Bone Structure Explains Racial Variance in Fractures

PHILADELPHIA — Bone geometry appears to confer femoral strength to older black men and may account for some of the differences seen in fracture risk and bone mineral density between older black and white men, according to data presented at the annual meeting of the American Society for Bone and Mineral Research.

Dr. Marc C. Hochberg, professor of medicine and epidemiology at the University of Maryland, Baltimore, and his colleagues used hip structural analysis based on dual-energy x-ray absorptiometry (DXA) scan data to assess parameters of structural geometry of the proximal femur in older black and white men, in an attempt to account for reported differences in hip fracture and hip bone mineral density (BMD).

The researchers used data collected as part of the Baltimore Men's Osteoporosis Study, which recruited 503 white men and 191 black men aged 65 years and older. Black men were slightly heavier (mean weight 87 kg vs. 83 kg for white men) and slightly younger (mean age 72 years vs. 75 years for white men).

The researchers used hip structural analysis to calculate several measures of bone geometry, including the outer diameter, the bone cross-sectional area, the section modulus (an indicator of bending strength), the estimated mean cortical thickness, and the estimated buckling ratio (an estimate of cortical stability in buckling) from DXA hip scans.

Hip structural analysis is an investigational technique used to assess bone geometry in cross-sections of three regions of the proximal femur: across the femoral neck at its narrowest point, in the intertrochanteric region (along the angle bisecting neck and shaft axes), and across the shaft (at a distance of 1.5 times the minimum neck width distal to the axes of intersection).

The geometric parameters were compared between racial groups, using age, height, lean mass, and lean mass fraction as covariates.

BMD was greater for black men at the narrow neck, intertrochanteric, and shaft regions. “Black men had more bone tissue and the bone was narrower, so the tissue was enclosed in a smaller volume,” said Dr. Hochberg.

However, there was no difference in the calculated section modulus (a measure of resistance to axial bending) between white and black men at any of the three sites.

“Since there were no differences in femur bending resistance between the black and the white men, narrower bone, therefore, requires more bone tissue to achieve the same bending strength,” said Dr. Hochberg. Narrower bone with thicker cortices would have a lower buckling ratio and, therefore, higher buckling strength.

Cortical thickness was significantly greater in black men than in white men at all three sites. This did correlate to lower buckling ratios, providing greater protection against buckling failure.

Overall, black men had greater cross-sectional area, which reflects more bone mass. They also had a narrower outer diameter (reflecting smaller bone), thicker cortices, and lower buckling ratios, which reduce the risk of failure on bending at all three sites within the hip. “These geometric factors may explain the lower rate of hip fracture in older black men than in older white men,” said Dr. Hochberg.

PHILADELPHIA — Bone geometry appears to confer femoral strength to older black men and may account for some of the differences seen in fracture risk and bone mineral density between older black and white men, according to data presented at the annual meeting of the American Society for Bone and Mineral Research.

Dr. Marc C. Hochberg, professor of medicine and epidemiology at the University of Maryland, Baltimore, and his colleagues used hip structural analysis based on dual-energy x-ray absorptiometry (DXA) scan data to assess parameters of structural geometry of the proximal femur in older black and white men, in an attempt to account for reported differences in hip fracture and hip bone mineral density (BMD).

The researchers used data collected as part of the Baltimore Men's Osteoporosis Study, which recruited 503 white men and 191 black men aged 65 years and older. Black men were slightly heavier (mean weight 87 kg vs. 83 kg for white men) and slightly younger (mean age 72 years vs. 75 years for white men).

The researchers used hip structural analysis to calculate several measures of bone geometry, including the outer diameter, the bone cross-sectional area, the section modulus (an indicator of bending strength), the estimated mean cortical thickness, and the estimated buckling ratio (an estimate of cortical stability in buckling) from DXA hip scans.

Hip structural analysis is an investigational technique used to assess bone geometry in cross-sections of three regions of the proximal femur: across the femoral neck at its narrowest point, in the intertrochanteric region (along the angle bisecting neck and shaft axes), and across the shaft (at a distance of 1.5 times the minimum neck width distal to the axes of intersection).

The geometric parameters were compared between racial groups, using age, height, lean mass, and lean mass fraction as covariates.

BMD was greater for black men at the narrow neck, intertrochanteric, and shaft regions. “Black men had more bone tissue and the bone was narrower, so the tissue was enclosed in a smaller volume,” said Dr. Hochberg.

However, there was no difference in the calculated section modulus (a measure of resistance to axial bending) between white and black men at any of the three sites.

“Since there were no differences in femur bending resistance between the black and the white men, narrower bone, therefore, requires more bone tissue to achieve the same bending strength,” said Dr. Hochberg. Narrower bone with thicker cortices would have a lower buckling ratio and, therefore, higher buckling strength.

Cortical thickness was significantly greater in black men than in white men at all three sites. This did correlate to lower buckling ratios, providing greater protection against buckling failure.

Overall, black men had greater cross-sectional area, which reflects more bone mass. They also had a narrower outer diameter (reflecting smaller bone), thicker cortices, and lower buckling ratios, which reduce the risk of failure on bending at all three sites within the hip. “These geometric factors may explain the lower rate of hip fracture in older black men than in older white men,” said Dr. Hochberg.

PHILADELPHIA — Bone geometry appears to confer femoral strength to older black men and may account for some of the differences seen in fracture risk and bone mineral density between older black and white men, according to data presented at the annual meeting of the American Society for Bone and Mineral Research.

Dr. Marc C. Hochberg, professor of medicine and epidemiology at the University of Maryland, Baltimore, and his colleagues used hip structural analysis based on dual-energy x-ray absorptiometry (DXA) scan data to assess parameters of structural geometry of the proximal femur in older black and white men, in an attempt to account for reported differences in hip fracture and hip bone mineral density (BMD).

The researchers used data collected as part of the Baltimore Men's Osteoporosis Study, which recruited 503 white men and 191 black men aged 65 years and older. Black men were slightly heavier (mean weight 87 kg vs. 83 kg for white men) and slightly younger (mean age 72 years vs. 75 years for white men).

The researchers used hip structural analysis to calculate several measures of bone geometry, including the outer diameter, the bone cross-sectional area, the section modulus (an indicator of bending strength), the estimated mean cortical thickness, and the estimated buckling ratio (an estimate of cortical stability in buckling) from DXA hip scans.

Hip structural analysis is an investigational technique used to assess bone geometry in cross-sections of three regions of the proximal femur: across the femoral neck at its narrowest point, in the intertrochanteric region (along the angle bisecting neck and shaft axes), and across the shaft (at a distance of 1.5 times the minimum neck width distal to the axes of intersection).

The geometric parameters were compared between racial groups, using age, height, lean mass, and lean mass fraction as covariates.

BMD was greater for black men at the narrow neck, intertrochanteric, and shaft regions. “Black men had more bone tissue and the bone was narrower, so the tissue was enclosed in a smaller volume,” said Dr. Hochberg.

However, there was no difference in the calculated section modulus (a measure of resistance to axial bending) between white and black men at any of the three sites.

“Since there were no differences in femur bending resistance between the black and the white men, narrower bone, therefore, requires more bone tissue to achieve the same bending strength,” said Dr. Hochberg. Narrower bone with thicker cortices would have a lower buckling ratio and, therefore, higher buckling strength.

Cortical thickness was significantly greater in black men than in white men at all three sites. This did correlate to lower buckling ratios, providing greater protection against buckling failure.

Overall, black men had greater cross-sectional area, which reflects more bone mass. They also had a narrower outer diameter (reflecting smaller bone), thicker cortices, and lower buckling ratios, which reduce the risk of failure on bending at all three sites within the hip. “These geometric factors may explain the lower rate of hip fracture in older black men than in older white men,” said Dr. Hochberg.