Ch. 74 Bone Biology and Fracture Healing

Question 1

a. The resting zone contains the least metabolically active chondrocytes and is farthest from the epiphyseal end of the growth plate.

b. In the proliferation zone, cell mitosis occurs in a plane parallel to the long axis of the bone to increase the length of the cell column.

c. Mammalian long bone growth in length occurs at the physis via endochondral ossification.

d. Chondrocytes mature, become encased in extracellular matrix, and assume a round morphology in the hypertrophic zone, where they continue dividing and hypertrophy.

Answer 1

c. Mammalian long bone growth in length occurs at the physis via endochondral ossification.

The resting zone contains the least metabolically active chondrocytes and is closest to the epiphyseal end of the growth plate.

In the adjacent proliferation zone, cell mitosis occurs in a plane perpendicular to the long axis of the bone to increase the length of the cell column.

Chondrocytes mature, become encased in extracellular matrix, and assume a round morphology in the hypertrophic zone, where they cease dividing and hypertrophy.

Question 2

a. The epiphysis, metaphysis, and cuboidal bones have comparatively thicker cortices than the diaphysis.

b. Cortical bone thickness of the diaphysis increases with proximity to the metaphysis.

c. The medulla contains hematopoietic bone marrow in immature animals that is gradually replaced with bone and fat-replete nonhematopoietic bone marrow with age.

d. Trabecular bone is less metabolically active and responsive than cortical bone.

Answer 2

c. The medulla contains hematopoietic bone marrow in immature animals that is gradually replaced with bone and fat-replete nonhematopoietic bone marrow with age.

The epiphysis, metaphysis, and cuboidal bones have comparatively thinner cortices than the diaphysis.

Cortical bone thickness of the diaphysis decreases with proximity to the metaphysis.

Trabecular bone, composed of three-dimensional networks of rods and plates, is more metabolically active and responsive than cortical bone.

Question 3

Which of the following statements is true

a. Trabecular osteons are called Haversian systems

b. Periosteum is attached to the bone surface by Sharpey fibers, connective tissue strands composed of predominantly type I collagen, a portion of which extend through the bone to the endosteum

c. The inner fibrous layer of periosteum is composed of fibroblasts, collagen, and elastin fibers, and has a nerve and microvascular network.

d. The inner cambium layer that contacts the bone surface contains adult mesenchymal progenitor cells, differentiated osteogenic progenitor cells, osteoblasts, fibroblasts, microvessels, and sympathetic nerves

Answer 3

d. The inner cambium layer that contacts the bone surface contains adult mesenchymal progenitor cells, differentiated osteogenic progenitor cells, osteoblasts, fibroblasts, microvessels, and sympathetic nerves

Periosteum is attached to the bone surface by Sharpey fibers, connective tissue strands composed of predominantly type III collagen, a portion of which extend through the bone to the endosteum

Cortical osteons are called Haversian systems and trabecular osteons are called packets

outer fibrous layer of periosteum is composed of fibroblasts, collagen, and elastin fibers, and has a nerve and microvascular network.

Question 4

a. a complex vascular network delivers between 10% and 15% of the resting cardiac output to bones

b. under normal conditions little to no blood passes centripetally from periosteum to cortex in mature animals because of a centrifugal pressure gradient across the cortical capillaries

c. In type I collagen, two of the three polypeptides, all consisting of about 1000 amino acids, are identical (α1) and the structurally similar third is genetically unique (α2)

d. all of the above

Answer 4

d. all of the above

Question 5

a. Proteoglycans provide flexibility and resilience to the organic matrix.

Tropocollagen helices self-assemble in a characteristic, staggered manner (periodicity) to form microfibrils that organize into fibrils, a process known as fibrillogenesis

Bone-lining cells regulate release of minerals into blood to maintain homeostasis and are among the first to respond to remodeling needs by facilitating both bone resorption and deposition

Toughness is the capacity of a material to sustain deformation without failure

Answer 5

Bone-lining cells regulate release of minerals into blood to maintain homeostasis and are among the first to respond to remodeling needs by facilitating both bone resorption and deposition

Question 6

a. Axial bones form by ossification of a hyaline cartilage model through intramembranous ossification

b. Flat bones of the skull, the mandible, maxilla, as well as the sesamoid bones form on a fibrous, connective tissue precursor in a process called endochondral ossification

c. Within the center of the Haversion system are small Haversion canals oriented perpendicular to the long axis of the bone that contain vessels and nerves

d. Trabecular osteons are composed of concentric lamellae and are semilunar in shape

Answer 6

d. Trabecular osteons are composed of concentric lamellae and are semilunar in shape

axial bones form by ossification of a hyaline cartilage model through endochondral ossification

flat bones of the skull, the mandible, maxilla, as well as the sesamoid bones form on a fibrous, connective tissue precursor in a process called intramembranous ossification

Within the center of the Haversion system are small Haversion canals oriented parallel to the long axis of the bone that contain vessels and nerves

Question 7

a. The inner cambium layer is a cellular structure between bone and bone marrow that covers the trabeculae, the medullary cavity and inner surfaces of bone canals

b. H lines separate osteons from interstitial bone tissue composed of matrix components, lamellar bone remnants, and remodeled osteon fragments.

c. The perisoteum provides the cells for fracture healing and appositional bone growth.

d. The inner fibrous layer of periosteum is composed of fibroblasts, collagen, and elastin fibers, and has a nerve and microvascular network.

Answer 7

c. The perisoteum provides the cells for fracture healing and appositional bone growth.

The endosteum is a cellular structure between bone and bone marrow that covers the trabeculae, the medullary cavity and inner surfaces of bone canals

Cement lines separate osteons from interstitial bone tissue composed of matrix components, lamellar bone remnants, and remodeled osteon fragments.

The outer fibrous layer of periosteum is composed of fibroblasts, collagen, and elastin fibers, and has a nerve and microvascular network.

Question 8

a. The endosteal niche in the periosteum contains stem, progenitor and stromal cells, growth factors, and extracellular matrix molecules that participate in hematopoiesis regulation

b. There are three sources of afferent blood supply in mature long bones,
1. the nutrient artery that enters the diaphysis,
2. the metaphyseal-epiphyseal vessel complex at the bone ends and
3. the periosteal vessels

c. 30% of the diaphyseal afferent blood flow is toward the cortex away from the medulla (centrifugal) and 70% toward the medulla (centripetal).

d. All of the above

Answer 8

b. There are three sources of afferent blood supply in mature long bones,
1. the nutrient artery that enters the diaphysis,
2. the metaphyseal-epiphyseal vessel complex at the bone ends and
3. the periosteal vessels

The endosteal niche in the endosteum contains stem, progenitor and stromal cells, growth factors, and extracellular matrix molecules that participate in hematopoiesis regulation

70% of the diaphyseal afferent blood flow is toward the cortex away from the medulla (centrifugal) and 30% toward the medulla (centripetal).

Question 9

a. under normal conditions little to no blood passes centripetally from periosteum to cortex in mature animals because of a centrifugal pressure gradient across the cortical capillaries

b. periosteal and endosteal circulatory network anastomoses permit blood flow in either direction, and the relative amount of centrifugal and centripetal blood flow in the afferent vascular system changes with growth and injury

c. endosteal circulation supplies the medulla and inner two-thirds of cortical bone, whereas periosteal arterioles supply the outer third.

d. all of the above

Answer 9

d. all of the above

Question 10

a. Bone is a composite material containing 10% water, 35% organic component and 55% inorganic components

b. 90% of the organic component of bone is Type II collagen

c. The basic structure of animal collagen is tropocollagen

d. None of the above

Answer 10

c. The basic structure of animal collagen is tropocollagen

Bone is a composite material containing 25% water, 35% organic component and 40% inorganic components

90% of the organic component of bone is Type II collagen

Question 11

a. In type I collagen, two of the three polypeptides, all consisting of about 1000 amino acids, are identical (α1) and the structurally similar third is genetically unique (δ2)

b. Individual α chains of type I collagen consist primarily of repeating glycine, proline, and hydroxyproline sequences.

c. Tropocollagen helices self-assemble in a characteristic uniform manner to form microfibrils that organize into fibrils, a process known as fibrillogenesis

d. COMP provide flexibility and resilience to the organic matrix.

Answer 11

b. Individual α chains of type I collagen consist primarily of repeating glycine, proline, and hydroxyproline sequences.

In type I collagen, two of the three polypeptides, all consisting of about 1000 amino acids, are identical (α1) and the structurally similar third is genetically unique (α2)

Tropocollagen helices self-assemble in a characteristic, staggered manner (periodicity) to form microfibrils that organize into fibrils, a process known as fibrillogenesis

Proteoglycans provide flexibility and resilience to the organic matrix.

Question 12

a. Proteoglycans are composed of a specific core protein with covalently linked glycosaminoglycan (GAG) chains

b. Bone sialoprotein and osteopontin are examples of proteins that regulate release of minerals into blood to maintain homeostasis

c. Toward the end of matrix production, 25% of osteoblasts undergo apoptosis

d. Bone-lining cells promote progenitor cell differentiation and matrix contributions by binding the cell membrane proteins such as integrins

Answer 12

a. Proteoglycans are composed of a specific core protein with covalently linked glycosaminoglycan (GAG) chains

Bone sialoprotein and osteopontin are examples of proteins that promote progenitor cell differentiation and matrix contributions by binding the cell membrane proteins such as integrins

Toward the end of matrix production, 50% to 70% of osteoblasts undergo apoptosis, some remain on the bone surface to become bone-lining cells, and about 15% entrapped in bone matrix differentiate into osteocytes within discrete lacunae

Bone-lining cells regulate release of minerals into blood to maintain homeostasis and are among the first to respond to remodeling needs by facilitating both bone resorption and deposition

Question 13

a. Two cytokines produced by stromal cells, receptor activator of nuclear factor-KB ligand (RaNKL) and macrophage colony-stimulating factor (M-CSF), are essential for osteoblast development

b. MCSF binds RaNKL to prevent osteoclast activation

c. Osteocytes secrete hydrogen ions to lower the pH and mobilize bone mineral as well as enzymes
tartrate-resistant acid phosphatase,
cathepsin k,
matrix metalloproteinase 9, and
gelatinase to digest organic matrix

d. Osteoblast function is regulated by locally acting cytokines and systemic hormones such as calcitonin, androgens, parathyroid hormone, insulin, interleukin IL-1, platelet-derived growth factor, and osteoprotegerin (OPG)

Answer 13

c. Osteocytes secrete hydrogen ions to lower the pH and mobilize bone mineral as well as enzymes
tartrate-resistant acid phosphatase,
cathepsin k,
matrix metalloproteinase 9, and
gelatinase to digest organic matrix

Two cytokines produced by stromal cells and osteoblasts, receptor activator of nuclear factor-κB ligand (RaNkl) and macrophage colony–stimulating factor (M-CSF), are essential for osteoclast development.

The protein OPG binds RaNKL to prevent osteoclast activation

Osteoclast function is regulated by locally acting cytokines and systemic hormones such as calcitonin, androgens, parathyroid hormone, insulin, interleukin IL-1, platelet-derived growth factor, and osteoprotegerin (OPG)

Question 14

a. elastic region = shows the ability to resist deformation, structure will return to its original form when the load is removed.

b. yield point = beyond which permanent deformation occurs in the plastic segment of the curve, will not return to its original shape when the load is removed.

c. ultimate load = load beyond which the structure essentially loses all capacity to withstand increasing forces.

d. All of the above

Answer 14

d. all of the above

Question 15

a. Stress (σ) is the intensity of the force divided by the area that it acts upon

b. Normal stresses occur when forces are applied parallel to the surface of a structure

c. Shear stresses occur when forces are applied perpendicular to the surface of a structure

d. Strain (ε) is capacity of a material to sustain deformation without failure

Answer 15

a. Stress (σ) is the intensity of the force divided by the area that it acts upon

Normal stresses occur when forces are applied perpendicular to the surface of a structure

Shear stresses occur when forces are applied parallel to the surface of a structure

strain (ε) is the change in dimension divided by the original dimension,

Question 16

a. Strain (ε) the original dimension divided by the change in dimension

b. Stress (ε) is the change in dimension divided by the original dimension

c. Toughness (σ) is the intensity of the force divided by the area that it acts upon.

d. Ductile material has extensive plastic deformation and high-energy absorption prior to failure

Answer 16

d. Ductile material has extensive plastic deformation and high-energy absorption prior to failure

Toughness is the capacity of a material to sustain deformation without failure

Strain (ε) is the change in dimension divided by the original dimension

Stress (σ) is the intensity of the force divided by the area that it acts upon.

Question 17

a. Bone is strongest in compression, weaker in tension, and weakest in shear

b. The ratio of lateral normal strain to longitudinal normal strain is called Poisson’s ratio (ν)

c. Shear strain, often measured in radians, refers to deformation in which a plane in the body is displaced perpendicular to itself.

d. Tension results in negative normal stress

Answer 17

b. The ratio of lateral normal strain to longitudinal normal strain is called Poisson’s ratio (ν)

Bone is strongest in compression, weaker in shear, and weakest in tension

Shear strain, often measured in radians, refers to deformation in which a plane in the body is displaced parallel to itself

Tension results in positive normal stress, and compression results in negative normal stress

Question 18

a. Cortical bone fails at a lower strain, albeit a higher load than trabecular bone owing to a higher toughness of cortical bone

b. Cortical bone stores more energy prior to failure compared with trabecular bone owing to a higher toughness of cortical bone

c. Trabecular bone stores more energy prior to failure compared with cortical bone

d. Trabecular bone fails at a lower strain, albeit a higher load than cortical bone

Answer 18

c. Trabecular bone stores more energy prior to failure compared with cortical bone, owing to higher toughness.

Cortical bone is more brittle than trabecular bone and fails at a lower strain, albeit a higher load

Trabecular bone stores more energy prior to failure compared with cortical bone, owing to higher toughness.

Question 19

a. Maximum stresses occur on a plane perpendicular to the applied tensile load and result in transverse fractures

b. When loaded in compression, maximum stresses occur in a plane perpendicular to the load as the bone shortens and widens

c. Compression fractures can be loosely considered a reflection of stress concentration and bone failure along Haversian network components.

d. All of the above

Answer 19

d. all of the above

Question 20

a. shear stresses are the product of the distance from the central axis and the torque from the applied load multiplied by the polar moment of inertia of the bone

b. the neutral axis is a plane within the bone that does not experience any stresses, and the greater the distance from the neutral axis, the larger the tensile and compressive stresses.

c. three-point bending fracture in a horse occurs at the top of a cast. The typical fracture contains a butterfly fragment on the tension side

d. None of the above

Answer 20

b. the neutral axis is a plane within the bone that does not experience any stresses, and the greater the distance from the neutral axis, the larger the tensile and compressive stresses.

shear stresses are the product of the distance from the central axis and the torque from the applied load divided by the polar moment of inertia of the bone, which in turn depends on the bone structure

three-point bending fracture in a horse occurs at the top of a cast The typical fracture contains a butterfly fragment on the compressive side

Question 21

a. Physeal fractures are examples of fractures from shear loads

b. Largely because of its microstructure, bone is stiffer when loaded at a faster rate, and hence it stores more energy prior to failure compared to slower loading rates

c. Endurance limit of a bone is the stress level under which no fractures can develop regardless of the number of loading cycles applied

d. All of the above

Answer 21

d. All of the above

Question 22

Which of these is incorrect regarding direct fracture healing

a. Direct fracture healing occurs when rigid fixation confers anatomic reduction with no space between fracture ends and minimizes interfragmentary motion

b. Involves direct remodeling of lamellar bone, the Haversian canals, and blood vessels with little or no periosteal callus formation.

c. Gap healing is a form of direct fracture healing

d. Gaps smaller than 0.01 mm with less than 10% interfragmentary strain heal by contact healing

Answer 22

d. Gaps smaller than 0.01 mm with less than 2% interfragmentary strain heal by contact healing.

Question 23

a. Contact healing occurs in gaps less than 800 μm to 1 mm

b. Fracture healing occurs from remodeling of bridging osteons into lamellar bone with formation of periosteal callus.

c. Osteoblastic activity is enhanced on electronegative surfaces and osteoclast activity is higher on electropositive surfaces according to Wolff’s law.

d. Osteoblastic activity is enhanced on electropositive surfaces and osteoclast activity is higher on electronegative surfaces according to Wolff’s law.

Answer 23

c. Osteoblastic activity is enhanced on electronegative surfaces and osteoclast activity is higher on electropositive surfaces according to Wolff’s law.

Gap healing occurs in gaps less than 800 μm to 1 mm

Fracture healing occurs from remodeling of bridging osteons into lamellar bone without formation of periosteal callus.