Week 6 joint Structure and Function, Connective Tissue

synarthroses

joint classification, slight to no movement, fibrous joints, cartilagenous joints, function to strongly bind and tranfer force between joints, example: pubic symphysis

diathroses

joint classification: moderate to extensive movement, synovial joints, example is shoulder and hip joint, move a lot, lots of range, often 3rd class, prone to injury

7 features of synovial joint

• articular cartilage

• joint capsule

• synovial membrane

• synovial fluid

• ligaments 

• blood vessels 

• sensory nerve 

(sometimes intra-articular discs which are fibrocartilage and deepen the joint or provide cushion)

hinge joint 

synovial joint characrerized but movement around a coronal axis (one plane of movement), example is elbow joint

pivot joint

synovial joint characterized by movement around a vertical axis, example is radiohumeral head

ball and socket joint

synovial joint characterized by movement in multiple planes- example is the shoulder

condyloid joint

synovial joint that is characterized by oval-shaped bone end fits into an elliptical cavity, allowing movement in two planes, example is the wrist (radiocarpal joint)

gliding/plane joint 

characterized by type of synovial joint characterized by flat or nearly flat bone surfaces that allow for limited, smooth, sliding or gliding movements in various directions, example is intercarpal joints 

saddle joint

synovial joint characterized by different concavity and convexity in two different planes, type of synovial joint characterized by flat or nearly flat bone surfaces that allow for limited, smooth, sliding or gliding movements in various directions, example is the thumb joint (trapezium with metacarpal)

types of connective tissues

• proper connective tissue (loose and dense)

• cartilage

• bone

• blood

periarticular connective tissue 

all made of ECM (specific mix of components give properties of different tissues) and cells that secrete the ECM components, no added mechanical properties, sparse, poor blood supply, examples are fibroblasts and chondrocytes

ECM components of periarticular CT

• fibrous proteins- collagen, elastin

• Ground substance- GAGs, water, solutes

Type I collagen

strong binder

Type II collagen

thinner, less tensile strength, scaffolding

elastin 

small fibrils that resist tensile force, return to former shape when force is released 

proteoglycan complex

looks like lots of bottle brushes on a logn string, hyaluronan backbone (special GAG) and proteoglycans- functions to keep the water content in connective tissue

proteoglycan

the “bottle brush”, core protein as the spine, GAG chain as the bristles, water is attracted to them

synovial fluid

viscoelastic, can store and disperse energy, involved in shear resistance, lubrication, and reduction of friction, a non-newtonian fluid

contents of synovial fluid

• water 95%

• hyaluronic acid

• lubricin (PG) proteins

• few cells

non-newtonian fluid

viscosity changes based on load, low shear with slow motion, thicker, cushions and resists shear, high shear with fast high load, thinner, reduced friction

Type I/Ruffini’s Ending 

joint sensory receptor responsible for position, acceleration through tension 

Type II/Pacini corpusles

joint sensory receptor responsible for acceleration through compression

Type III/Golgi-Like

joint sensory receptor responsible for tissue deformation at extreme ranges

Type IV/Free nerve endings

joint sensory receptor that is responsible for signaling the presence of noxious stimuli (chemical, mechanical, and inflammatory)

viscoelastic tissues 

• elastic properties: materials ability to return to normal shape after deforming load- collagen and elastin, stored potential energy

• viscous properties: material’s resistance to flow, PG and water, time and rate dependent, no stored potential energy, inversely prop to temp, prop to load and rate of loading 

factors to connective tissue behavior

adapts to loads- depends on tissue type! as well as age, trauma, altered activity level, weight bearing, immobilization

stress strain relationship

and strain increases on a tissue, the stress will increase along its toe region, elastic region, and into the plastic region past the yield point until ultimate failure in which the stress drops

young’s modulus

measure of the stiffness of a material, slope of the stress-strain curve, the stiffer the material the steeper the slope

poisson’s ratio

ratio of the lateral strain to the axial strain (change in diameter/change in length), strain that is perpendicular to the length of the tissue and applied load (tissue has strain both parallel and perpendicular to its axis)

features that viscoelastic tissue performance is dependent on

• time dependent (how long load is applied)

• rate dependent (how fast load is applied)

creep phenomenon 

time depenmdent deformation, constant load/stress, tissue deformation accumulates over time 

stress relaxation

time dependent, under constant deformation (strain), the stress inside the tissue will decrease over time (ex: hamstring stretch becomes less uncomfortable over time)

hysteresis

when viscoelatic tissue is stretched and the unloaded the tissue doesn’t return back to starting dimension immediately- some energy is lost as heat

strain rate sensitivity

strain of VE tissues is rate dependent, tissues response differs to slow or rapid loading, in general faster loading causes stiffer tissues, slower causes more pliability

stiffness 

as cell pushes/pulls on the ECM, the ECM may resist the cellular force through bending and stretching of ECM fiber 

Stiffening/non-linear elasticity

with increased forces from the cell, the ECM may stiffen due to local alignment in fibers

viscoelasticity

over the time of force application, the ECM may undergo creep and stresses may relax due to detachment of weak crosslinks and fiber arrangements

plasticity

when the cell detaches from the ECM, the ECM may retain permanent deformations resulting from reformation of weak crosslinks that lock in changes in fiber position and alignment

mechanotransduction 

cells sense and convert mechanical forces into biochemical signals that drive cellular responses- can be within a cell of transmitted from a sensor cell to an effector cell, makes the CT adaptable and responsive to demands placed on it 

ECM homeostasis

requires the balanced production and removal of constituents, response occurs via a negative feedback mechanism, fibrotic response occurs via positive feedback mechanism

anoikis

if ECM is too unloaded, cell death occurs (apoptosis)

acute trauma

• torn ligament, stretch capsule

• long levers increase risk

• generally includes inflammatory component

chronic trauma 

• overuse injury 

• accumulation of unrepaired relatively minor damage 

• can extend beyond an inflammatory stage 

osteoarthritis

• gradual erosion of articular cartilage with low inflammatory component

• can involve subchondral damage

connective tissue disorders

• Rheumatoid arthritis- destructive autoimmune CT disorder with strong inflammatory component

• Ehlers-Danlos- genetic disorder disrupting collagen production

what helps to maintain the CT 

homeostasis, healthy ECM, and fibroblasts 

bone fracture

viscoelasticity of the fracture hematoma promotes infiltration of the mesenchymal stem cells and the stiff bone surface promotes differentiation of MSCs into bone producing osteoblasts

immobilization

casting, confinement, paralysis, decreases forces on MSk system, periarticular CT composition is affected by decreased use (signaling molecules in the ECM), reduced ability to withstand load, implications for rehab— Movement is good! Loading is good!

aging effects on periarticular CT 

simiilar to changes with immobilization- tho is it due to age itself orrrr disuse?, there are age related histological changes which affect mechanical function, slowing of fibrous protein, GAGs, proteoglycan production and repair, and decreased osteoblast activity