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Equine Medicine and Surgery > Lecture 11: Bone Biology and Fracture Healing > Flashcards

Lecture 11: Bone Biology and Fracture Healing Flashcards

1
Q

What are the functions of bone

A
  1. Protect internal organs
  2. Provide rigid segments for muscles to generate forces of locomotion
  3. Largest reservoir of calcium and phosphate in body
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2
Q

Mineral composes ___ of the dry weight of bone

A

2/3

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3
Q

Maintenance of normal performance depends on ___through a dynamic remodeling process that gives bone the unique ability to repair itself without ___following a fracture

A

Constant structural renewal
Without scar

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4
Q

What do flat bones surround and what are examples

A

Surround vital structures
Skull/brain

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5
Q

What bones compose complex joints like the carpus and tarsus

A

Cuboidal bones

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6
Q

What bones are majority of the peripheral and appendicular system

A

Long bones

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7
Q

What are the 2 mechanical advantages of equine long bones compared to other species

A
  1. Much longer length contributes to superior power and speed
  2. Distribution of load forces across wide epiphyseal surfaces reduces stress experienced by joints
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8
Q

What component of long bone is near articular cartilage

A

Epiphysis

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9
Q

What component of long bone is the growth plate between epiphysis and diaphysis

A

Physis

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10
Q

What is the component of long bone that has longitudinal growth via endochondral ossification

A

Physis

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11
Q

What component of long bone makes up majority of of the bone

A

Diaphysis

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12
Q

What are the 4 distinct zones of endochondral ossification

A
  1. Resting cartilage
  2. Zone of proliferation
  3. Hypertrophic zone
  4. Zone of calcification
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13
Q

What is the resting
cartilage zone

A

Least metabolically active chondrocytes, closest to epiphyseal end of growth plate

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14
Q

What is the zone of proliferation

A

Cell division perpendicular to long axis of bone increases bone length

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15
Q

What is hypertrophic zone

A

Chondrocytes increase size, mature and become encased in ECM and crease dividing

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16
Q

What is the zone of calcification

A

Chondrocytes are replaced by mineralized bone via osteoblast recruitment

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17
Q

What is the mechanism in which long bone is formed

A

Endochondral ossification

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18
Q

What is appositional bone growth

A

Increases bone thickness

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19
Q

When do primary osteons form

A

Form during appositional bone growth

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20
Q

When do secondary osteons form

A

Created throughout life when osteoblasts deposit bone at the end of cutting cones created by osteoclasts during bone remodeling

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21
Q

What type of bone has a compact outer cortex and Haversian systems

A

Cortical bone

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22
Q

Where is the cancellous/ spongy/ trabecular bone located

A

Medulla

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23
Q

What is the function of cancellous/ spongy/ trabecullar bone

A

More metabolically active and responsive to metabolic homeostatic changes

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24
Q

What is the periosteum

A

Thin layer of osteogenic and fibroblast in cells within a well developed nerve and microvascular network

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25
Q

Where do long bone cortical surfaces attach

A

Periosteum

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26
Q

What are the 2 distinct layers of periosteum

A
  1. Outer fibrous layer
  2. Inner cambium layer
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27
Q

What is the outer fibrous layer composed of

A

Fibroblasts, collage, elastic and nerve and microvascular network

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28
Q

What is the inner cambium layer made of

A

Adult mesenchymal and progenitor cells, osteoblasts, fibroblasts, SNS nerves

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29
Q

Which layer of the periosteum provides cells for fracture healing and appositional bone growth

A

Inner cambium layer

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30
Q

How are mechanical properties of bone assesses

A

Evaluating response to externally applied forces called loads

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31
Q

What is deformation

A

A load is applied to bone and its size and shape is altered

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32
Q

What is the elastic region of the load-deformation curve

A

Bone maintains capacity to return to its original shape after removal of load

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33
Q

What does the slope of the load deformation curve indicate

A

Stiffness

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34
Q

What is the yield point in the load deformation curve

A

End of elastic deformation/ permanent deformation is about to occur

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35
Q

What is the plastic region of the load-deformation curve

A

Bone will not return to its original shape when load is removed

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36
Q

The energy from a load is dissipated when bone yields (yield point) and then ___

A

Fails/ failure point

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37
Q

What factors do deformation and strain response depend on

A
  1. Bone anatomy and composition
  2. Direction, rate, magnitude, frequency, duration of applied force
38
Q

When a crack starts to form, __ is released and ___are created

A

Energy, 2 new surfaces

39
Q

If the amount of energy is less than that required to form a crack, it will stop, otherwise more cracks will form=___

A

Catastrophic failure

40
Q

The more energy store in a bone prior to failure the greater the ___ that will be caused when a fracture occurs

A

Comminution and soft tissue damage

41
Q

A bone loaded ___fails at higher load and releases more energy than if loaded ___

A

Rapidly, slowly

42
Q

What type of fracture does tension cause

A

Transverse

43
Q

What type of fracture does compression cause

A

Oblique

44
Q

What type of fracture does torsion cause

A

Spiral

45
Q

What type of fracture does bending cause

A

Transverse with butterfly fragment

46
Q

What type of fracture does compression and torsion cause

A

Comminution (oblique and spiral)

47
Q

Identify the force applied and fracture caused in 1-5

A
  1. Tension—> transverse
  2. Compression—> oblique
  3. Torsion—> spiral
  4. Bending—> transverse with butterfly fragment
  5. Compression and torsion—> Comminution (oblique and spiral)
48
Q

Bone is strongest against what type of fracture force

A

Compression

49
Q

Bone is weakest against what type of fracture force

A

Tension

50
Q

Which is more brittle cortical bone or trabecular bone, therefore fails at lower strain, despite higher load

A

Cortical bone

51
Q

Trabecular bone or cortical bone: stores more energy prior to failure because of higher toughness

A

Trabecular bone

52
Q

What is the physiological process during biological fracture healing

A

Formation of callus to bridge at fracture site

53
Q

What are the 3 stages of biological fracture healing

A
  1. Inflammatory phase
  2. Repair phase
  3. Remodeling phase
54
Q

What occurs in the inflammatory phase of biological fracture healing

A
  1. Induction of immune response
  2. Disrupted osteocytes release lysosomal enzymes that destroy organic matrix and make necrotic material that induces intense inflammatory reaction
  3. Hematoma formation, angiogenesis, MSC migration and platelet aggregation
  4. Soft, hypoxic callus
55
Q

What happens during the repair phase of biological fracture healing

A
  1. Majority of callus is unmineralized matrix
  2. Mineralizes to form woven bone- distributed collagen fibrils
  3. Formation of a bony bridging callus is final step- point of clinical union
56
Q

What is the point of clinical union

A

Formation of bony bridging callus during repair phase

57
Q

How long is the repair phase in biological fracture healing

A

2-12 months

58
Q

What is the longest stage in biological fracture healing

A

Remodeling phase

59
Q

What occurs in remodeling phase of biological fracture healing

A
  1. Mineralized cartilage continues to be replaced by woven bone which is remodeled into lamellar bone
  2. Osteoclasts remove woven bone to create bone tunnels called cutting cones- filled with lamellar bone by osteoblasts around central capillary channel
60
Q

Remodeling is regulated by ___ and resulting ___charges

A

Mechanical environment (weight bearing) and piezoelectric

61
Q

Convex or concave have electronegative charge and therefore enhanced osteoblastic activity

A

Concave

62
Q

Convex or concave: electro positive charge and higher osteoclast activity

A

Convex

63
Q

What are the two types of structural fracture healing

A
  1. Direct/primary
  2. Indirect/secondary
64
Q

What happens during direct/primary structural fracture healing

A
  1. Reduction of fracture fragments by rigid internal fixation and minimal interfragmentary strain and motion
  2. Direct regeneration of Haversian systems between fracture fragments to restore mechanical integrity
  3. Healing occurs by direct growth of secondayr osteons from one fracture fragment to another
  4. Little to no callus formation
65
Q

Does direct/primary have callus formation

A

Little to none

66
Q

How does healing occur in direct/primary structural fracture healing

A

Direct growth of secondary osteons from one fracture fragment to another

67
Q

What is the most common structural fracture healing type in horses

A

Indirect/secondary

68
Q

How does indirect/ secondary structural fracture healing work

A

Occurs through endochondral bone formation when fracture fragments are not sufficiently immobilized or approximated for direct healing

Greater motion or more callus

69
Q

Does indirect/secondary structural fracture healing have callus formation

A

Yes, greater motion=more callus

70
Q

What are the goals of fracture healing

A
  1. Regenerated bone with organic and mineral components to resist stress and strains (reconstruction of original cortical bone)
  2. Remodeling of Haversian system
71
Q

What occurs in remodeling of Haversian systems

A
  1. Revascularization of necrotic bone at fracture sites
  2. Filling in interfragmentary gaps
72
Q

What are 3 specific requirements for Haversian remodeling across fracture

A
  1. Adequate reduction
  2. Rigid fixation
  3. Sufficient blood supply
73
Q

What are the complications of equine fracture healing

A
  1. Infection
  2. Fixation failure
  3. Delayed union
  4. Non-union
  5. Laminitis (adults)
  6. Contralateral angular limb deformity (foals)
74
Q

What age group is likely to get laminitis as complication from fracture healing

A

Adults

75
Q

Wha age group is likely to get contralateral angular limb deformity from fracture healing

A

Foals

76
Q

What occurs during infection of fracture healing

A

Compromised blood supply, swelling, edema, and necrotic tissue= bacterial proliferation

77
Q

Local infection can easily proceed through ___

A

Cortex and exposed bone marrow

78
Q

What type of fractures are more likely to remain uninfected

A

Closed

79
Q

What can cause fixation failure during fracture healing

A
  1. Inadequate fixation rigidity compared to mechanical demands placed on repair
  2. Forces experienced that exceed implant strength- recovery from anesthesia
  3. Duration of bone healing is longer than implants fatigue life
80
Q

What is delayed union

A

Healing progresses but at a slower rate compared to normal

81
Q

What is normal union rate in adults and foals

A

4 months in adults
3 months in foals

82
Q

What are the contributing factors for delayed union

A
  1. Fracture and incisional infection
  2. Inadequate reduction and immobilization
  3. Soft tissue disruption
83
Q

What are the radio graphic signs of delayed union

A
  1. Persistent fracture line
  2. Minimal callus
  3. Intramedullary sclerosis
84
Q

What is a non-union

A

Fracture healing ceases before the bony structure is restored

85
Q

What are the radiographic findings for non-union

A
  1. Lack of bone/callus across fracture site
  2. Sclerotic blunt fracture edges
  3. Persistent fracture lines
  4. Lack of progressive changes toward union on serial radiographs
86
Q

What causes laminitis to occur in fracture healing

A

Continued pain in fractured limb results in increased weight bearing on contralateral limb

Contralateral laminitis

87
Q

Laminitis is __induced in fracture healing

A

Stress (no metabolic component)

88
Q

What is the standard modality to assess fracture healing

A

Radiographs

89
Q

What are the radiographic findings in the inflammatory phase

A
  1. Sharp fracture margins visible up to a week after trauma
  2. 2-3 weeks after fracture gap appears to widen and develops in distinct margins due to osteoclasts and phagocytes removing necrotic bone
90
Q

What radiographic changes are in the repair phase

A
  1. Callus becomes evident
  2. Fracture lines disappear and callus increasing in opacity relative to adjacent bone
91
Q

What happens in remodeling phase on radiographs

A
  1. Woven bone of the callus transitions to lamellar bone
  2. Callus assumes original bone conformation
92
Q

How is bony union characterized radiographically

A

Bony callus, obliteration of fracture line and cortical bone bridging the fracture gap

Equine Medicine and Surgery (27 decks)

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