Bone Biology and Fracture Healing

Question 1

Skeletal bone is an organ, whose tissues constantly turn over by ____ and ____ activity

Answer 1

Skeletal bone is an organ, whose tissues constantly turn over by osteoclastic and osteoblastic activity

Question 2

cortical vs cencellous bone

Answer 2

cortical(compact)- 80% of the bone

• closely packed osteons
• porosity of 5-30%
• DIAPHYSEAL
• strong and resistant to bending

cancellous (trabecular bone)- 20%

• network of plates and rods to form struts
• not as strong as cortical bone, trabeculae follow the lines of stress
• metaphyseal
• 30-90% porosity– less dens
• 10% cortical bone strenght.

Question 3

osteoblasts

Answer 3

 OSTEOBLASTS - cells that form new bone (bone deposition). Build bone. Mesenchymal origin.

Question 4

origin of osteoblast

Answer 4

mesenchymal origin

Question 5

osteocytes

Answer 5

 OSTEOCYTES - some of the osteoblasts turn into
osteocytes while new bone is being formed. Can
sense stress on bone and help to direct
remodeling. Maintain bone and cellular matrix.

Question 6

osteoclasts

Answer 6

 OSTEOCLASTS - large cells that dissolve bone
(bone resorption). Hematopoietic origin.

Question 7

origin of osteoclast

Answer 7

hematopoietic origin (unlike blasts, which are mesenchymal origin)

Question 8

almost all bone is type ___ collagen

Answer 8

type I collagen.

Question 9

3 components of organic matter in bone. what percentage of bone is comprised of organic matter?

Answer 9

1. osteoid
2. type I collagen (90%)
3. provides flexibility and resilience
   - organic matter makes up 20-25% of bone ECM

Question 10

inorganic components of bone ECM

Answer 10

calcium, phosphate and hydroxyapatitie

• inorganic matter makes up 60-70% mature bone, and it provieds the hardness and rigidity

Question 11

bone is strongest in ___ and weakest during ___. ___ bone is stronger than __ bone.

Answer 11

bone is strongest in COMPRESSION and weakest during TENSION (PULLING APART). CORTICAL bone is stronger than CANCELLOUS bone.

Question 12

differentiate the blood supply of bone depending on the layers

Answer 12

the inner 2/3 of bone is endosteal– they are perfused by arteries in the bone

the outer 1/3 of bone is periosteal– they are supplied by arteries on top of the bone.

Question 13

Function of Bone (3 broad)

Answer 13

1. mechanical
2. biological (calcium homeostasis and end organ for hormones)
3. Hematopoesis.

Question 14

fracture healing: if left alone, the broken bone will heal by __ formation.

Answer 14

callus formation; calcium deposition at site of fracture. Callus is the natural reponse of living bone to interfragmentary movement.

Question 15

outline the stages of callus fracture healing. At what stage can you see the callus on XRAY?

Answer 15

you would not see soft callus on xray, but you would see hard callus on xray because that’s when remineralization occurs.

Question 16

callus formation is aka ___ bone healing

Answer 16

secondary bone healing.

Question 17

when you stabilize a fracture by a cast, the bone will heal by __ bone healing

Answer 17

secondary bone healing/callus– the bones are not activaly screwed into place and there is just relative stability.

Question 18

primary bone healing via anatomic ___ and ___ via screws results in absolute stability. Instead, it is healed by __ ___ and ___ ___ formation.

Answer 18

primary bone healing via anatomic REDUCTION and COMPRESSION via screws results in absolute stability. Instead, it is healed by CUTTING CONES AND LAMELLAR BONE FORMATION.

IN PRIMARY BONE HEALING, THERE IS NO CALLUS FORMATION.

Question 19

Outline some variables of hte injury, patient, tissue and treatment that can all affect fracture healing.

Answer 19

Question 20

metabolic bone abnormalities

 Vitamin D deficiency (____) – reduced bone mineralization

 ____ – quantitative bone loss
 ___ ____ procedure patients - calcium absorption is affected

 Diabetes mellitus - affects the ___ and ___ of bone

 HIV - higher prevalence of ____ fractures with associated delayed healing

 Excessive systemic inflammation –such as ___ ___, ____

Answer 20

 Vitamin D deficiency (Osteomalacia) – reduced bone mineralization

 Osteoporosis – quantitative bone loss

 Gastric bypass patients - calcium absorption is affected

 Diabetes mellitus - affects the repair and remodeling of bone

 HIV - higher prevalence of fragility fractures with associated delayed
healing

 Excessive systemic inflammation – Rheumatoid arthritis, polytrauma

Question 21

___ ___ is 100% required for primary bone healing

Answer 21

absolute stability. each piece of bone must be re-stabilized.

each piece is compressed across the fracture stem with screws.

there is no callus formation in primary healing– healing is all done through cone cutting and lamellar bone growht.

Question 22

Answer 22

Primary Bone Healing Healing via Cutting Cones Direct Osteonal Remodeling Minimal Callus

Question 23

what type of stability is occuring in the middle piece?

Answer 23

relative stabiltiy. this is like a mix of callus formation and primary bone healing. there will still be callus formation because the bone fragments are not being compressed by screws.