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Chapter 6
The Skeletal System
Functions of Bone
• Support and Protection
• It provides a framework for the body and gives it
shape.
• It supports and protects organs from injury.
• Leverage
• It provides a place for muscles, tendons,
ligaments and tendons of the body to attach.
• It helps make movement possible.
• Storage
• It stores minerals (Calcium)
• Blood Cell Formation
• It provides a place for hemotpoeisis
Bone Structure
• Two main types of bone:
• Cancellous Bone
• Light and spongy inner layer of bone.
• Consists of tiny spicules with bone marrow
between.
• Provides strength but prevents damage.
• Compact Bone
• Heavy and dense layer of outer bone
• Found in shafts of long bones
• Composed of haversian systems around a
haversian canal
Bone Structure continued
• Osteocytes- bone cells.
• Periosteum- covering of bone
• Inner layer contains osteoblasts.
• Endosteum- membrane that lines the
hollow interior surface of bones.
Haversian Systems
• Concentric layers of ossified bone matrix arranged around a
central Haversian canal
• Layers of ossified bone matrix
Bone Cells
• Osteoblasts
• Cells that form bone.
• Osteocytes
• Once osteoblasts are trapped
inside matrix of osseous material.
• Can revert back to osteoblasts
(remember this from last chapter?)
• Osteoclasts
• Eat bone away.
• Are the remodelers of bone
• Withdraw calcium when needed
from bone
• Why is this important?
Blood Supply to Bone
• Tiny vessels penetrate the periosteum.
• Volkmann’s canals- tiny channels in the
bone matrix that vessels pass through.
• Are at right angles to Haversian canals
that run lengthwise in the bone.
• Nutrient Foramina- Where large vessels
enter the bone.
• Carry blood into and out of bone
marrow.
• Can be mistaken for fracture on
radiographs.
Bone Formation
• Bone is formed in 2 ways:
• Endochondral Bone formation
• Intramembranous Bone
formation
• Bone formation and growth is
stimulated by Growth Hormone
(GH) from the anterior pituitary
(adenohypophysis) gland in the
brain.
Endochondral Bone Formation
• Endochondral Bone formation
• Cartilage bone formation
• Cartilage first, then bone
• How most bones develop
• Start as cartilage rods in long bones in
diaphysis (shaft).
• Contains primary growth center
• Cartilage is removed gradually as
bone is created and growth center
expands.
• Secondary growth center
• Develop in epiphysis (ends) of
bones
Growth plates
• Located between diaphysis and epiphysis.
• May be called epiphyseal growth plates.
• Sites of creation of new bone that allows bone to
lengthen as animal grows.
• Cartilage is created on epiphyseal side while bone
is created on diaphyseal side.
• When bone reaches full length, all cartilage is
replaced by bone and plates “Close”.
• Remodeling may take place but bone will not get
any longer.
• Young animals may have epiphyseal fractures
because this area is weaker than rest of bone.
Panosteitis
• “Growing Pains” in dogs.
• Inflammation of various bone layers
• Seen prevalently in young giant breed
dogs.
• Basically, body can not keep up as bones
are growing very quickly.
• Can be confirmed through Radiographs.
• May cause “Shifting Leg Lameness”
• Treated with rest and anti-inflammatories
• Usually occurs in the center of the bone.
Intramembranous Bone
Formation
• Occurs only in certain skull bones
• Bone forms in the fibrous membranes that
cover the brain in fetus.
• Bone forms directly from osteoblasts with
no cartilage intermediary.
Bone Shapes
•
•
•
•
Long Bones
Short Bones
Flat Bones
Irregular Bones
Long Bones
• Longer than they are wide.
• Has a proximal and distal epiphysis
consisting of cancellous bone.
• Main part of bone is diaphysis which
composed of compact bone.
• Found in digits and limbs.
Short Bones
• Shaped like cubes.
• Have core of cancellous bone covered by
compact bone.
• Carpal and tarsal bones.
Flat Bones
• Thin and flat bones
• Consists of two layers of compact bone
separated by cancellous bone.
• Bones in skull, pelvis, and scapula are
examples.
Irregular Bones
• Miscellaneous bones that
do not fit into another
category.
• May have characteristics of
more than one category.
• Include vertebrae and
sesamoid bones.
• Patella is largest
sesamoid bone in body.
Bone Marrow
• Fills the spaces within bones
• Has two types:
• Red bone marrow
• Hematopoietic tissue forms new blood cells.
• Majority of bone marrow in young animals
but less of older animals
• Yellow bone marrow
• Consists primarily of adipose connective
tissue.
• Common type of marrow in adult animals
• Does not produce blood cells but can revert
to red marrow if needed.
Common Bone Features
• Articular Surfaces
• Joint surfaces where bones come in
contact with each other to form joints.
• Consists of:
• Condyles
• Head
• Facet
• Covered by articular cartilage
• Composed of what type of cartilage?
Condyle
• Large, round articular surface.
• Major condyle is located on end of
humerus and femur.
• Also located in skull.
Head
• Somewhat spherical articular surface on
the proximal end of a long bone.
• Found on humerus, femur and rib.
• Head is usually joined with rest of bone by
a neck.
Femoral Head Osteotomy (FHO)
• Head of femur is removed in cases of
trauma or severe arthritis.
• A “false joint” forms which gives more
comfort to the patient.
Facet
• A flat articular surface.
• Found in carpal and tarsal bones as well
as in vertebrae, radius and ulna.
Processes
• All projections of a bone.
• Heads and condyles are considered to be
processes.
• Tendons may attach to processes
Holes and Depressed Areas
• Foramen: A hole in bone.
• Usually allow the passage of nerve or
blood vessel.
• May exist simply to lighten structure
(pelvis-obturator foramen)
• Fossa: A depressed of sunken area on the
surface of a bone.
• Usually occupied by muscles or
tendons.
Types of Skeletons
• Bones of head and trunk are Axial
Skeleton
• Bones of limbs and appendages are
Appendicular Skeleton.
• Some animals may have Visceral
Skeleton- bones formed in the viscera or
soft organs.
Axial Skeleton
bones of head & trunk
•
•
•
•
•
Skull
Hyoid bone
Spinal column
Ribs
Sternum
Skull
• Usually consists of 37 or 38 separate bones
• Most skull bones joined by sutures (fibrous joint)
• Mandible is connected to skull by a synovial joint (TMJ)
Skull
External bones:
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Frontal bones (2)
Occipital bones (1)
Parietal bones (2)
Temporal bones (2)
Incisive (2 )
Nasal (2)
Maxillary (2)
Zygomatic (2)
Mandible (2)
Palatine (2)
Turbinates (2)
Skull Bones Continued
• Categorized by:
• Bones of Cranium
• Bones of the ear
• Bones of the face
Bones of the Cranium
• Cranium-portion of skull that surrounds the
brain.
• External Bones of Cranium:
• Frontal Bones (2)
• Interparietal Bones (2)
• Occipital Bone (1)
• Parietal Bones (2)
• Temporal Bones (2)
• Internal Bones of Cranium:
• Ethmoid Bone (1)
• Sphenoid Bone (1)
External Bones of Cranium
Occipital Bone
• Forms caudoventral portion or base of
skull, most caudal skull bone.
• Important because:
• Where spinal cord exits skull
• Skull bone that articulates with first
cervical (neck) vertebrae.
• Foramen Magnum is in center of occipital
bone.
• Occipital Condyles are on either side of
foramen magnum
Interparietal Bones
• Small bones located on dorsal midline
between occipital and parietal bones
• Clearly visible in young animals, may fuse
together in older animals.
Parietal Bones
• Form the lateral walls of the cranium
• Well developed in dogs, cats and humans,
but relatively small in horses and cattle.
Temporal Bones
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•
•
•
Located ventral to the Parietal bones
Form walls of the cranium
Contain middle and inner ear structures
Form Temporamandibular Joints (TMJ’s)
with the mandible (Lower jaw)
Frontal Bones
• Form forehead region of skull.
• Located rostral to parietal bone.
• Frontal sinus is contained within frontal
bone.
• Horns are extension of frontal bone.
Internal Bones of the Cranium
• Sphenoid Bone
• Forms ventral portion of the cranium and
contains the pituitary fossa.
• This contains the pituitary gland.
• Contains the sphenoidal sinus in most animals.
• Ethmoid Bone
• Located rostral to sphenoid bone.
• Contains cribriform plate which has branches of
olfactory nerve passing through.
• In horses and humans also have ethmoidal
sinus in the ethmoid bone.
Bones of the Ear
• Hidden in the middle ear from the outside
in:
• The Malleus- hammer
• The incus- anvil
• The stapes- stirrup
• Function is to transmit vibrations from the
tympanic membrane (eardrum) to cochlea
where vibrations are changed into nerve
impulses.
External Bones of the Face
• Incisive Bones:
• Also called premaxillary bones
• In common domestic animals house
upper incisor teeth. (Ruminants have a
dental pad instead)
• Nasal Bones:
• Form the bridge of the nose.
• Size depends on length of nose of
animal.
External Bones of the Face
continued…
• Maxillary Bones:
• Make up upper jaw.
• House upper canine teeth, premolars
and molars.
• Houses maxillary sinuses.
• Forms hard palate with palatine bones.
• Lacrimal Bones:
• Form medial portion of the orbit of the
eye.
• Contain lacrimal sac which is part of
tear system.
External Bones of the Face
continued…
• Zygomatic Bones:
• Also known as the malar bones.
• Join process from temporal bones to form
zygomatic arch.
• Mandible:
• The lower jaw.
• Houses all lower teeth and is the only moveable
part of the skull.
• Forms TMJ with the temporal bone on each
side.
• Unite at mandibular symphysis at rostral end.
• Composed of shaft (horizontal portion) and
ramus (vertical portion).
Internal Bones of the Face
• Palatine Bones:
• Make up part of hard palate
• Pterygoid Bones:
• Support part of the lateral walls of the pharynx
(throat).
• Vomer Bone:
• Forms part of nasal septum (wall between left
and right nasal passages).
• Turbinates:
• Also called nasal conchae.
• Thin and scroll-like that fill most of nasal cavity
space.
Hyoid Bone
• Also called hyoid apparatus.
• Supports base of tongue, the pharynx, and
the larynx and assists in swallowing.
• Composed of several parts that are united
by cartilage.
• http://www.youtube.com/watch?v=Nc5IRj3
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Spinal Column
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Also called the vertebral column
Made up of vertebrae that extends from skull to tip of tail.
Vertebrae are divided into 5 portions:
• Cervical (neck)
• Abbreviated C
• Contain 7 vertebrae in dogs and cats
• Thoracic (chest)
• Abbreviated T
• Contain 13 vertebrae in dogs and cats
• Lumbar (abdomen)
• Abbreviated L.
• Contain 7 vertebrae in dogs and cats.
• Sacral (pelvis)
• Abbreviated S.
• Contain 3 vertebrae in dogs and cats.
• Coccygeal (tail)
• Abbreviated Cy.
• Number is variable.
•
Refer to vertebrae by letter designation and number designation.
Vertebrae Characteristics
•
Consists of:
• Body
• The main, ventral portion of the bone.
• Separated from other vertebrae by intervertebral disks
of cartilage.
• What type of cartilage makes this up?
• Arch (neural arch)
• Arch helps to make up vertebral foramen which allows
passage of the spinal cord.
• Processes
• Transverse Processes
• Laterally projecting
• Site of muscle attachement.
• Articular Processes
• Found on cranial and caudal ends of vertebrae,
help to join adjacent vertebrae.
• Spinous Processes
• Single and projects dorsally
Intervetebral Disk Disease (IVDD)
• When disks “slip”
• More predominant in long-backed breeds
(dachsunds, Bassets).
• Can confirm with radiographs.
• Usually once it occurs, animal is
predisposed.
• Curative procedure is surgery to fuse
spinal column together.
• Animals may become paralyzed (dragging
rear legs).
Cervical Vertebrae
• Atlas is C1
• Holds up head.
• Has “wings of the
atlas”
• Has no vertebral
body, just is a ring
which spinal cord
passes through.
• Axis is C2
• Has large spinous
processes.
Thoracic Vertebrae
• Have tall spinous processes.
• Have articular facets which communicate
with the ribs.
Lumbar Vertebrae
• Dorsal to abdominal region.
• Most massive-looking bones in spinal
column.
Sacral Vertebrae
• Fuse together to form one single, solid
structure.
• Called the sacrum.
• Joins pelvis via sacroiliac joint.
Coccygeal Vertebrae
• Bones of the tail.
• Appearance changes as bones progress
down the tail.
• In humans fuse into coccyx.
Ribs
• Flat bones that form the lateral walls of the
thorax.
• Usually rib number is equal to the number
of thoracic vertebrae.
• Have more of a moveable joints which is
allows lungs to expand.
• Term for rib is costal.
• Sternal ribs attach to sternum
• Asternal ribs make up caudal part of
thorax.
• Unattached ribs are called floating ribs.
Sternum
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Breastbone
Made up of sternebrae.
Most cranial sternebrae is manubrium
Most caudal sternebrae is called xiphoid
process.
• May be broken during CPR.
Appendicular Skeleton
•
Made up of bones of limbs.
• Thoracic limbs (front leg)
• Scapula
• Humerus
• Radius
• Ulna
• Carpal bones
• Metacarpal bones
• Phalanges
• Pelvic Limbs (back leg)
• Pelvis
• Ilium
• Ischium
• pubis
• Femur
• Tibia
• Fibula
• Tarsal bones
• Metatarsal bones
• Phalanges
Appendicular Skeleton (limb bones)
Thoracic Limb
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•
•
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Scapula
Humerus
Radius
Ulna
Carpal bones (carpus)
Metacarpal bones
• Phalanges
Scapula
• Most proximal bone of the thoracic limb.
• Flat and triangular.
• Has prominent ridge on lateral surface
referred to as “spine of the scapula”
• Glenoid cavity at distal end forms portion
of ball and socket shoulder joint.
Humerus
• Long bone of upper arm (brachium)
• Has head at proximal end with tubercles
(processes) where muscles attach.
• Condyle at distal end is composed of
trochlea, capitulum, medial and lateral
epicondyles, and olecranon fossa.
• Is not “funny bone” (actually is a nerve not
a bone).
Ulna
• One of two bones that form antebrachium
(forearm).
• Forms major portion of elbow joint with
distal end of the humerus.
• Has large olecranon process at proximal
end which forms the point of the elbow.
• Trochlear notch makes elbow tight.
• End of trochlear notch forms anconeal
process.
• Where triceps brachii muscle attaches.
• Coronoid process articulates with the
radius.
Radius
• Main weight bearing bone of the
antebrachium.
• Articulates with humerus and ulna.
• Styloid process articulates with carpus.
Carpal Bones
• Carpus has two rows of bones.
• Is the “wrist” of the animals
• Proximal row bones have names
(radial carpal bone, ulnar carpal
bone, accessory carpal bone)
• Distal row bones numbered
medial to lateral (1st carpal, 2nd
carpal, etc)
Metacarpal Bones
• Extend distally from distal row of carpal
bones to proximal phalanges of the digits.
• Numbered from medial to lateral (dewclaw
being number 1 in dogs and cats).
• Horses have one large metacarpal bone
(cannon bone) and two non-weight
bearing splint bones.
• Cattle have fused metacarpal bones with
sesamoid bones (proximal and distal).
Phalanges
• Each digit is made up of two or three
phalanges (single bones are phalanx)
• In horses phalanges are the long and short
pastern bone and coffin bone.
• Also have 2 proximal and 1 distal
(navicular bone) sesamoid bones.
• Dogs and cats have a ungual process that
surrounds the claw.
Appendicular Skeleton- Hind Limb
•
Connected to the axial skeleton at sacroiliac joint
Pelvic Limb:
• Pelvis
• Ilium
• Pubis
• Ischium
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Femur
Tibia
Fibula
Tarsal bones (tarsus)
Metatarsal bones
Phalanges
Pelvis
• May be referred to as the os coxae
• Develops as three separate bones on each side
that fuse into a solid structure.
• Joined at pelvic symphysis.
• Bones are:
• Ilium
• Cranial most bone of pelvis
• “Wings of the ilium” or hips.
• Ischium
• Most caudal pelvic bone
• Tailbone is ischial tuberosity.
• Pubis
• Smallest of the pelvic bones
Pelvic landmarks
• Acetabulum- portion of hip bone that forms
ball and socket joint with femur.
• We look at this area in cases of hip
dysplasia.
• Obturator foramen- large holes in pelvis
that help to lighten weight of pelvis.
• We look at this as landmark if
radiograph is straight or not.
Femur
• Long Bone of thigh
• Proximal end is the ball portion is called
head.
• Proximal end also contains the
trochanters where muscles attach.
• Distal end forms stifle joint (knee) with
condyles.
Patella
• Kneecap is largest sesamoid bone in the body.
• Formed in the distal tendon of the quadriceps
femoris muscle on the cranial aspect of the stifle
joint.
• Helps to protect tendon as it passes down over
the trochlea of the femur.
Patellar Luxation
• When trochlear groove is not deep enough
to contain patella so it slips in and out of
place.
• Usually will cause brief episodes of
lameness which can correct.
• May hear or feel “popping” in and out of
place.
• Found in small, toy breeds most
prevalently.
• Can be surgically corrected.
Fabellae
• Two small sesamoid bones located in the
proximal gastrocnemius or calf muscles.
• Not present in cattle or horses.
Tibia
• Main weight bearing bone of the lower leg
(shinbone).
• Forms stifle joint with femur.
• Forms hock (ankle) with tarsus.
• Medial malleolus- medial to distal articular
surface, knob of ankle.
• Tibial tuberosity of proximal end forms the
tibial crest.
• Where patellar tendon attaches.
Fibula
• Thin but complete bone in dogs and cats.
• Consists of proximal extremity, shaft, and
distal extremity.
• Serves as a muscle attachment site.
• Horses and cattle do not have shaft of
fibula.
• Forms lateral malleolus at distal end.
Tarsal Bones
• Ankle but in four legged animals is termed
the “hock”
• Consists of two rows of tarsal bones
(similar to carpal bones in wrist).
• Proximal row is named and distal row is
numbered.
• Contains calacaneal tuberosity which
forms the point of the hock. Site of
attachment for tendon of the
gastrocnemius muscle.
Metatarsal Bones
• Dogs and cats: four
metatarsal bones (II to V)
• Horses: 1 large metatarsal
bone (cannon bone) and 2
small metatarsal bones
(splint bones)
Pelvic Limb Phalanges
• Similar to thoracic limb phalanges
• Exceptions: dogs and cats
• Usually only 4 digits (II to V)
Visceral Skeleton
• Bones that form in organs
• Examples
• os cordis: in heart of cattle and sheep
• os penis: in penis of dogs, beaver, raccoons, and walruses
• os rostri: in nose of swine
Joints
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•
•
•
Junctions between bones
Can be moveable or immovable.
Arthro and articular refer to joints.
3 Types of joints:
• Fibrous Joints (synarthroses)
• Immovable
• Found in sutures of skull bones
• Cartilaginous Joints (amphiarthroses)
• Slightly moveable
• Vertebral disks between vertebrae
• Pelvic and mandibular symphisis
• Synovial Joints (diarthroses)
• Freely moveable
Characteristics of Synovial Joints
• Have Articular surfaces on bones
• Articular cartilag covering articular
surfaces
• Fluid-filled joint cavity
• Enclosed by a joint capsule
• Synovial membrane- outer
membrane
• Synovial fluid- lubricates joint
surfaces
• Ligaments - fibrous Connective tissue
that join bones to other bones.
Synovial Joint Movements
• Flexion and Extension
• Opposite movements
• Increase (extension) or decrease (flexion) angle
between two bones
• Adduction and Abduction
• Opposite movements
• Move an extremity toward (Adduction) or away
from (Abduction) medial plane
• Rotation
• Twisting movement of a part on its own axis
• Circumduction
• Movement of an extremity so that the distal end
moves in a circle
Types of Synovial Joints
•
•
Hinge Joints
• One joint surface swivels around another
• Only capable of flexion and extension
Gliding Joints
• Rocking motion of one joint surface on another
• Primarily capable of flexion and extension
• Abduction and adduction possible in humans
not dogs/cats
•
Pivot Joints
• One bone pivots (rotates) on another
• Only capable of rotation
•
Ball-and-socket joints
• Allow for all joint movements
• http://www.uen.org/utahlink/activities/view_
activity.cgi?activity_id=3052
• http://www.youtube.com/watch?v=REftXT
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