BONE GROWTH & REPAIR

Classification of Bone (by shape)Long Bones Elongated shaft with expanded ends Bones in limbs (except patella, wrist,

ankle) + clavicle Miniature long bones: phalanges,

metacarpals, metatarsals

Short Bones Equal sides, cube-shaped Carpals, tarsals, patella

Classification of Bone (by shape)Flat Bones Flat or “plate-like,” may be curved

Typically form boundaries of body cavities Scapula, ribs, sternum, cranial platesIrregular Bones Odd shaped bones, typically joins other

bones together Vertebra, coxa, calcaneus, mandible

Subcategory: Pneumatic bones – skull bones with cavities (sphenoid, ethmoid, maxilla)

Bone Development

Bone Development

Osteogenesis (Ossification)

The process of bone tissue formation Embryos: The

formation of a bony skeleton

Children: Bone growth

Adults: Bone remodeling & repair

Intramembranous Ossification Prior to ossification, structures exist as

fibrous membranes made of embryonic connective tissue known as mesenchyme.

Formation of skull, pelvic & pectoral girdles Skull (frontal, parietal, temporal, and occipital

bones) Facial bones Clavicles Pelvis Scapulae

Intramembranous Ossification

Endochondral Ossification

Begins with the formation of a hyaline cartilage model which will later be replaced by bone. Most bones in the body develop via this

model. More complicated than intramembranous

because the hyaline cartilage must be broken down as ossification proceeds.

Epiphyseal plate remains during adolescence to facilitate continued bone growth.

Bones & Blood

At birth medullary cavities contain red marrow

About half is replaced with yellow marrow starting around age of 5

Found in flat bones and epiphysis of long bones

https://www.youtube.com/watch?v=NM8zQLJ1ipQ

Infantile Skull

At birth an infants skull is not completely formed Allows skull to compress and change shape Intramembranous regions are known as

fontanels

Composition of Bone

Cells (osteocytes) Osteoblasts Osteoclasts

Extracellular Matrix (35%) Collagen fibers

Mineral Salts (65%) Ca, K, P, Na, S,

Mg, Cu Ions released into

blood when needed

Organic Inorganic

Structure of Bone

Osteons - multiple cylindrical structural units Function as

weight-bearing pillars.

Resists 25,000 psi of compression

Osteons

Each osteon consists of:

A single central canal

Concentric layers of calcified bone matrix (lamellae). Central canals

allow the passage of blood vessels, lymphatic vessels, and nerve fibers.

Interstitial Lamellae

Interstitial lamellae

Incomplete lamellae lying in between intact osteons. These fill the

gaps between osteons or are remnants of bone remodeling.

Bone Cells

Osteoblasts Create bone – secrete components of bone

matrix Osteoclasts

Dissolve bone Concentrated in the endosteum

Osteocytes Osteoblasts trapped in bone matrix Maintain bone tissue

Bone Growth

Epiphyseal cartilage (close to the epiphysis) of the epiphyseal plate divides to create more cartilage

The diaphyseal cartilage (close to the diaphysis) of the epiphyseal plate is replaced with bony tissue.

A remnant (epiphyseal line) is visible on X-rays (do you see them in the adjacent femur, tibia, and fibula?)

Bone Remodeling

Bone is a dynamic tissue. What does that

mean? Wolff’s law holds

that bone will grow or remodel in response to the forces or demands placed on it. Examine this with the bone on the left.

http://www.youtube.com/watch?v=78RBpWSOl08

Why might you suspect someone whose been a power lifter for 15 years to have heavy, massive bones, especially at the point of muscle insertion?

Astronauts tend to experience bone atrophy after they’re in space for an extended period of time. Why?

Fractures

Bone can crack or even break Extreme loads Sudden impacts Stresses from unusual

directions Healing of a fracture

depends on whether or not, the blood supply and cellular components of the periosteum and endosteum survive.

Fracture Repair

1.Blood vessels burst and form a hematoma.

Cells die due to lack of nutrition

Macrophages remove dead and damaged tissue.

2. A fibrocartilaginous callus forms to splint the broken bone.

Fibroblasts create collagen, chondroblasts create cartillage, and osteoblasts create spongy tissue to fill the break

Fracture Repair

3. Bony callus forms from the fibrocartilaginous callus

6-8 weeks

4. Over several months the bony callus is remodeled.• Osteoclasts work to

remove the temporary supportive structures while osteoblasts rebuild the compact bone and reconstruct the bone so it returns to its original shape/structure.

Simple Fracture

A break that does not break the skin. Simple fracture of the radius and

ulna

Compound Fracture

Breaks the skin and is open to infection

Compound fracture of the humerous

Spiral Fracture

A twisting motion breaks the bone at an angle

Spiral fracture of the femur

Greenstick Fracture

Incomplete break of the bone (like a young tree branch) Common in young children

What Type of Fracture?

SimpleFracture

What Type of Fracture?

SpiralFractur

e

Spiral fracture after surgery. You can see the pins that were placed through the bone.

What Type of Fracture?

Compound fracture of the tibia and fibula

http://trumbore.com/leg/