Clinical Application of the EOS Imaging System—The Broader Horizon

Abstract

Purpose: The purpose of this scoping review was to systematically identify and summarize the existing literature on non-spinal clinical applications of EOS imaging and identify related evidence gaps. Method: The study followed the PRISMA-ScR guidelines. A systematic literature search was conducted in Embase, MEDLINE, CINAHL, Scopus, Cochrane, Academic Search Premier, and OpenGrey databases in November 2022 and updated in December 2023. Original research from 2003 to 2023 was eligible if in English, Danish, French, German, Norwegian, or Swedish. Two authors screened articles by title and abstract, while data extraction from full texts was performed by seven authors using a structured template. Results: A total of 8176 articles were identified, with 1350 selected for full-text review and 268 included in data extraction. Among adults, 187 articles were included, with 88 focused on surgical applications like hip arthroplasty or osteotomy. In pediatrics, 68 general and 13 surgery-related articles were included. Lower extremity analysis was the most frequent topic, with other uses identified, such as rib cage geometry, patellar dislocation, and X-linked hypophosphatemia. Conclusions: Key clinical applications of EOS imaging include lower extremity analysis, e.g., leg length assessment and knee/hip arthroplasty planning), pelvic and spinal alignment studies, and emerging uses in rib cage geometry. Evidence gaps include limited research on the diagnostic accuracy of EOS for cerebral shunt placement, reliability in bone age estimation, and an unclear role in foot and ankle morphology.

1. Introduction

The EOS imaging system was originally designed to capture full-body radiographs with a focus on the spine, hips, and knees obtained in the weight-bearing position. The system depicts anatomical structures at their true size using slot scanning technology and allows for the simultaneous acquisition of two orthogonal radiographs [1]. The slot scanning technology used in the EOS imaging system is self-collimated and minimizes scattered radiation, which improves image quality and reduces the radiation dose compared to conventional X-ray [2,3,4]. The lower dose, in combination with high image quality, makes EOS a popular modality, particularly in pediatric and adolescent populations [5].

The EOS imaging system is particularly valuable in the evaluation of scoliosis, providing high-resolution, low-dose radiographs at a true size, enabling accurate assessment of spinal curvature [6]. Additionally, its ability to capture orthogonal images simultaneously allows for a comprehensive understanding of the three-dimensional nature of the deformity by subsequent three-dimensional modeling of the spine and individual vertebrae [6,7,8]. EOS has also become an important tool in presurgical planning for total hip arthroplasty (THA), allowing for optimized component positioning, potentially enhancing stability and minimizing wear-related complications [9].

A systematic review and economic evaluation of EOS systems concluded that, due to the higher cost compared to traditional radiographic systems, the key determinant of cost-effectiveness lies in optimal utilization [3]. This underscores the importance of optimizing EOS machine utilization to maximize efficiency and cost-effectiveness.

The low-dose aspect of the EOS system raises questions about whether this modality has additional clinical applications that could benefit patients through reduced radiation exposure, thereby improving patient safety. The potential for a broader clinical use of EOS technology has been discussed, for instance, in connection with chest radiography [10] and in the confirmation of the integrity of cerebral shunts [11]. To the best of our knowledge, there are no ongoing or published scientific reviews comprehensively addressing the broader clinical applications of the EOS system.

Therefore, the objective of this scoping review is to map and summarize the existing literature on non-spinal clinical applications of EOS imaging. Specifically, the objectives of this review were to do the following:

Identify the range of clinical applications of EOS imaging beyond spinal conditions.

Summarize the key areas where EOS has been utilized, including musculoskeletal imaging, surgical planning, and functional assessment.

Highlight gaps in the existing literature and provide recommendations for future research directions.

2. Materials and Methods

2.1. Methodology

The scoping review was conducted following the Joanna Briggs Institute (JBI) methodology for scoping reviews [12,13] and adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) [14]. The review protocol is reported in Open Science Framework (https://osf.io/yc85j/, accessed on 19 March 2025) and published as a scoping review protocol in JBI Evidence Synthesis [15].

2.2. Amendment to Protocol

The planned forward and backward citation searches, as well as author searching, were not executed due to the substantial number of articles retrieved. Secondly, it was initially planned to investigate whether EOS was in clinical use. However, due to inconsistencies in how EOS is reported across different settings, determining its clinical status proved uncertain. To maintain reliability, we decided to exclude this question from our analysis.

2.3. Search Strategy

The search strategy adhered to JBI’s 3-phased process [13]. The objective of the search strategy was to find both published and unpublished original articles. The search was developed with input from a science librarian using the following keywords: biplanar X-ray, biplanar radiograph, biplanar imaging, EOS imaging, and slot scanning (Appendix A). The literature databases Embase (Elsevier, Amsterdam, The Netherlands), MEDLINE (PubMed, U.S. National Library of Medicine, Bethesda, MD, USA), CINAHL Complete (EBSCO, Ipswich, MA, USA), Scopus (Elsevier, Amsterdam, The Netherlands), The Cochrane Library (The Cochrane Collaboration, London, UK), Academic Search Premier (EBSCO, Ipswich, MA, USA), and OpenGrey (INIST-CNRS, Vandoeuvre-lès-Nancy, France) were searched on 11 November 2022 and updated on 14 December 2023.

2.4. Eligibility Criteria

Although the EOS system was initially implemented in clinical settings in 2007 [1], the search filter included articles from 2003 onwards, as the prototype was tested in the years leading up to 2007. Quantitative articles describing the use of the EOS in a clinical setting were eligible for inclusion. Articles published in English, Danish, Norwegian, Swedish, French, and German were eligible for inclusion, given the proficiency of the author team in these languages. Language filters were incorporated into the search strategy, and the included languages were verified during the screening process. Non-original research was excluded.

2.5. Study Selection

All identified articles were uploaded into EndNote v.x20 (Clarivate Analytics, Philadelphi, PA, USA) where duplicates were removed from the dataset. The remaining articles were imported into Covidence (Veritas Health Innovation, Melbourne, Australia), where a second duplicate search was made. Two authors (KB and JJ) independently screened articles for applicability based on title and abstract. Subsequently, articles potentially eligible for inclusion were screened by full text. Exclusion reasons for full-text articles failing to meet the inclusion criteria were documented, such as lack of EOS modality usage, focus on spine-related research, absence of original research, and articles based on cadavers or within experimental frameworks. In cases where disagreements occurred between the reviewers at any stage of the selection process, they were resolved through discussion or with the involvement of a third reviewer. The screening process is presented in the PRISMA flow diagram [16] (Figure 1).

2.6. Data Extraction

Data extraction from included articles was carried out by pairs of two authors from a group of six (KB, JJ, BRM, MRP, SDM, MN), while validation was later performed by one of three authors (KB, JJ, and OB) using a data extraction tool developed by the authors [15].

Through various pilot tests, encompassing data extraction from a total of 50 articles, the original extraction sheet underwent a series of iterative modifications and revisions. These adjustments were made with the objective of augmenting the reliability and validity of the extracted data and, furthermore, to ensure the readability of the tables. Data were extracted on author and publication, clinical endpoints, age group and number of study participants, study type, and study design. Included articles were organized into four subcategories: Adult, Adult Surgery, Pediatric (including studies with mixed-age populations), and Pediatric Surgery (including studies with mixed-age populations). The articles within each table were organized under relevant headings and subheadings for easier navigation and reference. The categories were established after the completion of all data extraction processes. While all articles have been assigned a category, not all articles have been designated a subcategory.

3. Results

3.1. Search and Screening

A comprehensive search of the selected databases identified 8176 articles for potential inclusion. After applying the inclusion criteria and conducting title/abstract screening, 1350 articles were selected for full-text review. From these articles, 268 articles underwent data extraction. The included articles were primarily from Europe (n = 141), with France being the top contributor (n = 91), North America (n = 66), and Asia (n = 56). Additionally, articles were obtained from Oceania (n = 4) and South America (n = 1). The number of published articles grew substantially from 2004 to 2023, with a marked increase starting in 2012. The publication rate peaked at 41 articles in 2022, followed by a slight decline in 2023 (Figure 2).

Out of 268 articles included, 138 were prospective, 117 were retrospective, and 10 were both prospective and retrospective, while the methodology of 3 articles was unclear. The included articles encompassed various study designs, including 120 case–control/cohort/non-RCTs, 113 cross-sectional/case-series/case-reports, 107 articles that included reliability and/or accuracy, and two RCTs.

3.2. Adults

For the adult category, a total of 99 articles were found. The majority were on the lower extremity (34 articles), of which three specifically focused on leg length, followed by 31 articles that combined pelvis and lower extremity analysis, 11 of which focused on gait. The most prevalent subcategories were imaging comparison, followed by spine-related research. Rarer topics were subjects such as osteoarthritis, economics, obstructive sleep apnea syndrome, pain syndrome, and shoulder morphology (Appendix B).

3.3. Adult Surgery

For the adult surgery category, 88 articles were included. Articles focused predominantly on hip arthroplasty, totaling 53, and knee arthroplasty, with 21 articles. Additionally, there were articles on topics such as shoulder arthroplasty, tibial osteotomy, and femoral shaft fractures. The most common subcategory was risk factors and safety, followed by imaging comparison (Appendix C).

3.4. Pediatric

In the pediatric group, a total of 68 articles were included. The most examined topic was lower extremity analysis, with 29 articles, of which five focused specifically on gait and four on leg length. Rib cage geometry and thoracic analysis were covered in eight articles, and articles on maturity totaled six. Rarer topics were machine learning and foot and ankle analysis. In terms of subcategories for the pediatric group, the most common category was scoliosis, followed by cerebral palsy. The less frequent topics covered were patellar dislocation, X-linked hypophosphatemia, and cerebral shunt status (Appendix D).

3.5. Pediatric Surgery

Thirteen articles were included in the pediatric surgery category, six of which focused on rib cage geometry and thoracic analysis. In the subcategories for the pediatric surgery category, scoliosis was the most extensively studied area, followed by fracture, imaging comparison, Down’s syndrome, and shoulder (Appendix E).

4. Discussion

This scoping review provides a comprehensive overview of the non-spinal clinical applications of EOS imaging. Our findings indicate that EOS has been widely utilized in lower extremity analysis, particularly for assessing leg length discrepancies, knee and hip arthroplasty planning, and gait analysis. It also plays a role in pelvic and spinal alignment studies, offering precise weight-bearing assessments that contribute to surgical planning and biomechanical evaluations. Additionally, EOS has shown promise in rib cage geometry and thoracic assessments, including applications in pulmonary function evaluation and postural compensation analysis. Emerging uses have been identified in cerebral shunt assessment and bone age estimation, though these areas remain underexplored and warrant further research. The low radiation dose and high imaging precision of EOS make it particularly valuable in pediatric and orthopedic settings, where minimizing exposure while maintaining diagnostic accuracy is crucial. These findings highlight the diverse and expanding role of EOS imaging in clinical practice, with opportunities for further investigation into its full diagnostic potential.

To the best of our knowledge, this scoping review is the first to collate topics beyond spinal conditions that have been investigated or assessed in clinical articles using the EOS imaging modality. Providing a keyword summary of existing articles on non-spinal topics facilitates easy access, enabling practitioners and researchers to explore the current state of knowledge within these areas.

We included 268 articles that explored applications of the EOS system with a primary focus on non-spinal uses. As expected, many articles focused on topics such as leg length or knee and hip arthroplasty. Nonetheless, our search also identified several lesser-explored areas that could have a substantial clinical impact on further investigation. As an example, the use of EOS in diagnosing myeloma showed promising results; however, when the body mass index exceeded 30, diagnostic performance diminished significantly [17]. The upcoming updated EOS system with a photon-counting detector may improve noise reduction and potentially address this issue [18]. On the other hand, computed tomography is a well-established method for diagnosing myeloma, offering true 3D reconstruction and cross-sectional images. Another less explored topic is that of shunt control in children with hydrocephalus, where the diagnostic potential of EOS has been examined, showing promising results [11,19]. However, the limited number of articles, their retrospective designs, and their small sample sizes underscore the need for additional research. Nonetheless, given that many shunt patients are young and often undergo repeated follow-up imaging, additional exploration of this topic is warranted, as this group of patients could benefit from the reduced radiation dose provided by EOS imaging compared with conventional digital radiography. The low-dose capability of EOS imaging has been confirmed in multiple articles [20,21,22,23]. For instance, with the use of the Microdose feature in EOS, it has been shown that leg length can be measured accurately in an adolescent population [5], while EOS imaging for the pelvis delivered approximately half the radiation dose of conventional radiography [24].

Radiostereometric analysis (RSA) is a research method used to estimate micromotion between an orthopedic implant and the surrounding bone or between fracture fragments [25,26,27]. Traditionally, RSA involves the use of a setup with two X-ray tubes for simultaneous exposure [28]. The biplane simultaneous exposure capability of the EOS imaging system makes it a promising modality for exploring its capabilities in relation to RSA. A recent study found that when assessing knee implant motion, the precision of EOS was comparable to that of the traditional RSA method [29]. Additionally, the potential of using EOS and RSA for evaluating fracture stability has been investigated in relation to slipped capital femoral epiphysis with accuracy and precision comparable to that obtained with the traditional RSA system [30].

Within the adult population, the EOS system has demonstrated promising results, especially in the context of orthopedic procedures, with a particular focus on total hip arthroplasty (THA). One study introduced the “femur first” technique using EOS imaging for intraoperative guidance during THA, eliminating the need for computer-based navigation and highlighting its potential for real-time assistance and streamlined surgical procedures [31]. The use of EOS for analyzing THA component positioning in a standing position has been explored, utilizing the system’s capability to capture weight-bearing images, thus enhancing our understanding of implant behavior under typical loading conditions [32]. Exploring the post-surgical alignment, posture, and balance following THA are also topics of interest in recent EOS articles [33,34,35]. The 3D modeling abilities were used after surgery to check the placement of the femoral stem in hip replacements, offering a non-invasive alternative to CT scans that could lower radiation exposure [36]. This method might be useful for tracking how well hip prostheses work as patients move from standing to sitting [37]. The three-dimensional capabilities of the EOS system have also been explored to reconstruct the rib cage before and after surgery, enhancing the understanding of pulmonary function in patients with adolescent idiopathic scoliosis [38,39,40]. The ability to visualize rib cage alignment in a weight-bearing position may improve our understanding of thoracic biomechanics and respiratory function, but further research is needed to integrate EOS findings into routine clinical practice for pulmonary assessments. Additionally, the three-dimensional capabilities of the EOS system were explored regarding shoulder morphology [40,41] and kinematics [42,43,44], with the system showing promise as a low-dose supplement and/or alternative to existing imaging.

Despite the strengths of EOS imaging, this review identifies several key evidence gaps. The lack of standardized protocols for certain applications, such as bone age estimation and cerebral shunt assessment, limits its widespread adoption. Additionally, while EOS has been validated for reliability and accuracy in orthopedic applications, fewer studies have evaluated its diagnostic efficacy in comparison to gold-standard imaging modalities like MRI and CT.

Furthermore, the economic feasibility of implementing EOS in diverse clinical settings remains an important consideration. The relatively high initial cost of EOS systems raises questions about their cost-effectiveness, particularly in hospitals with limited imaging resources. However, its ability to reduce radiation dose and potentially replace multiple imaging sessions could lead to long-term cost savings, a hypothesis that warrants further economic evaluation studies.

Unlike systematic reviews, scoping reviews do not synthesize results through a formal quality appraisal of evidence, as their primary objective is to map the breadth of existing research rather than critically evaluate study validity [13]. While systematic reviews provide deeper analysis with specific criteria, they might miss broader ongoing research. This scoping review, however, identified key research areas and gaps, paving the way for future, more focused, systematic articles. The study’s comprehensive methodology is evident as it adhered to the JBI methodology for scoping reviews and followed the PRISMA-ScR guidelines, ensuring a rigorous and systematic approach [14]. The quality control measures applied in the data extraction, which involved iterative modifications and pilot tests of the data extraction tool, enhanced the reliability and validity of the data.

Resource limitations and time constraints led to deviations from the established protocol, such as omitting forward and backward citation searches and author searching. This approach could risk missing relevant articles and introduce potential biases in the study selection. However, the inclusion of more than 250 articles in this review is substantial, providing ample coverage of existing trends and developments in the field. The process of determining if articles were included in this article, i.e., non-spinal focus, was guided by their principal focus. In cases where articles touched upon themes pertinent to both the spine and broader applications, the decision necessitated a nuanced evaluation, where the decision to include or exclude was made to the best of our knowledge and judgment.

5. Conclusions

This review examined the literature on clinical applications of the EOS imaging system. The articles included demonstrate a consistent increase in research publications over time, with significant contributions from various global regions. We identified insights into its use across various areas. Key clinical applications of EOS imaging include lower extremity analysis, e.g., leg length assessment and knee/hip arthroplasty planning), pelvic and spinal alignment studies, and emerging uses in rib cage geometry. Evidence gaps include limited research on the diagnostic accuracy of EOS for cerebral shunt placement, reliability in bone age estimation, and an unclear role in foot and ankle morphology.

The relatively high economic break-even of the EOS system cannot be ignored. However, a broader application of the system may lead to more efficient planning and, consequently, lower costs per examination. This is, however, speculative and requires further economic evaluation.