Lecture 2 (revised).docx

21 Pages
67 Views
Unlock Document

Department
Kinesiology&Physical Education
Course
EDKP 206
Professor
David J Pearsall
Semester
Winter

Description
Tendons/Ligaments 2/12/2013 7:13:00 PM Composed of connective tissue  Provide and maintain form in the body and give support to body  3 kinds of connective tissue o syportive (bone cartilage) o connective tissue proper  dense- skin, ligaments, tendons  loose- not resistant to stress or train o specialized connective tissues (adipose and hematopoietic tissue) Note: shear force- two fibers/structures sliding in opposite directions from one another Tendons and ligaments  PASSIVE structures  do not actively produce motion o Reaction to motion that segments of bone creates  Rate dependant loading o Mechanical properties depend on loading rate  Ultimate stress and strain (i.e. strength) is higher for fast loading than for slow  Greater stiffness = increased strength  Ligaments o Attach articulating bones to one another ACROSS A JOINT o Function  Guide movement  Maintain joint congruity  Act as positional sensory for joint proprioception o Have a “crimped” appearance angled obliquely  Tendons o Attach muscle to bone  No sharp boundary b/w tendon and muscle  aponeurosis is a mix of both muscle and tendon  Attach via Tapered weaving (not flat) increased contact area o Functions  Transfer forces b/w muscle and bone  Store elastic energy  ~ 6% energy lost as heat  provide for optimal contractile conditions o arreantged in dense-parallell fibered collagenous tissues Factor influencing tissue properties  Immobilization – leads to atrophy of fibers (in terms of thickness) o Decreased stiff ness, decreased ultimate stress, decreased energy to failure  Age o Increased stiffness, decreased ultimate stress, decreased energy to failure  Strength training o Does not effect stiffness o Increased ulimate stress, increased energy to failure Composition  Cells ~20% o Primary type: fibroblast or fibrocyte  Secrete components of extracellular matrix  Extra cellular matrix o Fibers (collagen/elastin) and ground substance (gelatinous material that fills the space b/w cells and fibers)  Composed primarily of collagen ( = turn into aka hierarchy of fibers)  Tropocollagen  collagen microfibrils  subfibrils  fibrils (functional unit)  fibers o Arranged in parallel to make them adapted to resisting traction or tensile forces o Ground substance- containt proteoglycans which add the the ability of tendons/ligaments to withstand compression and tensile forces Mechanical behavior  Tensile strain = elongation per unti length of material in response to a tensile load o [New length – original length]/ original length = %  Tensile stress= externally applied tensile load/cross sectional area o F/A = N/mm  Response to stress = tension o Elastin – no response o Collagen – 108 MPa  Vs cortical bone ~ 125 for COMPRESSION  Response to strain o Elastin- 200%  Able to deform upto 200% from original starting structure  Good because- ex. ligamentum nuchae in the neck is primarily composed of elastin which gives us a greater range of motion in our neck o Collagen – 7%  Vs cortical bone 0.2%  very stiff structure, hard to deform  Failure to stress o 80-120 MPA  vs cortical bone ~125  can withstand more force than ligaments/tendons  Stress vs strain curve ( see slide 9 on lec 2 cont’)  o 5 main regions  toe  little increase in stress and the tissue elongates (very little strain though)  stress is sufficient to straighten collagen’s crimp  linear/elastic region  elongation due to stress continues to increase  loads that exceed those that produce crimp straightening result in tissue elongation by means of collagen fibers sliding WRT one another  plastic region (progressive failure)  point at which the elastic region translate to plastic region – yield point  enough stress to unravel the collagen fibers we see a decrease in the slope of the curve  thus, when force removed the tissue cannot return to original form  permanently deformed  can cause ligament sprain  region of major failure  serious fall in the curve  ligament/tendon intack, there is visible narrowing of structure  complete failure  stress and strain at this point = ultimate stress and ultimate strain  can be subjected to tensile strains up to 6%, when acute strain causes elongation >8% tendon will rupture  can occur in 3 ways  rupture where there is tearing through the substance of tissue  failure due to enthesis (insertion site)  pulling away a portion of boney atachement  avulsion fracture o the slope of this curve = Young’s Modulus (stress/strain)  represents the resistance of the tissue to elongation (i.e. stiffness of material)  steep slope = high modulus value = high degree of stiffness  low slope = low modulus value = low degree of stiffness (easily deformed)  strain o Toe ~ 3% (no change in structure for about 3% of total load) o Failure 8-10%  Vs cortical ~0.2%  can’t withstand much deformation before breaking  Young’s modulus (stiffness properties) o 0.8-2.0  vs cortical bone ~18  much more stiff  Energy loss (hysteresis) o 6-11% o Difference b/w energy expended and energy required o Hysteresis: when you move in one direction (i.e. apply tension) we have 1 stress-strain profile. When we move in the other direction (now relaxing that section) we will see a different path on the stress-strain curve.  i.e. a ligament that is being stretched has a different profile then one being relaxed  this difference is because of the VISCOUS component (which is time dependant)  During hold: the stress will decrease, but the strain remains constant (stress relaxation response)  red portion corresponds to the amount of energy lost (in the form of heat) o why when we warm up we are physically warming the ligaments/tendons  Composition o Low cellularity (fibroblasts = <20% volume) o Water (70% total body weight)  Significantly effects physical properties o Solid matrix (30% wet weight)  Collagen >75% dry weight  Elastin  Spring like component  Ligaments contain more elastin than tendons  Ground substance- material b/w fibrils to help divide/control them  Ex. proteoglycans & other proteins o Sparsely vascularized compared to bone  Effects their response to injury o Nerve receptors  Ex. golgi tendon apparatus – measures force magnitude o Viscoelastic materials  Main function: response to force  It is:  A viscous fluid ~ note that 70% are water  Able to dampen shearing forces  RATE DEPENDANT o The faster we push the fluid, the more resistance we will get  An elastic solid  Returns easily to original shape  Non-rate dependant  Resilient  Able to store and restore energy  At higher strain rates ligaments and tendons are  Stiffer (greater slope)  Stronger (greater ultimate stress)   BUT cortical bone has a greater rate-dependant increase (125 – 300+ MPA) in tensile strength than does ligaments Viscoelastic behaviors: see that the curves are NOT linear, but time dependant  Top graph o Initially no load, so no deformation is seen o At the point we increase the load, we see an instantaneous increase in deformation o While we hold the load constant we see that the deformation slowly increases  This phenomenon is called “CREEP” o At a certain point the deformation becomes constant  Bottom graph o Initially no deformation b/c no load is added o Once we see an increase in deformation, there is an instantaneous increase in amount of stress felt. o If deformation is held constant you see the stress gradually declines to a much lower resting level then seen at first initial stress  This process is called “STRESS RELAXATION”  the creep and stress relaxation response is a characteristic of vasoelastic structures  this can be advantageous for stretching o see that the best way to improve flexibility is to hold a certain stretch for a long period of time, this will relax the stress felt on the muscle allowing for even further deformation  Summary o Having a constant load will create a creep response (deformation) o Having a constant deformation will cause for the stress relaxation response o  recovery: apply a stress then decrease it will cause for the creep effect followed by the stress relaxation phenomenon o characteristic of recovery is that we see both occur  Rate effects o Increase the rate at which we apply the stress, we will see an increase in the stiffness and therefore the strength Ligaments  Attach articulating bones to one another across a joint  Function o Microscopic movements (fine tuning)  Guide movement (set end limits of movements) o Maintain joint congruity o Act as positional sensor for the joint  i.e. proprioception o Does some force transmission (minor function)  Want enough force to keep alignment of bone Note: mode of failure is highly related to age/skeletal maturity  Hierarchy of fibers (smallest – largest) o Tropo-collagen o Micro fibril o Sub fibril o Fibril o Fiber  Fiber arragements o Oblique, collagenous tissue that is crimped in resting state  Mechanical behavior (stress vs strain) Note: force = stress | strain = deformation   III- yielding point: some fibers may break  IV- full failure  Curve vs bone curve o Bones are more stiff  have a steeper slope o Ligaments have a lower tensile response  The curve remains low (aka toe region) until it reaches a linear portion   young’s modulus = stiffness properties  Tendons  Attach muscle to bone  Functions o Transfer forces b/w muscle and bone  Note: some muscles don’t have tendons o Store elastic energy  ~6% is los
More Less

Related notes for EDKP 206

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit