Fracture Biomechanics / Classification

Question 1

Bone Macroarchitecture

Answer 1

Rigid endoskeleton (epiphysis, metaphysis, diaphysis)

Mineralized osseous tissue (marrow, endosteum, periosteum, nerves, vessels, cartilage)

Question 2

Cortical bone

Answer 2

Shaft of long bones
Highly dense / relatively acellular
Develops in direct proportion to stress
Blood surrounds bone

Question 3

Trabecular bone

Answer 3

Ends of long bones
Porous network
Large surface area
Bathed in blood

Question 4

Microscopic bone anatomy

Answer 4

Cellular components + ECM (organic + inorganic)

Question 5

Osteoblasts

Answer 5

Cover bone surfaces
Form organic matrix osteoid

Question 6

Osteocytes

Answer 6

Osteoblasts incorporated into osteoid
(Bone cell)
Contain cytoplasmic projections

Question 7

Osteoclast characteristics

Answer 7

Large, multinucleated cells
Function: bone resorption (control by local acid environment)
Form from blood monocytes

Question 8

Organic components of ECM

Answer 8

95% Type I collagen
5% ground substance (Proteoglycans + glycosaminoglycans)

Question 9

Inorganic ECM components

Answer 9

Hydroxyapatite (Ca-phosphate)
Laid down by osteoblasts as unmineralized osteoid —> mineralized by alkaline phosphates

Question 10

Weak spot of bone during longitudinal growth

Answer 10

Zone of hypertrophy (where cells are stacked in rows)

Question 11

Function of bone

Answer 11

Protection
Shape
Blood cell production
Mineral/fat storage
Movement
Acid-base balance

Question 12

Bone formation

Answer 12

“Condensations” - aggregates of bone elements in fetal tissues - undifferentiated mesenchymal stem cells - osteoprogenitor cells

Intramembranous ossification (direct development from condensations)

Endochondral ossification (via cartilage intermediate)

Question 13

Intramembranous ossification

Answer 13

Flat bones of skull

Osteoprogenitor cells in cell condensation —> osteoblasts —> produce bone matrix

Bony spicules form + fuse —> trabeculae —> unit to form spongy bone

OP cells in spongy area produce marrow + periosteum —> osteoblasts of periosteum produce compact bone

Question 14

Endochondral ossification

Answer 14

OP cells —> chondrocytes —> growth of cartilaginous bone-to-be —> primary/secondary centers of ossification —> formation of articular cartilage and epiphyseal plate (growth/phsyeal plate)

Question 15

Primary center of ossification forms …

Answer 15

Before or after birth
Forms diaphysis

Question 16

Secondary center of ossification forms ..

Answer 16

After birth + forms epiphyses of long bones

Question 17

Hierarchical structure of bone designed to…

Answer 17

Maximize strength and lightness

Question 18

Bone structure corresponds to…

Answer 18

The forces it experiences

Question 19

Stress-strain curve

Answer 19

Elastic region —> yield point —> plastic region —> failure point

Question 20

Fracture biomechanics - forces

Answer 20

Tension (pulling away from center)
Compression (pushing toward center)
Bending
Shearing (two parts twisting towards each other)
Torsion (two parts twisting away)
Combined loading

Question 21

Tension (i.e. weight bearing) + bending results in …

Answer 21

Transverse fracture with butterfly fragment

Question 22

Bending of bone results in…

Answer 22

Transverse fracture +/- small fragment

Question 23

Torsion results in …

Answer 23

Spiral fraction

Question 24

Tension on a bone results in …

Answer 24

Transverse fractiure

Question 25

Compression results in …

Answer 25

Crushing injury

Question 26

Impact of loading rate on deformation

Answer 26

More rapidly a load is applied —> greater deformity Slow loading allows time to adjust —> less damage

Question 27

Fracture descriptions

Answer 27

Open vs closed Simple vs comminuted Anatomical location Displacement Articular vs nonarticular Physeal/growth plate injury

Question 28

Simple fracture

Answer 28

Two piece fracture No fragments (comminution) Transverse, oblique, or spiral Less complicated to fix

Question 29

Comminuted fractures

Answer 29

>2 pieces Greater forces —> comminutation Hit-by-car/gunshot/bite wound

Question 30

Fracture displacement

Answer 30

Described by distal fraction relative to proximal fragment Medial v lateral Cranial v caudal Dorsal v palmar Dorsal v plantar

Question 31

Salter Harris classification

Answer 31

P - I - Physis M - II - Metaphysis E - III - Epiphysis B - IV - metaphysis + epiphysis C - V - crushing

Question 32

Capital physeal fracture

Answer 32

Physeal injury of articular joint (acetabulum of femur)

Question 33

Sequelae of Physeal injury

Answer 33

Angular limb deformities

Question 34

Open fractures

Answer 34

Type I - fracture penetrates skin from within Type II - wound < 1 cm, communicates with fracture Type III - high energy trauma, major soft tissue damage +/- bone loss IIIa - no major plastic procedures IIIb - soft tissue insufficient for closure IIIc - arterial injury needing repair, amputation

Question 35

Articular fracture

Answer 35

Distal/proximal portion of bone Joint involvement Exact anatomic reduction / rigid fixation required