BE300: Articular Cartilage

Where do you find articular cartilage in terms of bones?

On the ends of long bones (articulating surfaces in joints)

What type of joint is articular cartilage present in?

Synovial

Why is there limited capacity for healing and repair of articular cartilage?

* There are no blood vessels, lymphatic vessels or nerves
* Nutrients are delivered by diffusion from synovial fluid

What is articular cartilage?

Load bearing cartilage found where bones come together to form joints

What are the functions of articular cartilage?

* distribute load over wider area to reduce contact stresses
* allow relative movement of 2 surfaces with minimal friction (AC on AC = one of lowest known frictionless surface frictions)

What is the friction coefficient of articular cartilage?

µ = 0.02

What are articular cartilage cells called?

Chondrocytes

What is the ECM?

Anything that is not cells

What makes up the ECM of AC?

* Type II collagen (15-20% by wet weight)
* Proteoglycans (4-7% by wet weight)
* Water (60-85% by wet weight)

What is sub-chondral bone?

The bone beneath articular cartilage

Draw diagram of AC in trabecular bone, highlighting the different zones

What are the 3 zones of AC?

* superficial - collagen fibres parallel to articulating surfaces, smooth surface, resistance on tension, low concentration of proteoglycans
* deep - collagen fibres are perpendicular to surface, this anchors AC to the sub-chondral bone, high concentration of proteoglycans
* middle - transitions collagen fibre orientation, medium concentration of proteoglycans

What is the core protein of proteoglycans?

Hyaluranon

What are the side chains of proteoglycans called?

Glycosaminoglycans (GAGs)

What are the 2 types of GAGs in proteoglycans?

* chondroitin sulphite
* keratin sulphite

What type of charge do sulphites have?

negative (SO₃−)

How is the ECM created by GAGs and collagen fibres?

The GAGs become entangled and entwined with the collagen fibres (-ve charges can’t move as they are fixed in place)

What is the amount of charge by unit volume called?

Fixed charge density (FCD)

Describe the Donnan Osmotic Pressure

Semipermeable membrane separates 2 solutions with different electrolytes - allows passage of water molecules but restricts movement of electrolytes. Donnan osmotic pressure important in AC for maintaining hydration and mechanical properties of tissue.

What % of stiffness do electrical effects account for?

\~ 60%, compression increases charge-charge repulsion forces

What % of stiffness do proteoglycans account for?

\~ 98% (PG volume = 38%)