Biomechanics Unit 2 Flashcards
what is the most abundant tissue in the body and what is its function
connective tissue
specialised to protect and support the body and its organs, connect and hold them together and to transport substances throughout the body
what are the 4 types of connective tissue
bone tissue
articular cartilage
tendon
ligament
what is the function of bones and what are the 4 groups
protect delicate structures such as the heart and lungs, and act as lever arms for movement
long bones, short bones, flat bones and irregular bones
what is bone tissue composed of
osteocytes [bone forming cells]
non-cellular component
- very strong collagen fibres embedded in jelly-like matrix called ground substance
- fibres are flexible but resist stretching
- 25-30% dry weight of bone
inorganic component
- calcium phosphate crystals within the matrix
- give the bone its characteristic hardness and rigidity
- 65-70% dry weigh of bone
what are the 2 types of bone
cortical [a.k.a compact]
- forms the outer layer of bones
- has a dense structure
cancellous
- inner part of short, flat and irregular bones
- lines the inner surfaces and makes up the greater part of the metaphyses and epiphyses in long bones
what is the other name for cancellous bone and why is it called this
spongy bone
due to its mesh like structure, the spaces of which contain red bone marrow
how do the cells in cancellous bone align themselves
align themselves in the direction that will best support the load
what is the basic structural unit of compact bone and how is this arranged
haversian system
- arranged longitudinally in columns
- in those units, the bone tissue is arranged in layers called LAMELLAE forming cylinders around a canal
- i.e. HAVERSIAN CANAL
what is maintained within the haversian canal
blood vessels and nerve fibres
what is located betweens lamellae, and what do they contain, how are they linked?
small cavities called LACUNAE
these contain OSTEOCYTES
osteocytes is linked to canal and other lacunae’s by channels called CANALICULI
[carries nutrients to blood vessel]
what inter-connects the layers of lamellae within the haversian system
collagen fibres
what is the weakest part of the haversian system
the cement-like ground substance that surrounds the haversian system
[as it contains no collagen fibres]
what is the basic structural unit of cancellous bone
TRABECULA
- are arranged in a latticework of branching sheets and coloumns
trabeculae are similar in structure to haversian system = consisting of layers of lamellae with lacunae containing osteocytes connected by canaliculi
what is the main difference
NO haversian canals
not needed as blood vessels pass though the marrow filled spaces - supplying nutrients to the osteocytes through the canaliculi.
what is the load acting to do in tension and compression
in tension - acting to stretch the material like in a rope.
in compression - load is acting to compress the material like in the supporting column of a building
what is definition, equation and unit for stress
Stress is defined as the force per cross-sectional area
Stress = Force/Area
unit = newtons per metre squared (N m-2)
[force increases, stress increases]
what is definition, equation and unit for strain
Strain is defined as the change in length divided by the original length
[measure of amount of deformation a material has undergone]
Strain = change in length/original length
No units as it is a ratio
what can be used to show the relationship between stress and strain
stress-strain curve
what are the 2 regions of the stress-strain curve and what divides these two regions
elastic region
plastic region
the yield point
[yield strain = strain at the yield point
yield stress = stress at the yield point]
what happens in the elastic region
curve is linear
stress is directly proportional to the strain
[stress doubles, strain doubles]
if the load is removed BEFORE the material hits the yield point, then it will return to its original size and shape once the load is removed
i.e. ELASTIC BEHAVIOUR
what happens in the plastic region
curve is not linear
bone yields to the applied load - for a small increase in stress the bone deforms by a large amount
once the material is deformed PAST the yield point, even after the load is removed, it WILL NOT return to its original shape and size
i.e. PLASTIC BEHAVIOUR
at the point of the graph where is shows that the bone has fracture, what is the name given to the strength and strain at this point
Ultimate strength [or stress]
Ultimate strain
what is young’s modulus, the equation and the units
the ratio of stress to strain, describes how flexible or stiff a material is
Young’s modulus = stress/strain
unit = newtons per metre squared (N m-2) [same as stress, as strain has no units]
what would a small young’s modulus mean and a large one
small = material is flexible, requires small amount of stress to produce a large strain
large = material is stiff, arge amount of stress to produce a small strain
what are the types of loading
tension compression bending shear torsion
what is shear loading
two forces acting in opposite directions tend to cause layers within the material to slip or shear.
what is the ultimate strength of bone in compression, tension and shear
Compression - 200 MN m-2
Tension - 130 MN m-2
Shear - 70 MN m-2
i.e. bone is strongest in compression and weakest in shear
what is an example of a bone fracture due to shear force
intra-articular shearing fracture of the femoral condyles
[fractures caused by shear alone are rare]
what is bending loading and what are types of it
loads are applied to a structure that tend to cause the structure to bend.
2 types
- cantilever
- 3 point bending
what is cantilever bending
one end of the object is fixed and a load is applied to the other end causing the object to bend
i.e. a diving board
what is 3 point bending
three forces are applied to the object
i.e. a seesaw
what happens when a structure is bent
one side is elongated
one side is in compression
between the 2 sides, there is a neutral axis along which no bending occurs
what happens when the femur is loaded vertically
the medial side being compressed and the lateral side elongated
neutral axis runs approximately along the centre of the femur
when a bone is bending what side is more likely to fracture and why
the side being elongated
as bone is stronger in compression than tension
what is a common example of a fracture due to a bending force
“boot top” fracture seen in skiers
due to 3 point bending
As the skier falls forward over the top of the ski boot a force is exerted on the proximal end of the tibia
As the distal end of the tibia is fixed in the boot, the tibia is bent over the top of the rigid ski boot
Tibia #