Bone formation, modeling and remodeling

Question 1

two mechanisms of bone formation

Answer 1

endochondral ossification

intramembranous ossification

Question 2

Endochondral Ossification

Answer 2

• -Formation of the appendicular skeleton
• -hyaline cartilage model is sequentially resorbed and then replaced with bone
• -emphasis on importance of blood supply
• -cartilage precursor

Question 3

endochondral ossification: longitudinal growth

Answer 3

1) epiphyseal cartilage removal: secondary center of ossification
2) After mineralization angiogenesis and resorption
3) woven bone deposition (primary spongiosa), remodeling to cortical bone
4) endochondral ossification of physeal cartilage between the primary and secondary centers of ossification

Question 4

Resting zone

Answer 4

small, inactive mesenchymal stem cells that divide and give rise to chondrocytes

Question 5

Proliferation zone

Answer 5

Columns of chondroblasts which quickly divide, pushing epiphysis away from the diaphysis
THIS LENGTHENS THE BONE

Question 6

maturation/hypertrophic zone

Answer 6

Chondrocytes mature and enlarge

Question 7

calcification zone

Answer 7

cartilaginous matrix calcifies resembling trabeculae

Chondrocytes die

Question 8

ossification zone

Answer 8

Osteoclasts degrade cartilage

osteoblasts form actual trabecular bone

Question 9

Intramembranous Ossification

Answer 9

Key difference: No cartilage intermediate

involves condensation and differentiation of mesenchymal tissues

Question 10

Circumferential bone growth

Answer 10

appositional bone growth occurs by direct deposition of bone at periosteal surface
–at same time bone is resorbed from the endosteal surface to cause the marrow cavity to increase in size

Question 11

Basic multicellular unit (BMU)

Answer 11

Osteoblast + osteoclast

Question 12

General bone remodeling

Answer 12

ARFF=activation, resorption, Reversal, Formation

Question 13

Trabecular bone remodeling

Answer 13

1) the BMU is located on the suface
2) covered by a canopy predominantly of mesenchymal cell origin with osteoclasts resobing bone
3) resorbed surface is cleaned up by lining cells and probably macrophages
4) osteoblast precursors differentiate to fill the space that has been resorbed

Question 14

cortical bone remodeling

Answer 14

1) BMU in cortex comprises a cutting zone led by osteoclasts
2) Cutting conce proceeds through bone followed by differentiating osteoblasts
3) resultant space is filled by blood vessels, nerves and connective tissue
4) like trabecular bone it can also occur on periosteal and endosteal surfaces

Question 15

what are cement lines

Answer 15

• -basophilic lines between lamellae
• -represent “reversal” points (bone is removed down to this level)
• -new bone is then added on top of the cement line
• -observed in both cortical and trabecular bone

Question 16

Modeling

Answer 16

Skeletal immaturity= formation»resorption and is longitudinal and appositional growth

involves changes in bone size and shape (formation and resorption on different surfaces)

Ex: Radial growth (increasing diameter) of growing bone

Question 17

At Skeletal Maturity

Answer 17

Formation=resorption (remodeling)

Question 18

turnover of skeleton

Answer 18

100%=first year of life

5-10% annually thereafter

Question 19

when resorption exceeds formation

Answer 19

the integrity of the bone is decreased

Question 20

what drives remodeling

Answer 20

1) mechanical loading
2) systemic and local hormones
3) Trauma
4) Microfractures-failure to remove leads to stress fractures

Question 21

Skeletal response to loading

Answer 21

bone remodels according to the forces acting upon it (wolff’s law)
bone can sense mechanical forces and transduce the signal and respond accordingly

Question 22

Bone deformation

Answer 22

1) piezo-electric currents
2) increase or decrease local bone formation
3) induce complementary osteoclast activity

Question 23

loading stimulates..

Answer 23

net formation (decreased activation, increased bone formation)

Question 24

Unloading stimulates..

Answer 24

bone resorption (increased activation frequency)

Question 25

Disuse osteopenia

Answer 25

due to Limb disuse (paralysis or surgery)

Question 26

Restoration of optimal bone

Answer 26

depends on anatomic alignment and a return to functional activity