Articular cartilage

Collagen

Most abundant protein in the body

Stronger under tension than compression

Boundary lubrication

A function of the chemical property of a lubricant, independent of its physical properties

Anisotropic

A material that has different mechanical properties when loaded along different axes

Porosity

The ratio of fluid volume to total volume (amount of fluid in the pores)

Permeability

The interconnected spaces between pores of a material

Fluid will remain squeezed out of high load areas and redistribute to low load areas

Creep

A constant force causes rapid initial deformation that slows until equilibrium is met

Controlled by fluid flow in joint. Allows cartilage to change dimensions within 4 hours

Stress relaxation

Constant deformation/position leads to high initial stress on a tissue followed by decreased stress

Stress rises as fluid is squeezed out, and relaxes as fluid redistributes in joint

Effects of OA

Disruption of collagen network leading to decreased tensile strength

Increased water content causes decreased compressive strength and increased permeability (like a worn out sponge)