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ch. 6 pt 4

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  • wolf's law

    states that bones grow or remodel in response to demands placed on them

    -bending compresses one side, stretches the other side

    -handedness-( right- or left-) results in thickers and stronger bone corresponding upper limb

    -trabeculae for trusses along lines of stress

  • mechanical stress causes remodeling when

    by producing electrical signals when bone is deformed

    -determines where it occurs

    -compressed and stretched regions are oppositely charged

    -compression/tension changes fluid flows within canaliculi, which may also stimulate remodeling

  • hormonal controls determine whether and when

    remodeling occurs in response to changing blood calcium levels

  • fracture classification

    -position of bone ends after fracture

    -completeness of break

    -whether skin is penetrated

    -described by location of fracture, external appearance, and nature of break

  • position of bone ends after fracture

    -nondisplaced: ends retain normal position

    -displaced: ends are out of normal alignment

  • completeness of break

    complete: broken all the way through

    incomplete: not broken all the way through

  • whether skin is penetrated

    open (compound): skin is penetrated

    closed (simple): skin is not penetrated

  • comminuted fracture

    3 or more pieces

  • compression fracture

    bone is crushed

  • spiral fracture

    twisting forces are applied to bone

  • epiphyseal fracture

    separates from the diaphysis along the epiphyseal line

  • depressed fracture

    bone is pressed inward

    -skull fracture

  • greenstick fracture

    bone breaks incompletely

    -common in kids

  • reduction

    realignment of bone

    -closed reduction: physician manipulates to correct position

    -open reduction: surgical pins or wires

    -immobilization: bone by cast

  • repair involves 4 major stages

    1. hematoma formation

    2. fibrocartilaginous callus formation

    3. bony callus formation

    4. bone remodeling

  • hematoma formation

    torn blood vessels hemmorrhage, forming mass of clotted blood

  • fibrocartliaginous callus formation

    -capillaries grown into hematoma

    -phagocytic cells clear debris

    -fibroblasts secrete collagen fibers

    -fibroblasts, cartilage and osteogenic cells begin reconstruction of bone (fibrocartilaginous callus)

  • bony callus formation

    within one week new trabeculae appear in fibrocartilaginous callus

    -callus is converted to bony callus of spongy bone

    -bony callus formation continues for about 2 months

  • bone remodeling

    -begins during bony callus formation and continues for several months

    -excess material on diaphysis exterior and within medullary cavity is removed

    -compact bone is lad down to reconstruct shaft walls

    -final structure resembles original structure

  • three main bone diseases

    -osteomalacia and rickets

    -osteoporosis

    -paget's disease

  • osteomalacia (adults) and rickets (children)

    -bones are poorly mineralized

    -osteoid is produced, but calcium salts not adequately deposited

    -soft, weak bones

    -results in bowed legs

    cause: vitamin D deficiency or insufficient dietary calcium

  • osteoporosis

    group of diseases in which bone resorption exceeds deposit

    -matrix is normal, bone mass declines

    -spongy bone and neck of femur most susceptible

    -postmenopausal women

    -insufficient exercise

    -smoking

    -genetics

    -hormone related

    -alcohol consumption

  • drugs for osteoporosis

    -bisphosphonates: decrease osteoclast activity and umber

    -denosumab:monoclonal antibody shown to reduce fractures in men with prostate cancer, improves bone density

  • Paget's Disease

    excessive and haphazard bone deposit and resorption cause bone to grow fast and develop poorly

    -very high ratio of spongy bone to compact bone and reduced mineralization

    -occurs in spine, pelvis, femur, skull

    -after age 40

    -cause: unknown

    -treatment: calcitonin and bisphosphonates