Abstract

Objective: This study evaluates whether bone assessment by radiofrequency echographic multi-spectrometry (REMS) is influenced by trabecular bone integrity compared to dual-energy X-ray absorptiometry (DXA) and the trabecular bone score (TBS). Additionally, we assess whether comparing fracture risk using FRAX and the National Osteoporosis Guideline Group (NOGG) using the T-score from each method results in differences within a Brazilian female population.

Subjects and Methods: A sample of women aged 30-80 underwent REMS and DXA scans of axial sites at Hospital São Paulo, Brazil. Subsequently, TBS was applied to DXA exams. Clinical data were collected through hospital records and phone interviews to calculate fracture risk.

Results: Among the 343 participants enrolled, 213 had comparable lumbar spine exams by REMS, DXA, and TBS, and 166 had comparable hip exams by REMS and DXA. The correlation between lumbar spine bone mineral density (BMD) by REMS and the TBS was low (r = 0.27, p < 0.001), as was the correlation between DXA and TBS (r = 0.39, p < 0.001). No significant differences were observed between the TBS classifications of osteoporotic lumbar spine by REMS and DXA (p = 0.178). Fracture risk data from FRAX showed 92% concordance in NOGG classifications for major osteoporotic fracture risk and 87% for hip fracture risk.

Conclusion: REMS performed similarly to DXA in assessing trabecular integrity using TBS. Additionally, no significant difference was observed in fracture risk assessment by FRAX based on NOGG recommendations.

Introduction

Osteoporosis, a disease characterized by decreased bone density and deteriorating bone microarchitecture, significantly increases fracture risk, especially in postmenopausal women. The World Health Organization (WHO) defines osteoporosis based on bone mineral density (BMD) measurements via DXA, with values 2.5 standard deviations below the mean BMD of a young, healthy population. While DXA remains the gold standard for diagnosing osteoporosis, it has limitations, such as its reliance on bone size and potential overestimation of BMD due to degenerative changes in the bone.

Radiofrequency Echographic Multi-Spectrometry (REMS) offers an alternative approach, using ultrasound to assess bone quality. Unlike DXA, which uses X-ray technology, REMS does not involve ionizing radiation, offering a safer, non-invasive method for bone health monitoring. This study aims to assess the effectiveness of REMS in evaluating trabecular bone quality, a crucial component of bone strength, and compare its results with those of DXA and TBS in a cohort of Brazilian women.

TBS, an index derived from DXA images, provides additional information about bone microarchitecture, which is not captured by BMD alone. Together, REMS, DXA, and TBS offer a comprehensive understanding of bone health, which could improve fracture risk prediction. This study also compares fracture risk assessment using the FRAX tool and the National Osteoporosis Guideline Group (NOGG) classifications.

Subjects and Methods

Study Population

The study adhered to the principles of the Declaration of Helsinki and was approved by the Scientific Committee and Research Ethical Commission of the Universidade Federal de São Paulo. A cohort of 343 women aged 30 to 80 years was recruited from the DXA Unit at Hospital São Paulo. Exclusion criteria included women with a BMI greater than 40 kg/m², those under 40 years of age, pregnant women, and individuals who were unable to position themselves correctly for the scans.

The final cohort consisted of 213 participants who completed both lumbar spine and hip scans using both REMS and DXA. Additional demographic and clinical information was gathered, including data on menopausal status, comorbidities, medication usage, and history of prior fractures.

Data Collection

Anthropometric measurements, including weight, height, and BMI, were recorded for all participants. Medical and clinical data were obtained through hospital records and phone interviews. TBS was calculated for DXA lumbar spine images using the TBS iNsight software. Bone mineral density measurements were recorded for both the lumbar spine and femoral neck.

Results

A cohort of 343 female participants was initially recruited for this study, with the final analysis including 213 participants who had comparable lumbar spine exams between REMS, DXA, and TBS, and 166 participants who had comparable hip exams between REMS and DXA. Several exams were excluded due to insufficient quality (e.g., positioning errors, acquisition problems, and analysis issues) as shown in Figure 1. The detailed breakdown of exclusions and re-inclusions for both lumbar spine and hip exams is provided.

Among the 343 recruited women (aged 30-80 years), the exclusions and re-inclusions occurred as follows:

• DXA Exclusions:
  • Lumbar spine: 41 exclusions (due to positioning issues, acquisition errors, and moderate scoliosis)
  • Hip: 30 exclusions (due to positioning, identification, and analysis errors)
• REMS Exclusions:
  • Lumbar spine: 67 exclusions (due to focus, depth, and vertebrae positioning errors)
  • Hip: 63 exclusions (due to focus, depth, and femoral neck positioning errors)

Following the exclusions and corrections, 213 participants had valid lumbar spine exams using all three methods (REMS, DXA, and TBS), and 166 participants had valid hip exams between REMS and DXA.

Flowchart demonstrating the selection of exams for the final analyses from the initial sample, with the reasons for exclusion for both methods.

Table 1: Baseline Characteristics of Participants

Baseline Characteristics : The baseline characteristics of the 213 participants with complete lumbar spine exams are presented in Table 1. The mean age of participants was 59.3 ± 8.6 years, with a BMI of 27.2 ± 4.3 kg/m². Most participants were post-menopausal (89.7%), and the cohort had a variety of comorbid conditions, including rheumatoid arthritis (1.4%), type 2 diabetes (13.1%), and use of antiresorptive agents (17.4%).

Bone Mineral Density (BMD) and Trabecular Bone Score (TBS) The correlation between BMD by REMS (BMDUS) and BMD by DXA (BMDDXA) in the lumbar spine was strong (r = 0.74, p < 0.001). However, when compared with TBS, both REMS and DXA showed poor correlations. For REMS, the correlation with TBS was r = 0.27 (p < 0.001), and for DXA, the correlation with TBS was r = 0.39 (p < 0.001). This suggests that while both REMS and DXA provide similar BMD readings, they do not correlate strongly with TBS, which assesses bone microarchitecture.

In further analysis, both methods showed a weak correlation between BMDUS and TBS, consistent with findings from other studies that show low to moderate correlation between BMDDXA and TBS.

TBS Classification of Osteoporotic Lumbar Spine Among the 54 lumbar spine exams classified as osteoporotic by REMS, the TBS distribution was as follows:

• 44.4% were classified as degraded
• 35.2% as partially degraded
• 20.4% as normal

In comparison, DXA classified 49 exams as osteoporotic, with the following TBS distribution:

• 57.1% as degraded
• 34.7% as partially degraded
• 8.2% as normal

The distribution of TBS classifications between REMS and DXA for osteoporotic lumbar spine exams was not statistically significant (p = 0.178). This suggests that despite differences in BMD classification by REMS and DXA, the TBS scores were similar between the two methods. This information is depicted in Figure 3.

Fracture Risk Assessment Complete data for calculating fracture risk using FRAX was available for 119 participants, of whom 13 (10.9%) had a prior fragility fracture. These fractures included vertebral fractures (n = 4) and peripheral fractures (n = 9). Participants with prior fractures had significantly lower BMD at both the femoral neck (p = 0.018) and total hip (p = 0.007) by DXA, as well as BMDUS at the total hip (p = 0.043) and TBS (p = 0.035) compared to participants without fractures.

Despite these differences, the fracture risk classifications between REMS and DXA for major osteoporotic fracture risk showed a high degree of agreement, with 92% concordance (κ = 0.71, CI 95%: 0.54 to 0.89), and 87% concordance for hip fracture risk (κ = 0.58, CI 95%: 0.38 to 0.77), indicating no statistically significant difference between the methods.

Correlation Between REMS, DXA, and TBS

The correlation between BMD measurements obtained by REMS and DXA at the lumbar spine was strong (r = 0.74, p < 0.001). However, the correlation between BMD and TBS was weak, with REMS showing r = 0.27 (p < 0.001) and DXA showing r = 0.39 (p < 0.001), suggesting that while BMD measurements are similar, the TBS index provides independent information regarding bone quality.

TBS Classification of Osteoporotic Lumbar Spine

The TBS classifications of osteoporotic lumbar spine by REMS and DXA were compared, showing no significant differences. Of the 54 exams classified as osteoporotic by REMS, 44.4% were classified as degraded by TBS, while 57.1% of the 49 osteoporotic exams by DXA were also classified as degraded.

Correlation between lumbar spine BMDUS and TBS in the different TBS categories. TBS = trabecular bone score; BMDUS = bone mineral density by REMS.

Distribution of TBS classifications among the lumbar spine exams classified as osteoporotic by REMS and DXA.

Discussion

The findings of this study suggest that REMS is comparable to DXA in assessing trabecular bone integrity using TBS. Both methods showed a similar ability to classify individuals based on major osteoporotic fracture risk, with 92% concordance in the NOGG classifications. While the correlation between BMD and TBS was weak, the distribution of TBS classifications was similar for both REMS and DXA, highlighting the potential value of TBS as an independent predictor of bone quality.

REMS provides several advantages over DXA, including the lack of ionizing radiation, portability, and reduced cost. It can serve as a useful diagnostic tool in regions with limited access to DXA, where its availability may be restricted due to infrastructure costs. Additionally, REMS could be particularly beneficial for patients who require frequent monitoring of bone health, as it can be performed more safely and without the concerns associated with repeated radiation exposure.

The study also revealed that the fracture risk assessment through FRAX using the TBS from both REMS and DXA was highly concordant, indicating that both methods can reliably predict the risk of fractures, particularly major osteoporotic fractures and hip fractures.

Conclusion

In conclusion, REMS is a promising and reliable alternative to DXA for diagnosing osteoporosis and assessing fracture risk. While the correlation between BMD and TBS is weak, the use of TBS remains an important tool in evaluating bone quality. The results of this study suggest that REMS could provide a non-invasive, portable, and cost-effective method for osteoporosis diagnosis and fracture risk stratification. Further studies are needed to explore the broader clinical applications of REMS, particularly in low-resource settings, and to evaluate its long-term effectiveness in predicting fractures.