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The Skeletal System
• Functions of the Skeletal System
– Support against gravity
– Leverage for muscle action - movement
– Protection of soft internal organs
– Blood cell production
– Storage - calcium, phosphorous & fat
The Skeletal System
• The skeletal system includes:
– Other connective tissues
Structure of Typical Long Bone
• Diaphysis - tubular shaft forming the axis of
– Composed of compact bone
– Central medullary cavity
– Contains bone marrow
• Epiphysis – expanded end of long bones.
– Composed mostly of spongy bone
– Joint surface is covered with articular (hyaline)
– Epiphyseal lines separate the diaphysis from
• Metaphysis – where epiphysis and diaphysis
Bone - Remodeling/Homeostasis
• Homeostasis and Mineral Storage
– Bones store calcium
• Contain 99% of body calcium
• Store up to 2 kg calcium
• Hormones control storage/release
– PTH, calcitriol release bone calcium
– Calcitonin stores bone calcium
• Blood levels kept constant
General Structure of Synovial Joints
• Articular cartilage
– Ends of opposing bones are
covered with hyaline cartilage
– Absorbs compression
• Joint cavity (synovial cavity)
– Unique to synovial joints
– Cavity is a potential space that
holds a small amount of synovial
– Depends on type of muscle tissue
– Depends on location of muscle tissue
• Posture Maintenance
• Joint Stabilization
(I) CONGENITAL MUSCULOSKELETAL
• Congenital disease of bone, cartilage ( joint
deformity), & muscle (congenital myopathy)
may be identifiable at birth or shorty
thereafter & often have an inherited etiology.
• Reduced growth in terms of skeletal
development or body wt. when compared
– normal littermates
– or a failure to attain the weight & height
standards characteristic of a given breed.
• Many diseases may result in retarded growth.
• Most patients with
have reduced skeletal
growth, characterized by
• They have long trunks &
• Occur in the skull, axial & appendicular
• Characterized by overrepresentation or a
partial or complete absence of one or more
• Severe joint malformation are rarely diagnosed.
• May ranges from complete absence of joints to
bony fusion of skeletal elements.
• It is group of primary, inherited diseases of
skeletal muscle identified within the first
weeks to months after birth.
(II) ACQUIRED MUSCLUOSKELETAL
• Do not have a primarily genetic etiology & are
not identifiable at birth.
Traumatic injuries (fractures)
• Approximately 40-50% of all dogs presented
to referral centers with traumatic injuries are
less than 1 year of age.
• Traumatic growth plate injuries have been
classified by Salter & Harris in an effort to
relate mechanisms, characterized by a
separation through the growth plate
• A type I growth plate injury is
characterized by a separation through
the growth plat.
• A type II injury is a combined growth
• A type III injury is a combined growth
plate separation-epiphyseal fracture.
• A type IV injury is characterized by a
combination of a growth plate
separation with an epiphyseal &
• Type V injuries are caused by
crushing of the growth plate, which
results in premature closure &
reduced bone length growth.
• Limb deformities with abnormally
shaped bones may be caused by
nutritonal diseases & growth plate
• Clinically this results in shortened
bones or asymmetrical growth
plate with subsequent angular
deformity & rotational deformities
of the affected bone.
• It includes nutritional secondary
hyperparathyroidism, hypovitaminosis D
(rickets), hypervitaminosis D, hypovitaminosis
A, hypervitaminosis A, hypovitaminosis E
Developmental orthopedic bone
• Craniomandibular osteopathy occurs in Terrier breeds.
• The bony formation along the mandible can be so
severe the affected dogs may not be able to prehend &
• In young large or giant
breed dogs, diaphyseal
pain in one or multiple
bones may be an
indication of panosteitis.
osteodystrophy is a
in immature, large, or
giant breed dogs in
which the metaphyseal
area of long bones
becomes swollen &
• Approximately 35% of dogs
younger than 1 yr of age
presented with a musculoskeletal
problems are diagnosed with an
• Arthopathies may be classified as:
– Non inflammatory
• Non infectious
• About 95% of the arthopathies in
growing dogs are non-
• Several breeds are
shoulder OC & 50-
70% heritability has
been estimated in
Radiographic image of osteochondrosis
dissecans (OCD) lesions of the caudal
aspects of the humeral head
• Lameness localized to the
elbow of young growing dogs
with no history of trauma is
usually caused by the
syndrome called elbow
• It includes ununinted
anconeal process, fragmented
medial coronoid process, OC
of the medial humeral
condyle, ununited medial
epicondyle & asynchronous
growth B/W radius & ulna.
• Medial patellar luxation occurs mainly in small
or miniature dog breeds.
• Lateral patellar luxation occurs mainly in large
• Canine hip dysplasia (CHD) is a developmental trait
primarily affecting medium & large breed dogs.
• It is characterized by faulty conformation & laxity of
the hip joint that usually affects both hips.
• Clinically, early synovitis & capsulitis caused by
subluxation is characterized by hindlimb lameness,
reduced exercise tolerance, reluctance to jump, a
“bunny hopping gait” & pain in hip joint.
• Affects all breeds of dogs, but more common in large
• Small Animal Pediatrics by Michael E.
Peterson & Michelle Anne Kutzler