Chapter 75 - Bone biology and fracture healing Flashcards
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.
What are the primary functions of bones in the body?
Bones protect internal organs, provide rigidity for force generation, and serve as a reservoir for calcium and phosphate.
What is the importance of the organic matrix, cells, and water in bones?
They contribute to the mechanical properties crucial for bone function.
What proportion of dry bone weight is composed of minerals?
Two-thirds of the dry weight of bone is mineral.
What factors influence bone healing?
Patient characteristics, site and severity of injury, and fracture management.
What process is essential for maintaining normal bone performance?
Dynamic remodeling is essential for maintaining normal bone performance.
How do bones repair themselves without forming scars?
Through secreted growth factors and interactions among cells and the microenvironment.
What are the three major categories of bones?
Long, cuboidal, and flat bones.
How do long bones provide a mechanical advantage for horses?
Their length contributes to superior power and speed.
What are the three regions of long bones?
Diaphysis, epiphysis, and metaphysis.
What separates the metaphysis from the epiphysis?
The physis, or growth plate.
How do axial bones form during embryonic development?
By ossification of a hyaline cartilage model through endochondral ossification.
What is intramembranous ossification?
A process where flat bones form from fibrous connective tissue precursors.
Describe the process in the hypertrophic zone of the growth plate.
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.
What happens to chondrocytes during endochondral ossification
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
What is the role of perichondrial cells in bone development?
They become osteoblasts and form a bone collar, guiding vascularization and mineralization.
What does vascular ingrowth form during endochondral ossification?
The primary spongiosa.
What occurs in the resting zone of the growth plate?
It contains the least metabolically active chondrocytes.
What is the difference in ossification centers between endochondral and intramembranous ossification?
Endochondral ossification forms in a cartilage model, while intramembranous ossification forms in sheets of connective tissue.
What happens in the ossification zone of the growth plate?
Chondrocytes mature, hypertrophy, and mineralize the extracellular matrix.
How does cortical bone thickness vary in long bones?
It decreases proximally towards the metaphysis.
What remains of the physis once skeletal maturity is reached?
An inactive physis as a narrow, indistinct line between epiphysis and metaphysis.
What type of marrow is found in the medulla of immature animals?
Hematopoietic bone marrow.
What are the two main types of bone tissue?
Cortical (compact) bone and trabecular (cancellous) bone.
What is the composition of osteons in cortical and trabecular bone?
Cortical osteons are Haversian systems; trabecular osteons are referred to as packets.
Why is trabecular bone considered more metabolically active?
Its structure allows for a higher rate of metabolic activity compared to cortical bone.
What distinguishes primary from secondary osteons?
Primary osteons form during growth, while secondary osteons form during remodeling.
How are Volkmann canals oriented relative to Haversian canals?
Volkmann canals are oriented at 90 degrees to Haversian canals.
What is the structure of Haversian systems?
Cylindrical shape with concentric layers (lamellae) surrounding central canals
What are cement lines, and what do they signify?
They separate osteons from interstitial bone tissue, indicating areas of bone resorption and formation.
What is bone remodeling, and when does it occur?
Local stress and strain, metabolic status, age, and sex.
What factors influence the composition and mineralization of cement lines?
Local stress and strain, metabolic status, age, and sex.
What are current research focuses in fracture healing?
Accelerating healing processes and reducing complications
What is bone remodeling, and when does it occur?
Bone remodeling is the process of bone resorption and formation occurring throughout life.
What are some mechanisms to assess fracture healing quality?
Noninvasive imaging techniques are critical for assessing healing quality.
What role do growth factors play in bone healing?
They facilitate communication and healing processes between bone cells.
What biological events are involved in the bone healing process?
A highly orchestrated sequence that includes inflammation, repair, and remodeling.
What complications can arise from poor fracture management?
Delayed healing, nonunion, or malunion of the fracture.
How does fracture stabilization influence bone healing?
Proper stabilization promotes optimal healing conditions and reduces complications.
How does the biomechanical environment affect bone health?
Mechanical stress and strain influence bone density, strength, and remodeling rates.
Why is understanding fracture configurations important?
What is the significance of bone’s ability to remodel?
It allows adaptation to mechanical loads and repair of micro-damage over time.
Mammalian long bone growth in length occurs at the physis via
endochondral ossification
The resting zone contains the least metabolically active ____(1w) and is closest to the epiphyseal end of the growth pla
chondrocytes
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
Chondrocytes mature, become encased in __(1w) matrix, and assume a round morphology in the hypertrophic zone, where they cease dividing and hypertrophy.
extracellular
When chondrocytes hypertrophy and remodel and mineralize the extracellular matrix around them forms the ___(1w) zone
calcification zone
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.
After hypertrophy, the chondrocytes die and the extracellular matrix around them is removed to create the ____________(1w) zone
ossification
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.
Cortical and trabecular bone are composed of ___(1w)
osteons
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
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.
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.
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.
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.
What percentage of resting cardiac output is delivered to bones?
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.
Identify the three sources of afferent blood supply in mature long bones.
The nutrient artery, the metaphyseal-epiphyseal vessel complex, and periosteal vessels.
What mineral primarily composes the mineral component of bone?
The mineral component is mainly crystalline hydroxyapatite.
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.
What is the composition of bone by volume?
Bone is composed of approximately 25% water, 35% organic components, and 40% mineral components.
What is fibrillogenesis?
Fibrillogenesis is the process where tropocollagen helices self-assemble to form microfibrils that organize into fibril
What is the primary function of proteoglycans in the bone matrix?
Proteoglycans provide flexibility and resilience to the organic matrix of bone.
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).
How do cytokines influence bone metabolism?
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.
What regulates osteoclast function?
Osteoclast function is regulated by local cytokines and systemic hormones such as calcitonin, parathyroid hormone, and others.
What happens to osteoblasts toward the end of matrix production?
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.
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.
Figure 75-4. Representative load-deformation curve characteristic of a whole bone structure (mechanical testing of the structural properties of the whole bone).
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.
Figure 75-5. Stress-strain curve typical of a bone sample (mechanical testing of the material properties of the bone sample).
What is the symbol of stress
Sigma (σ)
What is the definition of stress
the intensity of the force divided by the area that it acts upon
Units of stress
Pounds per square inch (psi) and pascals (Pa).
Stress forces are usually perpendicular or parallel to the surface in NORMAL
Perpendicular to the surface
Stress forces in shear are perpaendicular or parallel
parallel to the surface
What is the definition of strain
Change in dimension divided by the original dimension (x1−x0/x0)
In stress what is Poisson’s ratio (ν)
Ratio of lateral normal strain to longitudinal normal strain
What is the symbol of strain
Epsilon (ε)
Poisson’s ration (v) of strain
Ratio of lateral normal strain to longitudinal normal strain
What is the normal direction of strain
Perpendicular to the surface
what is the shear orientation of strain
Parallel to the surface
What is the primary difference between static and dynamic studies?
Static studies evaluate bodies at rest, while dynamic studies evaluate moving bodies.
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
What does deformation refer to in the context of bone mechanics?
The alteration of shape and size when forces act on an object.
What is the significance of the load-deformation curve in mechanical testing?
It graphically represents the relationship between load and deformation in bone.
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.
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.
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.
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.
