Models: You and your new work colleague decide to estimate the bending stiffness of bones in 85+ year old women and men by calculating the area moment of inertia for the diaphyseal shaft of an idealized long bone. You each decide to model it as a long hollow cylinder consisting of a cortical shell (outer bone diameter dob) surrounding a hollow intramedullary canal (with diameter dic). You estimate the cortical thickness as 7 mm for the model of the male bone. Your colleague assumes bone loss occurs at the outer bone surface (outer diameter) and therefore reduces the outer diameter 2 mm for the woman model. You assume the bone loss occurs at the inner cortical bone surface (inner diameter) and therefore increase the inner diameter 2 mm for the woman model. Colleague's model Your model 85 yo woman dob=32 mm dic=27mm dob = 34 mm dic =29mm 85yo man dob = 34 mm dic=27mm dic dob Intramedullary Canal Cortical Bone Figure 1: Assume a simplified bone modeled as a hollow cylinder of cortical bone only.

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Author:Sadiku, Matthew N. O.
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Changes in cortical bone density and bone geometry occur with aging in both men and women (Table 1 from Russo
2003). These changes manifest as decreased bone strength, which has the clinical impact of increasing the risk of fracture with increasing
age. However, elderly men are much less prone to fracture than elderly women. It has been suggested that age-related bone loss is the
consequence of endosteal bone resorption resulting in changes in bone geometry (~2mm less cortical bone thickness in women as they
age) and contributing to relative differences in fracture risk between men and women. Cortical bone area decreases in women between
the ages of 20 and 85, whereas there is no significant change in cortical bone area for men over the same age range (Table 1).
Table 1: Changes in bone density and cortical bone area - from Italian population of 612 men and 693 women
Age group (years)
ANOVA
20-39
Total bone density 4% (mg/cm³)
Men
Women
Cortical bone area 38% (mm²)
Men
318.9±47.9
Women 288.8 +41.2
342.344.9
307.134.8
40-49
Colleague's model
Your model
315.2 38.2
286.9±27.9
329.1±54.9
289.2 34.3
50-64
85 yo woman
dob = 32 mm
dic=27mm
dob = 34 mm
dic = 29mm
302.131.8
274.6±40.3
319.756.8
287.9 +53.5
85yo man
65-74
dob = 34 mm
dic=27mm
288.635.5
253.932.2
324.9±42.2
281.1+52.7
75-84
290.0+ 45.4
241.6±36.8
326.8+46.0
265.0+ 60.0
85+
Models: You and your new work colleague decide to estimate the bending stiffness of bones in 85+ year old women and men by
calculating the area moment of inertia for the diaphyseal shaft of an idealized long bone. You each decide to model it as a long hollow
cylinder consisting of a cortical shell (outer bone diameter dob) surrounding a hollow intramedullary canal (with diameter dic). You estimate
the cortical thickness as 7 mm for the model of the male bone. Your colleague assumes bone loss occurs at the outer bone surface (outer
diameter) and therefore reduces the outer diameter 2 mm for the woman model. You assume the bone loss occurs at the inner cortical
bone surface (inner diameter) and therefore increase the inner diameter 2 mm for the woman model.
284.845.1
229.233.1
332.751.2
230.2 72.4
p<0.0001
p<0.0001
dic
p=0.28
p<0.0001
dob
Intramedullary
Canal
Cortical Bone
Figure 1: Assume a simplified bone modeled
as a hollow cylinder of cortical bone only.
Q3 What is the percent difference of the moment of inertia between the 85 year old man and your colleague's 85 year old
woman model? What is the percent difference of the moment of inertia between the 85 year old man and your 85 year old
woman model?
Transcribed Image Text:Changes in cortical bone density and bone geometry occur with aging in both men and women (Table 1 from Russo 2003). These changes manifest as decreased bone strength, which has the clinical impact of increasing the risk of fracture with increasing age. However, elderly men are much less prone to fracture than elderly women. It has been suggested that age-related bone loss is the consequence of endosteal bone resorption resulting in changes in bone geometry (~2mm less cortical bone thickness in women as they age) and contributing to relative differences in fracture risk between men and women. Cortical bone area decreases in women between the ages of 20 and 85, whereas there is no significant change in cortical bone area for men over the same age range (Table 1). Table 1: Changes in bone density and cortical bone area - from Italian population of 612 men and 693 women Age group (years) ANOVA 20-39 Total bone density 4% (mg/cm³) Men Women Cortical bone area 38% (mm²) Men 318.9±47.9 Women 288.8 +41.2 342.344.9 307.134.8 40-49 Colleague's model Your model 315.2 38.2 286.9±27.9 329.1±54.9 289.2 34.3 50-64 85 yo woman dob = 32 mm dic=27mm dob = 34 mm dic = 29mm 302.131.8 274.6±40.3 319.756.8 287.9 +53.5 85yo man 65-74 dob = 34 mm dic=27mm 288.635.5 253.932.2 324.9±42.2 281.1+52.7 75-84 290.0+ 45.4 241.6±36.8 326.8+46.0 265.0+ 60.0 85+ Models: You and your new work colleague decide to estimate the bending stiffness of bones in 85+ year old women and men by calculating the area moment of inertia for the diaphyseal shaft of an idealized long bone. You each decide to model it as a long hollow cylinder consisting of a cortical shell (outer bone diameter dob) surrounding a hollow intramedullary canal (with diameter dic). You estimate the cortical thickness as 7 mm for the model of the male bone. Your colleague assumes bone loss occurs at the outer bone surface (outer diameter) and therefore reduces the outer diameter 2 mm for the woman model. You assume the bone loss occurs at the inner cortical bone surface (inner diameter) and therefore increase the inner diameter 2 mm for the woman model. 284.845.1 229.233.1 332.751.2 230.2 72.4 p<0.0001 p<0.0001 dic p=0.28 p<0.0001 dob Intramedullary Canal Cortical Bone Figure 1: Assume a simplified bone modeled as a hollow cylinder of cortical bone only. Q3 What is the percent difference of the moment of inertia between the 85 year old man and your colleague's 85 year old woman model? What is the percent difference of the moment of inertia between the 85 year old man and your 85 year old woman model?
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