Bones and Joints of the Distal Limb

M.8R, W.2, L.4

What are the arrows pointing at in the image?

carpus

List the species each of these are from

Left to right:

• Canine

• Equine

• Bovine

• Pig

What type of bones is the carpus composed of and what type of bones are they?

• Carpal bones

• Short bones

List the components of the canine carpus

• Proximal Row

  • Fused Radial Carpal Bone + Intermediate Carpal Bone (named RCB)

  • Ulnar Carpal Bone

  • Accessory carpal bone

• Distal Row

  • 1st, 2nd, 3rd, and 4th carpal bones

What bone is palpable on the canine carpus?

Accessory carpal bone

How many centers of ossification do short bones USUALLY have? List the two short bones that are the exception and how many centers of ossification they have

• SINGLE center of ossification

• Exceptions:

  • Fused Radial Carpal Bone + Intermediate Carpal Bone (RCB) - 3 centers

  • Accessory carpal bone (ACB) - 2 centers

List the 3 joints in the carpus, where they are located, which has the most + least movement

• Antebrachio-carpal joint

  • between antebrachium + proximal row of carpal bones

  • most movement

• Middle carpal joint

  • proximal + distal rows of carpal bones

• Carpo-metacarpal joint

  • distal row + metacarpal bones

  • least movement

What kind of joints are between bones and what type of joints are they?

Intracarpal Joints

• Fibrous joints (not a lot of movement)

When are joint spaces in the carpus palpable? and why is that clinicall relevant?

in FLEXION

• helps with carpal joint fluid sampling

What does the Accessory Carpal Bone act as for the distal limb?

acts as a LEVER for distal limb

What major muscles insert on the carpus and what ligament counteracts this?

• major carpal FLEXOR muscle

• counteraction by PALMAR LIGAMENT

Describe anatomically where the single joint capsule of the synovial joint extends. What kind of communication is there between compartments?

• Extends:

  • Proximally between radius + ulna

  • Distally between metacarpal bones

• Poor communication

List the 3 structures that provide the carpus with joint stability

• Collateral Ligaments

  • Lateral: ulna (lat. Styloid process) to 5th metacarpal

  • Medial: radius (medial styloid process) to 2nd metacarpal

• Cartilage plate

  • palmar aspect of joint capsule

• Retinaculum

List long bones of the hindlimb

• metacarpal / metatarsal bones

• Digits:

  • Proximal phalanx

  • Middle phalanx

  • Distal Phalanx

List sesamoid bones of the hindlimb

• Proximal sesamoids​

  • all species​

• Dorsal sesamoids ​

• Distal sesamoid​

List synovial joints of the hindlimb

• Metacarpo / metatarso-phalangeal joint

• Proximal Interphalangeal joint (PIP)

• Distal Interphalangeal joint (DIP)

Why do dogs and cats shed the 1st digit?

for speed

List the 3 different types of stances, give examples of species, what do they bear weight on, and what protects those structures

• Plantigrade

  • Eg. rabbits, bears, humans​

  • Bear weight on ​

    • Digits + metatarsals + tarsal bones​

• Digitgrade

  • Eg. Dogs, cats​

  • Bear weight on ​

    • Digits / phalanges​

    • Protected by foot pads​

• Unguligrade / Ungulates

  • Eg. Ruminant, horses​

  • Bear weight on distal phalanx only​ (tippy toes)

  • Protected by hoof​

what is usually similar between digitigrade species and unguligrade species?

distal fore & hind limb

How many centers of ossification do metacarpals & digits have and what is the exception?

• 2 centers of ossification

• Except:

  • Distal phalanx = 1

Why is it important to know the position of growth plates?

to be able to distinguish from joint spaces

Describe the Equine Metacarpal Bones (name, number metacarpal, purpose, articular surfaces

• CANNON Bone

• 3rd metacarpal / metatarsal

• weight bearing

• Distal Articular Surface = sagittal ridge

Describe the 2nd and 4th MC / MT (name, function, palpable?)

• Splint Bones

• Non-weight bearing (vestigial)

• Palpable - ‘button’ at distal end

What kind of joints and which ligament are between the splints and 3rd MT

• Fibrous joints

• Interosseous ligament

Describe sesamoid bones in all species (single or paired, location, embedded in what ligament, what do they protect)

• paired

• palmaro-distal to every MC3 /MT3

• embedded in suspensory ligament

• Protect:

  • Superficial Digital Flexor Tendons (SDFT)

  • Deep Digital Flexor Tendon (DDFT)

Describe the dorsal sesamoid bones in the canine ( single or paired, location, embedded in and protect what?)

• Single ​

• Dorsal aspect to every MCP / MTP joint

• Embedded in & protect: extensor tendons​

• Proximal Phalanx

• Long Pastern Bone + P1

• Raised V on palmar surface

  • oblique distal sesamoidean ligament

List the components of the metacarpo-phalangeal (MCP) / metatarso-phalangeal (MTP) joint

1. 3rd metacarpal / metatarsal bone​

2. Proximal phalanx​

3. Proximal sesamoid bones​

• Typical synovial joint​

• Large palmar pouch - incorporates proximal sesamoids​

  • Large dorsal pouch - cushions extensor tendons​

• Collateral ligaments​

• Sagittal ridge / groove​

• ​

• Movement:​

• limited to flexion & extension​

• ‘High motion’ joint​

What is the natural weight bearing position of the equine distal limb and what position is the distal limb forced into during locomotion?

• Extension

• Hyperextension

• originates proximal palmar MC3 / MT3

• Divides into two

• fuses with Common Digital Extensor tendon

List the function of the Suspensory Ligament

• acts like a sling

• returns joint to resting position

• relies on stability of proximal sesamoids

• Inter-sesamoidean ligament

• Fibrocartilage plate between proximal sesamoid bones​

• Smooth passage of DDFT and SDFT​

• B/ Collateral sesamoidean ligaments:​

• Goes from Proximal sesamoids to MC / MT 3 and PP​

• Medial & lateral​

• C/ Series of Distal sesamoidean ligaments:​

1. Cruciate - PP​

2. Short - PP​

3. Oblique ligament - PP​

• V-shaped trough on PP​

4. Straight ligament - MP​

• Inserts with SDFT​

List 4 things that the function of the Suspensory Apparatus relies on

Relies on interaction between:

• Suspensory ligament​

• Proximal sesamoids ​

• Sesamoidean ligaments​

• Common digital extensor tendon​

Describe the middle phalanx (MP) - (name, number phalanx,

• Short pastern bone

• p2

• saggital ridge

• saggital groove

• bony bumps

Describe the Distal Phalanx

• Pedal Bone / P3

• Extensor process

  • Attachment Common Digital Extensor tendon (CDE)

• Palmar Processes:

  • Support lateral cartilages​

• Solar surface

  • Attachment Deep Digital Flexor Tendon (DDFT)​

• Dorsal surface

Describe the distal interphalangeal joint

• “Coffin” joint - buried within hoof​

• ​

• Components:​

• Middle & distal phalanges​

• Distal sesamoid & distal phalanx​

• Distal sesamoid & middle phalanx​

• Typical synovial joint​

• Extensive joint capsule​

• Forms dorsal bursa to cushion extensor tendon​

• Accessible for injection into joint​Stability:​

• Collateral ligaments​

• Movement : ​

• flexion & extension​

• Some rotation to accommodate uneven ground​

Describe the Equine Distal Sesamoid

• “Navicular” Bone​

• 2 smooth articular surfaces​

• Cancellous centre with vascular channels​

• Absent in dog & cat​

• has a navicular / podotrochlear bursa

• Fluid filled pocket between distal sesamoid and DDFT​

• Cushions DDFT​

• Separated from joint space by impar ligament​

• Navicular disease syndrome

  • Forelimb lameness​

  • Erosion visible on radiographs​

  • Poor correlation between radiographic changes and clinical signs​

Which bone(s) of the forelimb has least contribution to the weight bearing function?

A. Carpal Bones

B. Humerus

C. Radius

D. Ulna

Ulna

In the horse, which ligament serves as a sling to support the proximal sesamoid bones and prevent the over-extension of the MCP joint?

A. Collateral Sesamoidean Ligament

B. Cruciate Ligament

C. Distal Sesamoidean Ligament

D. Suspensory Ligament