pith. sign in

arxiv: 2606.03893 · v1 · pith:MSEEIDFDnew · submitted 2026-06-02 · 💻 cs.CV

Electromagnetic Navigation for Femoral Osteotomy Using High-Accuracy X-ray-to-CT Registration

Roman Flepp , Arend Nieuwland , Bastian Sigrist , Philipp F\"urnstahl , Lilian Calvet , Thomas Dreher This is my paper

Pith reviewed 2026-06-28 10:56 UTC · model grok-4.3

classification 💻 cs.CV
keywords electromagnetic trackingfemoral osteotomyX-ray-to-CT registrationfluoroscopy-free navigationpatient-specific instrumentationsurgical accuracycorrective osteotomy
0
0 comments X

The pith

An electromagnetic tracking system for femoral osteotomies achieves patient-specific instrument accuracy using registration from only two fluoroscopic images.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper describes an integrated electromagnetic tracking navigation system that couples CT-based preoperative planning with one-time C-arm calibration and X-ray-to-CT registration computed from two fluoroscopic images. This setup supports real-time, fluoroscopy-free guidance of the saw blade and bone fragments relative to the plan during uniplanar or biplanar corrective osteotomies. The approach seeks to reduce both radiation dose and surgical exposure compared with free-hand methods or patient-specific instrumentation while preserving execution accuracy. In a study on 18 synthetic femora the system produced lower total angular error than free-hand execution and met statistical equivalence criteria to PSI for both angular and translational errors under identical minimal exposure conditions.

Core claim

The system transfers preoperative plans via high-accuracy X-ray-to-CT registration from two fluoroscopic images acquired at initialization, enabling real-time EMT navigation without further imaging; on synthetic femora this yielded total angular error of 3.05 ± 0.75° versus 6.32 ± 2.36° for free-hand (p=0.031) and statistical equivalence to PSI within ±2° and ±2 mm for angular (p≤0.02) and translational (p=0.048) errors.

What carries the argument

The one-time X-ray-to-CT registration from two fluoroscopic images at initialization, which anchors the preoperative plan for continuous electromagnetic tracking of the saw and fragments without additional fluoroscopy.

If this is right

  • EMT guidance produced no angular errors above the 5° clinical threshold while free-hand produced four outliers in six trials.
  • The method requires only two fluoroscopic images instead of more than thirty for free-hand or more than six for PSI.
  • No significant difference appeared in user questionnaire scores between EMT and PSI under the same minimal surgical exposure.
  • The registration-plus-EMT pipeline is stated to be compatible with both uniplanar and biplanar osteotomies.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same two-image registration step could be tested for other long-bone corrective procedures where repeated fluoroscopy is currently standard.
  • If the registration holds on deforming soft tissue, the workflow would reduce cumulative radiation dose for both patient and surgical team across multiple cases.
  • Surgeons without extensive experience in free-hand osteotomy might reach PSI-level accuracy with less custom hardware.

Load-bearing premise

The registration computed from the two initial fluoroscopic images stays accurate enough for the rest of the procedure even as the bone is cut and moved.

What would settle it

A trial on real cadaveric or patient femora in which total angular error under EMT guidance exceeds the ±2° equivalence band relative to PSI or produces more than one outlier above the 5° clinical threshold.

read the original abstract

Accurate execution of preoperative plans in corrective femoral osteotomies remains challenging. Current techniques are limited by variable accuracy, invasiveness, and radiation exposure, with free-hand methods and patient-specific instrumentation (PSI) often requiring >30 and >6 fluoroscopic images, respectively. We present an integrated, electromagnetic tracking (EMT)-based navigation system for femoral osteotomies that minimizes dissection and intraoperative fluoroscopy. The system couples CT-based preoperative planning with one-time intraoperative C-arm calibration and accurate X-ray-to-CT registration from two fluoroscopic images acquired at initialization. This enables real-time, fluoroscopy-free EMT navigation of the saw blade and bone fragments relative to the preoperative plan, and is compatible with uniplanar and biplanar osteotomies. In a feasibility study using 18 synthetic femora, EMT guidance significantly outperformed free-hand execution in total angular error ($(3.05 \pm 0.75)^\circ$ vs.\ $(6.32 \pm 2.36)^\circ$, $p=0.031$), assuming the same minimal surgical exposure for both. No EMT-guided trials exceeded the >5{\deg} clinical threshold, whereas free-hand produced 4 outliers of 6 trials. The system achieved statistical equivalence ($\pm 2^\circ$, $\pm 2,\text{mm}$) to PSI for total angular ($p \le 0.02$) and total translational ($p=0.048$) errors, with no significant differences in user questionnaire scores. By transferring preoperative plans using only two fluoroscopic images while matching PSI accuracy without additional surgical exposure, the proposed system motivates subsequent cadaveric and clinical validation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript presents an EMT-based navigation system for femoral osteotomies that couples CT preoperative planning with one-time C-arm calibration and X-ray-to-CT registration from two fluoroscopic images. This enables real-time, fluoroscopy-free navigation of the saw blade and bone fragments. On 18 synthetic femora, EMT guidance reduced total angular error versus free-hand (3.05 ± 0.75° vs. 6.32 ± 2.36°, p=0.031), produced no outliers above the 5° clinical threshold, and achieved statistical equivalence to PSI for total angular (p ≤ 0.02) and translational (p=0.048) errors.

Significance. If the reported registration accuracy and navigation performance hold under real anatomical conditions, the approach could meaningfully reduce intraoperative radiation exposure and dissection while matching PSI accuracy, addressing key limitations of current free-hand and PSI techniques in corrective osteotomies.

major comments (2)
  1. [Abstract] Abstract: The central performance claims (EMT vs. free-hand angular error and statistical equivalence to PSI) rest on the assumption that the one-time X-ray-to-CT registration from two initial fluoroscopic images remains sufficiently accurate for the entire fluoroscopy-free procedure. This assumption is evaluated only on synthetic femora; the manuscript provides no data on how soft-tissue, marrow, or cortical density variations on real bone would affect registration fidelity or introduce drift.
  2. [Abstract] Abstract and Results: With n=18 synthetic specimens and no reported error bars on all metrics, the statistical equivalence statements (p ≤ 0.02 and p=0.048) and outlier counts have limited power to support claims of clinical equivalence; the paper itself notes the need for cadaveric validation, indicating this is a load-bearing gap for the broader motivation.
minor comments (2)
  1. [Abstract] Abstract: The expression '>5{\deg}' is an incomplete LaTeX fragment and should be rendered as '>5°'.
  2. [Abstract] Abstract: The translational tolerance is written '±2,\text{mm}'; the stray comma should be removed to read '±2 mm'.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the constructive comments. We respond point-by-point to the major comments below, clarifying the scope of this feasibility study while acknowledging its limitations.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central performance claims (EMT vs. free-hand angular error and statistical equivalence to PSI) rest on the assumption that the one-time X-ray-to-CT registration from two initial fluoroscopic images remains sufficiently accurate for the entire fluoroscopy-free procedure. This assumption is evaluated only on synthetic femora; the manuscript provides no data on how soft-tissue, marrow, or cortical density variations on real bone would affect registration fidelity or introduce drift.

    Authors: The manuscript is framed as a feasibility study on synthetic femora and explicitly motivates cadaveric validation to address real anatomical conditions. We agree that no data on soft-tissue, marrow, or cortical density effects are provided, as the experiments used only synthetic specimens. The abstract has been revised to more clearly state the synthetic-bone scope and the assumption of registration stability under these controlled conditions. revision: partial

  2. Referee: [Abstract] Abstract and Results: With n=18 synthetic specimens and no reported error bars on all metrics, the statistical equivalence statements (p ≤ 0.02 and p=0.048) and outlier counts have limited power to support claims of clinical equivalence; the paper itself notes the need for cadaveric validation, indicating this is a load-bearing gap for the broader motivation.

    Authors: We acknowledge the modest sample size (n=18) limits statistical power for equivalence claims. Standard deviations are reported for all error metrics in the results; the TOST equivalence tests and outlier counts are presented as preliminary findings. The abstract and discussion have been updated to emphasize the preliminary nature of the results and the explicit need for larger cadaveric studies before clinical equivalence can be asserted. revision: partial

standing simulated objections not resolved
  • Data on how soft-tissue, marrow, or cortical density variations affect X-ray-to-CT registration accuracy and introduce drift under real anatomical conditions.

Circularity Check

0 steps flagged

No circularity: purely empirical feasibility study

full rationale

The paper reports an experimental comparison of an EMT navigation system against free-hand and PSI techniques on 18 synthetic femora. Performance metrics (angular/translational errors) are measured directly from physical trials; no equations, parameter fits, or derivations are claimed. The X-ray-to-CT registration is a one-time initialization step whose accuracy is evaluated by the same external benchmarks, not derived from itself. No self-citation load-bearing steps, ansatzes, or renamings appear. The work is self-contained against external benchmarks (free-hand, PSI) with no reduction of outputs to inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard domain assumptions in medical imaging and tracking rather than new free parameters or invented entities.

axioms (1)
  • domain assumption X-ray-to-CT registration from two images at initialization transfers the preoperative plan with sufficient accuracy for the duration of the osteotomy under minimal exposure
    Invoked in the abstract as the basis for fluoroscopy-free EMT navigation.

pith-pipeline@v0.9.1-grok · 5848 in / 1292 out tokens · 29161 ms · 2026-06-28T10:56:18.387152+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

20 extracted references · 14 canonical work pages

  1. [1]

    Gait & Posture36(3), 467–470 (2012) https://doi.org/10.1016/j.gaitpost.2012.04.017

    Dreher, T., Wolf, S.I., Heitzmann, D., Swartman, B., Schuster, W., Gantz, S., Hagmann, S., D¨ oderlein, L., Braatz, F.: Long-term outcome of femoral derotation osteotomy in children with spastic diplegia. Gait & Posture36(3), 467–470 (2012) https://doi.org/10.1016/j.gaitpost.2012.04.017

    work page doi:10.1016/j.gaitpost.2012.04.017 2012

  2. [2]

    Journal of the Amer- ican Academy of Orthopaedic Surgeons26(19) (2018) https://doi.org/10.5435/ JAAOS-D-17-00623 14

    Buly, R.L., Sosa, B.R., Poultsides, L.A., Caldwell, E., Rozbruch, S.R.: Femoral derotation osteotomy in adults for version abnormalities. Journal of the Amer- ican Academy of Orthopaedic Surgeons26(19) (2018) https://doi.org/10.5435/ JAAOS-D-17-00623 14

    2018

  3. [3]

    JAMA286(2), 188–195 (2001) https://doi.org/10.1001/jama.286

    Sharma, L., Song, J., Felson, D.T., Cahue, S., Shamiyeh, E., Dunlop, D.D.: The role of knee alignment in disease progression and functional decline in knee osteoarthritis. JAMA286(2), 188–195 (2001) https://doi.org/10.1001/jama.286. 2.188

    work page doi:10.1001/jama.286 2001

  4. [4]

    The American Journal of Sports Medicine 53(4), 848–854 (2025) https://doi.org/10.1177/03635465251314868

    Neopoulos, G., Jud, L., Vlachopoulos, L., Fucentese, S.F.: Combined correction of coronal and rotational deformities of the femur with distal femoral osteotomy using patient-specific instrumentation. The American Journal of Sports Medicine 53(4), 848–854 (2025) https://doi.org/10.1177/03635465251314868

    work page doi:10.1177/03635465251314868 2025

  5. [5]

    International Orthopaedics43(3), 619–624 (2019) https://doi.org/10

    Shi, J., Lv, W., Wang, Y., Ma, B., Cui, W., Liu, Z., Han, K.: Three dimen- sional patient-specific printed cutting guides for closing-wedge distal femoral osteotomy. International Orthopaedics43(3), 619–624 (2019) https://doi.org/10. 1007/s00264-018-4043-3

    2019

  6. [6]

    BMJ Paediatrics Open9(1) (2025) https://doi.org/10.1136/bmjpo-2025-003666

    Kriechling, P., Meichtry, F.L., Smolle, M.A., Preiss, H., Zellner, M., Kaeser, Y., Farshad-Amacker, N.A., Dreher, T.: Analysis of intraoperative radiation exposure in paediatric orthopaedic and trauma patients: A comparative cohort study. BMJ Paediatrics Open9(1) (2025) https://doi.org/10.1136/bmjpo-2025-003666

    work page doi:10.1136/bmjpo-2025-003666 2025

  7. [7]

    Journal of Experimental Orthopaedics12(1) (2025) https://doi.org/10.1002/jeo2.70088

    Grillo, G., Coelho, A., Pelfort, X., Fillat-Gom` a, F., Verdaguer Figuerola, A., Gil-Gonzalez, S., Pe˜ nalver, J.M., Yela-Verd´ u, C.: 3d-printed patient-specific instrumentation and the freehand technique in high-tibial osteotomy: A prospec- tive cohort-comparative study in an outpatient setting. Journal of Experimental Orthopaedics12(1) (2025) https://d...

    work page doi:10.1002/jeo2.70088 2025

  8. [8]

    Interna- tional Orthopaedics44(2020) https://doi.org/10.1007/s00264-020-04496-y

    Jud, L., Vlachopoulos, L., Beeler, S., Tondelli, T., F¨ urnstahl, P., Fucentese, S.: Accuracy of three dimensional-planned patient-specific instrumentation in femoral and tibial rotational osteotomy for patellofemoral instability. Interna- tional Orthopaedics44(2020) https://doi.org/10.1007/s00264-020-04496-y

    work page doi:10.1007/s00264-020-04496-y 2020

  9. [9]

    Current Reviews in Musculoskeletal Medicine18, 547–557 (2025) https://doi.org/10.1007/s12178-025-09987-2

    Khela, H.S., Khela, M.S., Sriram, V., Schroeder, G.G., Hollyer, I., Sherman, S.L.: Indications, technique, and outcomes of patient specific instrumentation for osteotomy about the knee. Current Reviews in Musculoskeletal Medicine18, 547–557 (2025) https://doi.org/10.1007/s12178-025-09987-2

    work page doi:10.1007/s12178-025-09987-2 2025

  10. [10]

    Current Reviews in Musculoskeletal Medicine14(2), 192–203 (2021) https://doi.org/10.1007/s12178-021-09699-3

    Casari, F.A., Navab, N., Hruby, L.A., Kriechling, P., Nakamura, R., Tori, R., Lourdes Dos Santos Nunes, F., Queiroz, M.C., F¨ urnstahl, P., Farshad, M.: Aug- mented reality in orthopedic surgery is emerging from proof of concept towards clinical studies: a literature review explaining the technology and current state of the art. Current Reviews in Musculo...

    work page doi:10.1007/s12178-021-09699-3 2021

  11. [11]

    Clinics in Orthopedic Surgery8(4), 349–357 (2016) https://doi.org/10.4055/cios

    Song, S.J., Bae, D.K.: Computer-assisted navigation in high tibial osteotomy. Clinics in Orthopedic Surgery8(4), 349–357 (2016) https://doi.org/10.4055/cios. 2016.8.4.349 15

    work page doi:10.4055/cios 2016

  12. [12]

    IEEE Reviews in Biomedical Engineering13, 212–232 (2020) https://doi.org/10.1109/RBME

    Sorriento, A., Porfido, M.B., Mazzoleni, S., Calvosa, G., Tenucci, M., Ciuti, G., Dario, P.: Optical and electromagnetic tracking systems for biomedical applications: A critical review on potentialities and limitations. IEEE Reviews in Biomedical Engineering13, 212–232 (2020) https://doi.org/10.1109/RBME. 2019.2939091

    work page doi:10.1109/rbme 2020

  13. [13]

    Version 2.0.1 (2022)

    Stryker Corporation: Ortho Q Guidance System. Version 2.0.1 (2022)

    2022

  14. [14]

    Medtronic Navigation, Inc.: StealthStation™S8 Navigation Platform System Manual. (2017). Version 2.0.1

    2017

  15. [15]

    Journal of Orthopaedic Research43(2), 362–369 (2025) https: //doi.org/10.1002/jor.26000

    Geisb¨ usch, A., Gramer, C., Dreher, T., Hagen, N., Hagmann, S., Renkawitz, T., G¨ otze, M.: Electromagnetic bone segment tracking in multiplanar osteotomies— a saw bone study. Journal of Orthopaedic Research43(2), 362–369 (2025) https: //doi.org/10.1002/jor.26000

    work page doi:10.1002/jor.26000 2025

  16. [16]

    IEEE Access8, 42010–42020 (2020) https://doi.org/10.1109/ACCESS.2020.2977072

    Liu, H., Baena, F.R.Y.: Automatic markerless registration and tracking of the bone for computer-assisted orthopaedic surgery. IEEE Access8, 42010–42020 (2020) https://doi.org/10.1109/ACCESS.2020.2977072

    work page doi:10.1109/access.2020.2977072 2020

  17. [17]

    In: 2024 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR)

    Gopalakrishnan, V., Dey, N., Golland, P.: Intraoperative 2d/3d image registration via differentiable x-ray rendering. In: CVPR, pp. 11662–11672 (2024). https:// doi.org/10.1109/CVPR52733.2024.01108

    work page doi:10.1109/cvpr52733.2024.01108 2024

  18. [18]

    International Journal of Computer Assisted Radiology and Surgery20(7), 1401–1408 (2025) https://doi.org/10.1007/s11548-025-03391-4

    Flepp, R., Nissen, L., Sigrist, B., Nieuwland, A., Cavalcanti, N., F¨ urnstahl, P., Dreher, T., Calvet, L.: Automatic multi-view X-ray/CT registration using bone substructure contours. International Journal of Computer Assisted Radiology and Surgery20(7), 1401–1408 (2025) https://doi.org/10.1007/s11548-025-03391-4

    work page doi:10.1007/s11548-025-03391-4 2025

  19. [19]

    https://www.imfusion.com

    ImFusion GmbH: ImFusion SDK and Suite. https://www.imfusion.com. Accessed: 2025-12-29

    2025

  20. [20]

    In: Hancock, P.A., Meshkati, N

    Hart, S.G., Staveland, L.E.: Development of NASA-TLX (Task Load Index): Results of empirical and theoretical research. In: Hancock, P.A., Meshkati, N. (eds.) Human Mental Workload, pp. 139–183. North-Holland, Amsterdam (1988) 16

    1988