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Published on: January 29, 2018
The prevalence of significant left-right differences in hip bone mineral density
R Hamdy1, G M Kiebzak, E Seier
1Osteoporosis Center, College of Medicine, East Tennessee State University and VAMC, Johnson City, TN, USA.
Insights
Significant left-right differences in hip bone mineral density (BMD) are common in women over 50. Scanning only one hip can lead to different osteoporosis classifications, highlighting the importance of assessing both hips for accurate diagnosis and fracture prevention.
Area of Science:
- Orthopedics
- Radiology
- Gerontology
Background:
- Left-right differences in hip bone mineral density (BMD) are prevalent in postmenopausal women.
- Dual-energy x-ray absorptiometry (DXA) is a standard tool for assessing BMD.
Purpose of the Study:
- To determine the prevalence of left-right hip BMD differences.
- To assess the impact of these differences on osteoporosis classification when only one hip is measured.
Main Methods:
- Retrospective analysis of DXA scans from 3012 women aged 50+.
- Comparison of left and right hip BMD, considering the least significant change (LSC).
- Classification of osteoporosis based on T-scores from total hip, femoral neck, trochanter, and lumbar spine.
Main Results:
- Significant left-right BMD differences exceeding LSC were found in 47% (total hip), 31% (femoral neck), and 56% (trochanter) of women.
- Diagnostic agreement for hip pairs with BMD differences exceeding LSC was 77%, compared to 87% when LSC was not exceeded.
- A notable percentage of women were classified as osteoporotic in only one hip, with BMD differences exceeding LSC.
Conclusions:
- High prevalence of left-right hip BMD asymmetry can lead to misclassification of osteoporosis when only one hip is scanned.
- Scanning both hips may improve osteoporosis detection rates and contribute to hip fracture prevention strategies.
- Public health implications suggest routine bilateral hip assessment for comprehensive osteoporosis management.
Introduction:
We determined the prevalence of left-right differences in hip bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA) and the resultant consequence, namely: the frequency at which patients would be classified differently if lumbar spine and only one hip (rather than both hips) were measured.
Methods:
This was a retrospective DXA scan reanalysis of 3012 white women >or=50 yrs who had scans of both hips using Hologic DXA systems. The difference between left and right hips was considered significant if it exceeded the least significant change (LSC) for any of three hip subregions (total hip, femoral neck, trochanter). The number of women with osteoporosis in both hips, the left hip only, or the right hip only was determined by lowest T-score from total hip, femoral neck, or trochanter.
Results:
Despite high left-right correlations of subregion BMD, significant left-right differences in BMD were common: the difference exceeded the LSC for 47% of women at total hip, 31% at femoral neck, and 56% at trochanter. Left-right differences in BMD that exceeded the LSC affected the percent agreement of left-right hip classification: for all women irrespective of spine status, there was 77% classification (diagnostic) agreement in hip pairs in which the left-right hip BMD difference exceeded the LSC versus 87% agreement in which LSC was not exceeded (significant difference in proportions, P<0.0001). The greatest risk of different classification would occur in women with normal spines as the diagnosis might be determined by hip T-scores. Using L1-4 lumbar spine T-scores, 1229 women were normal at the spine. Twenty-four (2%) were osteoporotic at both hips. However, 12 women (1%) were osteoporotic only in the left hip (significantly different from zero, P<0.001) and 11 (1%) only in the right hip (P<0.001); of these 23 women, the difference in BMD between the osteoporotic hip and the contralateral hip exceeded the LSC in 16 (70% of those with osteoporosis in only one hip). Using L1-4 lumbar spine T-scores, 1159 women were osteopenic at the spine. Of these, 126 (11%) were osteoporotic at both hips, 54 (5%) only in the left hip (P<0.001), and 42 (4%) only in the right hip (P<0.001); of these 96 women, the difference in BMD between the osteoporotic hip and the contralateral hip exceeded the LSC in 56 (58% of those with osteoporosis in only one hip).
Conclusions:
A statistically significant number of women with osteoporosis are potentially classified differently when scanning only one hip as a result of the high prevalence of left-right differences in BMD. Although the percentages are low, the total number of women affected may be large. From a public health perspective, the practice of scanning both hips could potentially identify more women with osteoporosis and may help prevent future hip fractures.
