In the evolving landscape of orthopedic innovation, a critical gap exists between how we image patients and how they move. Despite remarkable advances in surgical technique and implant design, total hip arthroplasty (THA) planning still relies predominantly on supine CT scans—capturing patients in a position they rarely maintain during daily life.

The consequences are telling: dislocation remains a leading cause of early revision surgery following THA. While patients stand, sit, and transition between postures throughout their day, their preoperative imaging captures none of these functional positions.

Recognizing this critical gap, a team of surgical technologists at the Royal National Orthopaedic Hospital (UK) and University College London (UCL) developed a bimodal imaging workflow designed to capture the dynamic behavior of the pelvis across functional positions.¹ By integrating high-resolution CT with biplanar low-dose radiography (EOS imaging) and using a semiautomated co-registration plugin developed with Synopsys Simpleware software, it was possible to align the 3D-CT pelvic models with standing and seated postures. This workflow brings dynamic, real-world biomechanics into clinical planning and surgical decision-making.

The Dynamic Pelvis: Why Position Matters

Dislocation remains a leading cause of early revision following THA.^2,3 While surgical technique and implant design have seen substantial advances, most pre-surgical planning continues to rely on imaging acquired with the patient in a supine position. The pelvis is not a static structure—it tilts, rotates, and shifts as we move between positions.^4–6 Individual variation compounds the challenge. Existing planning systems often fail to account for this variability, potentially compromising surgical outcomes.

Research has shown that sagittal pelvic tilt directly influences acetabular anteversion and inclination.^6–8 Failing to account for these changes can result in suboptimal implant positioning, edge-loading, impingement, and instability. A patient’s functional spinopelvic relationship must be integrated into surgical planning to achieve truly individualized care.

The common challenge is to develop a reproducible method for capturing real-world pelvic mechanics and translating them into meaningful insights for engineers and surgical teams, supporting the broader shift toward personalized, posture-informed orthopedic solutions.

Making CT “Upright”: Our Co-Registration Solution

The solution integrates two complementary imaging modalities:

• CT scanning: Provides high-resolution skeletal detail but only in the supine position.
• EOS imaging: Delivers full-body radiographs in functional standing and seated positions with minimal radiation exposure.

A semi-automated co-registration plugin that aligns detailed CT-derived 3D pelvic models with upright EOS images was developed. The anterior pelvic plane served as a reference, allowing precise quantification of pelvic movement across three planes.

The process is reproducible and designed for seamless integration into both device development and surgical planning ecosystems.

Clinical Application: Insights from 31 Patients

The CT-EOS workflow has so far been applied to a cohort of 31 patients with hip osteoarthritis undergoing primary THA. Each patient underwent supine CT and upright EOS scans in standing and seated positions. The results revealed significant, posture-specific differences in sagittal pelvic tilt. Most patients exhibited posterior rotation exceeding 30 degrees when moving from supine to seated. Coronal and axial tilt remained relatively stable.

These findings underscore why generic positioning strategies frequently fall short and highlight the critical need for personalized, position-aware planning.

Transforming Surgical Planning

Beyond basic clinical application, this workflow offers transformative possibilities for surgical preparation and execution.

For Surgical Teams:

• Visualize patient-specific pelvic mobility before entering the operating room
• Account for functional positions when planning component orientation
• Anticipate potential complications related to extreme pelvic kinematics

For Imaging Specialists:

• Provide surgeons with comprehensive biomechanical data rather than static snapshots
• Create standardized reports that quantify spinopelvic motion across multiple planes
• Identify patients with atypical mobility patterns who may require modified approaches

For Surgical Planning Platforms:

• Embed functional positioning data directly into preoperative software
• Enable surgeons to visualize how component performance will vary across patient activities

These insights align with broader industry trends, including personalization, predictive modeling, and the integration of functional biomechanics into the planning phase.

Incorporating Functional Imaging into Product Development Pipelines

CT-EOS co-registration offers a practical framework for device manufacturers to embed functional biomechanics into the design process. By integrating this workflow early, at the concept or prototyping stage, we can evaluate device behavior in upright and seated conditions, identify patients with extreme mobility patterns who may require additional attention, and better anticipate functional results by understanding position-dependent variables.

This imaging strategy is also highly relevant for surgical planning software, PSI workflows, and robotic systems where alignment is critical. Embedding functional alignment data at the planning stage boosts both technical performance and clinical confidence, positioning devices for greater success in an increasingly outcome-driven market.

Expanding Applications: From Hip to Knee Arthroplasty

While our initial research focused on total hip arthroplasty, this bimodal imaging approach is equally well-suited for knee arthroplasty procedures. The knee joint’s biomechanical function is similarly affected by positional changes, with weight-bearing postures revealing alignment characteristics that remain hidden in supine imaging.

For knee replacement planning, the CT-EOS workflow offers several key advantages.

• Assessment of functional knee alignment under realistic loading conditions
• Visualization of patellofemoral tracking across different flexion angles
• Quantification of the dynamic relationship between femoral and tibial rotation
• Evaluation of coronal alignment changes between supine and standing positions
• Better understanding of compensatory mechanisms in patients with complex deformities

Looking Forward: Functional Imaging as an Industry Standard

Beyond clinical applications, CT-EOS integration is scalable across R&D, manufacturing, and commercialization. As platforms increasingly embrace AI, cloud integration, and workflows that incorporate real-world alignment, data will be essential.

This imaging approach is also well-suited for surgical planning software, patient-specific instrumentation (PSI) workflows, and robotic systems, particularly where alignment is a critical factor (e.g., think about knee alignment in knee arthroplasty).

Incorporating functional alignment data during the planning phase enhances technical performance and supports greater clinical confidence, ultimately improving the likelihood of success in an increasingly outcome-focused healthcare environment.

Conclusion

In an increasingly outcome-driven healthcare environment, functional imaging isn’t just a technical enhancement—it’s becoming an essential standard for next-generation orthopedic surgery.

This work represents a collaboration between clinical orthopedic surgeons, orthopedic engineers, and imaging specialists at the RNOH and UCL focused on improving total hip arthroplasty outcomes through more comprehensive preoperative assessment and planning.

References

¹ Ramesh A, Henckel J, Lim X, Tompsett P, Hart A, Di Laura A. What Is the Functional Spinopelvic Relationship in Three Dimensions? A CT and EOS Study. Clin Orthop Relat Res. Published online 2025. doi:10.1097/CORR.0000000000003473,

² Bozic KJ, Ong K, Lau E, et al. Risk of complication and revision total hip arthroplasty among medicare patients with different bearing surfaces. Clin Orthop Relat Res. 2010;468(9):2357-2362. doi:10.1007/S11999-010-1262-3

³ Bolland BJ, Whitehouse SL, John Timperley A. Indications for Early Hip Revision Surgery in the Uk – A Re-Analysis of Njr Data. https://doi.org/105301/HIP20129184. 2012;22(2):145-152. doi:10.5301/HIP.2012.9184

⁴ Chevillotte T, Coudert P, Cawley D, et al. Influence of posture on relationships between pelvic parameters and lumbar lordosis: Comparison of the standing, seated, and supine positions. A preliminary study. Orthopaedics & Traumatology: Surgery & Research. 2018;104(5):565-568. doi:10.1016/J.OTSR.2018.06.005

⁵ LeBrun DG, Ondeck NT, Nessler JP, Marchand RC, Illgen RL, Westrich GH. Variability of pre-operative functional pelvic tilt in total hip arthroplasty patients. Int Orthop. 2023;47(5):1243-1247. doi:10.1007/S00264-023-05748-3

⁶ Pierrepont J, Hawdon G, Miles BP, et al. Variation in functional pelvic tilt in patients undergoing total hip arthroplasty. Bone and Joint Journal. 2017;99-B(2):184-191. doi:10.1302/0301-620X.99B2.BJJ-2016-0098.R1

⁷ Snijders TE, Schlösser TPC, Heckmann ND, et al. The Effect of Functional Pelvic Tilt on the Three-Dimensional Acetabular Cup Orientation in Total Hip Arthroplasty Dislocations. J Arthroplasty. 2021;36(6):2184-2188.e1. doi:10.1016/J.ARTH.2020.12.055

⁸ Loppini M, Pisano A, Ruggeri R, Della Rocca A, Grappiolo G. Pelvic tilt and functional acetabular position after total hip arthroplasty: an EOS 2D/3D radiographic study. HIP International. 2023;33(3):365-370. doi:10.1177/11207000211073668

Anna Di Laura is a senior research associate at the Royal National Orthopaedic Hospital NHS Trust. She is also an associate professor of Orthopaedic Engineering at University College London, Mechanical Engineering.

Xing Lim is a research assistant at University College London (UCL), London, U.K.

Angelika Ramesh is a research coordinator at the Royal National Orthopaedic Hospital NHS Trust.

Alister Hart is the director of research for implant science at the RNOH/UCLH Biomedical Research Centre. He is also a professor of Orthopaedic Surgery and a consultant orthopaedic surgeon.

Johann Henckel received the M.D. degree from the University College London (UCL), London, U.K., in 1998. He is a trainee orthopaedic surgeon. He is currently a Research Fellow with the Department of Surgery with research interests in developing imaging software solutions to aid the understanding of the biomechanics of the lower limb musculoskeletal system. His research includes surgical technology applied to hip and knee joint replacement, with expertise in the field of robotics and computer-assisted surgery.