An international validation of the AO spine subaxial injury classification system
Authors: Karamian Brian A. , Schroeder Gregory D. , Lambrechts Mark J. , Canseco Jose A. , Oner Cumhur , Vialle Emiliano , Rajasekaran Shanmuganathan , Dvorak Marcel R. , Benneker Lorin M. , Kandziora Frank , Schnake Klaus , Kepler Christopher K. , Vaccaro Alexander R. ,   AO Spine Subaxial Classification Group Members, Costa Bruno Lourenco , Estefan Martin , Dawoud Ahmed , Kaen Ariel , Yuh Sung-Joo , Fuego Segundo , Mannara Francisco , Ponnusamy Gunaseelan , Suri Tarun , Jayakumar Subiiah , Rodriguez Luis Cuchen , Cawley Derek , Godinho Amauri , Duerinck Johnny , Montemurro Nicola , Ozdener Kubilay , Hickman Zachary , Wael Alsammak , Gopalakrishnan Dilip , Santos Bruno , Morillo Olga , Sorimachi Yasunori , Miyakoshi Naohisa , Alkharsawi Mahmoud , Rahamimov Nimrod , Loya Vijay , Loughenbury Peter , Rodrigues Jose , Ankur Nanda , Alarcon Olger , Ampar Nishanth , Sprengel Kai , Subramaniam Macherla , Linn Kyaw , Subramanian Panchu , Osterhoff Georg , Mlyavykh Sergey , Martinez Elias Javier , Hadelsberg Uri , Silva Alvaro , Tsitsopoulos Parmenion , Munjal Satyashiva , Ayhan Selim , Gummerson Nigel , Rienmuller Anna , Vahl Joachim , Perez Gonzalo , Park Eugene , Pun Alvin , Madhivanan Kartigeyan , Pershin Andrey , Ullrich Bernhard , Khan Nasser , Lermen Olver , Robijn Hisco , Masanes Nicolas Gonzalez , Aziz Ali Abdel , Aoyama Takeshi , Fernandez Norberto , HJills Aaron , Roldan Hector , Longo Alessandro , Takeo Furuya , Kunej Tomi , Vaibhav Jain , Delgado-Fernandez Juan , Hernandez Guillermo Espinosa , Ramieri Alessandro , Fu Lingjie , Redaelli Andrea , Francis Jibin , Claudio Bernucci , Desai Ankit , Bazan Pedro , Manilha Rui , Diez-Ulloa Maximo-Alberto , Lozano Lady , Benzakour Thami , Koerner John , Medina Fabricio , Vieira Rian , West O. Clark , El-Sharkawi Mohammad , Cheng Christina , Paez Rodolfo , Benzarti Sofien , Elhewala Tarek , Corluka Stipe , Atan Ahmad , Santiago Bruno , Wilson Jamie , Kundangar Raghuraj , Bhatt Pragnesh , Bhandutia Amit , Zagorac Slavisa , Nerrkaje Shyamasunder , Denisov Anton , Linhares Daniela , Ricciardi Guillermo , Popescu Eugen Cezar , Bharat Dave , Darwish Stacey , Rasschaert Ricky , Mehrkens Arne , Faizan Mohammed , Tanaka Sunao , Hockley Aaron , Ufuk Aydinli , Triffaux Michel , Garashchuk Oleksandr , Dizon Dave , Murphy Rory , Alqatub Ahmed , Gurung Kiran , Tejeda Martin , Lakhey Rajesh , Viswanadha Arun , Riesenbeck Oliver , Rapetti Daniel , Singh Rakesh , Vallapureddy Naveenreddy , Amine Triki , Moraes Osmar , Ali Dalia , Balestrino Alberto , Luna Luis , Grassner Lukas , Laos Eduardo , Ramalu Rajendra Rao , Lener Sara , Zambito Gerardo , Patterson Andrew , Konrads Christian , Ganau Mario , Shoaib Mahmoud , Paterakis Konstantinos , Amin Zaki , Bhavuk Garg , Toluse Adetunji , Klezl Zdenek , Sartor Federico , Rioja Ribakd , Margetis Konstantinos , Pereira Paulo , Neves Nuno , Perovic Darko , Yurak Ratko , Balgopal Karmacharya , Rutges Joost , Milano Jeronimo , Figueiredo Alfredo , Lourido Juan , Russo Salvatore , Tannoury Chadi , Falcone David Orosco , Duarte Matias Pereria , Muthu Sathish , Aceituno Hector , Tokala Devi , Plaza Jose Ballesteros , da Rocha Luiz dal Oglio , Riera Rodrigo , Gyanendra Shah , Jun Zhang , Suarez-Fernandez David , Oner Ali , Tipper Geoffrey , Osundina Ahmad , Hamouda Waeel , Silk Zacharia , Bances Ignacio Fernandez , Nur Aida Faruk Senan , Gupta Anuj , Murrieta Saul , Tamburrelli Francesco , Georgiopoulos Miltiadis , Goyal Amrit , Zylbersztejn Sergio , Bas Paloma , Sharma Deep , Aithala Janardhana , Kornfeld Sebastian , Cruz-Morande Sebastian , Hussain Rehan , Pallero Maria Garcia , Nagashima Hideki , Elgafy Hossein , Patil Om , Guasque Joana , Wui Ng Bing , Bouras Triantafyllos , Naresh Kumar , Tsuang Fon-Yih , Morakis Andreas , Hartmann Sebastian , Girod Pierre-Pascal , Reihtmeier Thomas , Wimalachandra Welege 
Published: November 2022

Abstract
Purpose
To validate the AO Spine Subaxial Injury Classification System with participants of various experience levels, subspecialties, and geographic regions.

Methods
A live webinar was organized in 2020 for validation of the AO Spine Subaxial Injury Classification System. The validation consisted of 41 unique subaxial cervical spine injuries with associated computed tomography scans and key images. Intraobserver reproducibility and interobserver reliability of the AO Spine Subaxial Injury Classification System were calculated for injury morphology, injury subtype, and facet injury. The reliability and reproducibility of the classification system were categorized as slight (ƙ = 0–0.20), fair (ƙ = 0.21–0.40), moderate (ƙ = 0.41–0.60), substantial (ƙ = 0.61–0.80), or excellent (ƙ = > 0.80) as determined by the Landis and Koch classification.

Results
A total of 203 AO Spine members participated in the AO Spine Subaxial Injury Classification System validation. The percent of participants accurately classifying each injury was over 90% for fracture morphology and fracture subtype on both assessments. The interobserver reliability for fracture morphology was excellent (ƙ = 0.87), while fracture subtype (ƙ = 0.80) and facet injury were substantial (ƙ = 0.74). The intraobserver reproducibility for fracture morphology and subtype were excellent (ƙ = 0.85, 0.88, respectively), while reproducibility for facet injuries was substantial (ƙ = 0.76).

Conclusion
The AO Spine Subaxial Injury Classification System demonstrated excellent interobserver reliability and intraobserver reproducibility for fracture morphology, substantial reliability and reproducibility for facet injuries, and excellent reproducibility with substantial reliability for injury subtype.