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 plates Irregular 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

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 

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 OrganicInorganic

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.  WSOl08 WSOl08

 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? Simple Fracture

What Type of Fracture? Spiral Fracture

 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 