How Reliable is the Assessment of Fusion Status Following ACDF Using Dynamic Flexion-Extension Radiographs?

Christopher T Martin¹, Sangwook Tim Yoon², Ram Kiran Alluri³, Edward C Benzel⁴, Chris M Bono⁵, Samuel K Cho⁶, Dean Chou⁷, Xiaolong Chen⁸, Jason P Y Cheung⁹, Juan P Cabrera^{10

11}, Stipe Ćorluka^{12

13}, Andreas K Demetriades¹⁴, Matthew F Gary^{2

15}, Zoher Ghogawala¹⁶, Waeel Hamouda^{17

18}, Inbo Han¹⁹, Dimitri Hauri²⁰, Patrick C Hsieh²¹, Amit Jain²², Jun S Kim⁷, Hai V Le²³, Philip K Louie²⁴, Zhuojing Luo²⁵, Hans-Jörg Meisel²⁶, Sathish Muthu^{27

28

29}, Dal-Sung Ryu³⁰, Charles A Sansur³¹, Andrew J Schoenfeld³², Laura Scaramuzzo³³, Gregory D Schroeder³⁴, Shanmuganathan Rajasekaran³⁵, Veranis Sotiris³⁶, Gianluca Vadalà^{37

38}, Pieter-Paul A Vergroesen³⁹, Jeffrey C Wang^{3

21}, Yabin Wu²⁰, K Daniel Riew^{40

41}; AO Spine Knowledge Forum Degenerative

Affiliations

¹ Department of Orthopedic Surgery, University of Minnesota, Minneapolis, MN, USA.
² Department of Orthopaedics, Emory University, Atlanta, GA, USA.
³ Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
⁴ Department of Neurosurgery, Cleveland Clinic Foundation, Cleveland, OH, USA.
⁵ Department of Orthopaedic Surgery, Harvard Medical School, Massachusetts General Hospital, Boston, MA, USA.
⁶ Department of Orthopedic Surgery, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
⁷ Department of Neurosurgery, Columbia University Irving Medical Center, New York, NY, USA.
⁸ Department of Orthopedic Surgery, Xuanwu Hospital Capital Medical University, Beijing, China.
⁹ Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong SAR, China.
¹⁰ Department of Neurosurgery, Hospital Clínico Regional de Concepción, Concepción, Chile.
¹¹ Faculty of Medicine, University of Concepción, Concepción, Chile.
¹² Spinal Surgery Division, Department of Traumatology, University Hospital Centre Sestre Milosrdnice, Zagreb, Croatia.
¹³ Department of Anatomy and Physiology, University of Applied Health Sciences, Zagreb, Croatia.
¹⁴ Edinburgh Spinal Surgery Outcome Studies Group, Department of Neurosurgery, Royal Infirmary Edinburgh, Edinburgh, UK.
¹⁵ Department of Neurosurgery, Emory University, Atlanta, GA, USA.
¹⁶ Department of Neurosurgery, Lahey Hospital and Medical Center, Burlington, MA, USA.
¹⁷ Department of Neurosurgery, Kasr Alainy Faculty of Medicine, Research, and Teaching Hospitals, Cairo University, Cairo, Egypt.
¹⁸ Neurological & Spinal Surgery Service, Security Forces Hospital, Dammam, Saudi Arabia.
¹⁹ Department of Neurosurgery, CHA University School of Medicine, CHA Bundang Medical Center, Seongnam-si, Republic of Korea.
²⁰ Clinical Science, AO Innovation Translation Center, AO Foundation, Davos, Switzerland.
²¹ Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
²² Department of Orthopaedic Surgery, Johns Hopkins University, Baltimore, MD, USA.
²³ Department of Orthopaedic Surgery, University of California, Sacramento, CA, USA.
²⁴ Center for Neurosciences and Spine, Department of Neurosurgery, Virginia Mason Medical Center, Seattle, WA, USA.
²⁵ Department of Orthopaedic Surgery, Xijing Hospital, Forth Military Medical University, Xi'an, China.
²⁶ Department of Neurosurgery, BG Klinikum Bergmannstrost, Halle, Germany.
²⁷ Orthopaedic Research Group, Coimbatore, India.
²⁸ Department of Orthopaedics, Government Medical College, Karur, India.
²⁹ Department of Biotechnology, Karpagam Academy of Higher Education, Coimbatore, India.
³⁰ Department of Neurosurgery, College of Medicine, Inha University, Incheon, Korea.
³¹ Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, MD, USA.
³² Department of Orthopaedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
³³ Spine Surgery Unit, Department of Aging, Orthopaedic and Rheumatological Sciences, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy.
³⁴ Department of Orthopaedic Surgery, Rothman Institute and Thomas Jefferson University, Philadelphia, PA, USA.
³⁵ Department of Orthopaedics, Ganga Hospital, Coimbatore, India.
³⁶ Department of Neurosurgery, 251 General Air Force and Reserve Hospital, Athens, Greece.
³⁷ Operative Research Unit of Orthopaedic and Trauma Surgery, Fondazione Policlinico Universitario Campus Bio-Medico, Rome, Italy.
³⁸ Research Unit of Orthopaedic and Trauma Surgery, Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Rome, Italy.
³⁹ Department of Orthopaedic Surgery, Noordwest Ziekenhuisgroep, Alkmaar, The Netherlands.
⁴⁰ Department of Neurological Surgery, Weill Cornell Medicine, New York, NY, USA.
⁴¹ Department of Orthopedic Surgery, Columbia University, New York, NY, USA.

PMID: 39639494
PMCID: PMC11622210
DOI: 10.1177/21925682241303107

How Reliable is the Assessment of Fusion Status Following ACDF Using Dynamic Flexion-Extension Radiographs?

Christopher T Martin et al. Global Spine J. 2025 May.

. 2025 May;15(4):2450-2457.

doi: 10.1177/21925682241303107. Epub 2024 Dec 5.

Authors

Affiliations

¹ Department of Orthopedic Surgery, University of Minnesota, Minneapolis, MN, USA.
² Department of Orthopaedics, Emory University, Atlanta, GA, USA.
³ Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
⁴ Department of Neurosurgery, Cleveland Clinic Foundation, Cleveland, OH, USA.
⁵ Department of Orthopaedic Surgery, Harvard Medical School, Massachusetts General Hospital, Boston, MA, USA.
⁶ Department of Orthopedic Surgery, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
⁷ Department of Neurosurgery, Columbia University Irving Medical Center, New York, NY, USA.
⁸ Department of Orthopedic Surgery, Xuanwu Hospital Capital Medical University, Beijing, China.
⁹ Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong SAR, China.
¹⁰ Department of Neurosurgery, Hospital Clínico Regional de Concepción, Concepción, Chile.
¹¹ Faculty of Medicine, University of Concepción, Concepción, Chile.
¹² Spinal Surgery Division, Department of Traumatology, University Hospital Centre Sestre Milosrdnice, Zagreb, Croatia.
¹³ Department of Anatomy and Physiology, University of Applied Health Sciences, Zagreb, Croatia.
¹⁴ Edinburgh Spinal Surgery Outcome Studies Group, Department of Neurosurgery, Royal Infirmary Edinburgh, Edinburgh, UK.
¹⁵ Department of Neurosurgery, Emory University, Atlanta, GA, USA.
¹⁶ Department of Neurosurgery, Lahey Hospital and Medical Center, Burlington, MA, USA.
¹⁷ Department of Neurosurgery, Kasr Alainy Faculty of Medicine, Research, and Teaching Hospitals, Cairo University, Cairo, Egypt.
¹⁸ Neurological & Spinal Surgery Service, Security Forces Hospital, Dammam, Saudi Arabia.
¹⁹ Department of Neurosurgery, CHA University School of Medicine, CHA Bundang Medical Center, Seongnam-si, Republic of Korea.
²⁰ Clinical Science, AO Innovation Translation Center, AO Foundation, Davos, Switzerland.
²¹ Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
²² Department of Orthopaedic Surgery, Johns Hopkins University, Baltimore, MD, USA.
²³ Department of Orthopaedic Surgery, University of California, Sacramento, CA, USA.
²⁴ Center for Neurosciences and Spine, Department of Neurosurgery, Virginia Mason Medical Center, Seattle, WA, USA.
²⁵ Department of Orthopaedic Surgery, Xijing Hospital, Forth Military Medical University, Xi'an, China.
²⁶ Department of Neurosurgery, BG Klinikum Bergmannstrost, Halle, Germany.
²⁷ Orthopaedic Research Group, Coimbatore, India.
²⁸ Department of Orthopaedics, Government Medical College, Karur, India.
²⁹ Department of Biotechnology, Karpagam Academy of Higher Education, Coimbatore, India.
³⁰ Department of Neurosurgery, College of Medicine, Inha University, Incheon, Korea.
³¹ Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, MD, USA.
³² Department of Orthopaedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
³³ Spine Surgery Unit, Department of Aging, Orthopaedic and Rheumatological Sciences, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy.
³⁴ Department of Orthopaedic Surgery, Rothman Institute and Thomas Jefferson University, Philadelphia, PA, USA.
³⁵ Department of Orthopaedics, Ganga Hospital, Coimbatore, India.
³⁶ Department of Neurosurgery, 251 General Air Force and Reserve Hospital, Athens, Greece.
³⁷ Operative Research Unit of Orthopaedic and Trauma Surgery, Fondazione Policlinico Universitario Campus Bio-Medico, Rome, Italy.
³⁸ Research Unit of Orthopaedic and Trauma Surgery, Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Rome, Italy.
³⁹ Department of Orthopaedic Surgery, Noordwest Ziekenhuisgroep, Alkmaar, The Netherlands.
⁴⁰ Department of Neurological Surgery, Weill Cornell Medicine, New York, NY, USA.
⁴¹ Department of Orthopedic Surgery, Columbia University, New York, NY, USA.

PMID: 39639494
PMCID: PMC11622210
DOI: 10.1177/21925682241303107

Abstract

Study DesignReliability study.ObjectivesThe radiographic diagnosis of non-union is not standardized. Prior authors have suggested using a cutoff of <1 mm interspinous process motion (ISPM) on flexion-extension radiographs, but the ability of practicing surgeons to make these measurements reliably is not clear.Methods29 practicing spine surgeons measured ISPM on 19 levels of ACDF from 9 patients. Surgeons relied on these measurements to report on fusion status. Inter-observer correlation co-efficients (ICC), standard error (SEM) and the minimum detectable difference (MD) of these measurements were calculated. We screened for clerical errors by checking measurements more than one standard deviation from the group mean.ResultsThe ICC for ISPM was .76 (.64; .88) with a SEM of 1 mm and a MD of 2.76 mm. Agreement on fusion status was moderate, with an ICC of .6 (.44; .76). After screening for and removing clerical errors, the ICC improved to .82 (.71; .91), SEM improved to .83 mm, and MD improved to 2.29 mm. Six reviewers had an ICC >.9. The ICC from these high performing reviewers was .94 (.9; .97), SEM was .45 mm, and MD was 1.26 mm.ConclusionsThe MD of 2.29 mm in our study group was not precise enough to support a cutoff of <1 mm ISPM as the sole measurement technique in screening for non-union after ACDF, and there was only moderate agreement amongst surgeons on fusion status based on dynamic radiographs. More stringent techniques are necessary to avoid mis-diagnosing non-union in clinical studies. Future studies should consider auditing measurements to identify clerical errors.

Keywords: ACDF; fusion; interspinous process motion.

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Conflict of interest statement

Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

**Figure 1.**
Flexion (left) and Extension (right) images showing an example of using at least 150% magnification and adjusting the image contrast to identify bony landmarks (marked by arrow) for ISPM measurement.

**Figure 2.**
Measurement of ISPM (mm) from all reviewers in the first round of measurement.

**Figure 3.**
Measurement of ISPM (mm) from all reviewers after the removal of clerical errors.

**Figure 4.**
Measurement of ISPM (mm) from the six expert reviewers.

See this image and copyright information in PMC

References

1. Lin W, Ha A, Boddapati V, Yuan W, Riew KD. Diagnosing pseudoarthrosis after anterior cervical discectomy and fusion. Neurospine. 2018;15(3):194-205. doi:10.14245/ns.1836192.096 - DOI - PMC - PubMed
1. Riew KD, Yang JJ, Chang DG, et al. What is the most accurate radiographic criterion to determine anterior cervical fusion? Spine J. 2019;19(3):469-475. doi:10.1016/j.spinee.2018.07.003 - DOI - PubMed
1. Rhee JM, Chapman JR, Norvell DC, Smith J, Sherry NA, Riew KD. Radiological determination of postoperative cervical fusion: a systematic review. Spine. 2015;40(13):974-991. doi:10.1097/BRS.0000000000000940 - DOI - PubMed
1. Oshina M, Oshima Y, Tanaka S, Riew KD. Radiological fusion criteria of postoperative anterior cervical discectomy and fusion: a systematic review. Global Spine J. 2018;8(7):739-750. doi:10.1177/2192568218755141 - DOI - PMC - PubMed
1. Wang Z, Zhu R, Yang H, et al. Zero-profile implant (Zero-p) versus plate cage benezech implant (PCB) in the treatment of single-level cervical spondylotic myelopathy. BMC Musculoskelet Disord. 2015;16:290. doi:10.1186/s12891-015-0746-4. Published 2015 Oct 12. - DOI - PMC - PubMed

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How Reliable is the Assessment of Fusion Status Following ACDF Using Dynamic Flexion-Extension Radiographs?

Affiliations

How Reliable is the Assessment of Fusion Status Following ACDF Using Dynamic Flexion-Extension Radiographs?

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

References

LinkOut - more resources

Full Text Sources