Tissue Mechanics Exam #1

What are tissues composed of?

cells and extracellular matrix

What do forces and moments have?

direction and magnitude

What is torque?

forces that do not align with the center of mass

What is a deformable body?

a tissue that change shape in response to forces imposed on it

What is the amount of deformation dependent on?

-amount of applied force (stress)

-characteristics of material being deformed (properties, size, shape)

-environmental factors (temperature, humidity)

What are the types of internal forces that can cause deformation?

-tensile (pulling)

-compression (pushing)

-shear (pushing in opposite directions)

-bending (mixture of tension, compression and shear forces)

-torsion (mixture of tension, compression and shear forces)

What is stress?

the amount of force being applied over a certain area

What is strain?

the amount of deformation that occurs to an object

What is the Poisson effect?

when length is taken up in one dimension, it is added to another dimension of the object

What is elastic deformation?

restoration of object to original shape, deformation is reversible

What is plastic deformation?

object does not restore to original shape, irreversible deformation of an object

What is the failure point?

when material will break/fail completely

What is the yield point?

when the material begins to go into the plastic region

What is the ultimate stress point?

the point of maximal resistance of a material

What is toughness?

how much energy a material can absorb before failure

What is Young's Modulus?

-a measure of stiffness of a material

-stress/strain of elastic region

What does a higher modulus mean?

the material is stiffer

What is viscoelasticity?

a material that exhibits properties of a solid and liquid, continuous load will impose a continuous deformation (time-dependent and rate-dependent)

What is creep and recovery?

-under constant stress, measuring strain

-tissue gradually elongates over time

What is stress relaxation?

-under constant strain, measuring stress

-tissue will relax over time

What is hysteresis?

the amount of energy lost between loading and unloading (lower hysteresis->faster response to imposed loads)

What is Wolff's Law?

stress reaction, tissues respond to repeated stresses and make themselves stronger

How do we describe properties of materials?

-instantaneous resistance to loads (soft, hard, weak)

-how easily they fail (strong, weak)

-how they behave before failure (brittle, ductile)

What are the four types of tissue?

epithelial, connective, muscle, nervous

What are the types of connective tissue?

-irregular dense/loose connective tissue

-dense regular connective tissue

-cartilage

-bone

-adipose tissue

What are the main components of connective tissue?

water, ground substance, extracellular matrix and cells

What makes up the extracellular matrix in connective tissue?

fibers; collagen and elastin

What do fibers provide to connective tissue?

tensile strength and elasticity

What does collagen do in connective tissue?

provides tensile strength, 30% of protein makeup in body

How is collagen made?

-by fibroblasts

- procollagen-> tropocollagen microfibrils-> collagen fibrils-> collagen fibers

What does size and flexibility have to do with collegen?

- variations in diameter (to be able to pack in collagen fibers, bigger diameter=stronger)

-fibers become oriented in the direction of the forces (tendons=parallel, ligaments=mostly parallel with some diagonal) (this means they can take on different direction of forces)

What is type 1 collagen?

-bone

-most common

-strongest

-tendons, ligaments, bone, mature scars

What is type 2 collagen?

-cartilage

-thinner, slightly less strong

-provides framework for shape and consistency of structures

-hyaline cartilage, menisci, etc.

What is type 3 collagen?

-even thinner

-flexible and elastic

-fresh scars, skin, blood vessels, uterus, GI tract

What does elastin do in connective tissue?

provides elastic recoil to help return to original shape

What can tissues with more elastin do?

they can be stretched further

What is ground substance?

gel-like fluid that fills the space b/t cells and fibers that helps support the fibrous skeleton of the ECM (collagen and elastin) to be able to contribute to structural integrity of the tissue and determine mechanical properties of the tissue

What makes up the ground substance?

glycosaminoglycans (GAGs), proteoglycans, adhesive proteins, and water

What are glycosaminoglycans?

long unbranched chains of disaccharides with negative charge to attract water

What are proteoglycans?

-large molecules with protein cores

-binds GAG chain by adhesion molecules to resist compression, dissipate forces and lubricate joints

-helps stabilize collagen by slowly dissipating forces through water

What are adhesive proteins?

links GAG chain to proteoglycans and conveys forces by altering mechanical principles

What is macrotrauma?

-usually a high force injury

-typically there is a MOI

-can lead to rupture

-stress to a tissue that is greater than the yield point

What is microtrauma?

-usually, repetitive overload

-tissue healing can't keep up with the demand causing failure

-below the threshold for injury but slowly gets destroyed

What dictates how much a tissue gets damaged?

-magnitude, direction, frequency, and velocity of applied force

-tissue tolerance levels

-direction of applied force

-movement relative to applied force

-length of lever arm

-muscle action

-area of force application

-awareness of impeding injury

What will stressing an injury into plastic region result in?

creep (permanent elongation)

What sensations are felt by creep?

discomfort, aching, hurting, painful, unbearable

When do we not use pain as a reference for treatment?

someone who has chronic pain, they constantly have pain so hard for them to use it as a guide

When do we use pain as a reference for treatment?

- when we want to take someone to a certain point but not push them past that in order to adapt tissue (strengthen)

-use rule of 2

What does pain before the end feel mean?

pt is in inflammatory phase

What does pain at the end feel mean?

pt is in proliferation phase

What does pain after the end feel mean?

pt is in maturation phase

What is the toe region of the stress-strain curve?

-normal ROM

-uncrimping of collagen

What happens in the elastic region (4-6% stretch)?

-some microfailure

-physiologic ROM

-first resistance (end feel)

-yield point

What happens in the plastic region (6-8% stretch)?

-some injury

-anatomic ROM

-goes into 2nd resistance, past end feel

What happens in total failure region?

-high velocity, low amplitude

What does stress in the plastic zone look like?

quick movements, uncontrolled movement, large load and "cold tissue"-> plastic deformation (failure)-> trauma-> injury

OR

slow movements, small load, "warm tissue"-> plastic flow (lengthening)-> creep/stress relaxation-> tissue lengthening-> tissue remodeling

How do we classify injuries?

acute, subacute, chronic, and acute on chronic

What is an acute injury?

-typically lasts 7-10 days

-redness, swelling, warmth, painful, loss of function

-classic signs of inflammation

What is a subacute injury?

- typically 5-10 days after acute phase

- 12 to 20 days after injury

What is a chronic injury?

- typically 26-34 days after injury

-takes about 2 weeks to complete

-total healing can take up to 2 years to reach preinjury strength

-can turn into chronicity

What is chronicity?

-injury doesn't heal as it should

-characterized by excessive scarring and adhesions

-demonstrates persistent inflammation and healing

-effects ability for tissues to heal properly, continuous cycle of healing and damage

What is acute on chronic?

when an acute injury happens to a chronic pain (re-injury)

What are the four phases of healing?

clotting, inflammation, proliferation, maturation

What is the clotting phase?

-blood and lymph contents

-clotting is initiated by interaction of plasma and tissue components once in interstitial fluid

-prothrombinase + thromboplastin=thrombin

-thrombin turns fibrinogen in to fibrin to form a clot

-happens within hours and kick starts the inflammatory phase

What is the inflammatory phase?

-cardinal signs of inflammation

-release of the clot which increases vasodilation 10-fold

-mediators come from plasma and soft tissue to increase inflammation

-leukocytes come in to clean up from chemotaxis

What is the proliferation phase?

-fibrin clot breaks down and replaced with granulation tissue (scar tissue)

-growth of capillary buds to produce aerobic healing

-fibroblast synthesize ECM, elastin, ground substance, GAG's and fluid

-type 3 collagen replaced by type 1 collagen

What is the maturation phase?

-reduction of fibroblastic activities

-can last up to 1-2 years after injury

-using the injured area to realign the collagen with tensile stress

-rehabilitation consisting of SAID principle

What is primary pain?

-right after the injury occurs, sharp

-swelling to tissue b/c of cell damage

-via delta-A fibers - myelinated, quick response

What is secondary pain?

-delayed pain- dull and throbbing

-starts when swelling starts

-via C-fibers- unmyelinated, slow response, disinhibits endorphin release

-when icing, compression, etc. we are inhibiting the secondary pain

What are intrinsic factors that impede healing?

-degree of tissue damage

-type and size of wound

-blood supply

-amount of stress applied to tissue

-presence of swelling

-amount of pain

-stabilization of wound

-tissue characteristics

-presence of infection

What are systemic factors that impede healing?

-age

-concurrent illness

-nutritional state

-obesity

-stress

What are extrinsic factors that impede healing?

-medication

-temperature

-humidity

What factors can facilitate healing?

-nutrition

-pharmacology

-physical agents

-PEACE & LOVE

What is therapeutic exercise?

-systematic and planned performance on bodily movements, postures, or physical activities

-MUST BE individualized, goal oriented, and using appropriate parameters

What is the billing code for therapeutic exercise and what are the parameters?

-CPT 97110

-to improve aerobic capacity, improve muscular strength/power/endurance, muscular length, mobility of a joint or region of the body

What is the first rule of therapeutic exercise?

- "primum non nocere"

-first do no harm

What is the second rule of therapeutic exercise?

-Nonmaleficince

-least amount of harm for the best outcome

How do we use therapeutic exercise?

by applying the principles of muscle physiology, mechanics of muscle contraction, and muscle architecture

How do we determine if someone is in an acute inflammatory phase?

-history: time frame, severity of injury, how, when, why, MOI

-duration: typically 6-10 days post-injury

-pain before end feel

How do we treat proliferative contractile injuries?

-avoid: active movements and passive stretching

-allow: passive movements and active stretching

-active-assisted ROM-> active ROM-> resisted ROM

-low load and high repetitions

-passive stretching in elastic region

How do we treat proliferative capsule and ligament injuries?

-avoid: stretches in the movement that it resists passively and actively

-passive and active movements into elastic range-> isometric contraction-> dynamic strengthening

How do we treat proliferative articular cartilage injuries?

-avoid: excessive compression motions

-passive ROM /s compression-> passive ROM /c compression-> isometric-> active and assisted active ROM

-low pressure, high repetitions

How do we treat proliferative bone injuries?

-limited immobilization, the less the better but also don't want it to be too premature

-need to keep check on alignment of bone

-weight bearing is dependent on bone that was broken

How do we know if we have been too aggressive in the proliferation phase of injury?

if typical signs of inflammation/acute injury show

What is the main priority of treating injuries in maturation phase?

now that we have the mobility back, we focus on strengthening the area again

How do we determine if a patient is in the maturation phase of healing?

-history: most movements are pain free except for motions that use large ROM or high velocity

-duration: depends on the injury, minor= ~9 days, major= ~weeks to months

-end feel: pain occurs after the end feel

How do we treat maturation contractile tissue injuries?

-passive stretching to regain ROM

-resisted exercise program, working in high load and low reps, use rule of 2

-working on eccentric muscle actions (because most injuries happen in eccentric loading phase)

How do we treat maturation joint capsule and ligament injuries?

-early ROM: continue protection from tissue strain

-late ROM: gradual increase in strains to regain loss of motion

-cyclic, slow to moderate rate, low reps

-dynamic strengthening: high load, low reps

How do we treat maturation articular cartilage injuries?

-compression loading including active or assisted active ROM, open kinetic chain exercises, weight bearing

-NEVER USE HIGH WEIGHTS, HIGH COMPRESSION CAN CAUSE CRACKS, CAN'T GO BACK

How do we treat maturation bone injuries?

-immobilization discontinued around 6-8 weeks

-active ROM and active strengthening to offset atrophy and loss of motion from immobilization

-use rule of 2

Why does chronic inflammation occur?

-unresolved acute trauma

-repetitive trauma on tissue

What are some characteristics of chronic inflammation?

-persistent macrophage activity

-large number of fibroblasts

-producing large amounts of collagen

-feelings of stiffness

What are the big four exercises?

squat, lunge, single leg stance, plank

What is a squat?

-two legs fixed on the ground with body weight being decelerated towards ground

-squat can be dynamic as long as both feet hit ground

What is a lunge?

-must be dynamic

-requires moving one limb, loading it, and returning to start position

-proper hip, knee, ankle alignment

What is a plank?

-some portion of exercise with 4 points of contact with the ground

What is a single leg stance?

-standing on one leg

-incorporates balance including ankle and hip strategy

What is motor learning?

complex set of internal processes that involves the acquisition and relatively permanent retention of a skilled movement or task

What are the stages of motor learning?

cognitive, associative, autonomous

What is the cognitive stage of motor learning?

conscious awareness of the performance of an activity