Basic Science Of Fractures

Question 1

Composition of Bone

Answer 1

30% Organic –> Cells (2%)(Osteoblasts, osteocytes, osteoclasts), Matrix (Collagen)(98%)

70% Mineral –> Hydroxyapatite (95%), Mg, Na, K, F, Cl

Question 2

Intramembranous ossification

Answer 2

•mesenchymal progenitor cells differentiate into osteoblasts, which then directly form bone

Question 3

Endochondral ossification

Answer 3

mesenchymal progenitor cells diffentiate into chondrocytes, initially forming a cartilage intermediate that is replaced as bone is regenerated

Question 4

• Cortical or compact bone
• Trabecular or cancellous bone

Answer 4

• Cortical or compact bone - diaphysis/long bones mainly
• Trabecular or cancellous bone - flatbones

Question 5

Structure of Cortical Bone

Answer 5

• Haversian system (fundamental functional unit of long bone)
• Nutrient arteries
• Periosteum (outer lining)
• Endosteum (inner lining)

Question 6

Structure of Trabecular Bone

Answer 6

More lattice

Question 7

2 Types of Bone

Answer 7

Woven bone (laid down quickly, immature, disorganized, not as strong) vs. Lamellar bone (stronger, more organized, mature)

*Get woven bone first –> lamellar bone

Question 8

Initial Injury

Answer 8

Trauma –> Injury to cells, blood vessels, bone matrix, and surrounding soft tissues –> Hematoma & Damage to blood vessels leads to osteocyte death, necrotic material at the fracture site

Question 9

Phases of bone healing

Answer 9

Inflammation, repairative, remodeling

Question 10

Bone regeneration during fracture healing is analogous to the process that occurs during __________, it involves both __________ and __________, which are interrelated and simultaneous

Answer 10

•Bone regeneration during fracture healing is analogous to the process that occurs during embryonic development, it involves both intramembranous ossification and endochondral ossification, which are interrelated and simultaneous

Question 11

Inflammatory Phase

Answer 11

Release of inflammatory mediators from platelets and injured cells –> Vasodilation –> Edema

Migration of inflammatory cells (PMNs then macrophages and lymphocytes) - release of cytokinds, GSF, etc –> angiogenesis –> Fibroblast, osteoblasts, and chondrocytes appear and produce new matrix (osteoid) REPAIR & Monocytes → Osteoclasts which resorb necrotic tissue CLEANUP

Question 12

_______ = coccoon that surround fracture

Answer 12

Soft Callus

Question 13

Early repair

Answer 13

Migration of pluripotent mesenchymal cells - proliferate and differentiate

Pluripotent mesenchymal cells → Osteoblasts, Chondrocytes, Fibroblasts

Monocytes → Osteoclasts

–>

Fibrous tissue, Cartilage, Immature bone =Soft Callus (less movement) –> less pain

Question 14

________ not involved in fracture repair

Answer 14

Osteocytes

Question 15

Transition from soft callus to hard callus

• ___________ at periphery - proximal and distal to the injury site
• _________ occurs centrally - overlying the fracture site
• Fracture healing depends on the ______, _______, ________, and _________ of ______________ at the site of the fracture

Answer 15

• Intramembranous bone formation at periphery - proximal and distal to the injury site
• Endochondral bone formation occurs centrally - overlying the fracture site
• Fracture healing depends on the recruitment, proliferation, accumulation, and differentiation of pluripotent mesenchymal cells at the site of the fracture

Question 16

• The ability of a structure to resist torsional and bending loads is _______________
• Advantage of External Callus is to___________ of the bone

Answer 16

• The ability of a structure to resist torsional and bending loads is proportionate to R4
• Increase cylinder of the bone

Question 17

Clinical vs Radiographic Union

Answer 17

• Clinical union – fracture site becomes stable and pain free (according to pt)
• Radiographic union – plain radiographs show bone trabeculae or cortical bone crossing the fracture site, no radiolucency (according to xrays)

Which one we adhere to depends on location of fracture (i.e. clavicle clinical vs scaphoid radiographic)

Question 18

Remodeling Phase

Answer 18

• Replacement of woven bone by lamellar bone
• Resorption of unneeded callus
• May continue for years!

Question 19

Variables that influence fracture healing

Answer 19

• Injury variables
• Patient variables
• Treatment variables

Question 20

Injury Variables

Answer 20

• Soft-tissue damage –Open vs. closed (infection)
• Bone comminution and displacement
• Location of bone injury (i.e. metaphysis has high blood supply - heal well vs. stress fracture in 5th metatarsal)

Question 21

Patient Variables

Answer 21

Age is the big one

Illness (i.e. kidney failure, chemo)

Question 22

Treatment variables

Answer 22

Fracture stabilization

Question 23

Fracture repair after internal plate fixation

Answer 23

• Fracture gap closed by fixation
• No formation of external callus
• Lamellar bone forms directly across fracture line

Don’t get normal healing (callus) - rely on hardware

Different sequence of fracture healing

Question 24

*Maturation of bone occurs _____ to ______

Answer 24

*Maturation occurs distal to proximal

Question 25

3 important zones of bone growth

Answer 25

Proliferative zone

Hypertrophic zone - water, weakest

Metaphysis

**Sensitive growth cells are in distal area of growth plate