (two centres of ossification)
Which animal is the only one with the full complement of carpal bones?
Describe the complement of carpal bones in the horse and dog
- Dog - radial and intermediate carpal bones are fused to form a radial carpal bone, ulnar and accessory carpal bones are present, 1st-4th carpal bones are present but 1st bone is small
- Horse - all proximal carpal bones are present, 1st carpal bone is absent, 3rd carpal bone is the largest
What are the different joints in the carpus?
- Antebrachio-carpal joint = antibrachium + proximal row of carpal bones
- Middle carpal joint = proximal + distal rows of carpal joints
- Carpo-metacarpal joint = distal row + metacarpal bones
What type of joints are between carpal bones in the carpus?
What holds the carpal bones together?
True or false: if you inject a material into one part of the carpus join it will make it to the next part?
False - there is extension of the joint capsule to encompass all these joints. Therefore the carpus is compartmentalised.
Where does most/least movement occur in the carpus?
- Most = antebrachio-carpal joint
- Least = carpo-metacarpal joint
What must you do to be able to palpate the joint compartments of the carpus?
Flex the carpus
What helps to counteract the action of carpal flexor muscles on the accessory carpal bone?
The palmar ligament
What type of bones are the metacarpal/metatarsal bones and phalanges?
What is the function of sesamoid bones?
Protect tendons from friction and redirect forces over angled surfaces
What are the joints below the carpus?
- Metacarpo/tarsopharangeal joint
- Proximal pharangeal joint
- Distal pharangeal joint
How many digits do a) cats and dogs b) unguligrades c) horses have?
- a) 4 - the first digit has been shed for speed
- b) 2 - 3rd and 4th digits remain
- c) 1 - only 3rd digit remains
What are the three different stances?
- Plantigrade - bear weight on digits, metatarsals, tarsal bone
- Digitigrade - bear weight on digits and phalanges
- Unguligrade - bear weight on distal phalanx only
Which bone is the 'cannon' bone in horses?
3rd metacarpal bone
Which bones are the 'splint bones' in horses?
2nd and 4th metacarpal bones
What palpable feature is present on splint bones?
Which ligament are the proximal sesamoid bones embedded in?
Which structures run over the proximal sesamoid bones?
SDFT and DDFT
Which animal is the only species to have dorsal sesamoid bones?
In the dog, what structures do the dorsal sesamoid bones protect?
True or false: dorsal sesamoid bones are visible on radiographs?
What is the proximal phalanx sometimes referred to as?
Long pasture bone
What attaches onto the proximal phalanx?
Oblique distal sesamoideam ligament
What attaches to the middle phalanx?
Collateral ligaments for joints and insertion of tendons
With regards to P2, what is ringbone?
Where the tendons and ligaments insert onto P2 you often get new bone formation. This will not affect the horse unless new bone begins to form on the articular surface of the joint and affect movement.
What part of the distal phalanx does the common digital extensor tendon attach to?
The extensor process
What is the function of the palmar process on the distal phalanx?
It supports the lateral cartilages
On what aspect of the distal phalanx does the DDFT attach?
What is the function of the lateral cartilages?
What can happen to the lateral cartilages with age?
They can become mineralised with age and form 'sidebone'
What is the name of the distal sesamoid bone in the horse? Where is it located?
Navicular bone. It is located on the palmar aspect of the DIP joint.
What structure does the navicular bone guide over the DIP joint?
What is navicular disease syndrome?
Erosion of the navicular bone. This erosion can be seen on radiographs.
True or false: dogs have distal sesamoid bones?
False - they only have proximal and dorsal sesamoid bones
What are each of these different parts of the distal phalanx? a) Lingual process b) Ungual crest c) Extensor process d) Palmar process
- a) Supports claw
- b) Vascular root of claw
- c) Extensor tendons
- d) Flexor tendons
What is different about the 3rd and 4th metacarpal bones in ruminants?
They are fused
What is present in the palmar/dorsal pouch of the metacarpal/tarsalphalangeal joint?
- Palmar - incorporates proximal sesamoids
- Dorsal = cushions extensor tendons
What provides stability to the metacarpi/tarsophalangeal joint?
Collateral ligaments and the sagittal ridge/groove
What is the natural weight bearing position of the equine fetlock joint?
When are the fetlock joints forced into hyperextension?
- Forelimbs during landing
- Hindlimbs during takeoff
- Both during galloping and turning
Where does the suspensory ligament originate from?
Proximal palmar MC3/MT3
Describe the path of the suspensory ligament
2/3 of the way down the metacarpal/tarsal bone it divides in two. It attaches to the abaxial aspect of the proximal sesamoids and continues down the dorsal aspect of the limb until it fuses with the common digital extensor tendon.
What is the function of the suspensory ligament?
It acts like a string and returns the joint to a resting position.
What ligaments provide support to the proximal sesamoids?
- Inter-sesamoidean ligaments
- Collateral sesamoidean ligaments
- Distal sesamoidean ligaments (cruciate, short, oblique and straight ligament)
What makes up the suspensory apparatus?
- Suspensory ligament
- Proximal sesamoids
- Sesamoidean ligaments
- Common digital extensor tendon
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