Share this article on:

Introduction: Fracture and Dislocation Classification Compendium—2018International Comprehensive Classification of Fractures and Dislocations Committee

Kellam, James F. MD*; Meinberg, Eric G. MD**; Agel, Julie MA, ATC***; Karam, Matthew D. MD****; Roberts, Craig S. MD, MBA*****

Journal of Orthopaedic Trauma: January 2018 - Volume 32 - Issue - p S1–S10
doi: 10.1097/BOT.0000000000001063
Supplement Article

*Department of Orthopaedic Surgery, McGovern Medical School, University of Texas Health Sciences Center at Houston,

**Department of Orthopae dic Surgery, Zuckerberg San Francisco General Hospitial, University of California, San Francisco;

***Department of Orthopaedic Surgery, Harborview Medical Center, Seattle,

****University of Iowa Department of Orthopaedics and Rehabilitation, Iowa City,

*****Department of Orthopaedic Surgery; University of Louisville School of Medicine

Correspondence: James F. Kellam, Department of Orthopaedic Surgery, McGovern Medical School, University of Texas Health Sciences Center at Houston, 6431 Fannin Street, MSB 6.146, Houston Texas, 77030 (e-mail:

Disclosure: The authors report no conflicts of interest.

Material presented in this Compendium is based on the Comprehensive Classification of Fractures of Long Bones by M.E. Muller, J. Nazarian, P. Koch and J. Schatzker, Springer-Verlag, Berlin, 1990. The Orthopaedic Trauma Association is indebted to Professor Maurice Muller for allowing use of the system.

To encourage the use of this classification and this fracture classification compendium, the figures may be reproduced and the classification may be used for research, educational and or medical purposes without the need to request permission from the OTA, AO Foundation or the publisher. It cannot be used commercially or for-profit without permission.

Back to Top | Article Outline


Dear Colleague

We would like to introduce you to the 2018 OTA/AO (or AO/OTA) Fracture and Dislocation Classification Compendium. This is the second revision of the compendium which was first published in 1996 as a cooperative effort of the AO Foundation and the Orthopaedic Trauma Association (OTA). Both organizations were committed to assuring that there was a standardized and rational methodology of describing fractures and dislocation as well as a mechanism to code data for future recall. These principles were absolutely necessary to establish a consistent system for clinical interaction and research.

After 20 years of use, the current revision addresses the many suggestions to help improve the application of the system, correct errors, and add new classifications. The process was under the direction of a committee of four individuals representing both organizations, with experience in the day to day application of the compendium and fracture coding. The process was supervised and funded by the Classification Committee of the OTA and AOTrauma International Board (AOTIB). An ongoing agreement between both organizations to assure the ongoing collaborative support of the revision process of the compendium was also developed. Importantly, copyright will remain with both organizations so that its reproduction and promulgation will be unencumbered. This establishes not only mutual ownership but also responsibility and ensures continued collaboration and support.

We believe that this is an important step forward in the process of clinical research as well as standardizing day to day clinical communication. However, change is inevitable and both the OTA and the AOTIB encourage comment and criticisms so that the next revision process can continue to improve the compendium.

John H. Wilber MD

Chairman, AOTrauma International Board

Professor and Chair Department of Orthopaedic Surgery MetroHealth Medical Center

Hansjoerg Wyss Professor Orthopaedic Trauma Case Western Reserve University

Cleveland, Ohio

William M. Ricci MD

President, Orthopaedic Trauma Association

Chief, Combined HSS/NYP Trauma Service Hospital for Special Surgery

New York Presbyterian Hospital

New York, NY

Back to Top | Article Outline

Compedium introduction

The AO Foundation/Orthopaedic Trauma Association (AO/OTA) fracture classification was published as a compendium to the Journal of Orthopaedic Trauma (JOT) in 1996.1 Using the principles of the Comprehensive Classification of Fractures of the Long Bones (CCF) developed by Müller and collaborators, the OTA classification committee classified and coded the remaining bones.2 , 3 This helped bring order to the state of fracture classification with its multiple systems that had thwarted any possibility of a standardized language and accumulation of uniform data.

Since the compendium was published in 1996, the classification has resided on the OTA and AO Foundation websites and has been regularly used in trauma databases, scientific journals, and textbooks worldwide. It is the official classification of the OTA, the AO, and JOT. It has gained wide acceptance and its use has dramatically improved the way information about fractures is communicated, stored, and used to advance knowledge. In some anatomical areas, this classification has largely supplanted multiple options achieving one of the original intentsion.1 , 2 , 3

The classification is intended to be a flexible evolving system in which changes are made based on user feedback, criticism, and appropriate clinical research, thus serving the needs of the orthopedic community for both clinical practice and research.

In 2007, the AO and OTA classification committees undertook a revision to address issues of reliability, reproducibility, and need. This revision was based on the premise that changes needed to be validated prior to being implemented. The validation process was expensive and not practical so a decision was made to not validate all edits. The 2007 revision standardized the two different alphanumeric codes into one agreed-upon scheme, thus developing an internationally recognized uniform system for clinical research on fractures and dislocations.

The validated AO Pediatric Classification of Fractures developed by Slongo was also included in the compendium.4 , 5 The two committees confirmed the original premise that the revision process needed to be undertaken every 10 years.

Ongoing concerns about terminology, the relevancy of certain classification schemes, and the need to streamline codes provided the impetus to undertake the 2018 review.6–12 To make this an effective, economical, and efficient process, the AOTrauma International Board (AOTIB) and OTA appointed five persons to form the International Comprehensive Classification of Fractures and Dislocations Committee (ICCFC). The process began with the aims to address editorial errors, criticisms of the proximal humerus and proximal femur classification, and to simplify the coding process based on fracture pattern occurrence and complexity using a modified Delphi approach. A priority for this revision was to maintain the original principles of the CCF with regard to definitions and the basic coding system. It became apparent that many of the fracture patterns occurred so infrequently that there was no need to have a unique code for them, as they could easily be coded by a shortened generic system. Frequency plots of a large registry that uses these codes confirmed this. It became evident that it would be more accurate to code radius and ulna fractures separately and to align the system with ICD-10 terminology.13 The same was done for the other two-bone system by adding a new coding system for fibula fractures. The former editions had many qualifications and sub-qualifications for each fracture pattern, many of which were duplications. The committee decided to group these into a universal modifier list that could be applied to every fracture as desired by the end user, who codes the fracture. All fracture specific modifiers were maintained with their specific fracture or dislocation. As this classification system provides standard terminology and codes, it also felt appropriate to combine, insert, or reference other commonly accepted classifications (eg, Neer) into the AO/OTA descriptions and codes. This would assure consistency and greater clinical utility in fracture and dislocation classification.

Back to Top | Article Outline

The 2018 compendium revision

The compendium is branded as the AO/OTA or OTA/AO Fracture and Dislocation Classification Compendium. In publications, it will be cited as Meinberg E, Agel J, Roberts C, et al. Fracture and Dislocation Classification Compendium–2018, Journal of Orthopaedic Trauma. Volume 32: Number 1; Supplement, January 2018.

Future publications related to the revised Compendium will be authored and referenced as determined by the International Comprehensive Classification of Fractures and Dislocations Committee (ICCFC), irrespective of its member composition.

The mandates for the 2018 revision are the following:

  • a) Editorial, terminology, and typographical changes and corrections:
  • i. The terms "complex” and "multifragmentary” have created confusion in their application. The term "complex” did not describe a fracture pattern consisting of many fragments while "multifragmentary” does. Multifragmentary was previously used generically to refer to diaphyseal type B and C and did not have a specific alphanumeric code so was rarely used. Consequently, the committee felt that it is more concise to have three types of diaphyseal fractures: simple, wedge, and multifragmentary. "Multifragmentary” will no longer be used as a generic term for diaphyseal types B and C. A multifragmentary diaphyseal or end segment extraarticular fracture is one with many fracture fragments and after reduction there is no contact between the main fragments. A multifragmentary complete articular fracture is one with more than two fracture fragments of the articular surface.
  • ii. The diaphyseal fracture classification has been made consistent for all bones. The diaphysis is defined as that part of the bone between the two end segments and is divided into three equal parts defining the location of the diaphyseal fracture. The fracture location within the diaphysis is a qualification as follows:
  • a Proximal 1/3
  • b Middle 1/3
  • c Distal 1/3
  • iii. A more precise description of the intraarticular portion of proximal tibia fractures has been recommended.14,15 A modification to the proximal tibia classification as recommended by Mauricio Kfuri and Joseph Schaztker to better define the significant joint fragmentation or displacement is added as qualifications for type B and C proximal tibial intraarticular fractures.16
  • iv. The written description of fractures has been standardized so that each fracture is presented in a similar order highlighting the specific region or fracture morphology.
  • v. To facilitate data entry and lessen the error rate in coding, the hyphen in the code has been removed.
  • vi. A code for fibula fractures based on the principles of the CCF has been added.
  • vii. The Neer classification has been integrated into the fracture description for proximal humeral fractures to facilitate the clinician comprehension of the terms unifocal and bifocal fractures.
  • viii. The proximal femoral classification terminology has been a source of confusion as a variety of descriptive terms have been used to describe similar fractures. There has also been a problem defining fractures for group 31A2. Definitions have been added to help classify these fractures and the codes reorganized to better represent these fractures. The femoral neck fractures have been organized to better align the fracture types. By adding the Pauwels classification as a qualification for femoral neck fractures a more detailed evaluation of high-energy fractures is available.
  • ix. The Young-Burgess Classification of Pelvic Ring Injuries has been integrated into the AO/OTA pelvic fracture classification.
  • b) Addition of recently published validated classifications:
  • i. OTA Open Fracture Classification17
  • ii. AO/OTA Scapular Fracture Classification18,19
  • iii. Unified Classification of Periprosthetic Fractures20
  • iv. AOSpine Subaxial Cervical and Thoracolumbar spine injury classification21
  • v. AOSpine Sacral Fracture Classification22
  • c) At the request of the AOTK Thoracic Surgery Expert Group, a preliminary classification of rib and sternal fractures has been included. Publication of this classification will allow interested groups to assess its validity and reproducibility so in the next revision, a validated modification will be available.
  • d) Review of the codes with regards to frequency and applicability:
  • i. Many of the qualifications and subqualifications of the first two compendiums were repetitious and on a survey of users were not routinely used. To simplify the usage, the common modifiers were placed in a list called Universal Modifiers. This simplifies the presentation of the codes and allows each clinician to use these as they see fit for their circumstances.
  • ii. Certain qualifications were fracture-specific and were left as qualifications within the specific fracture types and groups.
  • iii. Complex injuries such as the terrible triad of the elbow and a transolecranon fracture dislocation are difficult to code related to the fact that fractures of radius and ulna were placed into one code. The committee decided to separate the radius and ulna and classify fractures in each bone. This simplifies the process and when combined with the universal modifiers makes classification of complex injuries about the elbow more consistent and accurate. It also follows the ICD-10 system where each bone is coded separately.

It was recognized by the committee that this revision must maintain the principles and definitions of the CCF and the prior two compendiums. This revision represents a streamlining of the 2007 version. The aim was to assure that the majority of fracture patterns were represented. This revision provides a more concise and clinically relevant compendium. The user will be able to choose the code that best meets their needs. It is hoped that with the recognition of other standard classifications being integrated into the codes that this compendium will be of increasing value to many other orthopedic subspecialities.

Back to Top | Article Outline

Fundamentals of fracture classification

Classification is the process by which related groups are organized based on similarities and differences.5 It provides the language necessary to convey information among individuals to ensure standardization. This classification process may be looked upon as the systematic methodology of describing a fracture or dislocation. It is critical to note that a fracture should be coded only after all the information is obtained. It must be remembered that if there is doubt, then waiting until the complete information is available is mandatory before determining the final classification.23–28 The final classification may be delayed until the operative procedure is completed and the fracture fully visualized.

This system provides the clinician with standardized definitions so the verbal fracture description is precise and consistent from bone to bone and fracture to fracture. These standard definitions and guidelines for application assure consistency in the classification process.16 , 24–37 With the improved consistency of fracture descriptions, future investigations assessing treatment guidelines, prognosis, and risk of complications will be more reliable and meaningful. The system also provides a mechanism to convert the verbal description into an alphanumeric code to allow for data storage and future recall. The use of this alphanumeric coding scheme is absolutely necessary for multicenter collaboration, retrospective comparison of results, international communication, and to standardize recording information about all fractures in a trauma database.

The classification offers several other benefits. It provides a hierarchy of severity as the descriptions generally proceed from simple to multifragmentary fractures. This hierarchy is based on the energy of injury or potential complexity of treatment. Ease of use is also an important aspect for a classification. This system allows the clinician to be as general or detailed as necessary according to their clinical or research needs. The classification is logical, comprehensible, and does not contain an unmanageable number of categories, a problem that ensures poor reliability.

Back to Top | Article Outline

Principles of fracture and dislocation classification

The principles of classification2 are based on understanding and applying standardized definitions. These definitions are universal and allow consistency in classification and communication. Although clinical decisions are sometimes made on incomplete information, this should be avoided as much as possible when classifying a fracture–the more precise the description the better the data recorded. Attention should be paid to upper-case versus lower-case letters and ( ) versus [ ] as this will aid in accurate fracture pattern retrieval from databases.

Back to Top | Article Outline

Fracture localization–bones and segments

The bone is identified ( Fig 1 ).

Fig 1

Fig 1

Next, it is necessary to determine where in the bone the fracture is located. This requires precise definitions of the parts of a bone. The proximal and distal end segments of the long bones are defined by a square whose sides are the same length as the widest part of the epiphysis/metaphysis in question (Heim's system of squares).23 Each bone has a proximal and distal end segment, between which the diaphysis or shaft is located. These definitions apply to any bone with articulations at both ends and a segment of cortical bone between the articulations, for example, a femur, or a metacarpal, or a phalanx. With the two bone systems now having separate codes, it was decided to maintain the standard definition of the end segments with bones not separated ( Fig 2 ).

Fig 2

Fig 2

Two exceptions are the proximal femur, defined as being above a line that passes transversely through the inferior edge of the lesser trochanter and the malleolar segment of the distal tibia.

The bone segments are numbered as:

Proximal end segment = 1

Diaphyseal segment = 2

Distal end segment = 3

The location of the fracture is determined by finding its center. This is defined as follows:

  • In a simple fracture, the center of the fracture is obvious (Fig 3).
  • In a wedge fracture, the center is at the level of the broadest part of the wedge (Fig 4).
  • In a fragmentary wedge and a multifragmentary fracture, the center can be determined only after reduction (Fig 4).
  • Any diaphyseal fracture associated with a displaced articular component is considered an articular fracture.
  • If a fracture is associated with an undisplaced fissure that reaches the joint, it is classified as a metaphyseal or diaphyseal fracture depending on its center.
  • If one bone has two completely separate fractures, one in the diaphysis and one in the proximal or distal end segments (eg, a femoral diaphysis and a femoral neck fracture), each fracture must be classified separately.
Fig 3

Fig 3

Fig 4

Fig 4

Back to Top | Article Outline

Fracture morphology: types, groups, subgroups, qualifications, and universal modifiers

The type (upper-case letter) is a general description of fracture patterns while the group (numerals) is a more specific description based on the individual bone or specific fracture pattern.

The morphology of the diaphyseal fracture is defined as:

SimpleType A fractures have a single circumferential disruption of the diaphysis. An oblique fracture forms an angle ≥30° to a line perpendicular to the long axis of the bone. (Fig 3).

WedgeType B fractures are characterized by contact between the main fragments after reduction usually restoring the normal length of the bone. The wedge fragment may be intact, or in multiple fragments (ie, fragmentary wedge). The differentiation between spiral and bending wedge is inconsistent and not easily determined so these terms were moved to the universal modifiers (Fig 4).

Multifragmentary–Type C fractures consist of many fracture lines and fracture fragments. These fractures were known as either wedge or complex fractures in the Müller comprehensive classification. “Complex” is a term that caused confusion because it is nonspecific and is replaced in the 2018 version by the term "multifragmentary" meaning many contiguous fracture fragments, and not a wedge fracture.

In the diaphyseal segment, the fractured segment is either intact or in many fragments so that after reduction if the fractured area were removed there would be no contact between the proximal and distal fragments. Fragmentary is used to describe fragmentation of a wedge or segment (Fig 5).

Fig 5

Fig 5

The morphology for end segment fractures is based on whether they are extraarticular (no extension into the articular surface) or intraarticular (has an extension into the articular surface).

Extraarticular–Type A: The fracture line may be metaphyseal or epiphyseal, but it always spares the articular surface although it may be intracapsular.

Partial articular–Type B: The fracture involves part of the articular surface while the remainder of the joint remains intact and is solidly connected to the supporting metaphysis and diaphysis.

Complete articular–Type C: There is a disruption of the articular surface and the articular surface is completely separated from the diaphysis.

Further description of fracture morphology at the articular surface or metaphysis use the previously defined terms of simple (single disruption of the joint surface) and multifragmentary (multiple disruptions of the joint surface) patterns. Avulsion fractures are always classified as extraarticular simple fractures (Fig 6).

Fig 6

Fig 6

Back to Top | Article Outline


The proximal end segment of the humerus and femur are exceptions:

  • Simple proximal humeral fractures involving one tuberosity or the metaphysis (unifocal or Neer 2-part fractures) and proximal femoral fractures involving the trochanteric area are type A
  • The partial articular type does not exist in the humerus or femur. Proximal humeral fracture involving one tuberosity and the metaphysis (bifocal or Neer 3-part fractures), and the proximal femoral fracture involving the femoral neck are type B.
  • Proximal humeral articular fractures involving the anatomical neck of the humerus and fractures involving the femoral head are type C.

The definitions or description of groups and subgroups are fracture specific.

Back to Top | Article Outline

Universal modifiers

The universal modifiers are descriptive terms of fracture morphology, displacement, associated injury, or location that are generalizable to most fractures. They provide detail that are optional for users.

Universal modifiers may be added to the end of the fracture code within square brackets, eg, [1].

Multiple universal modifiers may be contained within the same set of squared brackets and separated by a comma.

Example: A proximal humerus fracture-dislocation with displacement, anterior dislocation, cartilage injury, and osteopenia = 11A1.2[2,5a,8e,9]

Example: Humerus, proximal end segment, articular or 4-part fracture, with multifragmentary metaphyseal fracture and articular fracture with an anterior dislocation = 11C3.2 [5a]

  1. Nondisplaced
  2. Displaced
  3. Impaction
  4. 3a Articular
  5. 3b Metaphyseal
  6. No impaction
  7. Dislocation
  8. 5a Anterior (volar, palmar, plantar)
  9. 5b Posterior (dorsal)
  10. 5c Medial (ulnar)
  11. 5d Lateral (radial)
  12. 5e Inferior (with hip is also obturator)
  13. 5f Multidirectional
  14. Subluxation/ligamentous instability
  15. 6a Anterior (volar, palmar, plantar)
  16. 6b Posterior (dorsal)
  17. 6c Medial (ulnar)
  18. 6d Lateral (radial)
  19. 6e Inferior (with hip is also obturator)
  20. 6f Multidirectional
  21. Diaphyseal extension
  22. Articular cartilage injury #
  23. 8a ICRS Grade 0 Normal
  24. 8b ICRS Grade 1 Superficial indentation (A) and /or superficial fissures and cracks (B)
  25. 8c ICRS Grade 2 Abnormal lesions extending down to 50% of cartilage depth
  26. 8d ICRS Grade 3 (A) Severely abnormal with defects extending down >50% of cartilage depth; (B) down to calcified layer; (C) down to subchondral bone but not through; (D) blisters included
  27. 8e ICRS Grade 4 Severely Abnormal Cartilage loss through subchondral bone
  28. Poor bone quality
  29. Replantation
  30. Amputation associated with a fracture
  31. Associated with a nonarthroplasty implant
  32. Spiral type fracture
  33. Bending type fracture

#This grading system is used with the permission of the International Cartilage Repair Society.38

Back to Top | Article Outline


The fracture qualifications are descriptive terms of fracture morphology or location that are specific to each fracture.

  • All fracture classification qualifications are lower-case letters to differentiate them from the fracture type, which is always an upper-case letter.
  • All fracture qualifications are inserted in place of the asterisk in the fracture code as a lower-case letter within a round bracket, eg, (a).
  • Where appropriate in the classification sections, the qualification that corresponds to an the image is bolded.

Example: Humerus, proximal end segment, articular or 4-part fracture, with multifragmentary metaphyseal fracture and simple articular fracture with an anterior dislocation 11C3.2(x) [5a]

The process of classification and coding a diaphyseal fracture

The process of classification and coding a diaphyseal fracture

The process of classification and coding an end-segment fracture

The process of classification and coding an end-segment fracture

Back to Top | Article Outline

Alphanumeric structure of the AO/OTA classification



Back to Top | Article Outline


Since the original publication of the AO/OTA Fracture Classification in the 1996 Journal of Orthopaedic Trauma Compendium, there has been important progress in fracture classification toward the goal of a universally accepted comprehensive fracture language. The 21 years of use of the AO/OTA compendium has demonstrated its strengths and shortcomings. Although admirable, the process of classification validation has been time consuming and expensive and generally not practical in a retrospective manner for accepted classifications. With the increased use of validated patient outcomes, a standardized comprehensive classification of injury is necessary. The AOTIB and OTA Classification Committee through the International Comprehensive Classification of Fractures and Dislocations Committee realized the need to make the compendium as comprehensive and standardized as possible. This third compendium addresses many of the prior criticisms as well as updating the prior editions and adding new published classifications. These changes in content and presentation should make the compendium more universal and simpler to use. These standardized classification systems should make injury description more standardized and so improve research and fracture outcomes assessments.

The collaboration of the AOTIB and the OTA through their classification committees has resulted in the return of the compendium copyright to both organizations so it is available for any clinician to use without charge. This collaboration has allowed its worldwide dissemination in both print and electronic means. The organizations are committed to working together to continually evaluate the compendium and revise as necessary.

Back to Top | Article Outline


The committee would like to acknowledge and gratefully thank Jessica Schisel, Jecca Reichmuth, Marcel Erismann, and Kathleen Caswell, all the staff of the OTA office, and the AO Education Institute for their tremendous support and encouragement. The committee would also like to acknowledge the important contributions to the prior compendiums from Larry Marsh, MD, Theddy Slongo MD, and Laurent Audige PhD.

Back to Top | Article Outline


1. Association Committee for Coding and Classification. Fracture and dislocation compendium.J Orthop Trauma. 1996;10–154 Suppl 1 :v-ix, 1–154.
2. Muller ME, Nazarian S, Koch P. Classification AO des fractures. Tome I. Les os longs. 1st Ed. Berlin: Springer-Verlag; 1987.
3. Muller ME, Nazarian S, Koch P, et al. The Comprehensive Classification of Fractures of Long Bones. Berlin, Germany:Springer-Verlag;1990.
4. Slongo T, Audige L, Clavert JM, et al. The AO comprehensive classification of pediatric long-bone fractures: a web-based multicenter agreement study. J Pediatr Orthop. 2007;27:171–180.
5. Slongo T, Audige L, Lutz N, et al. Documentation of fracture severity with the AO classification of pediatric long-bone fractures. Acta Orthop. 2007;78:247–253.
6. Webster's New Riverside University Dictionary. Boston, MA: Riverside Publishing; 1984:268.
7. Martin JS, Marsh JL. Current classification of fractures. Rationale and utility. Radiol Clin North Am. 1997;35:491–506.
8. Brumback RJ, Jones AL. lnterobserver agreement in the classification of open fractures of the tibia. The results of a survey of two hundred and forty-five orthopaedic surgeons. J Bone Joint Surg Am. 1994;76:1162–1166.
9. Schatzker J, McBroom R, Bruce D. The tibial plateau fracture. The Toronto experience 1968–1975. Clin Orthop Relal Res. 1979;138:94–104.
10. Siebenrock KA, Gerber C. The reproducibility of classification of fractures of the proximal end of the humerus. J Bone Joint Surg Am. 1993;75:1751–1755.
11. Martin JS, Marsh JL, Bonar SK, et al. Assessment of the AO/ASIF fracture classification for the distal tibia. J Orthop Trauma. 1997;11:477–483.
12. Sidor ML, Zuckerman JD, Lyon T, et al. The Neer classification system for proximal humeral fractures. An assessment of interobserver reliability and intraobserver reproducibility. J Bone Joint Surg Am. 1993;75:1745–1750.
13. ICD-10-CM Expert for Physicians: The complete official code set. Optum360, LLC; 2015.
14. Luo CF, Sun H, Zhang B, et al. Three-column fixation for complex tibial plateau fractures. J Orthop Trauma. 2010 Nov;24(11):683–692.
    15. Parsons BO, Klepps SJ, Miller S, et al. Reliability and reproducibility of radiographs of greater tuberosity displacement. A cadaveric study. J Bone Joint Surg Am. 2005;87:58–65.
      16. Crist BD, Martin SL, Stannard JP. Tibial Plateau Fractures. In: Stannard JP Schmidt AH, eds. Surgical Treatment of Orthopaedic Trauma-Second edition. New York: Thieme; 2016:913–945.
      17. Evans AR, Agel J, DeSilva GL, et al. Orthopaedic Trauma Association: Open fracture study group. A new classification scheme for open fractures. J Orthop Trauma. 2010 Aug;24(8):457–464.
        18. Audige L, Kellam JF, Lambert S, et al. The AO Foundation and Orthopaedic Trauma Association (AO/OTA) scapula fracture classification system: focus on body involvement. J Shoulder Elbow Surg. 2014 Feb;23(2):189–196.
          19. Jaeger M, Lambert S, Sudkamp NP, et al. The AO Foundation and Orthopaedic Trauma Association (AO/OTA) scapula fracture classification system: focus on glenoid fossa involvement. J Shoulder Elbow Surg. 2013 Apr;22(4):512–520.
            20. Dunan CP, Haddad FS. The Unified Classification System (UCS): improving our understanding of periprosthetic fractures. Bone Joint J. 2014 Jun;96-b(6):713–716.
              21. Vaccaro AR, Schroeder GD, Kepler CK, et al. The surgical algorithm for the AOSpine thoracolumbar spine injury classification system. Eur Spine J. 2016 Apr;25(4):1087–1094.
                22. Bellabartba C, Schroeder G, Kepler C, et al. The AOSpine Sacral Fracture Classification. Global Spine J. 06(S 01). 2016 April DOI: .
                  23. Kristiansen B, Andersen UL, Olsen CA, et al. The Neer classification of fractures of the proximal humerus. An assessment of interobserver variation. Skeletal Radiol. 1988;17(6):420–422.
                  24. Bernstein J, Adler LM, Blank JE, et al. Evaluation of the Neer system of classification of proximal humeral fractures with computerized tomographic scans and plain radiographs. J Bone Joint Surg Am. 1996;78:1371–1375.
                  25. Flikkila T, Nikkola-Sihto A, Kaarela O, et al. Poor interobserver reliability of AO classification of fractures of the distal radius. Additional computed tomography is of minor value. J Bone Joint Surg Br. 1998;80: 670–672.
                  26. Humphrey CA, Dirschl DR, Ellis TJ. lnterobserver reliability of a CT- based fracture classification system. J Orthop Trauma. 2005;19:616–622.
                  27. Barker L, Anderson J, Chesnut R, et al. Reliability and reproducibility of dens fracture classification with use of plain radiography and reformatted computer-aided tomography. J Bone Joint Surg Am. 2006;88:106–112.
                  28. Dirschl DR, Adams GL. A critical assessment of factors influencing reliability in the classification of fractures, using fractures of the tibial plafond as a model. J Orthop Trauma. 1997;11 :471–476.
                  29. Petrisor BA, Bhandari M, Orr RD, et al. Improving reliability in the classification of fractures of the acetabulum. Arch Orthop Trauma Surg. 2003;123:228–233.
                  30. Schipper IB, Steyerberg EW, Castelein RM, et al. Reliability of the AO/ASIF classification for pertrochanteric femoral fractures. Acta Orthop Scand. 2001;72:36–41.
                  31. Walton NP, Harish S, Roberts C, et al. AO or Schatzker? How reliable is classification of tibial plateau fractures? Arch Orthop Trauma Surg. 2003;123:396–398.
                  32. Andersen DJ, Blair WF, Steyers CM Jr, et al. Classification of distal radius fractures: an analysis of interobserver reliability and intraobserver reproducibility. J Hand Surg Am. 1996 Jul;21(4):574–582.
                  33. Swiontkowski MF, Sands AK, Agel J, et al. lnterobserver variation in the AO/OTA fracture classification system for pilon fractures: is there a problem? J Orthop Trauma. 1997;11:467–470.
                  34. Kreder HJ, Hanel DP, McKee M, et al. Consistency of AO fracture classification for the distal radius. J Bone Joint Surg Br. 1996;78:726–731.
                  35. Oskam J, Kingma J, Klasen HJ. Interrater reliability for the basic categories of the AO/ASIF's system as a frame of reference for classifying distal radial fractures. Percept Mot Skills. 2001;92:589–594.
                  36. Audige L, Bhandari M, Kellam J. How reliable are reliability studies of fracture classifications? A systematic review of their methodologies. Acta Orthop Scand. 2004;75:184–194.
                  37. Audige L, Bhandari M, Hanson B, et al. A concept for the validation of fracture classifications. J Orthop Trauma. 2005;19:401–406.
                  38. International Cartilage Repair Society. ICRS SCORE/GRADE: ICRS Clinical Cartilage Injury Evaluation System. Available at:
                  Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.