Background/Purpose: The utility of bilateral hip dual energy x-ray absorptiometry scanning for identifying low bone mineral density has been a cause of debate.  Intraperson differences in density at the hip can affect categorization of a patient as osteoporotic.  Our study was designed to assess the correlation between sides of the hip in individual patients and to compare different sites of the hip for osteoporosis categorization. 

Methods: Bilateral hip measurement data on postmenopausal women over age 40 from a single facility scanned on a GELunar Prodigy or Prodigy Advance were retrospectively reviewed.  Data included patient demographics, bilateral scan BMD and T-score, presence of historical fragility fractures and data to determine clinical risk.

Results: Scans were evaluable for both proximal femurs in 12,741 women.  We found lower density values, reported as T-scores, on the right side of the hip at all regions of interest that were statistically significant.  Agreement in osteoporosis categorization between sides of the hip ranged by anatomic site from 82.7%-87.6%.  Mean values showed improved agreement (91.0%-93.5%) over the lowest obtained T-score at each hip site.  The total hip had the highest correlation in categorization and the closest association to previous fracture at each region of interest. Those categorized as osteoporotic by the mean value were as or more likely to have had a fracture than those with the lowest BMD.  Using logistic regression models the adjusted odds ratio for fracture was 3.00 in the osteoporosis category compared to normals.  Bilateral scanning effectively eliminated significant differences within an individual patient, but values were minimally divergent from unilateral measurements.

Conclusion: Our study demonstrates that, although there is a small difference between WHO classification of osteoporosis comparing the mean values of the hip to the lowest, the use of the mean value was as good as or better for predicting fractures as the lowest value.  This supports the use of bilateral hip scanning for diagnosis of osteoporosis and identifying individuals at risk for fractures.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-comparison-of-unilateral-and-bilateral-hip-bmd/