ANSC 2202 - Appendicular Skeleton

The Thoracic Limb

• Divided into two parts:

  1. Antebrachium - Forearm

     • Scapula

     • Humerus

     • Radius

     • Ulna

  2. Manus - Distal portion (hand)

     • Carpus

     • Metacarpus: between carpus and digit(s)

     • Digit(s)

Olecranon

Elbow

Equine Thoracic Limb Diagram

• The Ulna and Radius are sometimes fused in livestock

Equine: Metacarpus

• Metacarpal bones II-IV (medial to lateral)

• Mc II and IV are splint bones

• Mc III is the cannon bone

• Mc I is absent

Ruminant: Metacarpus

• Mc III and IV are fused to create the cannon bone

• Mc V is a small metacarpal bone

• Mc I and II are absent

Carnivore: Metacarpus

• Mc I is small and non-weight bearing (dewclaw)

• Mc II-V are all present

  • Very similar to humans

Digits

• Correspond to fingers and toes in humans; variable in number depending on the species

  • Proximal phalanx, P1 (long pastern* bone)

  • Middle phalanx, P2 (short pastern* bone)

  • Distal phalanx, P3 (coffin* bone)

  • Sesamoids (proximal and distal)

    • *Common names used in horses and ruminants

• Note: Phalanges is plural for phalanx

Equine: Digits

• Proximal phalanx (long pastern): one per foot

• Middle phalanx (short pastern): one per foot

• Distal phalanx (coffin bone): one per foot

• Sesamoid bones: one proximal sesamoid (two per foot) at the fetlock joint and one distal sesamoid (one per foot) at the coffin joint

  • Distal also known as the navicular bone

Equine: Digits vs Humans

Compared to humans

Ruminant: Digits

• Two weight bearing (3rd and 4th, circled)

• Two non-weight bearing (2nd and 5th)

  • Manifested as horny dewclaws on the palmar surface of the fetlock joint

• 1st digit is missing

Ruminant: Digits 2

• Proximal phalanx (long pastern): two per foot.

• Middle phalanx (short pastern): two per foot.

• Distal phalanx (coffin bone): two per foot

• Sesamoid bones: two proximal sesamoids (four per foot) at the fetlock joint and one distal sesamoid (two per foot) at the coffin joint.

Ruminant: Digits vs Humans

Compared to humans

Carnivore: Digits 2

• Four weight bearing digits (II-V)

• Non-weight bearing dewclaw (I)

  • May not exist

Carnivore: Digits 2

• Proximal phalanx

• Middle phalanx

• Distal phalanx

• Ungual Process

• Horny Claw

• Sesamoid bones: two sesamoid bones on the palmar/plantar surface of each metatarsophalangeal joint of each main digit (distal sesamoid bones are cartilaginous

Ungual Process

• a curved, cone-like extension of the distal phalanx that is covered by the horny claw

Horny Claw

• a curved, fingernail-like projection covering and protecting the ungual process (this is the toenail)

Carnivore: Digits vs Humans

Compared to humans

Pelvic Limb

1. Proximal portion

   • Os Coxae

   • Femur

   • Patella

   • Tibia

   • Fibula

2. Pes - hindpaw/distal portion of the pelvic limb (foot)

   • Tarsus

   • Metatarsus (Mt): between tarsus and digit(s)

   • Digit(s): phalanges and sesamoid bones

Equine Pelvic Limb Diagram

• The fibula is fibbing, so it hides behind the tibia

• Tibia and fibula are sometimes fused in livestock

Equine: Metatarsals

• Mt II-IV

• Mt III is the cannon bone

• Mt II-IV are splint bones

  • They are numbered the same as the thoracic limb

Ruminant: Metatarsals

• Mt III and IV are fused to create the cannon bone

• Mt II is a small metatarsal bone

• Mt I is absent

Canine: Metatarsals

• Mt I is small and non-weight bearing

  • Dewclaw — often absent

• Mt II-V are all present

Do the pelvic limb digits differ from the thoracic limb digits?

No, they are the same.

Anthrology

The study of joints

Articulation

• Two or more bones are united or joined to create a joint

How are joints classified? What are the classifications?

• Classified based on the number of bones that articulate with one another

• Simple joints: two bones that articulate with one another

  • Vertebrae, shoulder

• Compound joints: more than two bones articulating with one another

  • Carpus, tarsus, fetlock

Fibrous joint

• Often temporary

• Little or no movement

  • Skull

• Young animals

Cartilaginous joint

• United by fibrocartilage or hyaline cartilage

• Limited movement, such as compression or stretching (vertebrae)

• Cartilage is replaced by bone when the animal stops growing

  • Not in vertebrae, sometimes in epiphyseal plate

Synovial joint

• “True joint”

• Encasulated by articular capsule

• Filled with synovial fluid

  • Made by synovial membrane

• High motion joints (limbs)

• Cartilage covers bone ends

Scapulohumeral/shoulder joint

• Scapula and humerus

Cubital/elbow joint

• Humerus, radius, and ulna

Carpus/carpal joint

• Between radius/ulna and metacarpal(s)

Metacarpophalangeal/fetlock* joint

• Metacarpal(s), proximal phalanx and proximal sesamoid bones

  • *Equine/Ruminant term, not used for carnivores

Proximal interphalangeal/pastern* joint

• Proximal and middle phalanx

  • *Equine/Ruminant term, not used for carnivores

Distal interphalangeal/coffin* joint

• Middle and distal phalanx

  • *Equine/Ruminant term, not used for carnivores

Ringbone (arthritis)

• Periosteal bone deposition in the distal limb

  • High ringbone: deposition at the pastern joint

  • Low ringbone: deposition at the coffin joint

Onychectomy

• Declawing

  • Removal of the distal phalanx by disarticulating the distal interphalangeal joint

• Onych = nail

Sacroiliac joint

• Sacrum and ilium

  • White arrow

Coxofemoral/hip joint

• Acetabulum and femur

• Pink arrow

Stifle joint

• Femur, patella, tibia (and fibula)cetabulum and femur

Tarsus/Tarsal/Hock joint

• Between tibia and metatarsal bone(s)

Metatarsophalangeal/fetlock joint

• Metatarsal(s), 1st phalanx and proximal sesamoid bones

Are the joints on the digit(s) of the pelvic limb the same as the thoracic limb?

Yes, they are the same.

Tendons

• Story energy

• Support weight on skinny legs

• Allow animal to sleep standing

The Hoof

• Wall: visible outer portion of the hoof

• Bulbs of the heels: soft expanded part on caudal aspect of hoof

• Coronet/coronary band: where hair meets hoof; hoof grows downward from here (like human cuticles)

Ruminant Hoof

• Sole: concave portion of the hoof visible on the ground surface

• White line: Junction between wall and sole

  • Insensitive - where nails go in horse shoes

Equine Hoof and the Frog

• Frog: V-shaped structure that allows expansion of the foot at the heel (only in horses)

Equine Hoof and the Digital Cushion

• Wedge-shaped mass of fibrous and fatty tissue that is located INSIDE the hoof and functions to absorb concussive forces

Laminae

• Connects the hoof wall to the distal phalanx (coffin bone)

Laminitis

• “Founder”

• Degeneration or failure of the attachments between P3 and inner hoof wall.

• May result in the rotation of the coffin bone

  • Lameness and even puncturing of the sensitive laminae