Unit 3: Tissue mech/ Joint structure + Function

Recall 2 main types of joints

• Synarthrosis = slight to no movement

• Diarthrosis = moderate to extensive movement

Recall General composition of connective tissue

• Cells

• Extracellular matrix

  • Fibrillar component: collagen and elastin

  • Interfibrillar component (ground substance): glycoproteins, proteoglycans, and GAGs

Properties and functions of materials used in human joints

• Collagen provides tensile resistance.

  • Type I: resists tension

  • Type II: resists intermittent pressure

  • Type III: structural support

• Elastin resists tensile load but has more give and helps tissue return to original shape after deformation.

• Ground substance / GAGs / proteoglycans attract water, increase rigidity/stiffness, and help resist compression.

Identify The expected direction of deformation for a given load

• Compression → tissue shortens / is pressed together

• Tension → tissue elongates

• Shear → adjacent parts slide past one another

• Bending → one side is under tension and the other under compression

  • combo of forces (compression, tension, torsion)

• Torsion → twisting deformation around the long axis

Identify The plane of motion for any given motion at a specific joint

A quick rule:

• Flexion/extension → sagittal plane

• Abduction/adduction → frontal plane

• Internal/external rotation → transverse plane

For joint types:

• Hinge joints mainly allow motion in one plane

• Pivot joints mainly allow rotation/spin

• Ellipsoid, saddle, condyloid allow biplanar motion

• Ball-and-socket allows multiplanar motion including spin

• Plane joints mainly allow sliding with some rotation

The degrees of available motion at a given joint type

• Hinge: 1 degree of freedom

• Pivot: 1 degree of freedom

• Ellipsoid: 2 degrees of freedom

• Saddle: 2 degrees of freedom

• Condyloid: 2 degrees of freedom

• Ball-and-socket: 3 degrees of freedom

• Plane: mostly translation/sliding, with some rotation

Comprare stress and strain to load and deformation

• Load = external force applied to tissue

• Deformation = resulting shape change

• Stress = force divided by area

• Strain = change in length divided by original length, often as a percentage

So:

• Load is the input

• Deformation is the tissue response

• Stress normalizes load to area

• Strain normalizes deformation to original length

Compare tissue properties of types of collagen

• Type I collagen: strongest for resisting tension; found heavily in tendon, ligament, and bone

• Type II collagen: better for resisting intermittent pressure; important in hyaline cartilage

• Type III collagen: more structural support; seen in tendon sheaths and immature tissue

The role of collagen vs. elastin in maintaining tissue shape

• Collagen helps tissues resist deformation, especially tensile loading, and helps maintain structural strength.

• Elastin allows tissues to deform and then recoil back to original shape. It has more stretch or “give” than collagen.

Compare Composition and material properties of tendons, ligaments, bone, and cartilage

Tendon

• Connects muscle to bone

• Mostly Type I collagen

• Small amount of interfibrillar substance

• Built to handle high tensile loads along its line of pull

Ligament

• Connects bone to bone

• Mainly Type I collagen

• Has varying amounts of elastin

• Fibers align with tensile forces

• Also primarily resists tension

Bone

• Type I collagen plus inorganic mineral, especially hydroxyapatite

• Hydroxyapatite gives compressive strength

• Functions in support, protection, and movement

Cartilage

• In articular hyaline cartilage, ECM is mainly Type II collagen with abundant ground substance, PGs, and GAGs

• Designed to reduce friction, bear/distribute weight, and resist compression

• Compression resistance depends on water attraction by PGs and an intact collagen

Diagram of Typical load-deformation curve for a ligament or tendon, with identification of various regions on the curve

look at notes

Diagram of Typical stress-strain curve for a ligament or tendon

Look at notes

Explain

Expected change in force and elongation given a change in tissue stiffness

look at graphs in Notes

Explain

Expected change in force and elongation given a change in tissue length

look at graphs in Notes