Abstract

Purpose:
Radiofrequency echographic multi-spectrometry (REMS) is an ultrasound technology currently utilized for the densitometric evaluation of osteoporosis and has been validated against dual-energy X-ray absorptiometry. However, its use for bone densitometry in patients with severe motor and intellectual disabilities (SMID) has not been extensively reported. This study aimed to evaluate the feasibility of using REMS technology for assessing osteoporosis in SMID patients, specifically those with hip dislocation and severe scoliosis.

Methods:
Sixty-five patients with SMID, residing in a long-term care facility, underwent REMS scans of their femoral neck and/or lumbar spine. Data on anthropometric parameters, bone mineral density (BMD), clinical diagnostic classification, physical ability, presence of scoliosis and hip dislocation, and radiographs of the hip joints were collected. The participants were comprehensively assessed to ensure a thorough understanding of their physical condition.

Results:
The study involved 29 men and 34 women with a mean age of 52.6 years. Successful scanning was achieved for 82.5% of participants at the femoral neck and 95.2% at the lumbar spine. The BMD measurements obtained using REMS showed low values, with the mean BMD, T-score, and Z-score recorded at the femoral neck being 0.67 g/cm², -2.39 SD, and -1.38 SD, respectively, and at the lumbar spine 0.66 g/cm², -2.70 SD, and -1.87 SD. The average Cobb angle of the lumbar spine was 34.0°. Dislocation rates were not significantly different between those with and without successful BMD measurements. A significant correlation was observed between lumbar and femoral neck BMD T-scores.

Conclusion:
All patients with SMID were able to undergo successful BMD measurements at either the spinal or femoral neck regions, with 77.7% of patients completing measurements at both sites. The results indicate that REMS is an effective tool for assessing bone mineral density in patients with SMID, especially those residing in long-term care institutions. This technology holds promise for enhancing osteoporosis management in this vulnerable population.

Introduction

Osteoporosis is a metabolic bone disorder characterized by the loss of bone mass and alterations in the structure of skeletal tissues, leading to fragility fractures—fractures that occur from minimal trauma. This condition can be primary, due to age-related changes such as menopause in women, or secondary, arising from factors like cancer, metabolic diseases, and immobility. Osteoporosis is diagnosed through the measurement of bone mineral density (BMD), which is typically evaluated using dual-energy X-ray absorptiometry (DXA), the clinical reference standard. DXA measures X-ray attenuation through tissues to calculate BMD, which is then compared to a reference population’s T-score. However, DXA may present inaccuracies in specific conditions, such as in patients with scoliosis or certain types of femoral rotation, which may lead to false elevations in BMD readings.

Challenges in SMID Patients:

Patients with Severe Motor and Intellectual Disabilities (SMID) often face extreme physical limitations due to their sedentary or bedridden state and reduced intelligence quotient (IQ ≤35). This group experiences severe osteoporosis, which is compounded by immobility, nutritional disorders, and muscle tone impairment. These patients often reside in institutions where regular visits for DXA scans are not feasible. Additionally, the presence of severe scoliosis, hip dislocations, and limited range of motion further complicates BMD measurement using DXA. Given that fragility fractures are common in SMID patients, the need for a reliable method to measure BMD is critical for effective osteoporosis management.

REMS Technology:

Radiofrequency echographic multi-spectrometry (REMS) is a non-ionizing ultrasound technology developed to assess bone quantity and quality. Unlike DXA, which uses X-rays, REMS utilizes an analysis of the backscatter of ultrasound signals to determine BMD. The results are then compared to a proprietary reference database of spectral models, which allows the calculation of T-scores and Z-scores specific to the patient. REMS has been validated in various clinical studies and shown to correlate highly with DXA results, offering a reliable alternative for BMD measurement, particularly in challenging cases like those involving severe scoliosis or femoral rotation. The technology has demonstrated excellent sensitivity, specificity, and predictive value for identifying osteoporosis, making it a promising method for evaluating bone health in SMID patients, where traditional DXA might not be applicable.

Objective of the Study:

The study aimed to investigate the feasibility of using REMS to measure BMD in the spine and femoral neck of SMID patients, particularly those with complex bone morphology like scoliosis and hip dislocations. By establishing REMS as a viable method for BMD measurement in this population, the research hopes to improve osteoporosis diagnosis and treatment planning, ultimately contributing to better bone health management for patients with severe motor and intellectual disabilities.

Materials and Methods

Patients and Measurements:

This study was a single-center, cross-sectional, observational investigation conducted at Akitsu Ryoikuen, a facility in Tokyo, Japan, which provides long-term care for patients with Severe Motor and Intellectual Disabilities (SMID). The facility offers comprehensive medical and rehabilitation services tailored to the needs of patients with SMID. The inclusion criteria for participation were as follows: patients must have been enrolled at Akitsu Ryoikuen, be aged 20 years or older, and provide written informed consent, either personally or through their families. Exclusion criteria included patients who were unable to provide signed informed consent.

The study took place between May 2023 and December 2023, during which patients underwent bone mineral density (BMD) measurements using Radiofrequency Echographic Multi-Spectrometry (REMS) on their spine and femoral neck. In addition to BMD measurements, anthropometric parameters such as height and weight were recorded, and clinical diagnostic classifications, physical ability, and the presence of scoliosis and hip dislocation were assessed. Frontal radiographs of both hip joints were also obtained for further evaluation.

At the facility, the progression of scoliosis and hip joint dislocations in patients is studied every two years using longitudinal and bilateral frontal radiographs of the hip joints. Radiographs obtained within the past two years were utilized to assess the presence of scoliosis and hip dislocation. The Cobb angle, which measures the curvature of the spine, was used to assess scoliosis. In patients without scoliosis, the Cobb angle was set at 0°.

For REMS measurements, a stable supine position with a cushion was used to accommodate patients with a flexed or twisted trunk due to severe spasticity, which often limits the ability to position patients properly for imaging. Femoral imaging was conducted in cases of hip contracture or dislocation, with the non-dislocated hip being prioritized for imaging in cases of unilateral dislocation. In patients with bilateral high hip dislocation, imaging was performed on both sides.

REMS scans of the lumbar spine and proximal femur were performed using the EchoStation echographic device (Echolight Spa, Lecce, Italy). The scanning process involved moving the convex probe transabdominally along the L1–L4 vertebrae for the lumbar spine, and positioning the probe parallel to the femoral head-neck axis for the femoral neck. Each scan involved adjusting the transducer focus and scan depth to visualize the target bone interface. Automatic data processing for the REMS measurements was performed as per established guidelines.

The study variables included age, sex, height, weight, the presence of hip dislocation, Cobb angle for scoliosis assessment, and the success rate of REMS measurements at the femoral neck. Additionally, BMD, T-scores, and Z-scores were obtained from REMS scans of the femoral neck and lumbar spine.

Statistical Analyses:

Patients were divided into two groups: those with and those without successful BMD measurements at the femoral neck. Age, sex, height, weight, and the presence of hip dislocation were compared between the groups. Continuous variables such as age and Cobb angle were analyzed using the Mann–Whitney U test, while categorical variables were examined using Fisher’s exact test to assess associations with successful REMS measurements. Pearson’s correlation coefficients were calculated to determine the relationship between T-scores of the lumbar spine and femoral neck. The significance level was set at p < 0.05, and statistical analyses were conducted using Bell Curve for Excel 2016.

A priori power analysis was conducted using G*Power software, which determined that a sample size of 50 participants was required to achieve a statistical power of 0.80. A post-hoc power analysis indicated that the actual sample size of 63 provided a statistical power of 0.99, ensuring the study’s ability to detect significant differences.

Ethics:

The study was approved by the Research Ethics Committee of Tokyo Medical and Dental University (approval number: M2022–021, August 1, 2023) and was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent to participate in the study was obtained from the participants or their parents or guardians in cases where the participants were unable to provide consent themselves.

Results

Table 1: Characteristics of the Patients

The study was conducted at the Akitsu Ryoikuen facility, which houses 175 adult residents with Severe Motor and Intellectual Disabilities (SMID). A total of 63 patients, consisting of 29 men and 34 women, were recruited for this study, with an average age of 52.6 years (range: 22-77). The clinical diagnostic classifications of the participants included cerebral palsy (46 patients), developmental disorders (10), encephalopathy (5), and genetic abnormalities (2). In terms of physical ability, 10 patients could walk with assistance, 18 could sit independently, and 34 were bedridden. Patients who required walking assistance were classified as “SMID peripherals” but were included in the study.

Among the 63 patients, 15 had a history of fragility fractures, though none had multiple fractures. Bone mineral density (BMD) measurements of the lumbar spine were successful in 60 patients (95.2%) and unsuccessful in 3 patients (4.8%). For femoral neck measurements, BMD was successfully measured in 52 patients (82.5%) and unsuccessfully in 11 patients (17.5%). In every patient, BMD could be measured at least at one of the two sites.

Table 1 presents the characteristics of the patients based on the success of BMD measurements at the lumbar spine and femoral neck. The average age did not differ significantly between those with successful and unsuccessful BMD measurements. The mean Cobb angle of the patients was 34.0°, with a range from 0° to 122°. No significant difference in Cobb angle was observed between patients with successful and unsuccessful lumbar spine measurements, although the Cobb angle for those with unsuccessful femoral neck measurements was slightly lower at 28.3°.

Regarding hip dislocation, 19 patients (29.2%) had hip subluxation or dislocation, and 13 of these had successful lumbar BMD measurements, while 6 had unsuccessful femoral BMD measurements. A Fisher’s exact test revealed no statistically significant difference in the presence of hip dislocation between the two groups.

Bone Mineral Density (BMD) Results:

The average BMD for the lumbar spine was 0.67 g/cm² (range: 0.53–0.87), with a corresponding T-score of -2.70 SD and Z-score of 1.87. For the femoral neck, the average BMD was 0.66 g/cm² (range: 0.61–0.83), with a T-score of -2.39 SD and Z-score of 1.38. According to the World Health Organization’s criteria for osteoporosis, a T-score of ≤ -2.5 SD indicates osteoporosis. Approximately 65% of the patients had a lumbar spine T-score ≤ -2.5 SD, and 55.8% had a femoral neck T-score ≤ -2.5 SD.

There was a significant positive correlation between the T-scores of the lumbar spine and femoral neck (r = 0.530, p < 0.001). This suggests that lower BMD measurements at one site are generally associated with lower measurements at the other site.

Statistical Analysis:

The study used the Mann-Whitney U test for continuous variables and Fisher’s exact test for categorical variables. Pearson’s correlation coefficient was used to examine the relationship between T-scores for the lumbar spine and femoral neck. The results showed that there were no significant differences in age, height, or weight between patients with successful and unsuccessful BMD measurements. Additionally, the presence of hip dislocation did not significantly affect the success rate of BMD measurements at either site.

In summary, the majority of patients with SMID in this study demonstrated low BMD values, indicating a high prevalence of osteoporosis, especially at the lumbar spine. The correlation between lumbar spine and femoral neck T-scores suggests that both regions can provide consistent information about bone health in this patient population.

Representative radiographs of patients with severe motor and intellectual disabilities.

(a) Cobb angle of 96° with bilateral hip dislocation.
(b) Gas retention observed in the abdomen, which occasionally impedes bone visualization during REMS scanning.

Discussion

In this study, REMS (Radiofrequency Echographic Multi-Spectrometry) was successfully utilized to measure bone mineral density (BMD) in institutionalized patients with Severe Motor and Intellectual Disabilities (SMID). Notably, BMD measurement in the lumbar spine was achieved in 95.2% of the patients, despite an average Cobb angle deformation of 34.2°. Importantly, the severity of scoliosis, as indicated by the Cobb angle, did not significantly impact the success of the lumbar spine BMD measurement. Remarkably, even in patients with severe scoliosis (with Cobb angles up to 122°), BMD measurement was successfully performed. This suggests that the success of BMD measurement using REMS was not influenced by the degree of spinal deformity. Gas retention, commonly observed in the abdomen of patients with SMID, occasionally obstructed bone identification during REMS scanning. In these cases, gentle pressure applied to the abdomen helped displace the gas temporarily, allowing better bone visualization.

REMS was also used to measure BMD at the femoral neck, with a success rate of 82.5%. Among these patients, 25% had hip dislocation, but the success of BMD measurement was not significantly associated with the presence of hip dislocation. A detailed examination revealed that hip flexion contractures, often present in patients with SMID, may hinder femoral neck imaging. In patients with dislocated hips, the femoral head was often externally rotated and dislocated posteriorly, requiring careful manipulation of the probe to measure BMD accurately. For these cases, it was critical to approach the femoral neck from a different angle, bypassing the pelvis and tilting the probe to capture the appropriate bone structures.

In total, BMD measurement was successful at one or both sites (lumbar spine and femoral neck) in all patients, with 77.7% of the patients undergoing successful measurements at both sites. The correlation between lumbar spine and femoral neck T-scores (r = 0.530, p < 0.001) indicated that both measurements provided consistent information on bone health. This is significant, as patients with scoliosis often have discordantly high spinal BMD values despite having severe osteoporosis in the hips. Thus, REMS proved to be a valuable tool for diagnosing osteoporosis in patients with complex bone morphology, where DXA might be less reliable.

The utility of REMS in assessing BMD in patients with SMID is particularly noteworthy because it is a non-invasive, radiation-free technique, making it ideal for patients who may have difficulty traveling to a hospital for DXA scans. In addition to providing reliable BMD measurements, REMS offers an advantage in settings like rehabilitation or long-term care facilities where patients have limited mobility. Furthermore, REMS has demonstrated a superior diagnostic capability for detecting osteoporosis compared to DXA in patients with vertebral deformities or osteoarthritis, thus offering a more accurate assessment of bone health.

While REMS has proven beneficial in patients with SMID, this study has limitations. Firstly, it was conducted at a single center, and therefore, multicenter studies are necessary to validate these findings across a broader population. Additionally, the long-term efficacy of REMS in BMD monitoring and its correlation with clinical outcomes, such as fracture risk and treatment response, require further investigation.

Correlation between spinal and femoral REMS-measured BMD.
The scatter plot shows the relationship between lumbar spine and femoral neck BMD measurements using REMS. The x-axis and y-axis represent spinal and femoral REMS-measured BMDs, respectively, for patients who underwent both spinal and femoral measurements.

Gas retention in the abdomen, often seen in patients with SMID, occasionally obstructed bone visibility during scans. However, gentle pressure applied to the abdomen with the ultrasound probe allowed for the displacement of gas, enabling successful imaging.

Conclusion

The study demonstrates that REMS is an effective method for measuring BMD in patients with SMID, who often face challenges in undergoing traditional DXA measurements due to scoliosis, hip dislocation, or other mobility impairments. REMS successfully measured BMD in both the lumbar spine and femoral neck in these patients, with 77.7% of patients achieving successful measurements at both sites. This method’s ability to provide non-invasive, radiation-free assessments makes it a valuable tool for ongoing bone health monitoring in institutionalized patients with SMID, improving the management of osteoporosis and reducing fracture risk in this vulnerable population.

Future research is needed to explore the application of REMS in monitoring the effects of nutrition, physical activity, and disease severity on bone health in SMID patients, as well as its potential for evaluating treatment outcomes.