BIOMED 10/11b Soft Tissue and Bone Mechanics Flashcards
external loads that the body
- Gravity
- Wind
- Friction
- ***Impact
how does tissue deformation result in loads arising within tissue
- deformation to match external force
- meniscus in th eknee
- accommodates external load with internal forces
healthy tissue response to load
- deforms as much as it needs to
- goes back to original shape/position after unloading
- load response is tissue dependent
what do we need to focus on when doing an examination for a patient?
- what was the mechanism of injury?
- what tissue structures might be involved?
- what are the appropriate treatments for the patient
how do we define the mechanism of injury?
- was the injury a trauma or insidious onset?
- what does the MOI tell you about the potential movements and forces that occurred to cause the injury?
- what tissues were susceptible to damage through this MOI?
how do we determine the tissue’s response to load?
- tissue stress
- tissue strain
- stress strain diagram
what is tissue stress?
- pressure = force/area
- forces resisting the additional pressure added to a tissue
- measure of load or energy that stored within a tissue
- ex: rubber part of a balloon is stress as air is added into it
what is tissue strain?
- how much does it stretch out?
- the delta of the stretch
stress strain diagram
- y axis = stress
- x axis = strain
- helps estimate the behavior of the tissue
- the linear slope is the stiffness of the tissue
- young’s modulus determines how the tissue deforms in response to certain amounts of loads proportional to stiffness
nonlinear base region in the stress/strain diagram
-slack that is inherent to the tissue at rest
linear portion in the stress/strain diagram
stiffness of the tissue
-young’s modulus
at a high stiffness behavior, what is the young’s modulus?
high
at a low stiffness behavior, what is the young’s modulus?
low
Truly elastic material
returns back to its original state after load is released
Plastic Deformation
After yield point, tissue starts to change permanently
- serial casting
- muscle building
- stretching
- joint mobs
do tissues have a fluid like component to their behavior?
Yes, tissues have viscosity
-they have time dependent visco-elastic behaviors
at fast loading behaviors, what happens to the tissue?
it breaks fast
at slow loading behaviors, what happens to the tissue?
it stretches out
what determines how tissues respond to stress?
the organization of the tissue
creep in regards to serial casting
- over time, when something is subject to continuous load, it changes
- serial cast puts someone in a cast when they have a contracture
- tissue adapts to the stress from the cast
- it is essentially a prolonged low-load stretch
how does tissue deformation occur?
under continuous load
how do you evaluate if a tissue is elastic?
- stiffness
- young’s modulus
ankle sprain motions
plantar flexion and inversion
very high loading rate
in vivo
in human body
in silico
sillicon/computer based modelling
in vitro
outside of the body/pitri dish
as moment increases, what happens to the ACL strain during pivot landing
strain inceases as the moment increases
Important factors that impact MSK loads
Loading variables that determine how the tissues respond
- Loading Magnitude
- Loading Rate
- Loading typ
Define the significance of the loading magnitude
- High vs low load
- Cumulative load: keep increasing the yield capacity; can reach yield much faster because you are cumulatively loading and getting stronger
what eventually happens when you have cumulative loading over time?
you may reach the yield point much faster
what is the significance of loading rates with MSK loads?
- biological tissues are sensitive to load
- when loading occurs at a rate that the object is not built to respond to, the object will break
- slower rate = stretching/pulling/plastic deformation
- faster rate = injury/tear/ligamentous “explosion”
different loading types
- unloaded
- tension
- compression
- bending
- shear
- torsion
tension loading
two forces pull on an object in different directions
-lateral ankle sprain => severely tensioned as the foot rotates inward
compression loading
forces that push or pull the surfaces of objects together or brings the end of an object closer
-humerous is pulled against the glenoid by the deltoid muscle creating a compressive load between the bones
Bending Loads
deformation tissue that occurs at right angles to its longitudinal axis
- top is bending, bottom is stretching (concave side undergoes compression, convex side undergoes tension)
- Coxa vera results in an increased bending load on the neck of the femur (predisposed to fractures)
Shear loading
unaligned parallel forces that move on a part of the body in one direction and another part in the opposite direction
-delaminated articular cartilage away from acetabular roof (square peg in a round hole)
Torsion Loading
twisting force applied to tissue around its longitudinal axis
-ACL tear is a torsion load
describe process of delamination
think you were pulling up a carpet and pushing under it with your foot from the floor
-this pathology results in abnormal shearing at the joint and peels the articular cartilage off of the acetabulum
factors that influence a tissue’s ability to accept loads
- Age
- Disease or trauma
- Overuse or Underuse
Impact of overuse on the tissue
tissue gets damaged, then it starts to change/repair overtime, but is not able to ever reach equilibrium, then the pt starts loading again, and loading exceeds the tissue’s ability to repair itself
impact of underuse on the tissue
tissue atrophy
-Wolff’s law is unable to function => bone doesn’t get stronger because there is no stress to respond to
soft tissue genetic disorder that influence collagen
you can have hyperelastic tissue and if you don’t have the rebound of tissue, you can be prone to injuries and it will affect tissues that affect breathing
