Lecture 28: MSK 1 Flashcards
List 3 cell types in bone and their respective origin?
osteoblasts: mesenchymal cells on bone surface
- immature
osteocytes: mature osteoblasts that are found in lacunae surrounded by ECM
- cannaliculi allow communication
osteoclasts: multinucleated hematopoietic cells formed from the fusion of monocyte/macrophages
- found on bone in howships lacunae
What is the function of osteoblasts
make osteoid and initiate mineralization
What is the function of oseocytes
- stimulate formation and resorption of bone in response to mechanosensation
make regulatory factors and regulate Ca/P homeostasis
What is the function of osteoclasts
resorb bone via acid hydrolases
What is extracellular matrix of bone made out of
hydroxyapetite - inorganic
- Ca/P
- other minerals: carbonate/Mg/Zn/Ca
osteoid - organic
- 90% type 1 collagen
- glycoproteins
What is the periosteum
The outer fibrous layer containing blood and nerves
inner cambrium layer is osteogenic and spindle shaped
It is separated from bone by the layer of osteoblasts
Compare and contrast woven bone and lamellar bone
woven bone aka reactive or new bone
- immature (young or remodelling)
- disorganized collagen
lamellar
- mature
- concentric collagen lamellae
- long term stability
Compare and contrast compact and cancellous bone
compact aka cortical bone
- high density (lamellar or woven)
- cortex and subchondral plate
cancellous aka trabecular or spongey bone
- low density (lamellar or woven bone)
- medulla
What is intramembranous ossification? Provide examples of bones formed this way
Bone forming from the mesenchymal tissue
no cartilage precursor
ex. flat bone of the skull
form the periosteal surface of all bones
What is endochondral ossification
Bone forming from a cartilage precursor/ossification center
aka physeal growth - from a growth plate
What is a physis? What are the 3 main zones of a physics?
growth plate
reserve/resting zone: lazy chondrocytes
proliferative: active chondrocytes, accumulate glycogen
- lengthening
hypertrophic: old chondrocytes - becoming mineralized
What characterizes the epiphysis?
It is capped by trabecular bone
no bone growth on this side of the physis
What characterizes the metaphysis
Bone growth occurs on this side of the physics
It has primary spongiosa: the blueprint for bone growth
- there is an abrupt demarcation between the physis and hypertrophic regions
- spiracules of mineralized cartilage from the scaffhold
secondary spongiosa is remodelling
What are 5 reactions to injury bone can have
necrosis
change trabeculae
change size/shape/mass
produce new bone
periosteal reaction
What can cause bone necrosis?
Reduced or blocked blood supply
osteocytes phagocytose necrotic bone
What are 2 consequences of bone necrosis?
sequestrum: mummified necrotic bone
- it leaves just mineral
involucrum: sequestrum surrounded by fibrosis/osseus and granulation tissue
- form bone cyst
What can cause bone to change its trabeculae? What is the result?
disruption of the endochondral ossification at the physis - alter the appearance of the primary spongiosa
- due to trauma/damage - salter harris fx
it causes premature close of the growth plate
- either focal or complete resulting in asymmetrical or symmetrical reduced elongation of the bone
What is wolffs law
bone will adapt to use
What is remodelling? What are the types of remodelling
normal process of bone replacement
if it is normal there is no change in shape or amount of bone made
primary: resorption and replacement of bone in growth
secondary: continuous replacement through life
What can cause a bone to produce more bone? What kind of bone does it produce?
In normal fetal development this occurs
can also be stimulated by irritation
- bone formation in a mature skeleton is abnormal
forms woven bone
What is hyperosteosis
excess production of bone
What is a periosteal reaction bone can have
woven bone production that is perpendicular to the long axis of the cortex
What is exostosis
hyperoseosis
osteophyte formation
- restricted to periarticular new bone
- ‘ knobs around joint’
Compare and contrast the 2 types of fractures
traumatic: normal bone experiencing excess force (trauma)
pathologic: abnormal bone experiencing normal force
- osteomyelitis (T. pyogenes)
- neoplasia
-metabolic dz
What are 2 main factors that fx repair depends on
stabilization and complications
What are the 4 stages of fracture repair
- hematoma: inflammation within days of injury
- soft/primary callus: fibroblasts and cartilage form in days-weeks
- hard/secondary callus: woven bone replacing cartilage
- remodelling: lamellar bone replacing woven bone, shrinking callus
What can you infer from the size of the fx callus
it indicated the stability
larger callus = less stable fx
smaller callus = more stable fx
hyperplastic callus can complicate diagnostic interpretation
What is a salter harris fracture
A fracture in a young animal that affects their growth plate
it mainly affects the physis because that is the weakest point = most likely to break
What are 4 major factors that contribute to fracture complications
- instability: inhibiting hard callus formation
- can lead to pseudoarthrosis (false joint) - reduced blood supply: causing osteonecrosis and sequestrum formation
- infection: bacterial osteomyelitis
- systemic disease: malnutrition or cachexia
A young animal is brought in to you with a long bone fracture. What fracture type do you expect to see?
a type 2 salter harris fracture
- through the growth plate and metaphysis
this is the most common type of salter harris fracture
Compare the complication rate of the different types of salter harris fractures
least complications with type 1 and 2 salter harris
type 3, 4, 5 can permanently damage the physis
type 3 and 4 can cause angular limb deformities
- valgus or varus
Compare valgus and varus
valgus - lateral deviation of the distal limb
varus - medial deviation of the distal limb
List 5 causes of angular limb deformity
trauma
cartilage deformity
malposition in utero
joint laxity
hypothyroidism
What is epiphysiolysis? Why does it occur?
separation of the epiphysis
due to high amounts of shear forces
- transphyseal fissure
- underlying dysplasia
Give examples of epiphysiolysis in cat, pig, and dog
cat: slipped capital femoral epiphysis
pig
- gilt - femoral head
- sow - ischial tuberosity
dog - un-united aconeal process
What is the function of parathyroid hormone
increase blood Ca
reduce blood P
cause bone degredation
- increase excretion of P and absorption of Ca
What is the function of calcitonin
decrease blood Ca and P
increase bone density (PTH antagonist)
What is the function of vitamin D
increase blood Ca and P
causes reduced PTH and increased resorption in kidneys and intestines
- increase osteoclast activity
What is the function of fibroblast growth factor 23?
reduce blood P
cause increase PTH and inhibition of vitamin D synthesis
What are 3 general categories of dysfunction that result in osteodystrophies?
failure of
producing bone
mineralization
maintenance of bone
What 2 main factors contribute to metabolic bone disease
nutrition
hormones
What is osteoporosis
reduced amount of normal bone
- bone resorption exceeds bone prod
bone is porous, thin, and brittle
retains. abnormal shape
When is osteoporosis diagnosible via radiographs
When there is a minimum of 30% bone loss
early stages are often missed
What type of lesion is osteoporosis associated with commonly
pathological fractures
loss of trabecular bone preferentially
also loss of bone cortices
What is the most common metabolic bone disease
osteoporosis
What are 6 major causes of osteoporosis
malnutrition
Gi parasitism
secondary to lactation
malabsorption (chronic IBD)
starvation
disuse - wolffs law
Define serous atrophy of fat? What does this indicate? What is the common lesion affecting bone?
It is the preferential use of fat from body compartments due to a negative energy balance
SC > visceral > bone marrow
It causes watery and gelatinous bone marrow
What are growth arrest times? What causes them?
It is disruption in endochondral ossification due to a transient decrease in growth. It causes a temporary sealing of the growth plate
- can visualize in the trabecualr parallel to the physis
- as growth continues this line will be carried into the metaphysics
due to malnutrition or debilitation (ex. BVD/distemper)
Compare osteomalacia and ricketts
Osteomalacia
- mature animals
- occurs in areas of remodelling
Ricketts
- young animals
- in growth plates
They are both due to problems with mineralization
- vitamin D or P deficiency
List 2 common disease conditions that can occur due to calcium deficiency
fibrous osteodystrophy
osteoporosis
It will not cause ricketts or osteomalacia
What is the gross lesions associated with osteomalacia
unmineralized osteoid that persists
What are the gross lesions of ricketts
irregular thickening
tongues of cartilage in the metaphysis
enlargement of the costochondral junctions - rachitic rosary
soft and malleable bone
What is a characteristic histologic feature of ricketts
Persistent hypertrophic chrondrocytes
- normally they would initiate mineralization and apoptosis
List 4 causes of vitamin D deficiency
reduced UV light
vitamin D anatagonist ingestion (plant)
reduced dietary intake
congenital
What is fibrous osteodystrophy? Why does it occur?
It is the replacement of bone with fibrous tissue and woven bone
occurs in adults
due to chronically high PTH
List 2 causes of primary hyperparathyroidism and what is a common sequelae
parathyroid tumor
pseudohyperparathyroidism (hypercalcemia of malignancy)
both result in fibrous osteodystrophy
What are 2 types of secondary hyperparathyroidism and what is a common sequelae
renal
nutritional
both cause fibrous osteodystrophy
How does nutrition cause hyperparathyroidism? What species does it affect?
if there is an imbalance in the Ca:P ratio
- high P + low Ca
dogs/cats: all meat diets
horses/goats: high grain/cereal/oxalate diet
cause FOD
sheep/cows
- nutritional hyperparathyroidism will cause osteoporosis not FOD
A horse presents to you with a history of a high cereal grain diet and bilateral swelling of maxillary bones. What is your top differential? Why?
bighead disease
due to nutritional secondary hyperparathyroidism
it causes the bilateral swelling of the maxillary bones because horses are always chewing
can also cause displaced/loose teeth and compression of nasal passages
Describe the pathogenesis of renal secondary hyperparathyroidism
- CKD
- low GFR
- P retained (should be excreted)
4a. C and P precipitate (low blood P)
5a. Stimulate parathyroid = high PTH
4b. high fibroblastic growth factor 23
5b. reduced vitamin D
What are the gross features of fibrous osteodystrophy
swollen and weak bones
normal physis
- except if young with low vitamin D and concurrent ricketts
What animals are susceptible to vitamin A (retinol) deficiency? Why
cattle and pigs
if given unsupplemented ration or if given old hay (vit A will decrease over time)
What are the gross and clinical consequences of vitA deficiency?
causes defective remodelling of membranous bone
- asynchronous skull development
causing
- micropthalmia
- blindness due to optic foramina narrowing
- cerebellar herniation through foramen magnum because braincase doesn’t grow
What is the pathological and clinical consequences of vitC (ascorbic acid) deficiency
impairs collagen synthesis and osteoblast differentiation
causing bleeding
What 3 animals are primarily prone to vitC deficiency?
humans
guinea pigs
cetaceans
