Bone Healing And Grafts

Question 1

Primary osteons

Answer 1

Form during bone growth

Question 2

Secondary osteons

Answer 2

Form during remodeling

Question 3

Mechanisms of new bone formation

Answer 3

Cutting cones
Intramembranous ossification
Endochondral ossification

Question 4

Cutting cones

Answer 4

Primary bone healing + remodeling

Osteoclasts lead to remove bone, osteoblasts trail to lay down new bone

Question 5

Intramembranous ossification

Answer 5

Does not require cartilage precursor

Increases width of bone

Question 6

Endochondral ossification

Answer 6

Cartilage precursor

Chondrocyte hypertrophy —> calcification —> ossification

Increases bone length

Question 7

Prerequisites for bone healing

Answer 7

Adequate blood supply
Interfragmentary stability
Absence of infection (or subclinical/well-controlled infection)

Bone formation requires low strain (<2%)

Question 8

Strain

Answer 8

Change in length over length under an applied biomechanical force

Question 9

Goals of fracture stabilization

Answer 9

Decrease interfragmentary strain

Decrease fracture gap

Question 10

Indirect bone healing

Answer 10

1. Hematoma formation
2. Fibrocartilage callus formation
3. Bony callus formation
4. Bone remodeling

Question 11

Strain tolerance

Answer 11

Granulation tissue: 100%
Cartilage: 10%
Lamellar bone: 2%

Question 12

Types of fracture healing

Answer 12

1. Direct (primary) healing: contact healing, gap healing
2. Indirect (secondary) healing

Question 13

Direct (primary) bone healing

Answer 13

Occurs only with anatomic reduction + rigid stability

***no micromovement

<2% interfragmentary strain + <1 mm fracture gap (<0.01 for contact healing)

Cutting cones, lack of callus formation

Question 14

Contact healing

Answer 14

Occurs in zones of cortical bone contact (<0.01 mm gap)

Cutting cones, direct formation of lamellar bone in axial direction

Question 15

Gap healing

Answer 15

<1mm, <2% strain

Initially filled with loose connective tissue

Osteoblasts deposit lamellar bone in gap

Cutting cones formed longitudinally

Secondary osteoblasts reconstruction

Question 16

Indirect (secondary) bone healing

Answer 16

Less stable fractures
Callus formation to stabilize / decrease strain
Indirect healing through transformation of fibrous tissue and cartilage

Question 17

Stages of indirect bone healing

Answer 17

1. Inflammation (0-7 d)
2. Repair (soft callus 1-3, bony callus 3-6)
3. Remodel (> 8 wks to yrs)

Question 18

Inflammatory phase of indirect bone healing

Answer 18

Hematoma formation
Revascularization
Resorption of fragment ends + hematoma

Question 19

Repair phase

Answer 19

Hematoma —> granulation tissue

Granulation tissue —> fibrocartilage

Mesenchymal cells differentiate into chondrocytes or osteoblasts

Question 20

Remodeling phase

Answer 20

Regain function / strength

Formation of new secondary osteons

External callus disappears

Reestablishment of medullary cavity

Secondary remodeling - involves cutting cones

Question 21

Osteogenesis

Answer 21

Osteoblasts in bone graft material contribute to new bone growth

Question 22

Osteoinduction

Answer 22

Bone graft recruits osteoprogenitor cells and induces new bone formation

Question 23

Osteoconduction

Answer 23

Serves as a scaffold for osteoprogenitor cells

Question 24

Osteopromotion

Answer 24

Enhancement of osteoinduction without possession of osteoinductive properties (rare, i.e. enamel matrix)

Question 25

Bone graft functions

Answer 25

Osteogenesis Osteoinduction Osteoconduction Osteopromotion Structural support

Question 26

Bone graft indications

Answer 26

Augment repair, speed healing, promote healing of non-unions / infected fractures Enhancing healing (fracture, osteotomies, delayed/non-union) Bone loss (fracture, excision from neoplasm)

Question 27

Bone graft sources

Answer 27

Autograft Allograft Xeongraft

Question 28

Types of bone graft

Answer 28

Cancellous bone Cortical bone Corticocancellous bone Demineralized bone matrix Synthetic bone grafts

Question 29

Cancellous bone graft

Answer 29

Metaphyseal trabecular bone Endosteal + marrow cells Autogenous is gold standard Properties: osteogenic, osteoinductive, osteoconductive

Question 30

Cortical bone grafts

Answer 30

Strut of long bone providing mechanical support Osteoconductive (i.e. provides scaffold)

Question 31

Harvesting bone grafts

Answer 31

Cancellous - aseptic, prepare surgical site in advance, separate surgical instruments, drill hole through 1 cortex use currette to obtain cancellous bone

Question 32

Cancellous donor sites

Answer 32

SA: lateral tubercle of proximal humerus; proximomedial tibia; craniodorsal iliac spine, subtrochanteric region of medial condole of femur LA: ilium, sternum

Question 33

Bone graft substitutes

Answer 33

Synthetics: calcium phosphate, hydroxyapatite, bio active glasses, polymers (osteoconductive) Growth factors (BMP, TGF-B —> osteoinductive)

Question 34

Assesment of healing

Answer 34

SA: 2 orthogonal views, 3/4 cortices with bridging callus LA: 4+ views Callus formation, appearance of fracture site, margins of fracture fragments, bone opacity/density, periosteal/endosteal reaction