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Small Animal Surgery > Fracture Biomechanics > Flashcards

Fracture Biomechanics Flashcards

1
Q

What is stress? Strain?

A

external force applied to any cross-sectional area

deformation of a loaded material as compared to its normal form, typically measured in length

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2
Q

What is stiffness?

A

ability of a material’s ability to resist an applied force (stress)

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3
Q

What is deformation? What is the difference between elastic and plastic?

A

change in shape due to application of a force (stress)

  • ELASTIC: reversible change in shape, where material is able to return to its original shape when load is removed
  • PLASTIC: permanent change in shape, where material does not return to original shape when a load is removed
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4
Q

What is a yield point? Ultimate failure point?

A

point when material begins to deform plastically, where strain exceeds the material’s ability to recover and render it permanently deformed (between elastic and plastic)

when material cannot withstand anymore strain and fails

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5
Q

Stress-strain curve:

A
  • elastic region = bone able to return to original shape
  • past yield point = becomes plastic and unable to return to its original shape
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6
Q

What are the 5 forces applied to bone?

A
  1. tension
  2. compression
  3. torsion
  4. shearing
  5. bending
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7
Q

What is compression?

A

2 opposing forces meet each other on the bone, pressing down/up

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8
Q

What is torsion?

A

2 opposing forces twist in opposite directions around the bone

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9
Q

What is bending?

A

forces applied at the ends of bones cause the formation of a compression/tension zone

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10
Q

What are the 2 types of bone?

A

CANCELLOUS - spongy bone typically located at the ends of bones within the metaphysis and epiphysis, acting as the major shock absorber

CORTICAL - dense, and solid bone primarily located at the diaphysis that only requires 2% strain for failure

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11
Q

What is bone porosity? What does it mean when it is high and low?

A

ratio of open space to total bone within a bone

  • HIGH = long elastic phase and lower yield point (cancellous)
  • LOW = steep and short plastic phase, very brittle (cortical)
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12
Q

How does the compression and tension affect cortical bone?

A

higher compression pressure compared to tension pressure

  • osteons are disintegrated with compression
  • osteons slide past one another with tension
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13
Q

What is a bone’s anatomic axis? Mechanical axis?

A

line drawn proximal to distal in intramedullary canal, bisecting the bone in half

load axis - line passing through points of load-bearing points

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14
Q

What kind of fracture is caused by tension?

A

transverse fractures

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15
Q

What fracture is caused by compression?

A

oblique

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16
Q

What fracture is caused by torsional forces?

A

spiral - low energy, shear stress in axial and transverse directions propagating along the tensile stress line

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17
Q

What fracture is caused by bending forces? How is the radius most commonly affected?

A

butterfly fragment

inner compression, outer tension

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18
Q

What is viscoelasticity?

A

ability of the viscoelastic material to handle a load placed upon it, depending on the rate at which a load is applied and strain is induced

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19
Q

What is the difference between open and closed fractures?

A

OPEN = wound near the fracture, either due to the bone or an exterior wound

CLOSED = no breach of soft tissue

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20
Q

What is required to supply a complete description of fractures?

A

orthogonal - VD/CC, lateral

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21
Q

What’s the difference between Type I and Type II open fractures?

A

I - wound smaller than 1 cm (puncture), typically created by a bone fragment from the inside that penetrates the skin then retracts + mild/mod soft tissue contusion; simple treatment

II - open wound larger than 1 cm (external source) + soft tissue trauma without extensive soft tissue damage or flaps/avulsions - fracture is typically minimally comminuted

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22
Q

Type I open fracture:

A
  • wound < 1 cm
  • fragment causing wound not seen
  • wild soft tissue trauma
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23
Q

Type II open fracture:

A
  • larger wound and soft tissue involvement compared to Type I
  • no flaps or avulsions
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24
Q

What are the 3 subdivisions of Type III open fractures?

A

A - adequate soft tissue covering wound, large soft tissue laceration/flap

B - extensive soft tissue loss, bone exposure, stripper periosteum

C - arterial +/- nerve supply compromised, may require anastomosis or amputation

(all much more difficult to treat)

25
Q

Name the types of fractures:

A
  • transverse
  • oblique: short (30-60 degrees compared to diameter of the diaphysis)
  • spiral
  • comminuted: reducible with butterfly segment vs. non-reducible
26
Q

What are the 5 types of Salter-Harris fractures?

A

Precision Makes Every Boy (BOTH) Crazy

  1. physis
  2. metaphysis + physis
  3. epiphysis + physis
  4. epiphysis + metaphysis + physis
  5. compression (crush)
27
Q

What is a displacement? How is it described?

A

ends of a bone do not line up

distal fracture segment described relative to the proximal segment

28
Q

Describe this fracture:

A

closed, mid-diaphyseal, spiral fracture with caudal and proximal displacement of the right tibia and fibula

29
Q

Describe this fracture:

A

closed, mid-diaphyseal, spiral fracture of the femur with a butterfly fragment and proximal and cranial displacement

30
Q

Describe this fracture:

A

closed, mid-diaphyseal, short oblique fracture of the tibia with proximal and lateral displacement

31
Q

Describe this fracture:

A

closed, metaphyseal, short oblique fracture of the tibial with proximal and medial displacement

32
Q

What is fracture healing a race between? What are the 3 goals of fracture repair?

A

fracture healing vs. implant failure

  1. encourage healing
  2. restore function to bone and surrounding soft tissues
  3. obtain a cosmetically acceptable result
33
Q

What is bone healing? How does it occur?

A

regeneration of structurally functional and competent bone

  • intramembranous ossification
  • endochondral ossification
34
Q

What 5 things affect the mechanism by which bone heals itself?

A
  1. bone that is fractured
  2. mechanical environment
  3. biologic health of bone and patient
  4. whether surgical stabilization is incorporated
  5. type of surgical stabilization performed
35
Q

What is the strain theory of bone healing? How does the presence of tissue affect this?

A

smaller gaps between fracture segments allow for greater strain % the bone can handle, while larger gaps cannot handle as much strain %

  • granulation tissue can handle 100%
  • fibrocartilage can handle 10-15%
  • bone can handle less than 2%
36
Q

What are the goals of fracture stabilization?

A
  • eliminate interfragmentary strain with anatomic reconstruction, compression of bone ends, and rigid stability
  • maintain a low strain environment with bridging techniques
37
Q

What is primary bone healing? What occurs?

A

direct bone healing occurring under absolute stability with anatomic reconstruction and compression

intramembranous ossification - ossification of new bone at fracture without callous formation (contact and gap healing)

38
Q

What is seen with contact healing during primary bone healing?

A
  • fracture gap < 0.01 mm
  • strain > 2%
  • cutting cones develop at 50-100 um/day

(it is initially weaker than secondary bone healing)

39
Q

What is seen with gap healing during primary bone healing?

A
  • occurs between areas of contact healing, where gap initially fills with fibrin matrix that is replaced by lamellar bone, then cutting cones
  • fracture gap < 1 mm
  • strain < 2%
40
Q

When does secondary bone healing occur? What is its hallmark?

A

when fractures are not anatomically reconstructed

callous formation

41
Q

What are the 2 functions of secondary bone healing?

A
  1. decreases interfragmentary strain, where osteoclasts remove dead bone at margins to widen the fracture gap
  2. increases stability via callous formation on abaxial surface, which increases stiffness by increasing the radius of the bone
42
Q

What are the 5 phases of secondary bone healing?

A
  1. inflammation - organized hematoma
  2. intramembranous ossification - deposition of bone matrix
  3. soft callous - chondrogenesis with type I and III collagens
  4. hard callous - endochondral ossification where chondrocytes hypertrophy and mineralize into woven bone
  5. bone remodeling by Wolff’s law
43
Q

What is Wolff’s Law? What is piezoelectricity?

A

bone adapts to loads under which it is exposed to

bone generates an electrical potential when deformed

  • electropositivity = increases osteoclastic activity
  • electronegativity = increases osteoblastic activity
44
Q

What is the initial management of open fractures?

A
  • prevent infection
  • promote bone healing and fracture healing
  • repair soft tissue
  • restore function of the area
45
Q

What are the 3 keys to successful open fracture management?

A
  1. prompt aggressive debridement within 6 hours
  2. wound irrigation with sterile isotonic fluid
  3. restoration of soft tissue envelope
46
Q

What is the first priority to managing open fractures? What should happen next?

A

systemic stabilization

  • control arterial bleeds
  • analyze neurovascular integrity
  • antimicrobial therapy
  • prevent further contamination
47
Q

What is used for open wound management?

A
  • sterile water-soluble lubricant
  • clip fur wide around wound
  • clean surrounding skin with 4% chlorhexidine gluconate
  • culture wound bed
  • lavage wound
  • cover wound with sterile dressing
48
Q

What are the 7 most common bacteria that cause nosocomial open fracture infections?

A
  1. Staphylococcus
  2. Streptococcus
  3. Klebsiella
  4. Pseudomonas
  5. Clostridium
  6. Enterobacter
  7. Escherichia coli
49
Q

How are Type I and II open fractures managed?

A
  • debride and close wound
  • 1st or 2nd generation cephalosporins
  • repair in same manner as a closed fracture
50
Q

How are Type III open fractures managed?

A
  • wound management
  • 1st or 2nd generation cephalosporins and fluoroquinolones
  • external fixatory stabilization
51
Q

What is a mechanical fracture assessment score? What 3 factors affect it?

A

gives indication for how strong a fixatory needs to be

  1. number of limbs injured
  2. patient size/activity
  3. ability to achieve load bearing (reducible vs. non-reducible)
52
Q

What is a biologic fracture assessment score? What 4 factors affect it?

A

gives indication how fast a callous will form

  1. age
  2. general health
  3. open vs. closed fractures
  4. location - femur/humerus vs. tibia/radius, open vs. closed
53
Q

What is a clinical fracture assessment score? What 3 factors affect it?

A

factors that may affect healing and repair during the post-operative period

  1. client compliance
  2. patient compliance
  3. anticipated limb function
54
Q

What do low (0-3) fracture assessment scores indicate? What are the 4 suggested implants?

A
  • implant must bridge fracture and assume most or all load
  • delayed healing is likely
  1. lengthening plate or plate-rod combination
  2. Type II or III external fixator +/- tie-in
  3. interlocking nail
  4. plate-external fixatory combination
55
Q

What do moderate (4-7) fracture assessment scores indicate? What are 5 suggested implants?

A

less strength and/or endurance of required implant

  1. bone plate
  2. Type I or II external fixator
  3. external fixatory + IM pin
  4. interlocking nail
  5. IM pin and cerclage wire
56
Q

What do high (8-10) fracture assessment scores indicate? What are 3 suggested implants?

A

minimum implant stress, where the bone can share the load with enhanced healing potential

  1. Type I external fixator
  2. IM pin and cerclage wires
  3. external coaptation
57
Q

What is a reduction? What is the difference between closed and reduction?

A

process of reconstructing to anatomic configuration, limb length, and joint alignment

  • CLOSED = preserves soft tissue/blood supply, decreased risk of infection, reduced operating time
  • OPEN = visualization for anatomic accuracy and direct placement of implants, allows load sharing and graft placement
58
Q

What are the 4 strategies used with bone grafts?

A
  1. OSTEOGENESIS - directly supplies and supports bone-forming cells
  2. OSTEOINDUCTION - materials that induce bone formation and recruits mesenchymal stem cells with chemical signaling
  3. OSTEOCONDUCTION - provides a scaffolding for mesenchymal stem cells to migrate to
  4. OSTEOPROMOTION - material enhances regeneration of bone
59
Q

What are examples of grafts used for the 4 different strategies of bone grafts?

A
  1. OSTEOGENESIS - osteoblasts, mesenchymal stem cells
  2. OSTEOINDUCTION - demineralized bone
  3. OSTEOCONDUCTION - bioceramics
  4. OSTEOPROMOTION - platelet-rich plasma, calcium phosphate

Small Animal Surgery (34 decks)

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