Practical Application of the AO Spine Primary Infection Classification System: Clarifying Definitions, Borderline Cases and Common Misinterpretations.
15 affiliations
- 1Department of Spine and Neurotrauma, National Trauma Research Institute, Melbourne, VIC, Australia.
- 2Department of Neurosurgery, The Alfred Hospital, Melbourne, VIC, Australia.
- 3Department of Neurosurgery, Royal Melbourne Hospital, Parkville, VIC, Melbourne.
- 4Department of Orthopaedic Surgery, Rothman Institute, Thomas Jefferson University Hospital, Philadelphia, PA, USA.
- 5Department of Neurosurgery, Prince Mohammed Bin Abdulaziz Hospital, Riyadh, Saudi Arabi.
- 6Department of Orthopaedic and Trauma Surgery, Faculty of Medicine, Assiut University, Assiut, Egypt.
- 7Combined Neurosurgical and Orthopedic Spine Program, Vancouver General Hospital, University of British Columbia, Vancouver, Canada.
- 8Center for Spinal Surgery and Neurosurgery, Berufsgenossenschaftliche Unfallklinik Frankfurt Am Main, Frankfurt-Ost, Germany.
- 9Department of Neurosurgery, LMU University Hospital, Munich, Germany.
- 10Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA.
- 11Department of Orthopaedic Surgery, Stanford University, Redwood City, CA, USA.
- 12Department of Orthopaedic Surgery, Sri Balaji Action Medical Institute, New Delhi, India.
- 13Harborview Medical Center, University of Washington, Seattle, WA, USA.
- 14Neurosurgery Division, Department of Neurology, State University of Campinas, Campinas, Sao Paulo, Brazil.
- 15Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, VIC, Australia.
Abstract
Study DesignNarrative review.ObjectiveTo clarify nuances when applying the AO Spine Primary Infection Classification.MethodsThe international validation of the AO Spine Primary Infection Classification System was successful but recurring themes caused confusion. This included the exact definition and reasons for infections to transition between categories, definition of canal involvement or neural compression and whether an epidural infection superimposed on degenerative disease escalates infection severity. There was uncertainty regarding handling of multi-level or junctional infection and clinicians encountered difficulty applying the modifiers.ResultsThe difference between a Type 0 and Type 1 infection is reasonably distinct given the former is purely extraspinal whilst the latter involves spondylodiscitis or osteomyelitis without canal involvement. Type 2 infections include those with any canal involvement, regardless of whether CSF effacement occurs, in the absence of neural compression. The spinal canal is defined as the compartment dorsal to the posterior longitudinal ligament and excludes infections that are ventral to this ligament but bow into the canal. Any neural compression of the thecal sac centrally or within the foramen escalates categorization to a Type 3 infection.ConclusionsPrimary spinal infections have the potential to rapidly progress and cause devastating neurological deficits. The introduction of the AO Spine Primary Infection Classification establishes a universal language to communicate disease severity. We clarify common nuances encountered during international validation of this system including definition of canal involvement and relevance of CSF effacement, whether foraminal involvement constitutes neural compression and the nomenclature concerning multi-level or junctional disease.
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BibTeX
@article{kweh2026practical,
title = {{Practical Application of the AO Spine Primary Infection Classification System: Clarifying Definitions, Borderline Cases and Common Misinterpretations.}},
author = {Barry Ting Sheen Kweh and Alexander R Vaccaro and Gregory Schroeder and Mohamed Aly and Mohammad El-Sharkawi and Charlotte Dandurand and Jonathan Neuhoff and Brian Karamian and Grace Xiong and Harvinder Singh Chhabra and Richard Bransford and Andrei Fernandes Joaquim and Jin Wee Tee},
journal = {Global spine journal},
year = {2026},
month = oct,
doi = {10.1177/21925682261498682},
url = {https://europepmc.org/article/MED/42874070},
note = {CC BY-NC-ND},
}
RIS
TY - JOUR
TI - Practical Application of the AO Spine Primary Infection Classification System: Clarifying Definitions, Borderline Cases and Common Misinterpretations.
AU - Barry Ting Sheen Kweh
AU - Alexander R Vaccaro
AU - Gregory Schroeder
AU - Mohamed Aly
AU - Mohammad El-Sharkawi
AU - Charlotte Dandurand
AU - Jonathan Neuhoff
AU - Brian Karamian
AU - Grace Xiong
AU - Harvinder Singh Chhabra
AU - Richard Bransford
AU - Andrei Fernandes Joaquim
AU - Jin Wee Tee
PY - 2026
DA - 2026/10/14
JO - Global spine journal
DO - 10.1177/21925682261498682
UR - https://europepmc.org/article/MED/42874070
AB - Study DesignNarrative review.ObjectiveTo clarify nuances when applying the AO Spine Primary Infection Classification.MethodsThe international validation of the AO Spine Primary Infection Classification System was successful but recurring themes caused confusion. This included the exact definition and reasons for infections to transition between categories, definition of canal involvement or neural compression and whether an epidural infection superimposed on degenerative disease escalates infection severity. There was uncertainty regarding handling of multi-level or junctional infection and clinicians encountered difficulty applying the modifiers.ResultsThe difference between a Type 0 and Type 1 infection is reasonably distinct given the former is purely extraspinal whilst the latter involves spondylodiscitis or osteomyelitis without canal involvement. Type 2 infections include those with any canal involvement, regardless of whether CSF effacement occurs, in the absence of neural compression. The spinal canal is defined as the compartment dorsal to the posterior longitudinal ligament and excludes infections that are ventral to this ligament but bow into the canal. Any neural compression of the thecal sac centrally or within the foramen escalates categorization to a Type 3 infection.ConclusionsPrimary spinal infections have the potential to rapidly progress and cause devastating neurological deficits. The introduction of the AO Spine Primary Infection Classification establishes a universal language to communicate disease severity. We clarify common nuances encountered during international validation of this system including definition of canal involvement and relevance of CSF effacement, whether foraminal involvement constitutes neural compression and the nomenclature concerning multi-level or junctional disease.
SN - 2192-5682
SN - 2192-5690
ER -