Orthopaedic Biomechanics 1 (10/11b) [Biomedical]

Question 1

Force

Answer 1

push or pull that produces, arrests or modifies movement

Question 2

Torque

Answer 2

product of a force and its moment arm (EX: rotational force)

Question 3

Forces and torques are both ___ or ___, and occur simultaneously

Answer 3

internal or external

Question 4

Load

Answer 4

a force that acts on the body

Externally derived loads — gravity, impact, friction, wind

Internally derived loads — muscle activation, tissue deformation (EX: stretch, compression

Question 5

Tissue Loading

Answer 5

Joint reaction forces load different tissues

Tissue deform as much as they need to to accommodate stretching or compressing, results in loads arising within tissues

Cumulative loading can lead to eventual injury

Question 6

How do healthy tissues respond to load?

Answer 6

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

Question 7

Tissue Stress

Answer 7

Force or load generated within the tissue to resists deformation, divided by its cross sectional area

A measure of load or energy that stored within a tissue

Pressure = Force (N) /Area (m2)

EX: in a balloon → forces resisting being stretched out/expanded

Question 8

Tissue Strain

Answer 8

The amount a tissue deforms under a force or load

Usually expressed as a percent change in length (%), distance (mm), although truly a unit less measure

EX: in a balloon → measure of how much the balloon stretches/expands

Question 9

Stress Strain Diagram - Toe Region

Answer 9

represents taking up slack in the tissue

the nonlinear beginning of the diagram

Question 10

Stress Strain Diagram - Slope of Linear Region

Answer 10

represents stiffness of the tissue

Young’s Modulus

the linear upward slope of the diagram

Question 11

Stress Strain Diagram - Young’s Modulus (ε)

Answer 11

represents how much the tissue deforms in response to certain loads (aka stiffness)

High ε = high stiffness
Low ε = low stiffness

This behavior only exists in linear slope region of elastic region

Question 12

Stress Strain Diagram - Elastic Region

Answer 12

represents elastic deformation energy

Tissue returns to original shape/length after loading

All stored energy is released once tissue is unloaded

dark blue region of the diagram

Question 13

Stress Strain Diagram - Yield Point

Answer 13

represents the transition between elastic and plastic behavior

Point of no return (aka once you pass this point, you create permanent tissue change)

Additional load results in marginal increase in stress

point where it goes from dark blue to light blue on the diagram

Question 14

Stress Strain Diagram - Plastic Region

Answer 14

represents plastic deformation caused by micro-failure of tissue under continued load

Overstrained tissue is permanently deformed

Plastic deformation energy cannot be recovered once load is released

Can be good (EX: stretching, weight lifting, serial casting, joint mobilization) or bad (EX: injury)

light blue region of the diagram

Question 15

Stress Strain Diagram - Ultimate Failure Point

Answer 15

represents point where tissue fails and is unable to hold additional load

point in light blue region where sharp downward slope begins

Question 16

Biologic tissues exhibit ___-like and ___-like behaviors

Answer 16

fluid-like and elastic-like

Question 17

Biologic Tissues - Fluid Behaviors

Answer 17

Viscosity — fluid-like component to behavior of tissue, resistance to flow

EX: honey = high viscosity, water = low viscosity

Fluid-like behavior is a time dependent behavior

Slow loading can lead to stretching, fast loading can lead to tear (EX: silly putty)
- in general, not always the case

Question 18

Biologic Tissues - Elastic Behaviors

Answer 18

Elasticity — ability of material to return to original shape after loading

Does not mean “stretchy”, but rather a measure of how stiff/unstiff it is

Question 19

Bone, capsule and ligament, muscle, tendon, fibrocartilage, and articular cartilage all respond differently based on ___ ___

Answer 19

their makeup

Question 20

Tissues in the body are ___

Answer 20

viscoelastic

Question 21

Creep

Answer 21

continued deformation of a material over time as it’s subjected to a constant load

Prolonged, low load stretch

Time required depends on type of tissue

EX: serial casting → PT will use a cast to hold body in a certain position to force it to adapt to the stretch, and incrementally increase the stretch to improve motion

Question 22

Ankle Sprain Data

Answer 22

Most common cause is inversion plantarflexion

Most common injury in ankle is ATFL

Question 23

ACL Strain Data

Answer 23

It is usually a rapid load that causes an ACL tear

In vitro testing — in the lab testing, outside of the living organism

In vivo testing — in a living organism

In silica — completely computer modeled

Question 24

Factors that Impact Musculoskeletal Loads

Answer 24

Loading Magnitude
Loading Rate
Loading Type

Question 25

Loading Magnitude

Answer 25

how much the tissue is loaded High vs Low Load Cumulative load — you can keep increasing the yield capacity or reach yield capacity faster since you are starting at a higher load due to cumulatively loading or getting stronger

Question 26

Loading Rate

Answer 26

the speed at which a tissue is loaded Loading rate is a function of time Biologic tissues are sensitive to the rate at which they are loaded Tissues behave differently under different loading rate conditions Fast or slow loading rates lead to different injuries EX: loading in the ACL - Fast/high velocity → leads to complete ACL rupture - Slow/low velocity → leads to intact ACL with avulsion of tibial eminence (ligament pulls away from tibia)

Question 27

Loading Type

Answer 27

the way in which the tissue is loaded Tension, Compression, Bending, Shear, Torsion, Combined

Question 28

Loading Type - Tension

Answer 28

two forces pull on an object in different directions EX: lateral ankle ligaments are severely tensioned as the foot rotates inward

Question 29

Loading Type - Compression

Answer 29

forces that push/pull surfaces of objects together, or brings the end of an object closer EX: humerus is pulled against the glenoid by the deltoid muscle creating a compressive load between the bones

Question 30

Loading Type - Bending

Answer 30

deformation tissue that occurs at right angles to its longitudinal axis Concave side undergoes compression load Convex side undergoes tension load EX: coxa vara results in increased bending load on neck of the femur

Question 31

Loading Type - Shear

Answer 31

unaligned parallel forces that move on part of a body in one direction and another part in the opposite direction EX: cam type femoroacetabular impingement creates abnormal shear load between the femur and acetabulum, causing delamination (peeling off articular cartilage)

Question 32

Loading Type - Torsion

Answer 32

twisting force applied to tissue around longitudinal axis EX: noncontact ACL rupture

Question 33

Loading Type - Combined

Answer 33

multiple types of loading interacting on the tissue

Question 34

Factors That Influence Tissue Ability to Accept Loads

Answer 34

Age Disease/trauma Overuse Underuse

Question 35

Tissue Loading Ability - Age

Answer 35

cells in tissues change as we get older, which dictates tissue response (EX: osteoporosis)

Question 36

Tissue Loading Ability - Disease/Trauma

Answer 36

soft tissue disorders influence genes that code for the protein of collagen, if this is impacted it affects elasticity of tissues EX: Ehlers Danlos syndrome where tissues are overly stretchy and lack ability to return to normal shape

Question 37

Tissue Loading Ability - Overuse

Answer 37

when loading of the tissue exceeds the repair capacity of the tissue, leads to plastic deformation Can cause microtearing which changes tissue, you may give time to rest but not enough time for tissue to go back to its baseline EX: tendonitis

Question 38

Tissue Loading Ability - Underuse

Answer 38

when you don’t load tissue, it starts to lose its ability to accept loads Changes, like loss of bone or muscle mass, can occur over time Bone grows in response to stress — if you don’t load them, they will get weak