How Accurately Does Bone Mineral Density Predict Bone Strength? A Clinical Observational Study of Osteoporosis Vertebral Compression Fractures in Postmenopausal Women

Abstract

Objectives: Dual energy x-ray absorptiometry (DXA) provides incomplete information about bone strength. There are few data on the relationship between osteoporosis-related examinations and bone strength. The objective of the present study was to determine which osteoporosis-related examinations best predicted trabecular bone strength, and to enhance a formula for predicting bone strength on the basis of bone density examination.

Methods: This observational study included postmenopausal women (aged over 50 years) who underwent unilateral percutaneous kyphoplasty (PKP) surgery in the lumbar spine between September 2021 and June 2023. The pressure within each balloon expansion circle was extracted to reflect the true bone strength. The NHANES 2013-2014 data were used to assess the performance of the formula. The performance of the formula was compared with that of the observed actual fractures. Bland-Altman analysis was used to compare the agreement between the formula and the fracture risk assessment tool (FRAX) score.

Results: A total of 40 postmenopausal women (mean age ± standard deviation, 70.90 years ± 10.30) were enrolled. The average balloon pressure was 59.23 psi (± 12.40, means ± SDs). The mean BMD of total lumbar spine (average of L1-L4) was 0.89 g/cm² ± 0.20 (mean ± standard), and the Pearson correlation coefficient between lumbar BMD and bone strength was 0.516. After adjusting for age and BMI, the DXA response rate to bone strength reached 72%. Calibration plots of the observed actual fractures versus those estimated via the bone strength formula were considered good fits. The Bland-Altman analysis revealed a nonsignificant difference between the formula and the FRAX score in predicting fracture risk.

Conclusions: After adjustment, the DXA response rate to bone strength reached 72%, indicating a strong correlation. In addition, Bone Strength = DXA × 27 - Age × 0.585-BMI × 0.887 + 98.

Keywords: balloon pressure; bone mineral density (BMD); bone strength; dual energy x‐ray absorptiometry (DXA); percutaneous kyphoplasty (PKP)surgery.

FIGURE 1

(A, B). Normal (grade 0) to mildly deformed (grade 1) (grade 0: Normal; grade 1: 20%–25% reduction in anterior, middle, and/or posterior height and a reduction of area 10%–20%) (C, D). Intraoperative fluoroscopy of unilateral PKP surgery following standard surgical procedures.

FIGURE 2

Study flow diagram.

FIGURE 3

Forest plot of included factors.

FIGURE 4

Calibration plots of the classification model for predicting high fracture risk.

FIGURE 5

The Bland–Altman analysis for comparing the predictive bone strength and FRAX score. Y‐axis represents (predictive estimated value by bone strength model) − (predictive estimated value by FRAX score). Blue line represents the mean difference, upper red dashed line shows the upper limit of agreement, and lower red dashed line shows the lower limit of agreement. SD, standard deviation.