Articular Cartilage & Bone

what kind of tissue is 60-85% water by weight

○ 10-30% Collagen

■ >90% Type II

○ 8-10% Proteoglycans (PG) (aggrecan)

Hyaline cartilage

in the Extracellular matrix of cartilage; which part includes elastin and other types of collagen (type II 90-95%) ?

Fibrillar

which zone of cartilage is 10-20% of surface

• Collagen (Type II) Fibers oriented parallel (tangential) to joint surface

• Decreases friction of opposing joint surface

• Distributes forces over the joint

• Low permeability

• Low PG content

ZONE 1: Tangential Zone of cartilage

which cartilage zone makes up 40-60% of cartilage surface

● Collagen Randomly oriented loosely coiled fibers (open meshwork)

○ Contains the interfibrillar PG and water content

● Absorbs compressive forces

● Higher number of PGs

ZONE 2: Transition Zone of cartilage

which zone of cartilage makes up 30-40% of surface

● Perpendicular: Radiate Stratum

○ Interface of uncalcified and calcified cartilage

● Fibers oriented more perpendicular to the surface

● Greatest amount of compression resistance

● Largest diameter collagen

● Highest proteoglycan content

● Lowest water concentration

ZONE 3: Radial zone of cartilage

which zone of cartilage has Calcified Cartilage; secures the cartilage to the bone

● Beginning of Bone

● Tide mark does not permit water to pass

ZONE 4 (sometimes referred to as fourth zone) of cartilage

during loading under compression

Causes fluid to flow out into the joint space through pores in Zone 1

what kind of tensile stress in Zone 1 is caused by PGs & H20 compression in collagen network

Hoop Stress

○ ↓ Permeability = ↑ Stiffness

what kind of tissue is 10-25% Water by weight

○ 10-30% Type I collagen

○ 65-70% Inorganic minerals

bone composition

in the Organic bone phase; collagen, accounts for

flexibility & tensile strength

in the Inorganic bone phase hydroxyapatite, accounts for

compressive strength

When bending bone there is

BOTH tension (pulling) & compression (pushing)

Cortical bone generally fails in

tension or shear

describing fracture site:

proximal, diaphyseal, distal

which phase is when Fracture accompanied by bleeding

● Blood vessels break in the periosteum and deeper within bone

● Blood clots form a hematoma

● Lots of blood = fast healing

Fracture healing: inflammatory phase

New blood vessels grow into a clot in a few days

● Proliferation of osteoblasts near fracture site

● A soft callous is formed & made of fibrocartilage and hyaline cartilage

○ Starts at the ends of the bone and grow towards each other and eventually bridge

Fracture Healing: REPARATIVE PHASE/Soft Boney Callus

Within a week, trabecular bone begins to form in the callus

● Trabeculae span the width of the callus and unite fragments of broken bone

○ Soft callous becomes ‘bony or hard’ callus aka Clinical union

○ Usually can begin loading

● Trabeculae grow thicker and stronger

○ Becomes firm 2 months post injury

Fracture Healing: Hard bony callous

Over a period of months bony callous is remodeled

● Excess bony material is removed

● Compact bone is laid down to reconstruct shaft walls

● The repaired area resembles the original unbroken bone region since it responds to the same mechanical stress

Fracture healing: BONE REMODELING