10-11b Orthopedic Biomechanics Part I

Question 1

What are initial questions when encountering an acute injury?

Answer 1

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?

Question 2

Describe determining the mechanism of injury

Answer 2

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?

Question 3

What are possible structures involved in a knee injury?

Answer 3

patellar dislocation, ligament strain/sprain/tear

Question 4

What are possible structures involved in an ankle injury?

Answer 4

ligaments
fracture of distal fibula
fifth metatarsal evulsion fracture (perineal m. tries to evert m. and stabilize but instead pull the bone off)

Question 5

What is a force acting on the body called?

Answer 5

a load

Question 6

What happens when a tissue is loaded too much cumulative?

Answer 6

tears/fails

ex: ACL tear due to lateral force on the knee; abduction torque
ex2: running wears articular cartilage

Question 7

What are examples of external loads?

Answer 7

○ Gravity
○ Impact
○ Friction
○ Wind

Question 8

What cause internally derived body loads?

Answer 8

tissues resist deformation

Question 9

What causes tissue deformation? Example?

Answer 9

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

Question 10

How do healthy tissues respond to loading?

Answer 10

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

Question 11

What are the two ways we determine a tissue’s Strength?

Answer 11

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

Question 12

What determines the Behavior of the tissue?

Answer 12

Stress-Strain curve

Question 13

Describe the stress-strain curve

Answer 13

toe region: joint resting position/slack

Question 14

Describe the stress-strain curve

Answer 14

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

Question 15

What does Young’s modulus state?

Answer 15

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)

Question 16

Describe the stress-strain curve. What is only true under the elastic region?

Answer 16

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

Question 17

What does Young’s modulus state?

Answer 17

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)

Question 18

When a tissue is in the elastic region, what will it do when F=0/tissue is unloaded?

Answer 18

the tissue will elastically release stored energy and return to its original shape/length

Question 19

What is the definition of the yield point? What happens?

Answer 19

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

Question 20

What happens when the tissue is pushed to a point where it reaches its internal limit? Is this always bad?

Answer 20

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

Question 21

What is the ultimate failure point?

Answer 21

when the tissue fails and is unable to hold additional load

Question 22

What is the tissue’s viscosity dependent on?

Answer 22

Time

Question 23

What two properties do tissues exhibit?

Answer 23

viscosity (stretching pattern is time dependent) and elasticity (ability to return to its original shape after loading)

Question 24

Which tissues are highly viscoelastic?

Answer 24

Articular cartilage/fibrocartilage can withstand high velocities and are highly stiff

bones are stiff, tendons are good at handling slow loads, but are stretchy

Question 25

What is creep? Example?

Answer 25

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

Question 26

What combo of movements produces the most percent strain on the calcaneofibular ligament?

Answer 26

inversion in dorsiflexion

Question 27

How much does the ligament change in length depending on position tell us?

Answer 27

tells us the mechanism of injury

Question 28

What movement usually causes an ankle sprain?

Answer 28

plantarflexion and inversion of the ankle

Question 29

When the knee is taken into valgus, how much does it deform?

Answer 29

Higher moment, more strain in (anteriormedial) ACL bundle

Question 30

valgus moment on LCL with external rotation

Answer 30

ligament is slackened

Question 31

valgus moment on MCL with external rotation

Answer 31

ligament is taught

Question 32

Which factors are important in how a tissue responds to load

Answer 32

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

Question 33

What is a cumulative load?

Answer 33

Loading before the load is released = cumulative deformation/load over time > reach yield point quickly

many m. contracting with movement