Bones and Joints 1

Question 1

What is the non-cellular component of bone (matrix+mineral) called and made of

Answer 1

Bone matrix or osteoid: Made of type 1 collagen, gives bone its toughness + ground substance (proteoglycan glue)
Osteoid mineralized: deposition of Ca and P in crystalline formation, gives bone its hardness (hydroxyapatite crystals

Question 2

What happens in itntramembraneous ossification and which bones are made this way

Answer 2

Mesenchymal cells become osteoblasts making no need for a cartilaginous model, flat bones are formed this way

Question 3

What happens in endochondral ossification and which bones are formed this way

Answer 3

A pre-existing cartilage model mineralizes, limb bones (long bones) are formed this way

Question 4

Where is the physis, what are the 3 zones within it, and what happens at its distal end

Answer 4

The physis is the growth plate responsible for longitudinal growth. It has 3 zones of chondrocytes: the resting/reserve, the proliferative, and the hypertrophic. At the distal end, there is apoptosis, capillary invasion, matrix mineralization, and woven bone deposited

Question 5

Is the growth plate widest

Answer 5

Widest when growth is rapid, then narrows and closes at skeletal maturity

Question 6

How is the metaphysis formed and what do they become

Answer 6

Endochondral ossification results in bony trabeculae/struts/downgrowths from the physis. These ultimately are shaped/fused/compacted into the diaphyseal cortex (zone of compaction)

Question 7

What shape are metaphyseal capillaries and what can happen in these capillaries

Answer 7

Loops which can cause entrapment of emboli

Question 8

Describe woven/immature bone and when it is found

Answer 8

-It is bone with collagen interwoven, not layered
-Osteocytes are numerous
-Inferior strength to lamellar bone
-It is found in embryo, at growth plates, callus, as a response to injury, inflammation, and neoplasia, and places when rapid structural reinforcement required “get it down fast”

Question 9

Describe lamellar bone, where it is found, and name the two types

Answer 9

-Lamellar bone is mature and dense
-The two types are Haversian and trabecular (cancellous/spongy)
-Haversian bone is concentric, parallel around central vascular channels with longitudinal cylinders (osteons)
-Trabecullar bone is parallel with the surface of the trabeculae within the medullary cavity

Question 10

Describe remodeling

Answer 10

-aka turnover
Damaged units replaced with new units, but mass and shape remain constant
-Wear and tear= micro fractures

Question 11

Describe modeling

Answer 11

-Where shape/contour altered in response to growth (but also disease)

Question 12

What is Wolff’s law

Answer 12

-Response to abnormal use or structural damage
-Compressive forces=formation
-Tension on bone= resorption
-Trabeculae align along lines of stress

Question 13

What is an infraction

Answer 13

Compression fractures of trabeculae that do not result in external distortion of bone outline, often secondary to inflammation or neoplasia

Question 14

What is reactive periosteal woven bone and when is it formed

Answer 14

-Formed from osteogenic layer and radiates perpendicular to diaphyseal surface to form Codmans triangle
-Deposited as a non-specific response to injury: blunt trauma, inflammation, neoplasia

Question 15

What is the difference between malformation and deformity

Answer 15

-Malformation: abnormalities in in-utero development
-Deformity: abnormalities arising in a previously normal part

Question 16

What is chondrodysplasia/achondroplasia

Answer 16

-Inherited errors in genes controlling chondrogenesis
-dysplasia of cartilage growth at physes (EO) leading to premature closure and disproportionate dwarfism

Question 17

Why is the dwarfism disproportionate with chondrodysplasia

Answer 17

It affects bones that develop by EO (limbs/vertebrae/base of skull) but does not affect bones that develop by IO (flat bones of skull)

Question 18

What is osteopetrosis and what causes it

Answer 18

-It is when the bone becomes denser with way more osteoids and smaller “holes”
-Osteoclasts fail to “reshape”/model metphyseal trabeculae from physis leading to medullary cavities thus fill with “cones” of trabecullar bone
-Inherited defect in osteoclasts or effect of teratogenic viruses on osteoclasts

Question 19

Why are bones with osteopetrosis more fragile, and what is the equation for bone strength/rigidity

Answer 19

-Bones with osteopetrosis are more dense because they are more rigid
- Equation = (rp^4 - re^4)

Question 20

What is osteoporosis

Answer 20

-It is a reduction in bone mass making both cortical and trabecular bone more porous. Trabeculae are lost and medullary cavities are widened. Bones become easily fractured by things that wouldn’t normally cause a fracture (pathological fracture), and this is due to resorption-formation uncoupling

Question 21

What are some causes of osteoporosis and is it reversible

Answer 21

-Ca deficiency: PTH increases leading to increased bone resorption
-Starvation: decreased bone formation
-Inactivity: piezoelectrical signals which have a role in modeling/remodeling
-Steriods: Cushings in dogs requiring glucocorticoid use)
-Potentially reversible in growing animals, irreversible in adults as trabeculae cannot regenerate