Presentation on theme: "Bone Structure, Growth and Development"— Presentation transcript:
1 Bone Structure, Growth and Development Assignment:Read Ch 4 on bone growth and developmentReview stress-strain curves (pp 77-79)Homework (due Monday, February 21)Introductory problems 1,2, 3,8,10
2 ObjectivesExplain how material constituents and structural organization of bone affect its ability to withstand mechanical loads.Explain bone and other tissue loading modesExplain and interpret stress/strain curves as a descriptor of mechanical properties of boneDescribe the processes involved in the normal growth and maturation of bone.Describe the effects of exercise factors on bone mineral content.Explain the significance of osteoporosis and discuss current theories on its prevention.
3 Bone Structure and Integrity Architecture and dev -Microstructure of boneHow bones grow?Adaptability - Wolff’s lawMechanical properties of bonestress-strain relationshipstrength (density, mineral content, or BMC)elasticityenergy absorptionresistance to fatigueLoading modes -tension, compression, torsion, shear
4 Bone Gross Structure, Architecture and Development
8 Bone Composition & Structure Material Constituents:Calcium carbonate and Calcium phosphate60-70% bone weightAdds stiffnessPrimary determinant for compressive strength.CollagenAdds flexibilityGives bone tensile strengthWater25-30% bone weightContributes to bone strengthProvides transportation for nutrients and wastes.
9 Bone Composition & Structure Structural OrganizationBone mineralization ratio specific to boneTwo categories of porous bone:Cortical bone(70-95% mineral content)Trabecular bone (10-70% mineral content)More porous bones have:Less calcium phosphateMore calcium carbonateGreater proportion of non-mineralized tissue
10 Bone Composition & Structure Cortical BoneLow porosity5-30% bone volume is non-mineralized tissueWithstand greater stress but less strain before fracturing
11 Bone Composition & Structure Trabecular BoneHigh porosity30 - >90% bone volume is non-mineralized tissueTrabeculae filled with marrow and fatWithstand more strain (but less stress) before fracturing
12 Bone Composition & Structure Both cortical and trabecular bone are anisotropic, meaning the stress/strain response is directionalBone function determines structureStrongest at resisting compressive stressWeakest at resisting shear stress
13 Bone Growth & Development Longitudinal Growthat epiphyses or epiphyseal platesStops at 18 yrs of age (approx.)can be seen up to 25 yrs of ageCircumferential GrowthDiameter increases throughout lifespanMost rapid growth before adulthoodPeriosteum build-up in concentric layers
14 Bone Growth & Development OsteoblastsOsteoclastsAdult Bone DevelopmentBalance between oseoblast and osetoclast activityIncrease in age yields progressive decrease in collagen and increase in bone brittleness.Greater in women
15 Bone Growth & Development WomenPeak bone mineral content: yrs.0.5%-1.0% loss per year following age 50 or menopause6.5% loss per year post-menopause for first 5-8 years.Youth – bones are vulnerabe during peak growing yearsBone mineral density (BMD) is least during peak growing yearsGrowth plates are thickest during peak growing years
16 Bone Growth & Development AgingBone density loss as soon as early 20’sDecrease in mechanical properties and general toughness of boneIncreasing loss of bone substanceIncreasing porosityDisconnection and disintegration of trabeculae leads to weakness
23 Bone Response to Stress Wolf’s LawIndicates that bone strength increases and decreases as the functional forces on the bone increase and decrease.Bone Modeling and RemodelingMechanical loading causes strainBone ModelingIf Strain is greater than modeling threshold, then bone modeling occurs.
24 Bone Response to Stress Bone RemodelingIf Strain is less than lower remodeling threshold, then bone remodeling occurs.at bone that is close to marrow“conservation mode”: no change in bone mass“disuse mode”: net loss of bone massOsteocytes
25 Bone Response to Stress Bone mineral density generally parallels body weightBody weight provides most constant mechanical stressDetermined by stresses that produce strain on skeletonThink: weight gain or loss and its effect on bone density
26 Bone HypertrophyAn increase in bone mass due to predominance of osteoblast activity.Seen in response to regular physical activityEx: tennis players have muscular and bone hypertrophy in playing arm.The greater the habitual load, the more mineralization of the bone.Also relates to amount of impact of activity/sport
28 Bone AtrophyA decrease in bone mass resulting form a predominance of osteoclast activityAccomplished via remodelingDecreases in:Bone calciumBone weight and strengthSeen in bed-ridden patients, sedentary elderly, and astronauts
31 Osteoporosis Website on osteporosis: http://www.nof.org National Osteoporosis FoundationA disorder involving decreased bone mass and strength with one or more resulting fractures.Found in elderlyMostly in postmenopausal and elderly womenCauses more than 1/2 of fractures in women, and 1/3 in men.Begins as osteopenia
32 Osteoporosis Symptoms: Painful, deforming and debilitating crush fractures of vertebraeUsually of lumbar vertebrae from weight bearing activity, which leads to height lossEstimated 26% of women over 50 suffer from these fractures
33 Female Athlete Triad1) Eating Disorders affect 1-10% of all adolescent and college-age women.Displayed in 62% female athletesMostly in endurance or appearance-related sports2) Amenorrhea is the cessation of the menses.3) Osteoporosis is the decrease in bone mass and strength.
34 Position Statement of ACSM on Osteoporosis Weightbearing physical activity is essential for developing and maintaining a healthy skeletonStrength exercises may also be beneficial, particularly for non-weightbearing bonesAn increase in physical activity for sedentary women can prevent further inactivity-related bone loss and can even improve bone massExercise is not an adequate substitute for postmenopausal hormone replacementEx programs for older women should include activities for improving strength, flexibility, and coordination, to lessen the likelihood of falls
35 Osteoporosis Treatment Future use of pharmacologic agentsMay stimulate bone formationLow doses of growth factors to stimulate osteoblast recruitment and promote bone formation.Best Bet:Engaging in regular physical activityAvoiding the lifestyle (risk) factors that negatively affect bone mass.
37 Common Bone InjuriesBone stronger in resisting compression than tension, so the side loaded with tension will fracture first.Acute compression fractures (in absence of osteoporosis) is rareStress Fractures occur when there is no time for repair process (osteoblast activity)Begin as small disruption in continuity of outer layers of cortical bone (microtrauma) due to repetitive loading
38 Epiphyseal Injuries Include injuries to: Cartilaginous epiphyseal plateArticular cartilageApophysisEither acute or repetitive loading can injure growth plateLeads to premature closing of epiphyseal junction and termination of bone growth.
39 Epiphyseal Injuries Osteochondrosis Apophysitis Disruption of blood supply to epiphysesAssociated with tissue necrosis and potential deformation of the epiphyses.ApophysitisOsteochondrosis of the apophysisAssociated with traumatic avulsions.
40 SummaryBone is an important living tissue that is continuously being remodeled.Bone Strength and resistance to fracture depend on its material composition and organizational structure.Bones continue to change in density.Osteoporosis is extremely prevalent among post menopausal women.Osteoporosis can be prevented through lifestyle changes (including weight bearing and resistive exercise) and hormone replacement therapy