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Bone injury and repair Ch 4 Pt 1 - Coggle Diagram
Bone injury and repair Ch 4 Pt 1
Components of bone
cells: osteoblasts (initiate generation of new bone and cartilage) and osteoclasts (responsible for removal of the callus for lamellar bone to be laid down. Third type is osteocyte
Ground substance: calcium phosphate (makes bone hard and rigid, GAGs, hyaluronic acid
Fibrous components: collagen (helps to resist tensile stress), elastin (gives bone some resiliency
Effects of age on bone structure:
calcium related loss of mass and density
-osteoporosis disorder that decreases bone mineral content
-hormonal system regulating calcium metabolism is less efficient and responds poorly to the challenge of calcium incorporating process
-calcitonin (hormone responsible for decreasing serum levels) has decreased responsiveness to calcium challenge. This may account of slower fracture healing in geriatric patients
Older bones can withstand ~50% of strain that young people can
-less pliable
-less able to store energy
-more sedentary lifestyle of older adults may also account for these changes in bone health
Types of fractures
compound (open): sharp ends of broken bones protrude through skin or when some projectile penetrates skin into fracture site
closed: skin remains intact
depressed or fissured: sharply localized blow depresses area of cortical bone below that of surrounding bone (ie skull fracture)
greenstick: fracture on one side of bone but does not tear periosteum of opposite side (seen in children)
spiral: opposite rotatory forces pulling on bone (twisting)
oblique: fracture oriented at >/= 30 from axis of bone
transverse: oriented at right angle relative to axis of bone
avulsion: may be causes by sudden muscle contraction. muscle pulling off portion of bone to which it is attached. may also occur during traction to a ligament or capsular attachment
comminuted: multiple fracture segments
stress: fracture that results from stress repeated with excessive frequency to bone
pathologic: fractures that arise in abnormal or diseased bones> can occur in those with carcinoma, infection, and osteoporosis
stages of bone healing
First stage:
first aspect
-aka inflammatory, granulation, fracture or clot stage
-surviving cells sensitized to chemical messengers
-often completed within first 7 days
second aspect (lasts about 2 weeks)
-clot develops around fracture site (not stress fractures)
-granulation tissue forms in areas between fractures
-granulation activates macrophages which remove clot
second stage:
aka reparative/callous stage
soft callous phase: osteoblasts and chondrocytes synthesize cartilage and woven bone matrices in granulation
hard callous phase: begins ~1 week after soft callous phase. soft callous begins to mineralize (lasts several weeks)
-hard callus detectable on imaging
-creation and mineralization of callus can require 4-16 weeks
Third Stage:
-aka remodeling or consolidation phase
-callus is replaced by woven bone, which is in turn replaced by lamellar bone
-marrow cavity is restored
-replacement of callus with functionally competent lamellar bone can take 1-4 years
Conditions with negative effect on bone healing (chart pg 32)
technical factors:
-infection, poor reduction, distraction, repeated gross motion of fracture fragments, loss of local blood supply due to surgery and/or surgical procedure
Biological failures:
-vascular injury, failure to make or mineralize callus (metabolic abnormalities), formation of scar and fat tissue instead of callus, inability to replace woven bone with lamellar bone (ie osteogenesis imperfecta)
miscellaneous conditions:
-poor nutrition, alcohol abuse, smoking
effect of smoking:
-increased nonunions and dec callus formation in animal models given nicotine
-nicotine exposed bones significantly weaker in 3 point bending test compared to controls
-shown to delay revascularization and incorporation of bone grafts and inc pseudoarthrosis rate in spinal fusion patients
nicotine has shown direct inhibitory effects on bone cellular proliferation and function
-combined with vascular effects, decreases in quantity and maturity of fracture callus has been seen
-fracture risk is 2-6x higher in smokers
-damaged soft tissue and impaired nerve function can impede fracture healing by increasing metabolic demands on tissue repair system and limiting benefit of supportive muscle function around fracture sit
Nutrition:
-calcium plays important role in helping attain peak bone mass during bone development and preventing fractures later in life
-800mg/day is daily recommended allowance
-1500mg/day in post-menopausal and estrogen depleted women
-~75% of all women meet less than recommended amount
-men consume twice as much calcium at same age
bioactivity of calcium: effected by many factors
-high fat/fiber diets can decrease activity of calcium
-large doses of zinc or vitamin A can dec calcium bioactivity
-high protein diets can increase urinary excretion of calcium
alcohol can decrease absoption through sytotoxic effect on intestinal mucosa
-medications including glucocorticoids, heparin, and anticonvulsants can affect calcium activity
Vitamin D increases calcium absorption from intenstines and enhances parathyroid hormone stimulating reabsorption of bone
-intake of vitamin D alone has never been shown to improve fracture healing
Wolff's law: optimal stress on bone leads to greater bone deposition resulting in hypertrophy of periosteal bone and inc bone density