Applied Tissue Biomechanics

tropocollagen

structural unit of a collagen fiber

factors that determine how connective tissue responds to stress

amount of covalent bonds and location of the bonds

proteoglycans

core protein with glycosaminoglycans branching off

examples of loose connective tissue

subcutaneous tissue and superficial fascia

examples of dense irregular connective tissue

joint capsules, skin, periosteum

examples of dense regular connective tissue

tendons, ligaments, aponeurosis

fiber alignment in tendons vs ligaments

fibers are more aligned in tendons than ligaments

three layers of CT sheaths around tendons

endotenon, epitenon, paratenon

peritenon

made up of the epitenon and paratenon

tenosynovium

synovial-lined peritenon found on tendons in areas of high friction

location for greatest risk of injury in a tendon

myotendinous junction

entheses

attachment to bone

fibrocartilaginous attachment

tendon or ligament directly attaches to bone via calcification of the DRCT

fibrous attachment

tendon or ligament indirectly attaches to bone via Sharpey’s fibers and periosteum

zone 1 in articular cartilage

reduces friction between surfaces and resists shear forces

zone 2 in articular cartilage

absorbs forces to resist compression

zone 3 in articular cartilage

helps anchor cartilage to bone and resists stretching forces

articular cartilage

specialized hyaline cartilage with high type II collagen and proteoglycan content, sparse chondrocytes

fibrocartilage

high type I collagen content, sparse chondrocytes and fibroblasts, moderate proteoglycan content

how deeper layers of articular cartilage receive nutrients

compressive forces push synovial fluid deeper into the AC zones

trabeculae

small, beam-like or rod-shaped tissue structures that form supportive frameworks inside bones

mechanotransduction

process by which a mechanical load is converted into a cellular response

stress

force given over a certain area

strain

change in length/original length

toe region

beginning of tissue loading, collagen fibers straighten out

elastic region

tissue deforms with applied load but will return to original state once load is removed

Yonug’s modulus

slope of the elastic region

tissue stiffness

a mechanical property that measures the resistance to deformation when an external force is applied; measured in the elastic zone

plastic region

tissue deforms with applied load but does not retain to original state once load is removed

yield point

the transition point at which tissue cannot return to its original state after a load is removed

macrofailure

complete tissue disruption

properties of viscoelastic tissue

rate sensitivity, creep, stress-relaxation

rate sensitivity

faster loading results in less strain and deformation but quicker macrofailure

creep

a constant force gradually decreases the rate of deformation

stree-relaxation

the force needed to maintain a constant deformed state decreases over time