Lecture 11: Bone Biology and Fracture Healing Flashcards
1
Q
What are the functions of bone
A
- Protect internal organs
- Provide rigid segments for muscles to generate forces of locomotion
- Largest reservoir of calcium and phosphate in body
2
Q
Mineral composes ___ of the dry weight of bone
A
2/3
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
4
Q
What do flat bones surround and what are examples
A
Surround vital structures
Skull/brain
5
Q
What bones compose complex joints like the carpus and tarsus
A
Cuboidal bones
6
Q
What bones are majority of the peripheral and appendicular system
A
Long bones
7
Q
What are the 2 mechanical advantages of equine long bones compared to other species
A
- Much longer length contributes to superior power and speed
- Distribution of load forces across wide epiphyseal surfaces reduces stress experienced by joints
8
Q
What component of long bone is near articular cartilage
A
Epiphysis
9
Q
What component of long bone is the growth plate between epiphysis and diaphysis
A
Physis
10
Q
What is the component of long bone that has longitudinal growth via endochondral ossification
A
Physis
11
Q
What component of long bone makes up majority of of the bone
A
Diaphysis
12
Q
What are the 4 distinct zones of endochondral ossification
A
- Resting cartilage
- Zone of proliferation
- Hypertrophic zone
- Zone of calcification
13
Q
What is the resting
cartilage zone
A
Least metabolically active chondrocytes, closest to epiphyseal end of growth plate
14
Q
What is the zone of proliferation
A
Cell division perpendicular to long axis of bone increases bone length
15
Q
What is hypertrophic zone
A
Chondrocytes increase size, mature and become encased in ECM and crease dividing
16
Q
What is the zone of calcification
A
Chondrocytes are replaced by mineralized bone via osteoblast recruitment
17
Q
What is the mechanism in which long bone is formed
A
Endochondral ossification
18
Q
What is appositional bone growth
A
Increases bone thickness
19
Q
When do primary osteons form
A
Form during appositional bone growth
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
21
Q
What type of bone has a compact outer cortex and Haversian systems
A
Cortical bone
22
Q
Where is the cancellous/ spongy/ trabecular bone located
A
Medulla
23
Q
What is the function of cancellous/ spongy/ trabecullar bone
A
More metabolically active and responsive to metabolic homeostatic changes
24
Q
What is the periosteum
A
Thin layer of osteogenic and fibroblast in cells within a well developed nerve and microvascular network
25
Where do long bone cortical surfaces attach
Periosteum
26
What are the 2 distinct layers of periosteum
1. Outer fibrous layer
2. Inner cambium layer
27
What is the outer fibrous layer composed of
Fibroblasts, collage, elastic and nerve and microvascular network
28
What is the inner cambium layer made of
Adult mesenchymal and progenitor cells, osteoblasts, fibroblasts, SNS nerves
29
Which layer of the periosteum provides cells for fracture healing and appositional bone growth
Inner cambium layer
30
How are mechanical properties of bone assesses
Evaluating response to externally applied forces called loads
31
What is deformation
A load is applied to bone and its size and shape is altered
32
What is the elastic region of the load-deformation curve
Bone maintains capacity to return to its original shape after removal of load
33
What does the slope of the load deformation curve indicate
Stiffness
34
What is the yield point in the load deformation curve
End of elastic deformation/ permanent deformation is about to occur
35
What is the plastic region of the load-deformation curve
Bone will not return to its original shape when load is removed
36
The energy from a load is dissipated when bone yields (yield point) and then ___
Fails/ failure point
37
What factors do deformation and strain response depend on
1. Bone anatomy and composition
2. Direction, rate, magnitude, frequency, duration of applied force
38
When a crack starts to form, __ is released and ___are created
Energy, 2 new surfaces
39
If the amount of energy is less than that required to form a crack, it will stop, otherwise more cracks will form=___
Catastrophic failure
40
The more energy store in a bone prior to failure the greater the ___ that will be caused when a fracture occurs
Comminution and soft tissue damage
41
A bone loaded ___fails at higher load and releases more energy than if loaded ___
Rapidly, slowly
42
What type of fracture does tension cause
Transverse
43
What type of fracture does compression cause
Oblique
44
What type of fracture does torsion cause
Spiral
45
What type of fracture does bending cause
Transverse with butterfly fragment
46
What type of fracture does compression and torsion cause
Comminution (oblique and spiral)
47
Identify the force applied and fracture caused in 1-5
1. Tension—> transverse
2. Compression—> oblique
3. Torsion—> spiral
4. Bending—> transverse with butterfly fragment
5. Compression and torsion—> Comminution (oblique and spiral)
48
Bone is strongest against what type of fracture force
Compression
49
Bone is weakest against what type of fracture force
Tension
50
Which is more brittle cortical bone or trabecular bone, therefore fails at lower strain, despite higher load
Cortical bone
51
Trabecular bone or cortical bone: stores more energy prior to failure because of higher toughness
Trabecular bone
52
What is the physiological process during biological fracture healing
Formation of callus to bridge at fracture site
53
What are the 3 stages of biological fracture healing
1. Inflammatory phase
2. Repair phase
3. Remodeling phase
54
What occurs in the inflammatory phase of biological fracture healing
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
What happens during the repair phase of biological fracture healing
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
What is the point of clinical union
Formation of bony bridging callus during repair phase
57
How long is the repair phase in biological fracture healing
2-12 months
58
What is the longest stage in biological fracture healing
Remodeling phase
59
What occurs in remodeling phase of biological fracture healing
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
Remodeling is regulated by ___ and resulting ___charges
Mechanical environment (weight bearing) and piezoelectric
61
Convex or concave have electronegative charge and therefore enhanced osteoblastic activity
Concave
62
Convex or concave: electro positive charge and higher osteoclast activity
Convex
63
What are the two types of structural fracture healing
1. Direct/primary
2. Indirect/secondary
64
What happens during direct/primary structural fracture healing
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
Does direct/primary have callus formation
Little to none
66
How does healing occur in direct/primary structural fracture healing
Direct growth of secondary osteons from one fracture fragment to another
67
What is the most common structural fracture healing type in horses
Indirect/secondary
68
How does indirect/ secondary structural fracture healing work
Occurs through endochondral bone formation when fracture fragments are not sufficiently immobilized or approximated for direct healing
Greater motion or more callus
69
Does indirect/secondary structural fracture healing have callus formation
Yes, greater motion=more callus
70
What are the goals of fracture healing
1. Regenerated bone with organic and mineral components to resist stress and strains (reconstruction of original cortical bone)
2. Remodeling of Haversian system
71
What occurs in remodeling of Haversian systems
1. Revascularization of necrotic bone at fracture sites
2. Filling in interfragmentary gaps
72
What are 3 specific requirements for Haversian remodeling across fracture
1. Adequate reduction
2. Rigid fixation
3. Sufficient blood supply
73
What are the complications of equine fracture healing
1. Infection
2. Fixation failure
3. Delayed union
4. Non-union
5. Laminitis (adults)
6. Contralateral angular limb deformity (foals)
74
What age group is likely to get laminitis as complication from fracture healing
Adults
75
Wha age group is likely to get contralateral angular limb deformity from fracture healing
Foals
76
What occurs during infection of fracture healing
Compromised blood supply, swelling, edema, and necrotic tissue= bacterial proliferation
77
Local infection can easily proceed through ___
Cortex and exposed bone marrow
78
What type of fractures are more likely to remain uninfected
Closed
79
What can cause fixation failure during fracture healing
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
What is delayed union
Healing progresses but at a slower rate compared to normal
81
What is normal union rate in adults and foals
4 months in adults
3 months in foals
82
What are the contributing factors for delayed union
1. Fracture and incisional infection
2. Inadequate reduction and immobilization
3. Soft tissue disruption
83
What are the radio graphic signs of delayed union
1. Persistent fracture line
2. Minimal callus
3. Intramedullary sclerosis
84
What is a non-union
Fracture healing ceases before the bony structure is restored
85
What are the radiographic findings for non-union
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
What causes laminitis to occur in fracture healing
Continued pain in fractured limb results in increased weight bearing on contralateral limb
Contralateral laminitis
87
Laminitis is __induced in fracture healing
Stress (no metabolic component)
88
What is the standard modality to assess fracture healing
Radiographs
89
What are the radiographic findings in the inflammatory phase
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
What radiographic changes are in the repair phase
1. Callus becomes evident
2. Fracture lines disappear and callus increasing in opacity relative to adjacent bone
91
What happens in remodeling phase on radiographs
1. Woven bone of the callus transitions to lamellar bone
2. Callus assumes original bone conformation
92
How is bony union characterized radiographically
Bony callus, obliteration of fracture line and cortical bone bridging the fracture gap
