Whole Bone Modeling Using Bone Mineral data or Bones Are Not Amorphous blobs Thomas j. Beck, Sc D The Johns Hopkins university School of medicine
Whole Bone Modeling Using Bone Whole Bone Modeling Using Bone Mineral Data Mineral Data or Bones Are Not Amorphous Blobs Bones Are Not Amorphous Blobs Thomas J. Beck, Sc.D. Thomas J. Beck, Sc.D. The Johns Hopkins University The Johns Hopkins University School of Medicine School of Medicine
The Fundamental problem a Bones get less dense as we age d Old people with low density bones fracture easily a Space-flight rapidly causes bones to get less dense a Does space flight produce the same effects on bone as aging
The Fundamental problem The Fundamental problem Bones get less dense as we age Bones get less dense as we age Old people with low density bones Old people with low density bones fracture easily fracture easily Space -flight rapidly causes bones to flight rapidly causes bones to get less dense get less dense Does space flight produce the same Does space flight produce the same effects on bone as aging? effects on bone as aging?
The human Femur toona Head Bone loss causes L668 troche ntenrocnanmteric fragility of proximal (upper)end of femur Fractures are major cause of death(indirect) and Medial disability in elderly Patellar surface Adductor epicondyle ucon Concern that space-flight Vesa rainny might have similar Literal n consequences Ia) Anterior surface (b) Posterior surface
The Human Femur The Human Femur Bone loss causes Bone loss causes fragility of proximal fragility of proximal (upper) end of femur (upper) end of femur Fractures are major cause Fractures are major cause of death (indirect) and of death (indirect) and disability in elderly disability in elderly Concern that space Concern that space -flight might have similar might have similar consequences consequences
Bone dynamics a Bone is a dynamic tissue and is constantly being absorbed and rebuilt throughout life. a Because bones get less dense with age physicians interpret this as an imbalance between resorption and formation. a Old people with low density bones fracture easily so it is assumed that bone density is a measure of likelihood of fracture
Bone Dynamics Bone Dynamics Bone is a dynamic tissue and is constantly Bone is a dynamic tissue and is constantly being absorbed and rebuilt throughout life. being absorbed and rebuilt throughout life. Because bones get less dense with age Because bones get less dense with age physicians interpret this as an imbalance physicians interpret this as an imbalance between between resorption resorption and formation. and formation. Old people with low density bones fracture Old people with low density bones fracture easily so it is assumed that bone density is a easily so it is assumed that bone density is a measure of likelihood of fracture. measure of likelihood of fracture
Current bone Measurements DXA Scan Image of Hi Digital image with all soft tissues subtracted and only bone mineral present Pixel values represent areal mass in g/cm Areal mass is averaged over part of region containing bone (femoral neck region shown) Result approximates volumetric density and is called bone mineral density (BMD)
Current Bone “Density”Measurements Current Bone “Density”Measurements DXA Scan Image of Hip DXA Scan Image of Hip •Digital image with all soft tissues subtracted and only bone mineral present • Pixel values represent areal mass in g/cm2 •Areal mass is averaged over part of region containing bone (femoral neck region shown) •Result approximates volumetric density and is called bone mineral density (BMD)
Femoral Neck bmd 1.6 1.4 1.2 0.8 06 0.4 20 60 80 100 Age(Years)
Femoral Neck BMD Femoral Neck BMD 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 20 40 60 80 100 Age (Years) BMD (g/cm2 )
Looking at the details Why do bones get less dense as we age? a Does this necessarily mean that bones are getting weaker? a Why do astronauts lose bone Z Are their bones getting weaker? a What factors are common between aging and microgravity and how do they differ?
Looking at the details Looking at the details Why do bones get less dense as we age? Why do bones get less dense as we age? Does this necessarily mean that bones are Does this necessarily mean that bones are getting weaker? getting weaker? Why do astronauts lose bone? Why do astronauts lose bone? Are their bones getting weaker? Are their bones getting weaker? What factors are common between aging What factors are common between aging and microgravity microgravity and how do they differ? and how do they differ?
Reduced Bone Strength Is an Engineering Problem Possible reasons 1. The material is less able to withstand coaaing stresses Or 2. The structure is altered to increase loading stresses
Reduced Bone Strength Reduced Bone Strength is an Engineering Problem is an Engineering Problem Possible reasons: Possible reasons: 1. The material is less able to withstand 1. The material is less able to withstand loading stresses loading stresses Or 2. The structure is altered to increase loading 2. The structure is altered to increase loading stresses stresses
Structure vS, Material Properties a Evidence exists that bone material strength declines with age but effect disappears when corrected fo porosity No good evidence that space-flight influences material properties a (no reliable way to measure in vivo anyway) a Without question bone structure changes with age and as a result of space -flight
Structure vs. Material Properties Structure vs. Material Properties Evidence exists that bone material strength declines Evidence exists that bone material strength declines with age but effect disappears when corrected for with age but effect disappears when corrected for porosity porosity No good evidence that space No good evidence that space -flight influences flight influences material properties material properties (no reliable way to measure (no reliable way to measure in vivo in vivo anyway) anyway) Without question Without question bone structure changes with age bone structure changes with age and as a result of space and as a result of space -flight
An engineering perspective Long bones act as inefficient levers, with actions due to muscle forces Greatest mechanical stresses are in bending and torsion
An engineering perspective An engineering perspective Long bones act as inefficient levers, Long bones act as inefficient levers, with actions due to muscle forces with actions due to muscle forces Greatest mechanical stresses are in Greatest mechanical stresses are in bending and torsion bending and torsion
