Lecture 3 - Tissue Mechanics: Bone & Cartilage Flashcards
What two principle structure components are found in bone?
collagen and hydroxyapatite
What is collagen?
organic material found in all the body’s connective tissues
What is the % of bone organic content does collagen make up?
90%
What is the % of bone dry weight does collagen make up?
40%
What type of collagen is found in bones?
type I collagen
What are hydroxyapatites?
calcium phosphate-based mineral found primarily between the collagen fibers
What is the % of bone dry weight does hydroxyapatite make up?
60%
How can hydroxyapatites be found?
in crystal form as a mineral
What is bone growth?
from immature to mature bone
What is woven bone?
immature bone with cartilage fibers randomly distributed to give some strength in all directions
What do osteoclasts do?
dig tunnels into the bones as it matures
What do osteoblasts do?
dig tunnels with type I collagen
What do osteocytes do?
mineralize collagen with hydroxyapatites
What are osteons?
the hollow canals which represent the structural units of bone
What is the biomechanics of bones determined by?
gravity, PA, hormones, age
Functions of bones
- protect internal organs
- support body weight
- provide rigid kinetic links and muscle attachment sites
- facilitates muscle action
- storage for minerals
- manufactures blood cells
What are the 2 kinds of bones?
cortical and cancellous
What kind of bone is cortical bone?
dense bone (compact)
Where are cortical bones found?
in the mid shaft of the femur
What % of skeletal mass does cortical bone comprise?
80%
What % of bone surface does cortical bone comprise?
33%
What kind of bone is cancellous bone?
spongy or trabecular
What % of skeletal mass does cancellous bone comprise?
20%
What % of bone surface does cancellous bone comprise?
67%
Where are cancellous bones found?
in the interior of the femoral head
What is Wolff’s Law?
form = function
What does an applied bending moment in bones create?
compression and tension
What are the loading modes of bones?
tension, compression, torsion, shear, bending
What are cortical bones’ response to strain?
2%
What are cancellous bones’ response to strain?
7%
How are bones classified?
anisotropic
What does anisotropic mean?
different mechanical properties in different directions
Which bone is stronger and stiffer for more strenuous activities?
cortical bones
What happens at very high strain rates?
ultimate strain decreases and cortical bone exhibits a ductile (due to viscous properties)
What do changes in mechanical properties of bone depend on?
age and activity
Are are the 5 steps of fracture healing?
- inflammatory response
- repairs cells gather at fracture site
- in 2 weeks, a callus begins to form
- callus calcifies and becomes woven bone
- woven bone undergoes remodelin
When does callus strength increase?
as bone mineral density increase
What are the 3 kinds of cartilage?
articular cartilage, fibrocartilage, elastic cartilage
Where is articular cartilage found?
in synovial joints to permit motion between bony segments
Examples of articular cartilage
hip, knee, elbow
What is fibrocartilage?
inflexible and tough, considerable tensile and compressive strength
Examples of fibrocartilage
annulus fibrosis of the intervertebral disc, meniscus
What is the function of elastic cartilage?
helps to maintain the shape of structures
Examples of elastic cartilage
ear, trachea
Does cartilage have a blood supply?
no
How are joints enclosed?
in a fibrous tissue capsule
What is the fibrous tissue capsule lined with?
the synovial membrane that secretes synovial fluid
What does articular cartilage in synovial joints provide?
a bearing surface to reduce friction and wear by helping to distribute loads between opposing bones
What is cartilage mostly made of?
water (70-85%)
What is the remainder of cartilage mostly made of?
proteoglycans, collagen, lipids
What makes the electrical charge of the proteoglycan spread out?
the electrical charge
What is the spread of proteoglycans limited by?
the collagen framework, contributing to the compressive stiffness
What happens when the collagen framework is damaged?
the compressive stiffness decreases
What is the mechanical response of cartilage linked to?
the flow of fluid through the tissue
What is viscoelasticity?
time dependant behaviour due to a fluid-like component
What is anisotropic?
different properties in different directions
As the water content in cartilage increases…
cartilage becomes less stiff and more permeable
How does mechanical failure of cartilage happen?
by shear stress more than tensile
