DOI: 10.1055/s-0038-1677459
The Comprehensive AO CMF Classification System for Mandibular Fractures: A Multicenter Validation Study
Publication History
14 September 2018
04 November 2018
Publication Date:
31 January 2019 (online)

Abstract
The AO CMF has recently launched the first comprehensive classification system for craniomaxillofacial (CMF) fractures. The AO CMF classification system uses a hierarchical framework with three levels of growing complexity (levels 1, 2, and 3). Level 1 of the system identifies the presence of fractures in four anatomic areas (mandible, midface, skull base, and cranial vault). Level 2 variables describe the location of the fractures within those defined areas. Level 3 variables describe details of fracture morphology such as fragmentation, displacement, and dislocation. This multiplanar radiographic image-based AO CMF trauma classification system is constantly evolving and beginning to enter worldwide application. A validation of the system is mandatory prior to a reliable communication and data processing in clinical and research environments. This interobserver reliability and accuracy study is aiming to validate the three current modules of the AO CMF classification system for mandible trauma in adults. To assess the performance of the system at the different precision levels, it focuses on the fracture location within the mandibular regions and condylar process subregions as core components giving only secondary attention to morphologic variables. A total of 15 subjects individually assigned the location and features of mandibular fractures in 200 CT scans using the AO CMF classification system. The results of these ratings were then statistically evaluated for interobserver reliability by Fleiss' kappa and accuracy by percentage agreement with an experienced reference assessor. The scores were used to determine if the variables of levels 2 and 3 were appropriate tools for valid classification. Interobserver reliability and accuracy were compared by hierarchy of variables (level 2 vs. level 3), by anatomical region and subregion, and by assessor experience level using Kruskal–Wallis and Wilcoxon's rank-sum tests. The AO CMF classification system was determined to be reliable and accurate for classifying mandibular fractures for most levels 2 and 3 variables. Level 2 variables had significantly higher interobserver reliability than level 3 variables (median kappa: 0.69 vs. 0.59, p < 0.001) as well as higher accuracy (median agreement: 94 vs. 91%, p < 0.001). Accuracy was adequate for most variables, but lower reliability was observed for condylar head fractures, fragmentation of condylar neck fractures, displacement types and direction of the condylar process overall, as well as the condylar neck and base fractures. Assessors with more clinical experience demonstrated higher reliability (median kappa high experience 0.66 vs. medium 0.59 vs. low 0.48, p < 0.001). Assessors with experience using the classification software also had higher reliability than their less experienced counterparts (median kappa: 0.76 vs. 0.57, p < 0.001). At present, the AO CMF classification system for mandibular fractures is suited for both clinical and research settings for level 2 variables. Accuracy and reliability decrease for level 3 variables specifically concerning fractures and displacement of condylar process fractures. This will require further investigation into why these fractures were characterized unreliably, which would guide modifications of the system and future instructions for its usage.
References
- 1 Cornelius CP, Audige L, Kunz C. , et al. The comprehensive AOCMF classification system: mandible fractures- Level 2 tutorial. Craniomaxillofac Trauma Reconstruction 2014; 7 (Suppl. 01) S15-S30
- 2 Audigé L, Cornelius CP, Di Ieva A, Prein J, Group CC. ; CMF Classification Group 6. The first AO classification system for fractures of the craniomaxillofacial skeleton: rationale, methodological background, developmental process, and objectives. Craniomaxillofac Trauma Reconstr 2014; 7 (01) (Suppl. 01) S006-S014
- 3 Manson PN, Hollier L, Schubert W. CMF classification. Craniomaxillofac Trauma Reconstr 2014; 7 (01) (Suppl. 01) S001-S003
- 4 Audigé L, Bhandari M, Hanson B, Kellam J. A concept for the validation of fracture classifications. J Orthop Trauma 2005; 19 (06) 401-406
- 5 Cornelius CP, Audigé L, Kunz C. , et al. The comprehensive AOCMF classification system: mandible fractures-Level 3 tutorial. Craniomaxillofac Trauma Reconstr 2014; 7 (01) (Suppl. 01) S031-S043
- 6 Neff A, Cornelius CP, Rasse M. , et al. The comprehensive AOCMF classification system: condylar process fractures - level 3 tutorial. Craniomaxillofac Trauma Reconstruction 2014; 7 (Suppl. 01) S44-S58
- 7 Buitrago-Téllez CH, Audigé L, Strong B. , et al. A comprehensive classification of mandibular fractures: a preliminary agreement validation study. Int J Oral Maxillofac Surg 2008; 37 (12) 1080-1088
- 8 Müller ME, Nazarian S, Koch P, Schatzker J. The Comprehensive Classification of Fractures of Long Bones. Berlin, Heidelberg: Springer; 1990
- 9 Lowe HJ, Ferris TA, Hernandez PM, Weber SC. STRIDE--An integrated standards-based translational research informatics platform. AMIA Annu Symp Proc 2009; 2009: 391-395
- 10 Audigé L, Cornelius CP, Kunz C, Buitrago-Téllez CH, Prein J. The comprehensive AOCMF classification system: classification and documentation within AOCOIAC software. Craniomaxillofac Trauma Reconstr 2014; 7 (01) (Suppl. 01) S114-S122
- 11 Fleiss JL. Measuring nominal scale agreement among many raters. Psychol Bull 1971; 76 (05) 378-382
- 12 Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977; 33 (01) 159-174
- 13 Slongo T, Audigé L, Schlickewei W, Clavert JM, Hunter J. ; International Association for Pediatric Traumatology. Development and validation of the AO pediatric comprehensive classification of long bone fractures by the Pediatric Expert Group of the AO Foundation in collaboration with AO Clinical Investigation and Documentation and the International Association for Pediatric Traumatology. J Pediatr Orthop 2006; 26 (01) 43-49
- 14 Kreder HJ, Hanel DP, McKee M, Jupiter J, McGillivary G, Swiontkowski MF. Consistency of AO fracture classification for the distal radius. J Bone Joint Surg Br 1996; 78 (05) 726-731
- 15 Schipper IB, Steyerberg EW, Castelein RM, van Vugt AB. Reliability of the AO/ASIF classification for pertrochanteric femoral fractures. Acta Orthop Scand 2001; 72 (01) 36-41
- 16 Martin JS, Marsh JL, Bonar SK, DeCoster TA, Found EM, Brandser EA. Assessment of the AO/ASIF fracture classification for the distal tibia. J Orthop Trauma 1997; 11 (07) 477-483
- 17 Rigby AS. Statistical methods in epidemiology. v. Towards an understanding of the kappa coefficient. Disabil Rehabil 2000; 22 (08) 339-344
- 18 Zhou Z, Li Z, Ren J. , et al. Digital diagnosis and treatment of mandibular condylar fractures based on Extensible Neuro imaging Archive Toolkit (XNAT). PLoS One 2018; 13 (02) e0192831-e0192814