bone ossification and fracture

  1. primary v. secondary fracture healing
    • primary: repair thru membrane of osteoprogenitor calls in periosteum - like intramembranous ossification
    • secondary: cartilaginous intermediate endochondral ossification
  2. secondary healing zones
    • 1) resting zone
    • 2) hypertrophic cartilage zone
    • 3) mineralized cartilage zone
    • 4) ossification zone
  3. secondary healing phases
    • inflammatory phase (48h): hemorrhage, vessel constriction, 2-5d hematoma (blood clot) seals site, necrotic bone, macrophages initiate and clean up
    • reparative phase (bone callus): 2nd wk-months, neovascularization, granulation tissue forms as pluripotent cells differentiate into fibroblasts, chondroblasts, osteoblasts
    • remodeling, osteoclasts remove matrix to form cartilage spicules, woven bone deposited, osteoblasts produce lamellar spicules
    • remodeling
  4. primary healing
    • takes place where there is rigid internal fixation (pins etc)
    • osteoprogenitor cells (periosteum) form membrane for bony spicule formation
  5. risk factors for delayed healing
    • delayed healing: 16-20wks
    • nonunion: 9mo+
    • smoking
    • infection/bone pathology
    • inadequate immobilization
    • malnutrition, alcoholism, drug abuse
    • NSAIDs during inflammatory phase
  6. bones w/ poor blood supply, likely to have problems healing
    • femoral neck
    • scaphoid
    • talus of foot
    • dens of axis (C2)
  7. fractures in children
    • periosteum is thicker, more vascularized
    • les underlying disease
    • unless it occurs @physis, likely to heal faster
    • physis = cartilage, weaker than bone, will break before ligaments will tear
  8. epiphyseal fractures Salter-Harris classification
    • type 1-5
    • 1 is where the physis comes off w/the metaphysis
    • 5 is a compression, most severe
  9. compound v/ comminuted
    • compound: breaks skin (eg GSW)
    • comminuted: more than 2 fracture segments
  10. diagnosis of hidden fracture
    • fat pad sign on xray
    • fat in joint aspirate
    • fat leaks out of marrow
  11. osteoid
    • ECM produced by osteoblasts
    • Fibers: type I collagen (90%), procollagen -procollagen peptidase-> tropocollagen-> collagen microfibrils-> collagen fiber
    • Ground substance: hyaluronan (GAG), proteoglycans (GAG+core protein aggrecan), adhesion glycoprotein molecules osteocalcin/osteonectin/osteopontin
  12. osteogenesis imperfecta
    • deficiency of collagen type I synth, aka "brittle bone disease"
    • Type I: normal life span, increased childhood fractures
    • Type II: fractures in utero, death shortly after birth
  13. mineralization
    hydroxyapatite crystals formed by minerals attaching to osteoid
  14. osteocytes
    • osteoblasts trapped in lacuna of rigid bone matrix
    • cell processes extend into canaliculi
  15. regulation of osteoclast activity
    • calcitonin (C cells of thyroid stroma): binds to osteoclast receptors to inhibit activity
    • parathyroid hormone (chief cells of parathyroid gland): stimulate osteoclasts to produce RANKL, which binds to RANK receptors on other osteoclasts and activates them
  16. bone resorption
    • plamsa membrane of osteoclasts = ruffled border, increases SA for absorption
    • resorption pit between ruffled border and Howship's lacuna on the bone
  17. cancellous bone
    • responds best to compression forces
    • lamellar bone, shaped like bony spicules
  18. cortical bone
    • responds best to torsional forces
    • lamellar bone in solid sheets
    • circumferential lamellae: on inside and outside surfaces
    • osteons: circles of lamellar bone, majority of bone, core is Haversian canal which is formed off of Volkmann's canals and lined w/endosteum
    • interstitial lamellae: connects osteons
  19. blood supply of long bones
    • periosteal arteries: along ligament or tendon insertions
    • nutrient artery: thru nutrient canal in diaphysis
    • epiphyseal and metaphyseal arteries: unite when growth plate closes
    • medullary vascular system: where nutrient artery and metaphyseal/epiphyseal arteries unite
  20. intramembranous ossification
    • takes place in a membrane of mesenchymal cells
    • clavicle, flat bones of skull, some facial bones
    • ossification centers w/osteoblasts producing woven bone spicules which are replaced w/lamellar bone
  21. endochondral ossification
    • primary ossification center forms in diaphysis of hyaline cartilage: chondrocytes hypertrophy, cartilage matrix becomes mineralized, chrondocytes die b/c fluid can't diffuse thru matrix
    • blood vessels invade and bring osteoprogenitor cells
    • collar of bone is formed
    • in long bones, a secondary ossification center @ the epiphysis will form
    • vertebra have multiple ossification centers
  22. achondroplasia
    • growth plate disease
    • reduced chondrocyte differentiation
    • very short arms and legs, normal otherwise
  23. Paget's disease
    • imbalance of remodeling process
    • often asymptomatic
  24. BMUs
    • basic multicellular units remodel the bone
    • osteoclasts tunnel in a cutting zone
    • remodel or replace 10% of bone annually
    • mechanical stress is needed for stimulation (can cause sclerosis)
    • cement line = where reversal of degradation occured
Card Set
bone ossification and fracture
healing of fractures, blk4 wk3