Ch. 38-39 MS Tissues and Fracture Biology Flashcards
what are glycoproteins?
polypeptides that contain covalently linked carbohydrates Proteoglycans are a large and important class of glycoproteins
What embryonic tissue do most musculoskeletal structures derive from? Where does the nucleus pulposus of the intervertebral disc come from?
most musculoskeletal tissues com from mesenchymal tissues derived from the embryonic mesoderm
Nucleus pulposus of the intervertebral disc comes from neuroectodermal (notochordal) origin
what is the difference between stress and strain in basic terms?
stress is the force per unit area
strain is the deformation in a given direction
what do all collagen types share in common?
a tertiary structure consisting of a triple helix made up of three separate polypeptide molecules called alpha chains
What are the two most abundant homotypic collagen types? and what does that mean?
Type II and III are homotypic meaning they each have three identical alpha chains
What is the most abundant heterotypic collagen?
type V which has multiple alpha chains
What are alpha chain gene products?
variable length polypeptides with a major central region consisting of (Gly-X-Y)n repeats, flanked by shorter globular N terminal and C terminal telopeptide domains
What is the rate limiting step in collagen biosynthesis?
proline hydroxylation
what is fibrillogenesis?
the assembly of tropocollagen into macromolecular fibrilar complexes within the extracellular matrix
what are the two groups of glycosaminoglycans? What do they contain?
- glucosaminoglycans (heparan sulfate and keratan sulfate) with D-glucosamine
- galactosaminoglycans (chondroitin sulfate and dermatan sulfate) with D-galactosamine
what are metalloproteinases?
large family of zinc dependent endopeptidases including collagenases, gelatinases, and stromelysins that cleave a broad range of extracellular matrix proteins
t/f
the majority of matrix metalloproteinases play a key role in morphogenesis of collagen
false - a deficiency in just a metalloproteinase doesnt seem to make a huge difference but in contrast, a deficiency of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) leads to an array of morphogenic defects
what is the monomeric component of elastin?
tropoelastin - 70 kDaltons
vertebrates have a single tropoelastin gene but the primary gene transcript undergoes alternative splicing to have all the different forms
what is coacervation?
temperature dependent alignment and macromolecular assembly of tropoelastin monomers
incorporation of tropoelastin into nascent elastic fibers involves coacervation and cross linking
what is the hexose/hexuronic acid and hexosamine for the GAG: chondroitin sulfate
Hexose/hexuronic acid: (2-sulfo)-glucuronic acid
Hexosamine: (4/6-sulfo) - N- acetyl glucosamine
Chondroitin sulfate is the most abundant GAG in the body
what is the hexose/hexuronic acid and hexosamine for the GAG: dermatan sulfate
Hexose/hexuronic acid: (2-sulfo)-iduronic acid or glucuronic acid
Hexosamine: (4/6-sulfo) - N- acetyl glucosamine
dermatan sulfate is different from chondroitin because of the presence of iduronic acid
what is the hexose/hexuronic acid and hexosamine for the GAG: heparan sulfate
Hexose/hexuronic acid: (2-sulfo)-iduronic acid or glucuronic acid
Hexosamine: (6-sulfo) -N- acetyl glucosamine or (6-sulfo) -N- sulfo glucosamine
heparan sulfate is the most negatively charged GAG
what is the hexose/hexuronic acid and hexosamine for the GAG: keratan sulfate
Hexose/hexuronic acid: (6-sulfo)-galactose
Hexosamine: (6-sulfo) -N- acetyl glucosamine
keratan sulfate is prevalant in bone and cartilage
what is the hexose/hexuronic acid and hexosamine for the GAG: hyaluronic acid
Hexose/hexuronic acid: glucuronic acid
Hexosamine: N- acetyl glucosamine
hyaluronic acid is a non sulfated GAG
what is a haversian unit
a unit made up of a central Haversian canal surrounded by concentrally arranged bone lamellae
what is the periosteal extracellular matrix rich in?
type I collagen
proteoglyans
elastin
how much mineral and water does living bone contain (%)?
5-10% water
70% mineral
how much (%) does collagen account for the organic matrix of bone
90%
What collagen types are in bone?
mostly type I but minor amounts of type III and V are present
what three proteins majorly contribute to the nucleation (start) of calcium hydroxylapatite crystal formation on collagen fibrils?
bone sialoprotein
osteocalcin
alkaline phosphatase
what force is bone strongest in? why?
strongest to compressive forces - the mineral component of bone extracellular matrix provides high stiffness and strength to resist compressive stresses
**the organic component is what has to handle the tensile stresses so that may be why bone is weakest in tension
how much of articular cartilage is water?
70%
what is the constitution of articular cartilage on a dry weight % basis?
50% collagen
35% proteoglycan
10% other glycoproteins
2-10% chondrocytes
how long does collagen turnover take in the adult dog? proteoglycan turnover?
120 years for collagen - no idea how they figure that
300 days for proteoglycan
what collagen predominates in articular cartilage?
85% to 90% is type II
what is aggregan?
- the major proteoglycan in articular cartilage - rich in chondroitin sulfate and in many species keratan sulfate
- large core protein of aggrecan is 240 kDa
- 90% of aggrecan is carbohydrate
- many aggregan monomers can be linked to a single hyaluron backbone and weigh more than 2x10^5 kDa
what are the main leucine rich proteoglycans in articular cartilage?
chondroitin sulfate/dermatan sulfate groups –> decorin and biglycan
keratan sulfate –> fibromodulin
how do decorin and fibromodulin regulate collagen synthesis
they bind to type II collagen fibrils and regulate fibrillogenesis
what is the major fibronectin splice variant?
(V+C)- isoform which lacks the V, III, and I protein domains and can bind to decorin
what are the two main lubricating fluids?
lubricin (a boundary lubricant) that is most critical under high load, low motion conditions hyaluronic acid (viscous lubricant)
what characteristic of articular cartilage lends itself to allow tissue deformation that increases the congruity of opposing articular cartilage surfaces?
low modulus of elasticity
what is the main contributor of osmotic pressure of the proteoglycans?
75% of the osmotic pressure is made up by GAGs
what are the properties of fibrocartilage?
- rich in type I collagen
- small amount of proteoglycans
- component of many parts of the MS system: annulus fibrosus of the intervertebral disc, mensici of the stifle, TMJ, parapatellar fibrocartilaginous insertions of the quadriceps
- fibrocartilage is very tough but flexible with variable elasticity
what is an aponeurosis?
flattened structure that connects muscles to bones or to other fascial elements, or that form connective tissue leaves within the substance of a pennate muscle (like the rectus abdominus)
what are positional tendons?
discrete and relatively stiff structures that transfer muscular forces to bones to cause joint motion
may be wrap around that change direction and engage in specialized pulley like grooves in bones as they traverse a joint
what are energy storing tendons?
have greater elastic fiber content and are adapted to respond to the forces of weight bearing by energy storage and elastic recoil. ex. is the common calcaneal tendon
what are the three types of tendons?
- aponeuroses
- positional tendons
- energy storing tendons
what is epiligament?
a thin vascularized connective tissue sheath that surrounds intra-articular ligaments and will merge with the periosteum at the ligament attachments
what is the primary collagen of tendons and ligaments?
type I
what does it mean that tendons and ligaments are highly anisotropic
high stiffness and strength in longitudinal tensile loading but negligible stiffness and strength when loaded transversely
what does it mean that tendons and ligaments exhibit a viscoelastic response?
the rate of loading affects the response - both stress relaxation and creep can occur at low load over long time periods
how does the hierarchical structuring of collagen fibrils aid in tendons/ligaments withstanding high loads?
- large diameter fibrils provide greater stiffness and will withstand high loads
- smaller diameter fibrils provide more fibrillar surface area to finely control the viscoelastic properties of a structure through variations in interfibrillar cross linking and proteoglycan content
- healed ligament or tendon is higher in those small fibrils so that is probably why it isnt as good at withstanding high loads
what are entheses?
specialized regions of a tendon or liagament at sites of insertion or attachment to bone
can be fibrous or fibrocartilagenous
What are Sharpey’s fibers
fibrous entheses where muscles attach to diaphyseal bone and are composed of dense bands of collagen
they will merge with periosteal membrane and penetrate deeply into the cortical bone
what are fibrocartilagenous entheses?
contain a zone of fibrocartilage at the osteotendinous or osteoligamentous attachment that forms a transition between the collagen fibers of the tendon or ligament and the bone
periosteum is not present at fibrocartilaginous entheses
the fibrocartilaginous zone consists of both non mineralized and mineralized regions that are separated by a tidemark
what kind of enthesis typically forms after surgical reattachment of tendons or ligaments to bone after avulsion or laceration?
usually fibrous enthesis instead of fibrocartilagenous. That is a problem because the fibrous enthesis may not be able to resist higher levels of loading
what are the major molecular components of muscle?
intracellular myofibrillar proteins
*the extracellular matrix makes up a small proportion of the muscle, unlike most of the rest of the MS system
what does it mean that innervation is trophic to skeletal muscle?
trophic is relating to feeding or nutrition
because innervation is trophic to skeletal muscle, denervation of a muscle leads to profound atrophy
what is the endomysium
a loosely organized soft tissue encasement that surrounds myofibers into muscle fibers
the endomysium contains a population of mononuclear myoblastic progenitor cells called satellite cells, which are capable of self renewal and myocytic differentiation
what is the perimysium?
the connective sheath that bundles fibers into muscle fasicles
what is the epimysium?
connective tissue that bundles muscle fascicles into muscle bellies and makes up the deep muscle fascia
what is translation?
the displacement from one location to another without a change in orientation
what is rotation?
a change in orientation that is induced when applied forces result in a net moment
what is a moment?
a moment is generated when a force acts on a body at some distance from a potential axis of rotation
the distance between the line of action of a force and the axis of rotation is called the moment arm
the product of the moment arm and the applied force is the moment
what is isotropic vs anisotropic?
isotropic = same response to mechanical loading no matter the orientation of the material anisotropic = the response to mechanical loading varies with orientation
what is the difference between a linear and non linear material?
a material is linear when the change in the deformation state is constant and proportional to the change in load. if the change in the deformation state is not constant and proportional to the change in load, it is non linear
what makes a material elastic?
if there is a one to one relationship between the state of deformation and the applied force and if the relationship between the state of deformation and applied load is independent of the rate at which the load is applied (that would be viscoelastic)
what elements should you consider when performing a mechanical analysis on a material or structure?
- the loading conditions
- the deformations involved
- the constitutive properties of the material or structure
what is ductility
the ability to plastically deform prior to failure and is equivalent to the magnitude of strain that can be achieved between the proportional limit and the point of failure
what is toughness
the area under the entire stress strain curve and is a measure of the energy absorbed by the material prior to failure
what is strain rate sensitivity
the stress strain behavior of a viscoelastic material depends on the rate at which the load is applied
what is creep recovery
material will exhibit some immediate strain response that will be folloed by a creep response. The material will instantaneously stretch to some length with application of the load and then slowly creep toward an equilibrium stretch level. When the load is removed, the material instantaneously recoils to some residual stretched state
what is stress relaxation?
when a sample is stretched in a stepwise manner and held in a constant deformed state, there is an initial spike in the induced stress that decreases with time as the material relaxes
ex. broaching a press fit THR stem –> you can drive the stem a little further after waiting for the bone the relax
what is hysteresis?
the tendency for some materials to exhibit different mechanical behaviors based on weather a load is being applied or removed
what are five behaviors/tendencies of biologic (viscoelastic) materials to consider when testing them?
- sensitive to conditioning
- strain rate sensistivity
- creep recovery behavior
- stress relaxation
- hysteresis
what is lamella?
a thin layer or plate like structure
3-7 um thick
arranged in sheets
what is woven bone?
lattice like structure that contains pores within a sea of mineralized collagen type I
can be rapidly formed
what is primary bone?
bone that has formed in a location in which bone has not previously existed
directly deposited on a substrate without the resorption of preexisting bone
what are features of the cement line?
- it is the point at which osteoclastic bone resorption ceased and bone formation began
- collagen deficient
- dampens forces within the cortical bone and therefore improves the fatigue properties of cortical bone
what are the four functional bone envelopes?
periosteal
endocortical
cancellous
intracortical
properties of periosteum
- periosteal envelope is composed of the outer surface of the diaphysis of long bones where bone interacts with the periosteum
- the periosteum is a bilayered fibrous and cellular membrane that contributes to bone formation, innervation, and vascular supply
- has a highly cellular inner layer (cambium) and an outer fibrous portion
- cambium has many osteogenic percursors
- the periosteal envelope is capable of the methodical formation of highly organized lamellar bone or rapid formation of disorganized woven bone
properties of the endocortical envelope
- the surface of bone that surrounds the marrow cavity
- endocortical surface is lined with a layer of osteoprogenitor cells called “lining cells”
- lining cells are associated with capillaries adjacent to the endosteal surface of bone and the sinusoids of bone marrow and they are important for the regulation of calcium exchange between bone and extracellular fluid space
properties of the cancellous envelope
on the surface of the struts of trabecular bone
lining cells are in contact with the marrow and participate in nutrient and ion exchange
properties of the intracortical envelope
- interaction of cells on the surface of the Haversion canal and is covered with a layer of resting osteoprogenitor cells
- in direct contact with the neurovascular bundle within the haversion canal and regulate - nutrient exchange between the vascular system and the extracellular space within cortical bone
perichondrium
fibrous membrane that surrounds the hyaline cartilage template in endochondral ossification
it is the reservoir for progenitor cells for enlargment of the hyaline cartilage template
anlage
the cartilage model made during endochondral ossification
what is formation bone modeling
bone modeling by osteoblasts
bone REmodeling uses coordination of osteoblasts and osteoclasts
mostly occurs at the epiphyseal region and along the endosteal surface
what is resorptive bone modeling
bone modeling by osteoclasts
bone REmodeling is coordination of osteoblasts and clasts
mostly occurs along periosteal surface as well as the region previously occupied by epiphyseal cortex
what is the poisson effect
The Poisson effect is defined as a material’s tendency to expand in a direction perpendicular to the compression direction.
what is special about collagen X?
unique to hypertrophic chondrocytes and is a common histologic marker of chondrocyte hypertrophy and endochondral ossification
how can you generate a more compliant plate construct?
- select an implant with a lower moment of inertia
- select an implant with a lower modulus of elasticity
- increase the overall length and functional working length of the selected bone plate - small increases in functional working length dramatically increase compliance because the compliance is related to working length to the third power
how can bridging plates fail?
- plate bending (plastic deformation) - like picking a too compliant plate
- fatigue of the plate leading to fracture - usually from too short a working length
- pull out of the outermost screw - usually when a short plate with a short working plate is used
In a juvenile dog, pull out is most likely because juvenile dogs have thin cortices
