Dr Nick Birch, OsteoscanUK, Great Britain
Paul Magee, Profortis Ltd, Great Britain
Alison Johnson, Cal-C-Health Group Ltd, Great Britain
Dr Kim Zambito, Qualis OS, United States
Marsha Samuels, OsteoScan USA, United States
Dr David Tognarini, Bone Compass, Australia
Re: Bobelyak M, Vaculik J, Stepan JJ. Bone mineral density assessment using
Radiofrequency Echographic Multi Spectrometry (REMS) in patients before and after
total hip replacement, Osteoporos Int 2025; https://doi.org/10.1007/s00198-025-
07685-w
And:
Re: Pocock N, Chan D. Editorial: Is REMS-BMD Truly a Measured Parameter? A Call
for Transparency and Technical Clarification. Osteoporos Int 2025;l
https://doi.org/10.1007/s00198-025-07699-4
Summary of Concerns
This rebuttal addresses substantial flaws in the methodology and interpretation of data
in the recent article by Bobelyak et al. (2025), which evaluated REMS bone mineral
density in patients undergoing hip arthroplasty. In addition, there are concerns with the
accompanying negatively slanted Editorial which misrepresents the methodology and
results of the Bobelyak paper.
The study design of the paper contravened manufacturer guidance and used an
inappropriate patient population. It also mischaracterized the role of demographic
inputs in REMS analysis. These issues, combined with poor quality-controlled imaging
and an underpowered volunteer sub-study, render the authors' conclusions invalid.
Their findings stand in contradiction to a large, established body of international
evidence confirming the accuracy, reproducibility, and clinical value of REMS.
The publication
Osteoporosis International, a highly reputable journal with impeccable academic
credentials, published the paper on 19 September 2025. The authors, Bobelyak M,
Vaculik J and Stepan JJ are affiliated with the orthopaedic and rheumatology
departments of the First Faculty of Medicine, Charles University, Prague, Czech
Republic.
The paper examined femoral neck bone mineral density using REMS in 50 men and
women with hip arthritis before and after hip replacement. The authors concluded that:
“Approximately 90% of the variability in REMS-BMD of the femoral neck can be
attributed to the patient’s age, sex, and BMI. Further research is needed to determine
the extent to which REMS-BMD reflects areal or volumetric BMD, and how
backscattered radiofrequency ultrasound signals influence the REMS-BMD.” (Abstract,
Conclusion)
The authors also state in their Discussion that “differences observed in the REMS-BMD
results when the operator inputted either their actual or fictitious age and BMI … are
attributed to the algorithm used for calculating REMS-BMD. When an incorrect age or
BMI is input, the algorithm automatically aligns the measured spectral deformation with
inappropriate reference models.” (Discussion, last paragraph)
The inference that the paper draws the reader to, is that REMS does not actually
measure BMD but acts only as a sophisticated calculator basing the results on an
algorithm that overly prefers age and weight inputs, rather than radiofrequency
backscatter data.
Device Use Contrary to Manufacturer Instructions
An international group, affiliated to IIMHE, has examined the data in the paper and has
significant concerns regarding the methodology and conclusions of the study.
The Methods section stated that the single REMS operator had appropriate training
from the local Echolight distributor. That being the case, they should have been aware
that the user manual for the EchoStation explicitly states that if a hip prosthesis is
present scanning should be performed on the non-operated side as a proper
acquisition of REMS data is not possible when a prosthesis has been implanted. As a
result, a study that tried to examine metal implants with ultrasound-derived
radiofrequency backscatter data would not be recognised as scientifically valid.
Neither the peer review process used by Osteoporosis International nor the Editorial
appear to have detected this methodological error.
Protocol and Methodological Concerns
The authors report that they acquired femoral neck bone density data in 50 patients
before and after undergoing total hip replacement for osteoarthritis. This study was
described as forming part of a Fracture Liaison Service research program, aiming to
evaluate the clinical value of REMS in orthoapedic practice. However, none of the
patients in the study had sustained fragility fractures and all were undergoing elective
hip replacement. Therefore, it is unclear why such patients would be included in a
Fracture Liaison Service study. Although the authors state that the study had hospital
ethics committee approval, there is no reference to a prospectively registered protocol
on a recognised clinical trials registry such as ClinicalTrials.gov. The Editorial does not
comment on this lack of methodological rigour.
The results of the 100 hip scans, before and after elective total hip replacement, were
very similar despite the difference in material scanned (bone before and metal
afterwards). As a result, the authors claimed that the REMS technology could not
actually be measuring the bone parameters but was merely basing results on the age
and weight of the patients. The implication therefore would be that REMS is not a valid
form of bone densitometry. The Editorial mischaracterize these results stating that all
of the participants in the study had multiple scans with different demographic
parameters applied (change in age and change in weight). This is an error since the
Bobelyak paper explicitly states that the scans performed with variation in age and
weight were only carried out in a very small sub-study of men affiliated with the authors’
institution. This error casts doubt on the conclusions the Editorial draws from the
Bobelyak paper as it appears the authors did not understand the methodology of the
paper.
The paper states that “The echographic device enabled the measurement of REMS-
BMD in all fifty patients after total hip arthroplasty, where the proximal femur had been
replaced with metal”. This statement is at odds with the experience of three of the most
experienced IIMHE members, two of whom are consultant orthopaedic surgeons.
Combined, they have performed more than 10,000 hip scans with REMS and all three
have on occasion scanned hip joints that have been replaced by total hip
arthroplasties. However, they have been unable to acquire femoral neck REMS data in
patients who have such operations, except in the rare cases of femoral neck bone
preservation. The Czech team included in their paper an example x-ray of the total hip
replacement operation they performed, and it is evident the procedure did not conserve
the femoral neck.
Quality Control of the REMS Scan Images
The REMS quality control images in the paper demonstrate a substandard pre-operative
femoral neck ultrasound acquisition. The pre-operative and post-operative femoral
neck ultrasound acquisition images are virtually identical suggesting ether inadequate
performance by the operator or scans that are focused more on the femoral trochanter
or even the femoral shaft, rather than the femoral head and neck. The trochanter or
shaft would provide some bone mineral density data, but it is not representative of the
femoral neck region, which could not be measured by REMS after surgery as it had been
replaced by metal.
To help illustrate this, a screenshot of the Echolight User manual (see Figure 1 below)
provides images of proper femoral neck REMS acquisitions. Throughout the process of
REMS training the quality of femoral neck acquisitions is emphasized and it is clearly
stipulated that the correct orientation of the femoral neck should be below the focal
line, centered with the femoral head “above” the focal line and the trochanter also
inclining above the focal line (Expanded figure below). This ensures that the femoral
neck is essentially isolated within the REMS acquisition window. The example from the
authors in Figure 1C does not show this required orientation. It is perhaps more
representative of the trochanter or femoral shaft, and not femoral neck. Therefore,
perhaps a reason why Figure 1C closely resembles Figure 1D is that the operator was
not scanning the required location. Such a systematic error would explain the small
differences in BMD measurements before and after surgery. Conclusions from this part
of the study are therefore likely to be invalid. The Editorial does not comment on the
erroneous performance of the femoral scans, despite one of the authors being a
formally trained REMS user who will have received the full set of user manuals when
they took ownership of their REMS device.
Misrepresentation of the Role of the REMS Algorithm
The authors also carried out a very small separate study where they repeatedly scanned
hips of seven male volunteers from their institution, inputting varying age and weight
data. They claimed that the degree of variation of bone mineral density indicated that
there was little input to the results from the REMS radiofrequency backscatter data and
almost all the variation in bone density could be attributed to age and weight. The
influence of weight and age on bone mineral density is well established in the scientific
literature when measured with DXA scans. In 2023 a paper by Aflatooni (Sports Med
Health Sci 2023,5:308-13) described such a process, showing that DXA bone mineral
density results could be predicted accurately from demographic and anthropometric
data. The same applies to REMS. REMS scans produce a spectrum of radiofrequency
backscatter frequencies which is referred to a proprietary database to be translated
into a bone mineral density value. For REMS, in the published literature it is clearly
stated that the database, the acquired radiofrequency spectra are referred to, is age
clustered (5-year age groups from 20 – 90-years of age) and there is consideration of
body composition within those clusters, so it makes sense that any radiofrequency
backscatter spectrum can only be interpreted in terms of the demographics i.e. age and
weight. The Editorial cites the published scientific papers that very transparently
describe the mathematical process of radiofrequency backscatter spectral analysis
performed by REMS. However, the authors do not appear to have considered this
information when commenting on the results of the Bobelyak study as a result of which
they come to conclusions that are not supported by the published scientific literature.
The authors chose to alter the volunteers’ BMI values to far extremes by increasing and
decreasing the recorded weight by 15 Kg to give an effective BMI of 13.9 Kg/m2 at the
lowest and 43 Kg/m2 at the highest. There was also an adjustment in age by minus 30
years or plus 10 years. These seem extreme settings in which to try and compare the
actual RF backscatter signal to a fictitious (and highly unlikely) patient presentation.
The authors indeed state that a BMI of 13.9 is not physiologically plausible. A more
useful comparison would have been smaller and systematic incremental changes to
elucidate the associated REMS derived BMD values. Pushing any medical diagnostic
device to extreme situations invites error, which may explain some of the results
presented in this paper. The conclusions from this very small sub-study therefore do
not withstand scrutiny.
Conclusions
In conclusion, the paper published by Osteoporosis International has significant
methodological flaws and the conclusions are not justified by the science of REMS or
the data presented. The accompanying Editorial does not recognise the limitations of
the paper, unjustifiably infers a lack of transparency in the REMS process and casts
doubt on the value of REMS as a diagnostic tool. Such conclusions do not appear to be
warranted by the information contained in the Bobelyak paper and from the published
scientific literature.
REMS practitioners and patients having REMS scans can be reassured that this small,
flawed study does not undermine the leading-edge technology produced by Echolight
SpA that has revolutionized bone health assessment in the last decade. REMS is
accredited as a valid bone density measurement technology in over 40 regions in the
world including the USA, Canada, UK, EU, Australia, Japan and South America. Over
100 peer-reviewed papers attest to the quality, accuracy and reproducibility of REMS
when compared to reference bone density measurement technologies.
Figure 1.
