MEC322: Skeletal System Flashcards
What are the spatial subdivisions of the skeleton?
Axial skeleton
Appendicular skeleton
What components make up the skeletal system?
Bones (skeleton)
Joints
Cartilages
Ligaments
What are the functions of bones?
- Support the body
- Protect soft organs
Skull and vertebrae protect brain and spinal cord
Rib cage protects thoracic cavity organs - Attached skeletal muscles allow movement
- Store minerals and fats
Calcium and phosphorus
Fat in the internal marrow cavity - Blood cell formation (hematopoiesis)
How many bones does an adult skeleton have?
206
Name the two basic types of bone tissue
compact bone
spongy bone
Describe compact bone
dense, smooth and homogeneous
Describe cancellous (spongy) bone
small needle-like pieces of bone
many open spaces
Name the four different types of bone shape and give an example of each
long bone
flat bone
short bone
irregular bone
Describe long bone
Typically longer than they are wide shaft with heads situated at both ends contain mostly compact bone all bone in limbs are long bones (except wrist, ankle and kneecap) examples: humerus femur
Describe short bones
Generally cube-shaped
Contain mostly spongy bone
Include bones or wrist and ankle
Sesamoid bone are a type of short bone that form w/in tendons (patella)
examples: carpals
tarsals
Describe flat bones
Thin, flattened and usually curved
Two thin layers of compact bone surround a layer of spongy bone
Examples
- skull
- ribs
- sternum
Describe irregular bones
Irregular shape
do not fit into other bone classification categories
Examples
- vertebrae
- hip bones
In a bones structure what is the diaphysis?
- shaft
- makes up most of bones length
- composed of compact bone
What is the periosteum?
Outside covering of the diaphysis
Fibrous connective tissue membrane
Perforating (Sharpey’s) fibers secure periosteum to underlying bone
What is the epiphysis?
Ends of the bone
Composed mostly of spongy bone enclosed by thin layer of compact bone
What is the articular cartilage?
Covers external surface of the epiphyses
Made of hyaline cartilage
Decreases friction at joint surfaces
What is the epiphyseal plate?
Flat plate of hyaline cartilage seen in young, growing bone
Causes lengthwise growth of a long bone
fuses when growth stops
What is the epiphyseal line?
Remnant of the epiphyseal plate
Seen in adult bones
What is the marrow (medullary) cavity?
Cavity inside the shaft
Contains yellow marrow (mostly fat) in adults
Contains red marrow for blood cell formation in infants
In adults where is red marrow situated?
cavities of spongy bone and epiphyses of some long bones
What is the osteon (Haversian system)
?
Compact bone micro-anatomy
A unit of bone containing central canal and matrix rings
What is the cantral (haversian) canal?
Compact bone micro-anatomy
Opening in the center of an osteon
Runs lengthwise through bone
Carries blood vessels and nerves
Where are osteocytes situated?
Compact bone micro-anatomy
cavities called lacunae
How are lacunae arranged?
in concentric rings called lamellae
What are lamellae?
rings situated around the central (Haversian) canal
What is an osteocyte?
bone cell, maintains bone tissue
What is an osteoblast?
a cell which secretes the substance of bone
act in group
What is an osteoclast?
a large multinucleate bone cell which absorbs bone tissue during growth and healing.
What is the extracellular matrix of bone composed of?
Water
Collagen fibers and other organic molecules which provides bone its tensile strength
Crystallized mineral salts which gives bone its hardness
What is ossification?
Process of bone formation
Occurs on hyaline cartilage models or fibrous membranes
What is endochondral ossification?
Osteoblasts (bone-forming cells) cover hyaline cartilage model
Enclosed cartilage is digested away, opening up a medullary cavity
What are the two regions of long bone that are not converted from cartilage by birth? (they remain cartilage)
Articular cartilages
Epiphyseal plates
New cartilage is formed continuously on external face of these two cartilages
Old cartilage is broken down and replaced by bony matrix
What to factors dictate bone remodelling?
Blood calcium levels
Pull of gravity and muscles on the skeleton
When is parathyroid hormone release and what does it do?
Released when blood calcium levels are low Activates osteoclasts (bone-destroying cells) Osteoclasts break down bone and release calcium ions into the blood
What does hypercalcemia prompt? and what is it?
- calcium storage in bones
- high blood calcium levels
What is osteoporosis?
bone thinning disease
Disease makes bones fragile, and bones can easily fracture
Vertebral collapse results in kyphosis (also known as “dowager’s hump”)
Who is affected by osteoporosis?
50 percent of women over age 65
20 percent of men over age 70
How does estrogen aid in womens health?
Estrogen aids in health and normal density of a female skeleton
In mechanical terms what is the function of bone?
Provide mechanical support for each body segment
Act as a lever system to transfer muscle forces
What properties must bone have?
stiff, strong, tough and light
What do tension and compression lines do?
Help spread out load in bone
What two phases is bone made up of?
mineral (strong and brittle) & collagen (weak and ductile)
What does bone mechanics depend on?
types of loading
bone density
What types of loading can bone be put under?
tension - doesn’t work v well as naturally not subjected to tension a lot
compression
bending
torsion
If a bone deforms elastically what does that mean?
no permanent deformation
If a bone deforms plastically what does that mean?
permanent deformation
What is the yield point?
strain where plastic range begins
What is the ultimate strain/stress?
fracture occurs
Compare bone to a tendon under a load
bone has a higher Young’s modulus and UTS but a tendon is a lot more ductile and can undergo more strain
What strain are the tendons and bone put under when running?
Achilles tendon ~ 6% (Yield=8%)
Tibia ~ 0.07% (yield=0.7%)
tendons operate v close to their yield strength
Will bone break under tension, shear or compression first?
shear
tension
compression (Highest load)
Torsion results in a….
spiral fracture
Bending results in a….
butterfly fracture
Compression results in a…
oblique fracture
Tension results in a….
transverse fracture
Does higher density make bone stiffer?
Yes
compact bone is the stiffest 1.8 g/cm^3
cancellous 0.3-0.9 g/cm^3
How is strength of bone related to density?
strength ∝ 𝜌^2
Describe fracture by single load/high stress
Tensile fractures usually induced by rigorous muscle contractions
Compression fractures induced by impacts
Most fractures involve bending, torsional, or combined loads
Describe fracture by multiple loads/low stress
fatigue fractures (stress fractures) no. of repetitions is important bone repairs during recovery after exercise
How is bone remodelling dependent on mechanical loading? (mechanosensitive)
Wolff’s Law 1892
Bone laid down where needed
Resorbed where not needed
Bone response to loading is site specific, not general
Bone responds to high loads and impact loading
Trabecular bone lost most rapidly during unloading (bed rest, spaceflight etc.)
describe fatigue injuries of tissue
Number of repetitions: Muscle fatigue increases stress on bones
Time between repetitions: Bone cannot repair rapidly enough
What is the peak bone stress on anteromedial sufrace of tibia felt when running and walking?
Walk (1.4 m/s)
compression 2MPa
tension 3-4MPa
Running (2.2 m/s)
compression 3 MPa
tension 11-12MPa
How is cancellous bone different to compact bone?
it is more porous
What is the tensile strength of compact bone at 20 and 80yrs ?
20: 140MPa
80: 120MPa
How does the bone age?
Higher porosity leads to higher loss in cancellous bone
Some changes in gross geometry
How can exercise help bone ageing?
increase in bone density
higher bone mineral density
What is a joint also know as?
articulation
Describe a joint
a point of contact between bones, between cartilage and bones, or between teeth and bone
What does a joints structure determine?
combination of strength and flexibility
What two criteria is the structural classification of joints based on?
1) presence or absence of a space between the articulating bones, called a synovial cavity
2) type of connective tissue that holds the bones together.
What are the three classifications of joints structurally?
- fibrous joint
- cartilaginous joint
- synovial joint
Describe a fibrous joint
no synovial cavity and bones are held together by dense irregular connective tissue.
Synarthrosis
Describe a cartilaginous joint
no synovial cavity and the bones are held together by cartilage.
Amphiarthrosis
articulating bones tightly connected by either hyaline cartilage or fibrocartilage
Describe a synovial joint
united by the dense irregular connective tissue of an articular capsule, and often by ligaments.
synovial cavity between articulating bones
Diarthrosis
What does the functional classification of joint relate to?
degree of movement they permit
Name the functional classification of joints?
Synarthrosis – An immovable joint.
Amphiarthrosis – A slightly movable joint.
Diarthrosis – A freely movable joint.
What does the synovial membrane do?
secretes synovial fluid, which forms a thin, viscous film over the surfaces within the articular capsule. (envelope surrounding synovial joint)
What do many synovial joints also contain?
accessory ligaments, articular discs, fibrous & synovial membranes.
Name the types of synovial joint based on shape
Plane joint Hinge joint Pivot joint Condylar joint Saddle joint Ball-and-socket joint
Movement of a plane joint
non-axial
bones in hand (palm)
Movement of a hinge joint
uniaxial
elbow humerus and ulna
Movement of a pivot joint
uniaxial
elbow ulna and radius
Movement of a condylar joint
biaxial
finger metacarpal and phalanx
Movement of a saddle joint
biaxial
finger carpal and metacarpal
Movement of ball-and-socket
multiaxial
shoulder head of humerus
What is tendonitis?
inflammation of tendon sheaths
What is arthritis?
inflammation or degenerative disease of joints
over 100 types, most crippling widespread disease in US
initial symptoms: pain, stiffness, swelling of the joint
Movement in the sagittal plane
flexion extension
Movement in the coronal plane
lateral flexion
Movement in the transverse plane
rotation of neck
internal external - shoulder and hip
What is the function of the synovial joint?
Lubrication (no tangential forces)
Distribution of normal forces over a large area
How is the function of the synovial joint achieved by synovial fluid and articular cartilage?
Both are biphasic (mixture of solid and fluid phases)
Synovial fluid: Fluid mixed with elastic solute aggregates
Cartilage: Elastic solid network inundated by fluid
What biphasic mixture (colloid) is blood?
sol
solid in liquid
clotting blood is a gel
liquid in solid
Define biocompatability
material the induces no measurable harm to the host
chemical and physical; interactions and design
Give an example of a class I medical device
lowest risk
bandages, surgical scalpel
Give an example of a class IIa medical device
Low risk
contact lenses, epidural catheter, pregnancy test
Give an example of a class IIb medical device
Moderate risk
orthopaedic implants, dental implants, diagnostic ultrasound system
Give an example of a class III medical device
High
HIV test kit, pacemaker, angioplasty catheter
List the essential considerations made in design of metallic biomaterials
Excellent biocompatibility (non-toxic) High corrosion resistance Suitable mechanical properties High wear resistance Osseo-integration (in the case of bone prosthetics)
What guidance is given for biocompatibility?
Match elements that are present in body
Trace elements can be toxic at higher levels
No metals are completely inert or non-toxic
Use alloys with virtually inert element
Use highly corrosion resistant element (e.g. Ti)
What guidance is given for corrosion resistance?
The body environment is very different from ambient conditions
Different part of the body have different pH and oxygen concentration
Normal pH: 7.2-7.4 but 3-4 at inflammation sites
Lower oxygen accelerates corrosion of metal
What guidance is given for mechanical properties?
Materials must be able to match original tissue
Metals are able to bear significant loads and undergo plastic deformation prior to failure
Higher elastic modulus: implant will bear all load
Stress shielding effect
More exposure to cyclic loading
Normal walk: 1000s steps at 1Hz
At hip, loading stress ~50MPa
For a person that walks 2000 steps/day: 1x107 cycles !
What guidance is given for wear?
Wear is inevitable in joints ⇒ Material choice dictated by joint type
Which is the best pair of materials for ball and socket joints?
ceramic on ceramic
What guidance is given for Osseo-integration?
For bone prosthetics:
Ability of an implant surface to bond to adjacent bone
Failed osseo-integration creates fibrous tissue, which leads to loosening
Modulated by surface properties (chemistry, roughness and topography)
Why might iron be/not be biocompatible?
found in blood, necessary for proper function
too much can create free radicals
Why might chromium be/not be biocompatible?
Regulator of sugar levels in body
High levels lead to DNA damage and liver toxicity
Why might nickel be/not be biocompatible?
Involved in many functions (unknown until 1970s)
High levels is toxic to cells in-vitro and in animal studies
List these alloys of steel in decreasing toxicity: nickel, cobalt, iron, vanadium titanium, chromium
cobalt, vanadium, nickel, chromium, titanium, iron (least toxic)
Name the mechanical properties of 316L steel (good biocompatibility)
depends on alloy & processing
stronger than bone
but commonly fails as implant
fatigue strength in salone solution ~200-300MPa
How do stainless steel implants fail?
fatigue
due to poor machining
What need to be developed before iron-less stainless steel can be used?
toughening method
Why are steel implant popular?
Readily available Lower cost Excellent fabrication properties Accepted biocompatibility Toughness
How is cobalt based alloys better than stainless steel?
better corrosion resistance
less toxic
Why might cobalt be/not be biocompatible?
constituent of B12
At high level: heart damage
Why might molybdenum be/not be biocompatible?
essential for many enzymes
no acute toxicity
Why might tungsten be/not be biocompatible?
no role in human body found yet
no clear toxicity levels
What do metal on metal implants lead to?
elevated serum metal ion levels
How do the mechanical properties of the cobalt alloy compare to stainless steel?
Better mechanical properties due to packed crystal structure
Cobalt-Chromium yield strength > 500 MPa
Fatigue properties
Higher than stainless steel
Under physiological conditions, with 107 cycles, corrosion fatigue strength is below 200 MPa
No better than stainless steel after 20 years …..
What is a cobalt based alloy most popular for?
implant for joint bearing system
How are titanium implants superior
specific strength (strength/density)
Biocompatibility
Enhanced corrosion resistance
excellent bone bonding capabilities
How are titanium implants inferior
Inferior in tribological properties
poor shear strength
wear resistance
Why might titanium be/not be biocompatible?
not found in humans
non toxic even in large dose
Why might vanadium be/not be biocompatible?
role not well defined in humans
could be toxic in large dose
Why might aluminium be/not be biocompatible?
function not well known in humans causes neurological disease at large dose
Why might niobium be/not be biocompatible?
function not well known in humans very toxic at large does, DNA damage
Compare titanium to cobalt and steel
UTS comparable to stainless steel but lower than cobalt
same with yield strength
higher fatigue strength than ss but lower than cobalt
