Biomechanics unit 1 SAQs Flashcards
explain the difference between creep and stress relaxation?
creep is the phenomenon of a material changing length over a period of time, elongating when a constant load is applied to them
what is the basic structural unit in compact bone?
haversian system
the bone tissue is arranged in layers called?
lammellae
and forms concentric cylinders around a central canal called a ?
haversian canal
haversian canal contains?
nerve fibres and blood vessels
between lamellae, there are small cavities called?
lacunae
lacunae contain?
osteocytes
each osteocyte is linked to other osteocytes and the central canal by minute channels called?
cannaliculi
what do canalliculi do?
carry nutrients from the blood vessels
what is the weakest part of the bones microstructure?
between haversian systems. each haversian system is surrounded by a ground like cement substance, but there are no coollagen fibres, probably accounts for less strength.
basic structural unit in cancellous bone?
trabeculae (a latticework of branching sheets and columns)
trabeculae do not contain haversian canals. Although they are similar in structure. Blood vessels travel through marrow filled spaces between the latticework of trabeculae.
Y
why does cancellous bone not contain haversian systems
blood vessels pass through marrow filled spaces between the latticework of trabeculae and supply nutrients to the osteocytes via the canaliculi.
units for stress?
Nm-2
Is cortical bone stronger in shear or tension?
tension
when is cortical bone strongest?
compression
why are fractures more likely in athletes when they are fatigued?
muscles can’t contract to neutralise the tension and compress bones, and so more likely to fracture
2 types of bending?
cantilever and three point
What is the neutral axis?
point along the beam where no deformation occurs
Along which surface will a fracture most likely occur when an excessive bending load is applied to a long bone?
the elongated side
in vertical loading of the femur, which side would more likely fracture?
the lateral (elongated side)
where is the neutral axis in symmetrical structures?
along the geometric centre
torsional fractures have a characteristic _______appearance?
spiral
in torsion, where is the greatest stress and strain on a bar?
outer surface of a bar
if a torsional load is increased, where will a fracture occur
on the outer surface of the bar
the hollow structure of bones increases its strength to weight ratio
If the same quantity of bone tissue was used to construct a completely solid bone rather than a hollow one the bone would be smaller in diameter and would be less able to resist torsional loads
When considering torsional loads, do hollow or solid bars have the best strength-to-weight ratio?
hollow
why is the distal end of the tibia more likely to fracture than the proximal?
the cross sectional area is reduced. There is the same amount of bone tissue, but the distal end is less able to resist torsional loads
Name five types of loadings.
tension, compression, bending, shearing, torsion
what is combined loading?
more than one type of loading
What is the difference between bone hypertrophy and bone atrophy?
bone atrophy is bone resorption, due to lack of use. hypertrophy is bone being laid down in response to physical activity. at sites carrying greater load than usual.
how is a fatigue fracture sustained?
A fracture resulting from the repeated application of a load that is smaller than the ultimate strength of the bone is called a fatigue fracture
Why are children prone to greenstick fractures but not adults
children have more collagen in their bones, making them more ductile
cartilage is a connective tissue consisting of?
cartilage cells, fibres, ground substance (CFG)
In what type of joints is articular cartilage found?
synovial
What are the two main roles of articular cartilage?
to cushion joints while at same time provides a smooth, lubricated bearing surface. also has shock absorbing properties. allows large loads to be distributed evenly over a large surface area
which cartilage forms the tip of the nose?
hyaline
epiglottis and external ear?
elastic cartilage
which forms the pubic symphysis and intervertebral disks?
fibrocartilage
articular cartilage is a form of ________?
hyaline cartilage
hy el fi
hyaline, elastic, fibrocartilage
roles of articular cartilage
provides a cushioning surface and also a lubricated, smooth bearing surface. also has shock absorbing properties that allows large loads to be spread evenly over a large surface area
what is articular cartilage made of?
an organic matrix of non cellular material, interspersed with cells and fluid.
what is the non cellular material mainly made of?
collagen
how is collagen arranged in articular cartilage?
fibrils
fibrils are enmeshed in a concentrated solution of ?
proteoglycans
fibrils make up 50-80% of the dry weight and 10-20 % of the wet weight
y
large protein based molecules important to the mechanical properties of articular cartilage. they make up 3-10 percent of the wet weight
what are proteoglycans?
where are proteogl… most concentrated?
in the middle layer of the articular cartilage, less in the deeper layers associated with the bone
what are the cells called in ac?
chondrocytes
where are the cells more densely packed?
deeper layers more close to the bone
what is the interstitial fluid that occupies the spaces in the matrix mainly made of?
water. 65-85% of weight weight in AC
3 zones the AC can be split into?
superficial tangenital zone
middle zone
deep zone
what is the tide mark?
line between the deep zone and the calcified cartilage layer
in superficial zone, how are fibrils arranged?
tightly woven into sheets, parallel to articular surface
chondrocytes in super?
oblong with longitudinal axis parallel to articular surface
in middle zone, fibrils?
arranged more randomly but still basically parallel to AS.
why are they less densely packed together?
to accommodate the high concentration of proteoglycans.
chondrocytes in middle layer?
circular and randomly distributed
deep zone?
the collagen fibrils are arranged in larger fibre bundles that are anchored in the underlying bone tissue. Ie they attach articular cartilage to bone
below the deep zone there is a thin layer called the calcified cartilage layer which gradually merges with the underling subchondral bone
interface between the articular cartilage and the cc is called the tidemark
how are chondrocytes arrange in the deep layer?
arranged in loose columns aligned perpendicular to the line dividing the articular cartilage and the underlying bone
