10-11b Orthopedic Biomechanics Part I Flashcards
What are initial questions when encountering an acute injury?
What was the mechanism of injury?
What tissue structures might be involved (based on mechanism/patient info)?
What are the appropriate treatments for this patient?
Describe determining the mechanism of injury
Was the injury a trauma or insidious (“straw breaks the camel’s back”)/Mechanical issue in movement leads to altered loading of tissue
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?
What are possible structures involved in a knee injury?
patellar dislocation, ligament strain/sprain/tear
What are possible structures involved in an ankle injury?
ligaments
fracture of distal fibula
fifth metatarsal evulsion fracture (perineal m. tries to evert m. and stabilize but instead pull the bone off)
What is a force acting on the body called?
a load
What happens when a tissue is loaded too much cumulative?
tears/fails
ex: ACL tear due to lateral force on the knee; abduction torque
ex2: running wears articular cartilage
What are examples of external loads?
○ Gravity
○ Impact
○ Friction
○ Wind
What cause internally derived body loads?
tissues resist deformation
What causes tissue deformation? Example?
a tissue deforms to the level it needs to match the external force
Meniscus: moves out of the way to accommodate the force it’s experiencing, while there are also internal forces resisting
How do healthy tissues respond to loading?
Can deform but resist change in structure and shape
Internal forces that arise within the structure under load can resist the external forces placing the tissue under the load
Load response is tissue dependent
should return to original shape
What are the two ways we determine a tissue’s Strength?
Tissue Stress (pressure): Force (N)/ Area (m^2); Force or load generated within the tissue to resists deformation, divided by its cross sectional area
Tissue Strain: how much the tissue deforms under a force or load; Usually expressed as a percent change in length (%), distance (mm), although truly a unit less measure
What determines the Behavior of the tissue?
Stress-Strain curve
Describe the stress-strain curve
toe region: joint resting position/slack
Describe the stress-strain curve
toe region: joint resting position/slack
linear region: tissue starting to deform under the load (slope determines the stiffness of the tissue
elastic region: area under the linear slope
What does Young’s modulus state?
determines how much the tissue deforms in response to certain amounts of loads:
high stiffness (High young’s modulus): if pulled on, requires more (F/area)/stress/pressure to deform the tissue a certain percentage (% strain)
low stiffness (low young’s modulus): if pulled on, requires little (F/area)/stress/pressure to deform a tissue a certain percentage (% strain)
Describe the stress-strain curve. What is only true under the elastic region?
toe region: joint resting position/slack
linear region: tissue starting to deform under the load (slope determines the stiffness of the tissue
elastic region: area under the linear slope; stiffness = stress/strain
What does Young’s modulus state?
determines how much the tissue deforms in response to certain amounts of loads:
high stiffness (High young’s modulus): if pulled on, requires more (F/area)/stress/pressure to deform the tissue a certain percentage (% strain)
low stiffness (low young’s modulus): if pulled on, requires little (F/area)/stress/pressure to deform a tissue a certain percentage (% strain)
When a tissue is in the elastic region, what will it do when F=0/tissue is unloaded?
the tissue will elastically release stored energy and return to its original shape/length
What is the definition of the yield point? What happens?
the Transition Between Elastic and Plastic Behavior
additional load results in marginal increase in strain/deformation
once the yield point has passed, you reach the point of no return
What happens when the tissue is pushed to a point where it reaches its internal limit? Is this always bad?
Micro-failure of tissue under continued load results in plastic deformation (fibers tear)
Overstrained tissue is permanently deformed
Plastic deformation energy cannot be recovered once load is released
can be good with tissue mobilization/strength training/serial casting
What is the ultimate failure point?
when the tissue fails and is unable to hold additional load
What is the tissue’s viscosity dependent on?
Time
What two properties do tissues exhibit?
viscosity (stretching pattern is time dependent) and elasticity (ability to return to its original shape after loading)
Which tissues are highly viscoelastic?
Articular cartilage/fibrocartilage can withstand high velocities and are highly stiff
bones are stiff, tendons are good at handling slow loads, but are stretchy
What is creep? Example?
continued deformation of a material over time as its subjected to a constant load (low load)
serial casting; tissue adapts to stretch and deforms over time
What combo of movements produces the most percent strain on the calcaneofibular ligament?
inversion in dorsiflexion
How much does the ligament change in length depending on position tell us?
tells us the mechanism of injury
What movement usually causes an ankle sprain?
plantarflexion and inversion of the ankle
When the knee is taken into valgus, how much does it deform?
Higher moment, more strain in (anteriormedial) ACL bundle
valgus moment on LCL with external rotation
ligament is slackened
valgus moment on MCL with external rotation
ligament is taught
Which factors are important in how a tissue responds to load
Loading Magnitude – how much the tissue is loaded
Loading Rate – that speed at which a tissue is loaded
Loading Type – the way in which the tissue is loaded
What is a cumulative load?
Loading before the load is released = cumulative deformation/load over time > reach yield point quickly
many m. contracting with movement
