Lecture 17 - Autograft/Bone Biology

Question 1

Bone Autograft

Answer 1

• Take bone somewhere else in body
• Greater chance of bone fusion
• Contains bone cells/bone inducing proteins

Question 2

Disadvantages of Autograft Bone Harvesting

Answer 2

• Harvest (incision, chiseling, etc.)
• Infection
• Donor site morbidity
• Hard to match properties/mechanics

Question 3

Synthetic Bone Grafts

Answer 3

• Chemistry: Type IV (tricalcium phosphate, concerned about rate of degradation vs. new bone formation), HA
• Physical: Porous structure (balance between porosity for bone ingrowth and large struts around pores to withstand load)

Question 4

Osseointegration

Answer 4

• Bone ingrowth up to/into surface of implant without soft tissue at interface (without fibrous encapsulation)
• HA layer deposited on surface of implant, causes mechanical gradient

Question 5

Axial Bone

Answer 5

Center of body

Question 6

Appendicular Bone

Answer 6

Appendages of body

Question 7

Bone Function

Answer 7

• Provide support
• Provide protection of organs
• Facilitate movement
• Store minerals (growth factors)
• Store hematopoesis

Question 8

Macroscopic Bone Structure

Answer 8

Compact (Lamellar) bone
- Low porosity 
- Appears smooth from naked eye
Cancellous bone
- Trabeculae (mineralized component)
- Increased porosity (40-95%)
- Red or yellow marrow
- Lamellae made of collagen with osteoclasts trapped inside

Question 9

Long Bone

Answer 9

• Diaphysis: compact bone collar over marrow-filled medullary cavity (midsection of bone)
• Epiphyses: bone ends, compact over spongy, articular cartilage, epiphyseal line (remnant of epiphyseal plate-growth)
• Membranes: periosteum (highly vascularized osteogenic progenitors-heal bones with large defects)

Question 10

Flat Bone

Answer 10

• Compressive loads, more simple
• Thin periosteum covering compact bone
• Endosteum covered spongy bone on inside
• No diaphysis or epiphysis (same everywhere)
• Bone marrow filling spaces between trabeculae

Question 11

Short Bone

Answer 11

• Thin layer of compact bone surrounding spongy bone

- Low density with increased flexibility

Question 12

Irregular Bone

Answer 12

• Complicated shape (doesn’t fit in other categories)

- Composed of spongy bone and marrow covered with compact bone

Question 13

Microscopic Bone Structure

Answer 13

Cellular components:
- Osteogenic cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Constituents
- Collagen 
- Mineral (HA)

Question 14

Woven Cortical Bone

Answer 14

• No osteons
• Can be formed de novo (doesn’t require existing cartilage/bone)
• Found in young skeletons
• Adults (only in disease or injury)
• Most disorganized structure
• Most osteocytes
• Quickly deposited, weak mechanical properties initially

Question 15

Osteons

Answer 15

Circumferential structure (lamellae of mineralized collagen/blood vessels)

• Lamellae (oseocyte lacunae, osteocyte canaliculi)
• Cement lines (lines of previous remodeling process)

Question 16

Osteonal Bone

Answer 16

• Blood vessels surrounded by concentric rings of bone tissue
• Primary: formed from existing collagen, less lamellae
• Secondary: formed by replacement of existing bone, includes interstitial bone (parts of other lamellae left behind)

Question 17

Lacunae

Answer 17

• Holes in bone where osteocytes site
• Osteocytes within extracellular fluid (maintain health)
• Osteocytes get trapped within bone during mineralization

Question 18

Canaliculi

Answer 18

• Small tunnels connecting lacunae

- Cell-cell communication (mechanical communication, coordinate adaptive process)

Question 19

Lamellae

Answer 19

• Layers of bone
• Oriented concentrically around Haversion canal
• Contain collagen and materials
• Collagen oriented to produce high toughness/fracture resistance
• Stops crack, can remodel

Question 20

Cement Lines

Answer 20

• Only in secondary osteonal bone
• Result of remodeling process
• From where osteoclast resorption ends and new bone deposition begins
• Collagen I deficient structures (weaker)

Question 21

Spongy Bone Structure

Answer 21

• Multiple layers of structure
• Multiple material types (ceramic and polymer)
• Difficult to engineer in bottom up approach if want biologically reactive

Question 22

Flat Bone Development

Answer 22

• Ossification center appears in fibrous connective tissue membrane (osteoblasts)
• Bone matrix (osteoid) secreted within fibrous membrane
• Woven bone and periosteum form
• Bone collar of compact bone forms and red marrow appears (cortical bone on outside, trabecular bone on inside)

Question 23

Long Bone Development

Answer 23

• Formation of bone collar and ossification center (osteoblasts)
• Spongy bone formation, blood vessels
• Formation of medullary cavity as ossification continues, ossification centers form in epiphyses
• Ossification of epiphyses, epiphyseal plate cartridge (growth) between epiphyses and diaphysis