3: Principles of Bone Healing - Carnevale

Question 1

breakdown of bone

Answer 1

• 35% organic

- 65% inorganic

Question 2

matrix of bone

Answer 2

95% collagen type I

5% non-collagenous prtns

Question 3

unmineralized bone =

Answer 3

osteoid

Question 4

pluripotent mesenchymal cell that can form osteoblasts

Answer 4

osteoprogenitor

Question 5

cells that initiate mineralization

Answer 5

osteoblasts

- synthesize and transport prtn (like type 1 collagen) and osteoprotegerin

Question 6

what receptor on osteoclasts stimulates osteoclastic bone resorption

Answer 6

RANK receptor

- RANK ligand is produced by osteoblasts

Question 7

become osteocytes when surrounded by matrix

Answer 7

osteoblasts

- osteocytes are matured osteoblasts that regulate daily serum calcium and phosphorus

Question 8

responsible for bone resorption

Answer 8

osteoclasts

• mutliple nuclei
• live in howship lacunae

Question 9

osteoprotegerin

Answer 9

acts as decoy on RANK receptor on osteoclast

Question 10

what are osteoclasts derived from?

Answer 10

hematopoietic progenitor cells

Question 11

role of estrogen in bone growth

Answer 11

• increases bone formation by increasing collagen synthesis by osteoblasts
• prevents bone resorption by inhibiting osteoclast differentiation

Question 12

when is woven bone normal?

Answer 12

• fetal skeleton
• growth plates
• pathologic in adults almost always

Question 13

only type of normal bone in adults

Answer 13

lamellar bone

- highly orderly

Question 14

terms

• end of long bone
• growth plate
• next to growth plate
• shaft
• bone covering (blood vessels, nerves)

Answer 14

epiphysis
epiphyseal plate
metaphsis
diaphysis
periosteum

Question 15

describe bone remodeling cycle

Answer 15

1. osteoclast precursors recruited to bone surface, where thy fuse, differentiate, and mature
2. osteoclasts resorb both organic and inorganic bone matrix
3. resorption phase ends with osteoclast apoptosis
4. in reversal phase, osteoblasts differentiate from mesenchymal precursors, under influence of factros from osteoclasts, and secrete new bone matrix (osteoid)
5. at end of cycle, some osteoblasts have been incorporated into bone as osteocytes and others remain on the surface as quiescent bone-lining cells

Question 16

why do we need vit C for bones?

Answer 16

• maintenance of normal connective tissue
• synthesizes collagen
• responsible for bone formation –> synthesizes organic matrix
• inorganic calcified portion of capillary walls

Question 17

clinical syndrome related to problems with osteoid synthesis AND collagen support of blood vessels

Answer 17

scurvy (vit C deficiency)

• note hemorrhages found around corkscrew hairs
• poor wound healing
• subperiosteal hemorrhage

Question 18

three phases of fracture healing

Answer 18

1 = organization of hematoma at fracture site –> soft, organizing PROCALLUS (hematoma organizing by end of 1st wk, anchorage, no structural rigidity)

2. conversion of procallus to FIBROCARTILAGINOUS CALLUS : reactive mesenchymal cells (deposition of woven bone and new cartilage); 3rd wk; max enlargement
3. replacement of mesencymal cells by OSSEOUS CALLUS; eventually remodeled along lines of weight bearing; completes repair (endochondral ossification forms bony networl; fractured ends bridged by bone callus)

Question 19

“callus”

Answer 19

orderly progression of cartilage into microtrabecular new bone

Question 20

inhibitory factors to fracture healing

Answer 20

• infection
• non union
• inadequate immobilization
• poor circulation, poor nutriton
• drugs (corticosteroids, immunosuppressives, cytotoxic therapy)
• systemic abnormality

Question 21

mechanisms of avascualr necrosis (infarction of bone and marrow resulting from ischemia)

Answer 21

• fracture
• corticosteroids
• uncertain cause idiopathic
• sickle cell disease

Question 22

most common route of osteomyelitis

Answer 22

hematogenous

Question 23

most common agents of osteomyelitis

Answer 23

pyogenic (staph aureus) agents or mycobacterium tuberculosis

Question 24

cause of osteomyelitis in sickle cell patients

Answer 24

salmonella

Question 25

sequestrum

Answer 25

residual necrotic bone post osteomyelitis - may be resorbed or surrounded by rim of reactive bone called involucrum

Question 26

brodie abscess

Answer 26

when well-defined rim of sclerotic bone surrounds residual abscess - viable organisms may persist