Chapter 75 - Bone biology and fracture healing Flashcards
1
Q
A
Figure 75-1. Illustration of an immature equine tibia with bone regions
and types indicated. The top right inset is a schematic of bone microstructure
showing major osteonal components. The lower right inset
shows the major bone vessels. A, Collagen fibers; B, vessels and nerves
in Haversian canal; C, concentric lamellae with osteocytes (dots); D,
periosteum fibrous layer; E, periosteum cambium layer; F, Haversion canal
in cortical bone; G, Volkmann’s canal in cortical bone; H, endosteum; I,
nutrient artery; J, metaphysis artery; K, epiphysis artery; L, distal articular
surface; M, distal physis; N, trabecular bone; O, medullary canal; P,
epiphyses; Q, metaphyses; R, diaphysis; S, caudal cortex.
1
Q
What are the primary functions of bones in the body?
A
Bones protect internal organs, provide rigidity for force generation, and serve as a reservoir for calcium and phosphate.
2
Q
What is the importance of the organic matrix, cells, and water in bones?
A
They contribute to the mechanical properties crucial for bone function.
3
Q
What proportion of dry bone weight is composed of minerals?
A
Two-thirds of the dry weight of bone is mineral.
4
Q
What factors influence bone healing?
A
Patient characteristics, site and severity of injury, and fracture management.
4
Q
What process is essential for maintaining normal bone performance?
A
Dynamic remodeling is essential for maintaining normal bone performance.
5
Q
How do bones repair themselves without forming scars?
A
Through secreted growth factors and interactions among cells and the microenvironment.
5
Q
What are the three major categories of bones?
A
Long, cuboidal, and flat bones.
6
Q
How do long bones provide a mechanical advantage for horses?
A
Their length contributes to superior power and speed.
6
Q
What are the three regions of long bones?
A
Diaphysis, epiphysis, and metaphysis.
6
Q
What separates the metaphysis from the epiphysis?
A
The physis, or growth plate.
7
Q
How do axial bones form during embryonic development?
A
By ossification of a hyaline cartilage model through endochondral ossification.
7
Q
What is intramembranous ossification?
A
A process where flat bones form from fibrous connective tissue precursors.
8
Q
Describe the process in the hypertrophic zone of the growth plate.
A
Mature chondorcytes in this zone they cease dividing and hypertrophy and assume a round shape of hypertrophy. They also remodel and mineralize the extracellular matrix around them to form the calcification zone. After hypertrophy, the chondrocytes die and the extracellular matrix around them is removed to create the ossification zone.
8
Q
What happens to chondrocytes during endochondral ossification
A
They cluster, differentiate, and undergo hypertrophy; those at the center cease proliferation. After hypertrophy, the chondrocytes die and the extracellular matrix around them is removed to create the ossification zone. Based on current evidence, the chondrocytes promote ossification through both formation of cartilage tissue and secretion of molecules
9
Q
What is the role of perichondrial cells in bone development?
A
They become osteoblasts and form a bone collar, guiding vascularization and mineralization.
9
Q
What does vascular ingrowth form during endochondral ossification?
A
The primary spongiosa.
10
Q
What occurs in the resting zone of the growth plate?
A
It contains the least metabolically active chondrocytes.
11
Q
What is the difference in ossification centers between endochondral and intramembranous ossification?
A
Endochondral ossification forms in a cartilage model, while intramembranous ossification forms in sheets of connective tissue.
12
Q
What happens in the ossification zone of the growth plate?
A
Chondrocytes mature, hypertrophy, and mineralize the extracellular matrix.
13
Q
How does cortical bone thickness vary in long bones?
A
It decreases proximally towards the metaphysis.
14
Q
What remains of the physis once skeletal maturity is reached?
A
An inactive physis as a narrow, indistinct line between epiphysis and metaphysis.
15
Q
What type of marrow is found in the medulla of immature animals?
A
Hematopoietic bone marrow.
16
Q
What are the two main types of bone tissue?
A
Cortical (compact) bone and trabecular (cancellous) bone.
17
What is the composition of osteons in cortical and trabecular bone?
Cortical osteons are Haversian systems; trabecular osteons are referred to as packets.
18
Why is trabecular bone considered more metabolically active?
Its structure allows for a higher rate of metabolic activity compared to cortical bone.
19
What distinguishes primary from secondary osteons?
Primary osteons form during growth, while secondary osteons form during remodeling.
19
How are Volkmann canals oriented relative to Haversian canals?
Volkmann canals are oriented at 90 degrees to Haversian canals.
20
What is the structure of Haversian systems?
Cylindrical shape with concentric layers (lamellae) surrounding central canals
21
What are cement lines, and what do they signify?
They separate osteons from interstitial bone tissue, indicating areas of bone resorption and formation.
22
What is bone remodeling, and when does it occur?
Local stress and strain, metabolic status, age, and sex.
22
What factors influence the composition and mineralization of cement lines?
Local stress and strain, metabolic status, age, and sex.
23
What are current research focuses in fracture healing?
Accelerating healing processes and reducing complications
23
What is bone remodeling, and when does it occur?
Bone remodeling is the process of bone resorption and formation occurring throughout life.
24
What are some mechanisms to assess fracture healing quality?
Noninvasive imaging techniques are critical for assessing healing quality.
24
What role do growth factors play in bone healing?
They facilitate communication and healing processes between bone cells.
24
What biological events are involved in the bone healing process?
A highly orchestrated sequence that includes inflammation, repair, and remodeling.
25
What complications can arise from poor fracture management?
Delayed healing, nonunion, or malunion of the fracture.
25
How does fracture stabilization influence bone healing?
Proper stabilization promotes optimal healing conditions and reduces complications.
26
How does the biomechanical environment affect bone health?
Mechanical stress and strain influence bone density, strength, and remodeling rates.
26
Why is understanding fracture configurations important?
26
What is the significance of bone's ability to remodel?
It allows adaptation to mechanical loads and repair of micro-damage over time.
27
Mammalian long bone growth in length occurs at the physis via
endochondral ossification
28
The resting zone contains the least metabolically active ____(1w) and is closest to the epiphyseal end of the growth pla
chondrocytes
29
In the adjacent proliferation zone, _______(2w) occurs in a plane perpendicular to the long axis of the bone to increase the length of the cell column
cell mitosis
30
Chondrocytes mature, become encased in __(1w) matrix, and assume a round morphology in the hypertrophic zone, where they cease dividing and hypertrophy.
extracellular
31
When chondrocytes hypertrophy and remodel and mineralize the extracellular matrix around them forms the ___(1w) zone
calcification zone
32
Bones are composed of varying ratios of peripheral ________(compact) bone and a __________ medulla containing bone marrow and ___________(cancellous) bone.
Bones are composed of varying ratios of peripheral cortical (compact) bone and a central medulla containing bone marrow and trabecular (cancellous) bone.
32
After hypertrophy, the chondrocytes die and the extracellular matrix around them is removed to create the ____________(1w) zone
ossification
33
epiphysis, metaphysis, and cuboidal bones have comparatively thinner/thicker (choose) cortices than the diaphysis.
epiphysis, metaphysis, and cuboidal bones have comparatively thinner cortices than the diaphysis.
34
Cortical and trabecular bone are composed of ___(1w)
osteons
34
Trabecular bone, composed of three-dimensional networks of rods and plates, is less metabolically active and responsive than cortical bone - true or false
FALSE is more
Trabecular bone, composed of three-dimensional networks of rods and plates, is more metabolically active and responsive than cortical bone
34
What is the periosteum
The periosteum is a thin layer of osteogenic and fibroblastic cells with a nerve and microvascular network that covers the outer surface of cortical bone.
35
What are the two layers of the periosteum, and what is their primary function?
The outer fibrous layer provides support, while the inner cambium layer contains progenitor cells essential for fracture healing and appositional bone growth.
35
How is the periosteum attached to the bone surface?
It is attached by Sharpey fibers, which are connective tissue strands composed mainly of type III collagen.
36
What is the role of the endosteal niche in bone?
The endosteal niche contains stem and progenitor cells, growth factors, and extracellular matrix molecules that regulate hematopoiesis.
37
What percentage of resting cardiac output is delivered to bones?
37
What does the endosteum cover, and what types of cells does it contain?
The endosteum covers the trabeculae, medullary cavity, and inner surfaces of bone canals, containing osteoblasts, osteoclasts, fibroblasts, macrophages, endothelial cells, and adipocytes.
38
Identify the three sources of afferent blood supply in mature long bones.
The nutrient artery, the metaphyseal-epiphyseal vessel complex, and periosteal vessels.
39
What mineral primarily composes the mineral component of bone?
The mineral component is mainly crystalline hydroxyapatite.
40
How does the blood flow direction differ between diaphyseal and endosteal circulation?
Diaphyseal flow is predominantly centrifugal (70% towards the cortex), while endosteal circulation supplies the medulla and inner cortical bone.
41
What is the composition of bone by volume?
Bone is composed of approximately 25% water, 35% organic components, and 40% mineral components.
41
What is fibrillogenesis?
Fibrillogenesis is the process where tropocollagen helices self-assemble to form microfibrils that organize into fibril
42
What is the primary function of proteoglycans in the bone matrix?
Proteoglycans provide flexibility and resilience to the organic matrix of bone.
42
Describe the basic structure of type I collagen in bone.
Type I collagen consists of a right-handed triple helix formed from three polypeptide chains, two of which are identical (α1) and one is unique (α2).
43
How do cytokines influence bone metabolism?
44
What is the pathway of differentiation for osteoblasts?
Osteoblasts arise from multipotent mesenchymal stem cells, progressing through osteoprogenitor cells and preosteoblasts before maturing into osteoblasts.
44
What regulates osteoclast function?
Osteoclast function is regulated by local cytokines and systemic hormones such as calcitonin, parathyroid hormone, and others.
45
What happens to osteoblasts toward the end of matrix production?
46
What are the roles of RANKL and M-CSF in osteoclast development?
RANKL triggers osteoclast formation, while M-CSF is essential for the differentiation, survival, and cytoskeletal changes of osteoclast precursors.
46
What is the osteocyte lacuno-canalicular system?
It is an extensive communication network formed by osteocyte filopodia that allows direct cellular communication and sensing of mechanical forces.
47
Figure 75-4. Representative load-deformation curve characteristic of a whole bone structure (mechanical testing of the structural properties of the whole bone).
47
How do osteoclasts contribute to bone resorption?
Osteoclasts attach to bone matrix via integrin receptors, form a sealing zone, and secrete enzymes and hydrogen ions to mobilize bone mineral and digest organic matrix.
47
Figure 75-5. Stress-strain curve typical of a bone sample (mechanical testing of the material properties of the bone sample).
48
What is the symbol of stress
Sigma (σ)
49
What is the definition of stress
the intensity of the force divided by the area that it acts upon
49
Units of stress
Pounds per square inch (psi) and pascals (Pa).
50
Stress forces are usually perpendicular or parallel to the surface in NORMAL
Perpendicular to the surface
51
Stress forces in shear are perpaendicular or parallel
parallel to the surface
52
What is the definition of strain
Change in dimension divided by the original dimension (x1−x0/x0)
53
In stress what is Poisson’s ratio (ν)
Ratio of lateral normal strain to longitudinal normal strain
54
What is the symbol of strain
Epsilon (ε)
54
Poisson's ration (v) of strain
Ratio of lateral normal strain to longitudinal normal strain
54
What is the normal direction of strain
Perpendicular to the surface
54
what is the shear orientation of strain
Parallel to the surface
55
What is the primary difference between static and dynamic studies?
Static studies evaluate bodies at rest, while dynamic studies evaluate moving bodies.
55
What is the units of strain
Normal strain is dimensionless and sometimes expressed as a percentage ([x1−x0/x0] × 100)
S
hear strain is often measured in radians
55
What does deformation refer to in the context of bone mechanics?
The alteration of shape and size when forces act on an object.
55
What is the significance of the load-deformation curve in mechanical testing?
It graphically represents the relationship between load and deformation in bone.
55
Define the toe region of a load-deformation curve.
A low-force, high-deformation region reflecting tissue fluid motion and fiber stretching.
55
What happens at the yield point on a load-deformation curve?
Permanent deformation occurs, meaning the structure won't return to its original shape.
56
What does the ultimate load signify in bone mechanics?
The load beyond which the structure loses all capacity to withstand increasing forces.
56
Differentiate between normal stress and shear stress.
Normal stress occurs perpendicular to a surface, while shear stress occurs parallel to it.
57
Explain Poisson’s ratio and its significance.
The ratio of lateral strain to longitudinal strain, indicating how a material deforms under stress.
58
What is Young's modulus?
The slope of the elastic segment of the stress-strain curve, indicating material stiffness.
59
Describe the concept of resilience in materials.
The ability of a material to absorb energy without permanent deformation.
60
What is the relationship between toughness and the area under a stress-strain curve?
A larger area indicates a tougher material capable of sustaining more deformation before failure.
61
How does bone exhibit anisotropic properties?
Its mechanical properties depend on the direction of the applied forces.
62
Why is bone strongest in compression but weakest in tension?
Due to the arrangement of protein fibers and mineral distribution.
63
What does the term "ductile" refer to in material properties?
A material that undergoes extensive plastic deformation before failure.
64
What factors contribute to the anisotropic properties of cortical bone?
Protein fiber arrangement, osteon composition, and mineral distribution.
65
Define compliance in mechanical terms.
The measure of a material's ability to deform under applied stress; the opposite of stiffness.
66
What does the area under the stress-strain curve represent?
The toughness of the material.
67
How is the slope of the stress-strain curve indicative of material properties?
It reveals stiffness; a steeper slope indicates a stiffer material.
68
What is meant by the term "failure load"?
The load at which a structure can no longer withstand applied forces and fails.
69
Explain the significance of the elastic region in a load-deformation curve.
It indicates the range where the material can return to its original shape after load removal.
70
How do the mechanical properties of trabecular bone differ from those of cortical bone?
Trabecular bone is more resilient and absorbs more energy before failure.
71
What types of forces result in tension and compression in bone?
Positive normal stress results in tension, while negative normal stress results in compression.
72
What does the term "brittle" imply regarding a material’s failure behavior?
It indicates a material that fails suddenly with little or no plastic deformation.
73
How does shear strain differ from normal strain?
Shear strain measures deformation parallel to a plane, while normal strain measures deformation perpendicular to the force.
74
What does the term "catastrophic failure" mean in biomechanical contexts?
A sudden and complete failure of a material, often resulting in significant damage.
75
Figure 75-6. Schematic representations of bone-loading conditions. (A) No load; (B) tension; (C) compression; (D) bending; (E) shear; (F) torsion; (G) combined compression and torsion.
76
Figure 75-6. Schematic representations of bone-loading conditions. (A) No load; (B) tension; (C) compression; (D) bending; (E) shear; (F) torsion; (G) combined compression and torsion.
77
What does anisotropic mean in the context of bone mechanics?
Bone's mechanical properties vary with the direction of applied forces.
78
What is the difference between isotropic and anisotropic materials?
Isotropic materials have uniform mechanical properties regardless of loading orientation, while anisotropic materials do not.
79
How does the arrangement of protein fibers affect the properties of cortical bone?
It contributes to its anisotropic behavior, affecting strength and load-bearing capacity.
80
What additional factor contributes to anisotropy in trabecular bone compared to cortical bone?
Bone porosity.
80
In what conditions is bone strongest and weakest?
Bone is strongest in compression, weaker in shear, and weakest in tension.
81
What influences the deformation and strain of bone?
Bone anatomy, composition, direction, rate, magnitude, frequency, and duration of the applied load.
81
How does cortical bone differ from trabecular bone in terms of brittleness and energy storage?
ortical bone is more brittle and fails at lower strain but can withstand higher loads, while trabecular bone stores more energy prior to failure due to higher toughness.
82
Why is replicating complex loading conditions in the lab complicated?
It involves multiple simultaneous forces from various directions, making data interpretation challenging.
83
What are the types of loading strategies typically reduced to in experiments?
Single-axis loading in tension, compression, bending, shear, and torsion.
84
Describe the failure mechanism of bone during tension testing.
Maximum stresses occur on a plane perpendicular to the tensile load, leading to transverse fractures due to osteonal pullout.
85
What fracture configuration is typical when bone is loaded in compression?
Fractures are offset about 45 degrees from the direction of maximum shear forces. Oblique fracture
86
Example of compression fracture in horse
dorsal metacarpal stress fracture
87
Example in the horse of tensionfractures originate transverse
proximal ulna
proximal sesamoid bones
patella
calcaneus
88
What is the relationship between microcracks and bone failure?
Microcracks can initiate and propagate along stress-concentrating osteons, leading to eventual failure.
89
How does torsion testing affect the bone structure?
It causes rotational displacement of bone ends and generates shear stresses distributed throughout the bone.
90
Example of a tosion fracture in the horse - pattern
Pattern is spiral fracture
91
Bending resultus of a combination between
tension and compression
92
What is a typical three point bending fracture in a horse?
occurs at the top of a cast when a horse steps in a hole and the limb hits the top edge
93
Example of shear fractures in horse
Physeal fractures are examples of shear loads
94
What are shear stresses, and how are they related to torsion?
Shear stresses occur due to the angular deformations resulting from applied torques and increase with distance from the neutral axis.
95
Explain the concept of the neutral axis in bending.
It's the plane within the bone that does not experience stress, with tension and compression occurring on opposite sides.
96
How does three-point bending differ from four-point bending in testing?
Three-point bending involves three forces producing two moments, while four-point bending uses two force couples for a uniform moment distribution.
97
What typically causes a fracture in a horse during three-point bending?
Fractures often occur at the tensile surface and propagate toward the compressed surface, usually resulting in a butterfly fragment.
98
How does shear loading deform a bone?
It applies loads parallel to a bone's surface, causing angular deformation and shear stress.
99
What are physeal fractures, and how do they relate to loading?
Physeal fractures result from shear loads and indicate the susceptibility of bone to shear stresses.
100
Why is studying multiaxial loading important for predicting fractures?
Bones rarely experience uniaxial loading; understanding multidimensional loading helps in fracture prediction and stabilization.
101
How does bone anatomy influence its structural mechanical properties?
It affects cross-sectional area, bone distribution, and the proportion of cortical versus cancellous bone, all influencing stiffness and strength.
102
What is the area moment of inertia, and why is it important?
It reflects the bone's distribution around the neutral axis and its resistance to deformation.
103
How does the rate of load application affect bone response?
Faster loading rates increase stiffness and energy storage, leading to higher loads at failure compared to slower rates.
104
What distinguishes high-energy fractures from low-energy fractures?
High-energy fractures often result in significant comminution and soft tissue damage, while low-energy fractures typically have less damage.
105
What causes fatigue failure in bone?
It results from repeated loads leading to microcrack initiation and propagation
106
What is the endurance limit of a bone?
The stress level under which no fractures develop regardless of the number of loading cycles.
107
Why is cortical bone particularly vulnerable to cyclic stresses?
Repeated application of compressive stress can lead to microcrack accumulation.
108
How does stress level influence microdamage accumulation in bone?
At high stress levels, damage initially increases nonlinearly and then stabilizes, while at lower stress levels, damage accumulates rapidly.
109
What role do microcracks play in bone remodeling?
Microcrack formation can trigger the remodeling process, with new bone deposition helping to arrest their propagation.
110
What is the relationship between stress levels and remodeling rates in bone?
A balance is needed for effective remodeling to mitigate fatigue-induced microcracks.
111
How do shear stresses relate to bone loading configurations?
Shear stresses arise from angular deformations caused by loads applied in configurations like bending and torsion.
112
What does the term "comminution" refer to in fracture mechanics?
The fragmentation of bone into multiple pieces during a fracture.
113
How do loading conditions during normal activities affect bone?
Bone experiences complex loading from multiple directions, influencing its structural integrity and response.
113
How does bone's microstructure contribute to its viscoelastic properties?
Bone exhibits greater stiffness and energy absorption at faster loading rates due to its microstructural characteristics.
114
Why is three-dimensional analysis preferred for studying bone loading?
It provides a more realistic assessment of the complex loading behavior of bone compared to simplified models.
115
What is the impact of joint angle and gait on bone loading?
These factors influence the distribution and magnitude of forces acting on the bone.
116
What is the significance of the bending moment in bone mechanics?
It quantifies the internal loads generated by applied forces, influencing the bone's structural response.
116
In what way does the length of a bone affect its internal loads?
Longer bones experience higher internal loads due to greater distances between force-application points.
117
How does energy release during fracture relate to strain energy?
Strain energy is stored during loading and released upon fracture, contributing to damage.
118
What is the potential impact of surrounding structures on bone loading?
They can alter the forces acting on the bone, affecting its mechanical response and susceptibility to injury.
119
What distinguishes indirect fracture healing from direct healing?
Indirect healing involves callus formation and occurs when fracture stability is insufficient for direct healing
119
What are the two main types of fracture healing?
Direct (primary) and indirect (secondary) healing.
120
How does direct fracture healing occur?
It occurs with rigid fixation that minimizes interfragmentary motion and allows for direct remodeling of bone.
121
What is the role of hematoma in fracture healing?
It forms during the acute inflammatory response and is populated by cells that facilitate healing.
122
Which proinflammatory molecules peak within 24 hours of a fracture?
Tumor necrosis factor-α (TNF-α) and interleukins (IL)-1 and IL-6.
123
What is the function of mesenchymal stem cells (MSCs) in bone healing?
They are recruited to the injury site to aid in the healing process.
124
How long does the acute inflammatory phase last in bone healing?
It is typically complete by 7 days post-injury.
125
What types of growth factors are involved in bone formation during healing?
Members of the transforming growth factor-β (TGF-β) superfamily, including bone morphogenetic proteins (BMPs)
126
What occurs in the matrix template at the end of the acute inflammatory phase?
A highly cellular, fibrin-rich callus forms between the bone ends.
127
What is the timeline for soft callus formation after a fracture?
Soft callus forms around 7 to 9 days post-trauma.
128
What structural change marks the transition to hard callus?
RepReplacement of collagen types II and III with collagen type I and the clustering of calcium hydroxyapatite crystals.
128
How do chondroblasts contribute to fracture healing?
They proliferate and secrete cartilage-specific matrix, which matures into cartilage.
129
What type of ossification is associated with indirect bone healing?
Both endochondral and intramembranous ossification.
130
Which cells are responsible for resorbing hard callus during the remodeling phase?
Osteoclasts.
130
What is the significance of Wolff’s law in bone remodeling?
It states that bone adapts to the mechanical loads placed upon it, affecting the activity of osteoblasts and osteoclasts.
131
Healing that occurs when gaps are smaller than 0.01 mm with minimal interfragmentary strain.
Healing that occurs when gaps are smaller than 0.01 mm with minimal interfragmentary strain.
131
How does gap healing differ from contact healing?
Gap healing occurs in larger gaps (0.8 mm to 1 mm) without concurrent bone union and Haversian remodeling.
132
What is required for effective clinical assessment of fracture healing?
Consideration of factors like patient signalment, initial fracture configuration, and imaging results.
133
What changes are visible on radiography within the first week post-fracture?
Sharp fracture margins are typically visible.
134
What does the presence of a smooth fracture line indicate about healing?
It suggests that healing is progressing well, with a narrowing fracture gap.
134
What is osteomyelitis?
Bone inflammation due to infection, often resulting from pathogen seeding.
134
What are common complications of equine fracture healing?
Infection, delay or failure of union, laminitis, and fixation failure.
135
What are typical organisms cultured from infected equine bone?
Staphylococcus, Streptococcus spp., and Enterobacteriaceae.
135
What factors contribute to delay or failure of fracture union?
Infection, inadequate reduction, immobilization, and soft tissue disruption.
136
How can perioperative antibiotic administration affect fracture healing?
It reduces the incidence of nosocomial infections in orthopedic cases.
137
What does nonunion mean in the context of fractures?
It occurs when fracture repair ceases before the bony structure is restored.
138
What is a hypertrophic nonunion?
A type of nonunion characterized by abundant blood supply and exuberant callus formation.
139
What is stress-induced laminitis and how is it related to fractures?
It occurs from increased weight-bearing on the contralateral limb due to lameness after fracture fixation.
140
What factors can lead to surgical implant complications?
Inadequate stabilization and mechanical demands exceeding fixation strength.
141
What is the primary goal of fracture stabilization?
To return to weight bearing on the affected limb as quickly as possible.
142
How do high loads during recovery affect fracture healing?
They can lead to fixation failure or delayed healing.
143
What is the importance of a good blood supply in bone healing?
It is essential for successful remodeling and preventing nonunion.It is crucial for supplying nutrients and oxygen to the healing tissue.
144
What are the radiographic signs of delayed union?
Persistent fracture lines and minimal callus formation.
145
What is the effect of motion at the fracture site on callus formation?
Greater motion results in a larger callus.
146
Why is it important to combine imaging modalities in fracture assessment?
To provide a comprehensive evaluation of fracture diagnosis and healing progress.
147
Figure 75-11. Bone sequestrum (arrow) on an equine radius that resulted from a devascularized bone fragment when the bone was fractured by a kick from another horse.
148
Figure 75-12. Radiographic images of a fourth metatarsal osteotomy from immediately postoperative to 12 weeks after treatment of the gap with recombinant human bone morphogenetic protein-2 combined with calcium phosphate cement demonstrating progression toward union by 10 weeks.
149
What is distraction osteogenesis?
A surgical technique that promotes bone growth by applying gradual traction on each side of an osteotomy.
150
Why is distraction osteogenesis limited in equine long bones?
The strength of adjustable external fixators is usually inadequate for anything other than small foals.
151
What is the typical rate of linear bone generation during distraction osteogenesis?
Linear bone generation can reach 200 to 400 μm/day.
152
What factors are essential for successful distraction osteogenesis?
Fixation stability, blood supply, minimal soft tissue disruption, and physiological bone use.
152
How many periods is distraction osteogenesis divided into?
Three periods: latency, activation, and consolidation.
153
What occurs during the latency period of distraction osteogenesis?
The time between bone transection and the start of distraction.
154
What happens during the activation period?
Bony ingrowth occurs as distraction begins.
155
What characterizes the consolidation period?
Mineralization and remodeling of bone and osteoid to create mature bone structure.
156
What is transchondroid bone formation?
Chondroid bone formation by chondrocyte-like cells without capillary invasion.
157
What concerns exist with allogeneic bone grafts?
Potential for pathogen transmission and variability in graft quality.
157
How do autogenous bone grafts facilitate healing?
They provide cells for osteogenesis, induce bone formation, and offer a scaffold for bone growth.
157
What are the key properties of bone grafts?
They provide cells for osteogenesis, induce bone formation, and offer a scaffold for bone growth.
157
What types of ossification occur during distraction osteogenesis?
Osteogenesis, osteoinduction, and osteoconduction
158
What principle underlies many energy-based treatments for bone healing?
Wolff’s law, which states that living bone adapts its structure to mechanical stress.
159
How does extracorporeal shock wave therapy work?
It uses high-pressure acoustic waves to stimulate healing through pressure and shear forces.
160
What risks are associated with extracorporeal shock wave therapy?
Anecdotal reports of catastrophic fractures suggest it should be used cautiously.
161
What is needed for effective MSC application in fracture healing?
Culture-expanded or purified MSC populations to ensure sufficient and consistent osteogenic potential.
162
What challenges exist in using MSCs for equine fracture repair?
Variability in MSC numbers and plasticity among individuals and harvest sites.
162
Why are adult mesenchymal stem cells (MSCs) significant in bone healing?
They exhibit osteogenesis in vitro and may enhance fracture-repair strategies.
163
What is the role of BMPs in fracture healing?
They accelerate bone repair when administered via carriers or vectors.
163
Which bone fillers showed better outcomes in a study involving equine fractures?
Biodegradable magnesium phosphate demonstrated superior results compared to calcium phosphate.
164
What physiological effect does traction have on callus tissue?
It stimulates metabolic activity and proliferation in the distraction gap.
165
How is callotasis related to distraction osteogenesis?
Callotasis is a specific form of distraction osteogenesis often used for deformities.
166
What is the expected outcome of distraction osteogenesis?
Progressive growth of bone and soft tissues, leading to improved structural integrity.
167
What role does blood supply play in distraction osteogenesis?
Adequate blood supply is critical for healing and bone remodeling.
168
How do mechanical forces contribute to bone adaptation according to Wolff's law?
They generate electric fields through deformation, promoting structural changes in bone.
169
What is the main challenge with using allogeneic grafts in fracture repair?
Risk of immune rejection and transmission of pathogens.
