Using LOINC to link ten terminology standards to one unified standard in a specialized domain

Abstract

Despite the existence of multiple standards for the coding of biomedical data and the known benefits of doing so, there remain a myriad of biomedical information domain spaces that are essentially un-coded and unstandardized. Perhaps a worse situation is when the same or similar information in a given domain is coded to a variety of different standards. Such is the case with cephalometrics – standardized measurements of angles and distances between specified landmarks on X-ray film used for orthodontic treatment planning and a variety of research applications. We describe how we unified the existing cephalometric definitions from ten existing cephalometric standards to one unifying terminology set using an existing standard (LOINC). Using our example of an open and web-based orthodontic case file system, we describe how this work benefited our project and discuss how adopting or expanding established standards can benefit other similar projects in specialized domains.

1.0 INTRODUCTION

The benefits of using standardized terminologies for the coding of biomedical information are well described.[1] Perhaps equally well described are the difficulties, costs, complexities, and limiting historical precedents that often conspire to make it difficult to do so.[2, 3] Indeed, the existence of the perfectly coded biomedical data set may be more of a theoretical concept to aim for rather than an obtainable goal. The existence of a plethora of terminology standards illustrates the complexity of the task. The National Library of Medicine’s Unified Medical Language System (UMLS) ® is a set of tools that attempts to catalog and where possible, inter-relate the over one million biomedical concepts from over 100 source terminology standards. Despite the standards, powerful tools, and recognized benefits of doing so, the coding of biomedical data sets using recognized standard terminologies remains a daunting challenge with only limited success when compared with the size of and number of biomedical data sets that could benefit from such standardization.

As part of a project to create an open, de-identified, web-based case file system in support of orthodontic treatment, training, and research,[4] we came upon a biomedical domain ripe for standardization; that of cephalometric measurements.

Cephalometrics are measurements (angles and linear distances) defined by anatomical points as measured on X-ray film of the human head taken in a standardized manner. Some authors credit the scientist and painter Petrus Camper (1722–1789) or even earlier artists for originating cephalometric studies.[5] Most trace modern cephalometry to the efforts of Herbert Hofrath (1899–1952) in Germany and B.H. Broadbent, Sr., (1894–1977) in the United States, who simultaneously introduced radiography to the standardized study of facial skeletons and teeth. Broadbent, working with T. Wingate Todd (1885–1938) developed the “roentgenographic craniometer” which produced X-rays films of living human heads in a standardized manner, allowing accurate and reproducible scientific measurements.[6] This device was used as part of the Bolton-Brush Growth Study, a large, prospective, longitudinal cohort study of children intended to establish a detailed cephalometric data set on normal human growth and development.[7] Over time, cephalometric techniques have been elaborated and refined, and have become commonplace tools in growth studies as well as orthodontic training and practice. Today, while some question the value of cephalometric data in orthodontic treatment planning[8] several computerized systems exist to allow orthodontic practitioners to compare their patients’ measurements with the data collected in the aforementioned growth studies, e.g. Dolphin Imaging[9] and CephX[10]. Additionally, cephalometric data has been used in a variety of other applications, including studies of facial attractiveness[11] and forensic anthropology.[12, 13]

Because we understand impact of radiation on human growth and development, especially on young children, the data from these studies could not ethically be reproduced today. Despite the broad availability of modern three dimensional imaging technologies, cephalometrics still continue to be useful despite the fact they are measurements of the three-dimensional human head as projected onto a two-dimensional X-ray film. Since these data are the foundation of what is now known about normal human skeletal growth and development, much contemporary research continues to actively reference these valuable data.

The advent of Cephalometry as a scientific tool spawned a number of studies and analyses of cephalometric data sets. As the number of studies increased and as time went on, the terminology that defined the cephalometric landmarks and measurements diverged until at present, the same measurement may be defined in up to five different cephalometric “atlases” or “analyses”.

One of the design requirements of the orthodontic case files database we developed was to make it possible for additional cases to be donated from other institutions or orthodontics practices. It became clear that to accept a donated case that included cephalometric data, a major step in the accession process would be to determine what the cephalometric measurements actually are. If, for example, a case used a given standard, it would be necessary to record that fact and then convert certain measurements to whatever standard our project would choose as the standard. Simply choosing one of the existing standards for our project would be arbitrary because each has its own proponents and yet none comprehensively represents all existing cephalometric measurements.

We also see the case file system’s database could be used in the future as a source for web-based cephalometric analysis tools or perhaps even linked to other similar databases. To achieve these functionalities the data will have to be structured in such a manner to support semantic interoperability between the case file database and any cephalometric analysis tools or other databases. The most efficient way to achieve semantic interoperability would require one grand unifying terminology standard. Like any good terminology standard, the grand unifying standard would also require an infrastructure for expansion, revision, and support. In summary our problem required a unified cephalometric standard that would satisfy the following requirements:

1. All cephalometric measurements in the existing standards can be directly mapped or represented in the unified standard. This would help solve the problem of managing donated cases with cephalometric data coded to different standards. By asking the donor to which standard the cephalometric measurements were made, all measurements can be directly mapped to the unifying terminology, allowing for a greatly simplified data representation in the database.

2. The unified standard must have a robust process for continuous improvement, maintenance, and expansion. As a starting point, our project used the cephalometric measurements used by one forward thinking orthodontist in Albuquerque, NM.[14–16] However, we anticipate expansion of the number of cephalometric measurements as new, and perhaps more exotic cases are donated to the collection over time.

3. The unified standard must be authoritative, internationally recognizable, and as widely known as possible. We did not want to create yet another standard that would have little credibility.

4. The unified standard must have tools and support to assist in the discovery of existing terms that are either already defined or come close to defining what specific cephalometric measurements we want to standardize. Such tools will assure that users of the standard can find the right terms and facilitate efficient maintenance of the existing corpus of terms.

Because of these requirements we chose to use the Logical Observations Identifiers Names and Codes (LOINC®) standard[17] as the unifying standard for the cephalometric measurements contained in our collection of cephalometric measurements. LOINC was first released by the Regenstrief Institute in April of 1996.[18] Since its inception, LOINC has been developed as an open standard and freely distributed worldwide. LOINC is a terminology standard focused specifically on providing observation identifiers. The development of LOINC is divided into two divisions: the Laboratory division focuses on the observations and measurements that can be made on specimens withdrawn from the body, and the Clinical division focuses on the observations and measurements that can be made on patients. The most recent LOINC release (Version 2.36, June 2011) contains 65,003 terms, of which 45,428 are laboratory terms and 19,575 are clinical terms.[19]

LOINC has been widely adopted in both the public and private sectors, within the United States and more than 140 other countries. Several countries (including Brazil, Canada, Germany, the Netherlands, Mexico, and Rwanda) have adopted LOINC as a national standard, and there are large health information exchanges using LOINC in Spain, Singapore, and Korea as well. Within the U.S., LOINC has been adopted by many health information exchanges, large national reference laboratories, healthcare organizations, insurance companies, research programs, and national standards. LOINC has long been a source vocabulary included in the National Library of Medicine’s Unified Medical Language System. Furthermore, the Department of Health and Human Services adopted LOINC as the standard across federal agencies for laboratory result names, laboratory test order names, and federally required patient assessment instruments.

LOINC is distributed at no cost from its website (http://loinc.org) as a database that contains the LOINC codes, term names, and many other attributes such as synonyms, alternate display names, example units of measure, etc. New versions of LOINC are published twice yearly (typically June and December). In addition, The Regenstrief Institute develops and distributes at no cost a software program called RELMA (the Regenstrief LOINC Mapping Assistant) that helps browse and search the LOINC database, review the detailed accessory content for each term, and map local terms to LOINC.

Because of its open development approach, new content additions to LOINC are welcomed, and added based on submissions from the worldwide LOINC user community. There is a well-defined mechanism for creating new term requests (documented in the LOINC User’s Guide) and rigorous quality review process that ensures that LOINC follows best practices for terminology development.[2] Requests for new content in domains not previously modeled in LOINC are discussed at one of the public LOINC Committee meetings that occur regularly.

We previously published a detailed rationale for choosing LOINC over a number of existing terminology standards for representation of cephalometrics.[20] This analysis considered representing cephalometrics using MeSH (Medical Subject Headings),[21] SNOMED-CT (Systematized Nomenclature of Medicine-Clinical Terms),[22] ICD-10 (International Classification of Diseases, 10^th Edition),[23] LOINC,[19] CDT(Current Dental Terminology),[24] CPT (Current Procedural Terminology),[25] ICD-DA (Application of the International Classification of Diseases to Dentistry and Stomatology),[26] SNODENT (Systematized Nomenclature of Dentistry – a subset of SNOMED), UMLS,[27] HL-7 (Health Level Seven),[28] and DICOM (Digital Imaging and Communications in Medicine).[29] This analysis involved looking at content coverage, scope, hierarchical structure, and term composition of each standard. For example, with regard to hierarchical structure, most medical vocabularies are arranged in hierarchies.[2, 3] Though cephalometric measurements can be categorized by dimensionality (angles vs. distances), analysis type (Downs, Ricketts, Steiner, etc.), or landmark type (skeletal, dental, or soft tissue), many of the benefits attributed to hierarchical arrangement do not apply to cephalometric measurements. All cephalometric measurements fall at essentially the same level of detail. Therefore, the pedagogical grouping by analysis type has limited applicability in actual clinical practice. It makes little clinical sense to speak of “all angular measurements” or “all Ricketts’ measurements” in the same way you can sensibly generalize about “all infections” or a nonspecific “inflammatory process.”[20] This is one of several reasons we chose LOINC over SNOMED-CT that is a comprehensive ontology of medicine, containing nineteen top level hierarchies. The lack of hierarchy in the cephalometric domain and our project’s requirements favored the selection of a terminology standard such as LOINC that was also essentially “flat.”

2.0 METHODS

The method to perform the cross referencing of the cephalometric measurements contained in orthodontic cases in our case file system is as follows:

1. Identify the anatomical points that define the cephalometric measurements used in our collection of case files.

2. Verify that the variable name for each point is consistent with the existing point naming convention.[30]

3. Define cephalometric measurements used in our case files based on the defined anatomical points.

4. For each of the cephalometric measurements from #3 above, manually examine the ten atlases and analyses to identify cephalometric measurements (that may have different names or identifiers) and cross reference these identical measurements to one unifying cephalometric measurement definition we proposed for the LOINC database.

The orthodontic records that make up our case file system contain approximately 150 unique cephalometric measurements. We proposed new LOINC terms for a subset of 88 of these because these were the measurements most commonly and currently used in the collection (from the 1990s forward in time). The case file system as a whole contains records of 5910 unique patients including records of approximately 600 sibling pairs and several multi-generational families who entered orthodontic treatment in Albuquerque, NM between 1972 and 1999.[4] For each cephalometric measurement used in the case file collection, we identified the anatomical points necessary to define it, using the convention established in the existing literature[30] ultimately creating a list of 43 unique anatomical points.

The ten existing cephalometric standards (atlases and analyses) we cross referenced with are listed in Table 1. For each cephalometric measurement we identified in the case file system, our cephalometrics expert (SD) first identified the points used to define that measurement and then manually searched all the atlases and analyses to identify identical measurements. For example, the measurement Cd-Go (mandibular condyle to Gonion) was defined in the London and Riolo Atlases. (The manual review of the other atlases and analyses showed that this measurement was not defined or represented in the eight other atlases and analyses.) This measurement is represented in the London Atlas as “Ramus Height” while the identical measurement is represented in the Riolo atlas as “CO-GO.” Although these definitions have different names in each atlas the measurement and point definitions match exactly. We created a new LOINC term definition “Condylion to gonion”, where we included cross references to the London and Riolo definitions in the LOINC database definition. In this way, the new LOINC term (60656-6) defines the measurement precisely and disambiguates the definitions between the two existing standards.

Table 1.

List of Common Names of Ten Cephalometric Atlases and Analyses Cross Referenced

“Downs Analysis” Downs WB (1948). Variations in Facial Relationships: Their Significance in Treatment and Prognosis. American Journal of Orthodontics, 34: 812–840.

“Steiner Analysis” Steiner CC (1953). Cephalometrics for You and Me. American Journal of Orthodontics, 39: 729–755.

“Tweed Analysis” Tweed CH (1954). The Frankfort Mandibular Incisal Angle (FMIA) in Orthodontic Diagnosis, Treatment Planning, and Prognosis. The Angle Orthodontics, 24: 121–169.

“Jarabak-Bjork Analysis” Jarabak JR, Fizzell JA (1972). Technique and treatment with light-wire edgewise appliances. Saint Louis: C. V. Mosby Co.

“Michigan Atlas” Riolo ML, Moyers RE, McNamara JA, Hunter WS (1974). An Atlas of Craniofacial Growth: Cephalometric Standards from the University School Growth Study, The University of Michigan. Ann Arbor: The University of Michigan.

“Ricketts Analysis” Ricketts RM, Roth RH, Chaconas SJ, Schnlhof RJ, Engel A (1982). Orthodontic Diagnosis and Planning, Volumes I and II. Denver: Rocky Mountain Orthodontics.

“Soft Tissue Analysis” Holdaway RA (1983). A Soft Tissue Cephalometric Analysis and its Use in Orthodontic Planning, Part I. American Journal of Orthodontics, 84: 1–28. Holdaway RA (1984). A Soft Tissue Cephalometric Analysis and its Use in Orthodontic Planning, Part II. American Journal of Orthodontics, 85: 279–293.

“London Atlas” Bhatia SN, Leighton BC (1993). A Manual of Facial Growth: A Computer Analysis of Longitudinal Cephalometric Growth Data. Oxford: Oxford university Press.

“McNamara Analysis” McNamara JA Jr, Brundon WL (2001). Orhtodontic and Dentofacial Orthopedics. Ann Arbor: Needham Press.

“Frontal Analysis” Epker BN, Fish LC(1986). Dentofacial Deformities: Integrated Orthodontic and Surgical Corrections Volume I. Saint Louis: C. V. Mosby Co. Grummons DC, Kappeneye van de Coppelo MA (1987). A Frontal Asymmetrical Analysis. The Journal of Clinical Orthodontics, 21: 448–465. Grummons DC, Ricketts RM (2004). Frontal Cephalometrics: Practical Application. World Journal of Orthodontics, 5: 99–119.

Note: Atlases differ from analyses. Atlases are books for which each measurement is given with a description and a drawing. In comparison, analyses are journal publications which may or may not contain drawings for each measurement.

For each cephalometric measurement, we initially had one cephalometric expert (SD) check all ten atlases/analyses we referenced. The data from the existing ten standards is only available in book or paper form. This required manual reviews of each standard by our cephalometrics expert to cross reference identical measurements that appear in one or more of the ten existing standards. To do this systematically, we created a large spreadsheet listing each of the cephalometric measurements in rows with the ten existing standards in columns. We chose to use a large table to record the cross reference information rather than to design a custom database because we found visualizing the entire table was useful for quickly comparing similarly named measurements across multiple atlases and analyses. Because we choose to cross reference only the 88 cephalometric measurements most commonly used in our case file system, this “tabular” method was feasible. If we were attempting to standardize significantly more than 88 measurements, a database would have likely been necessary.

The table was then reviewed by a group of biological anthropologists with expertise in oral facial development and cephalometrics in particular. (SD, EFH, and HJHE) Once the group reached consensus, two of the authors (PJK and SD) presented a proposal to establish the new LOINC terms for each of the 88 identified measures at the Clinical LOINC Committee Meeting in Murray, Utah, July 16, 2010. For each measurement, the proposal recommended including within the LOINC database a narrative definition and the cross references to the existing cephalometric standard(s) that defined it. By including the reference standards in the LOINC database itself, we essentially linked the cephalometric measurements represented in our case file collection to the ten existing cephalometric standards through the LOINC definition.

LOINC constructs “fully specified” names according to its established model that contains six main axes, as described in the LOINC User’s Guide.[18] The names are fully-specified in the sense that they contain sufficient information to distinguish among similar clinical observations. The atomic elements that comprise a fully-specified LOINC name are called LOINC “parts”. Each LOINC part is also assigned an identifier, and there are links established between the full LOINC term and the parts that comprise it. The LOINC parts are used in many ways: supporting translation into foreign language, adding synonymy, building hierarchies, creating alternate display names, linking descriptive text, and more. In each case, linking accessory content to a LOINC Part such as “Skull” allows that content to be associated with every LOINC term that contains it. Thus, our anatomical point variable names generated LOINC Parts to which we could attach narrative definitions. The LOINC part codes serve largely as internal building blocks for constructing the LOINC terminology, and are not developed or maintained in concept-oriented manner in the same way that the full LOINC observation codes are. As such, they are not distributed as a part of the main LOINC table distribution but rather used internally within the RELMA program. We mention them here only in an attempt to illustrate the rigor we used when working with the LOINC support staff in creating cephalometric definitions for the LOINC database.

3.0 RESULTS

An illustration of the anatomic point locations is contained in Figure 1 and a summary of the anatomical point definitions is listed in Table 2. The cephalometric terms we defined in the LOINC database, their assigned LOINC codes, and which of the ten standards they map to is summarized in Table 3. We created a total of 83 new LOINC codes and 100 new LOINC Part definitions. Cephalometric “measurements” that only define a plane in the referenced standards were specified only as LOINC parts. Planes are unitless entities and by definition do not constitute a measurement in LOINC but importantly are used in LOINC cephalometric term definitions.

Figure 1.

Anatomical Point Locations and Standard Abbreviations

Table 2.

Anatomical Point Definitions and Variable Names

Standard Abbreviation	Variable Name	Definition
1L, LIE	Lower Central Incisor	The occlusal tip of the lower central incisor
1U, UIE	Upper Central Incisor	The occlusal tip of the upper central incisor
A point, A	A point	The deepest point of the curve of the maxilla between the anterior nasal spine and the dental alveolus
A′ point, A′	Soft tissue A point	The soft tissue point that is horizontally projected, parallel to Frankfort Horizontal, from the deepest point of the curve of the maxilla between the anterior nasal spine and the dental alveolus
ANS	Anterior Nasal Spine	tip of the anterior nasal spine
Ar	Articulare	the point of intersection between the posterior border of the mandibular condyle and the lower border of the cranial base
B point, B	B point	the deepest point on the bony curvature between the crest of the alveolus and pogonion
Ba	Basion	The most anterior-inferior point on the margin of the foramen magnum
CC	Center of Cranium	cephalometric landmark formed by the intersection of the two lines Ba-Na and Pt-Gn
Cd	Condyle	the most superior point on the condyles of the mandible
CF	Center of Face, Polar Center	a center on the Frankfort horizontal plane at a perpendicular dropped at the anterior border of pterygoid plates near the union with the body of the sphenoid
Forehead	Forehead	The most anterior portion of the cranium when viewed from a lateral position
Gl	Glabella	the height of curvature of the bone overlying the frontal sinus
Gl′	Soft tissue Glabella	the most prominent or anterior point in the midsagittal plane of the forehead at the level of the superior orbital ridges
Gn	Gnathion	The most posterior-inferior point on the outline of the mandible, lies on the contour of the chin at the point of intersection of the facial axis
Gn, constructed	Gnathion, constructed	Lies at the intersection of the mandibular plane (Go-Me)and the facial plane ( Na-Pg)
Go	Gonion	the midpoint at the angle of the mandible
Go, constructed	Gonion, constructed	the intersection of the mandibular plane with a plane through Articulare, Posterior and along the portion of the mandibular ramus inferior to it
L6	Lower first molar	a point on the occlusal plane perpendicular to the distal surface of the crown of the lower first molar
Li	Labrale Inferius	the median point on the lower margin of the lower membranous lip
LIA	Lower central incisor root apex	the root tip of the mandibular central incisor
Lnt	Lower nasal tangent	the base of the nose
Ls	Labrale Superius	a point indicating the mucocutaneous border of the upper lip, usually the most anterior point of the upper lip
Me	Menton	the most inferior point on the symphyseal outline
Me′	Soft tissue Menton	the most inferior point on the soft-tissue chin
Na, N	Nasion	the most anterior point on the frontonasal suture
Na′, N′	Soft tissue Nasion	the deepest point on the concavity overlying the area of the frontonasal suture
Or	Orbitale	The most inferior point on the lower border of th ebony orbit
Pg, P	Pogonion	the most anterior point on the mandibular symphysis
Pg′	Soft tissue Pogonion	the most prominent or anterior point on the soft-tissue chin in the midsagittal plane
Pm	Protruberance menti/supragonion	a point selected where the curvature of the anterior border of the symphysis changes from concave to convex
PNS	Posterior nasal spine	the tip of the posterior nasal spine
Po	Porion	The most superior point on the outline of the external auditory meatus
Pt	Pterygoid	the posterior-superior border of the pterygo-maxillary fissures
Sd	Supradentale	the most anterior inferior point on the maxilla at its labial contact with the maxillary central incisor
Se, S	Sella Turcica	the center of sella turcica
Sls	Superior Labial Sulcus	the point of greatest concavity in the midline of the upper lip between Sn and Ls
Sn	Subnasale	a point located at the junction between lower border of the nose and beginning of the upper lip at the midsagittal plane
Sts	Stomion Superious	the lowermost point on the vermilion of the upper lip
Sti	Stomion Inferious	the uppermost point on the vermilion of the lower lip
U6	Upper first molar	a point on the occlusal plane perpendicular to the distal surface of the crown of the upper first molar
UIA	Upper central incisor root apex	the root tip of the maxillary central incisor
Xi	Xi Point	a point located at the geometric center of the ramus, location of Xi is keyed geometrically to Pr-Or and a perpendicular through Pt, found by locating R1–R4

Table 3.

Cephalometric Variables’ Reference Summary

Variable Name	LOINC Code	Downs	Frontal	Jarabak	London	McNam	Ricketts	Riolo	Soft	Steiner	Tweed
1L-APg	60601-2				•	•	•	•
U6_PtV	60602-0						•
Molar rel	60603-8						•
1L-NB	60604-6				•			•		•
Overjet	60605-3				•		•
IMPA (1L-GoMe)	60606-1	•			•						•
IMPA (1L-GoMe) (constructed)	60607-9							•
1L-NB	60608-7				•			•		•
1U-NA	60609-5				•			•
1U-ANSPNS	60610-3				•
1U-SeNa	60611-1			•	•			•
IMPA (1L-GoGn)	60612-9							•
1U-1L	60613-7	•			•		•	•		•
Cd-Gn	60614-5				•	•		•
Cd-ANS	60615-2				•
Cd-A	60616-0				•	•
UIE-A FH	60617-8					•
Go-Gn-A	60618-6						•
NaPg-FH	32937-5	•			•			•	•
NAP	60619-4	•			•			•	•
ANSPNS-GoMe	60661-6				•
ANSPNS-GoMe (constructed)	60662-4							•
SeNa-GoMe	60663-2				•
SeNa-GoMe (constructed)	60664-0							•
1U-St	60620-2
Pg-Pg′	60621-0				•				•
Ls-Sd	60672-3				•				•
Pg′Ls-Sls	60622-8								•
A-A′	60673-1				•				•
Lnt-Sn-Ls	60623-6				•	•
Na′-Pg′-Ls	60624-4								•
N-FH	60625-1					•
BaNa-CC	60626-9				•	•
BaNa-CC (constructed)	60627-7						•
FH-SeGn	60628-5				•			•
FH-SeGn (constructed)	60629-3	•
SeNa-SeGn	60630-1				•			•
Se-Go	60631-9			•	•			•			•
Ar-Go	60632-7				•			•
Ar-Go (constructed)	60633-5			•
ANS-Me	60634-3				•			•			•
Ar-Go-Me	60635-0				•
Ar-Go-Me (constructed)	60636-8			•				•
FMA	32864-1				•
FMA (constructed)	60637-6					•		•			•
CF-Go	60638-4						•
SeNa-NaPg	60671-5				•			•
SNB	32925-0				•			•		•	•
SNA	32945-8				•			•		•	•
ANB	32928-4				•			•		•	•
Face Low/All	60594-9		•
Face Incisor-Chin/Low	60658-2		•
Face Mid/Low	60659-0		•		•
Face Incisor-Chin/All	60660-8		•
Face Mid/All	60595-6		•
Face Incisor-Chin/Mid	60596-4		•
Face Upper/All	60597-2		•
Face All	60598-0		•
Face Low Incisor-Chin	60599-8		•
Face Low	60639-2		•		•
Sn-Me′	60670-7				•
Face Mid	60665-7		•
Gl-Sn	60669-9				•
Face Upper	60600-4		•
Li-Pg′	60640-0
Sti-Me′	60641-8		•
Ls-Pg′	60642-6
Na-Me	60643-4				•			•
Sn-Pg′	60644-2
Sn-Li	60645-9		•
Sts-Sn	60646-7		•
ANS-Pg	60647-5
Adenoid	60648-3					•
Tonsil	60649-1					•
AO-BO	60650-9				•						•
Cd-Xi-Pm	60651-7						•
ANS-Xi-Pm	60652-5						•
SeNa-ANSPNS	60666-5				•			•
ANSPNS-GoGn	60667-3
ANSPNS-GoGn (constructed)	60668-1
Li-Me′	60653-3		•
NA-A	60674-9					•
Se-Ar	60654-1			•				•
CC-Na	60655-8						•
Go-Me	60675-6				•			•
Overbite	60686-3				•		•
Cd-Go	60656-6				•			•
Sn-Ls	60657-4				•

Many of the cephalometric measurements used in the case file collection were taken from more than one cephalometric standard. A total of seven were not defined in any of the ten standards but were defined and used in our specific collection of records so we created LOINC codes for these new measurements using the same convention as those that did have a reference.

In addition to the LOINC database of term definitions, the LOINC committee has recently added functionality to the definitions database to include image files. To insure even more clarity over what measurement is represented by each LOINC term, we supplied the LOINC Committee with image files that illustrate the anatomical points and the measurements for each cephalometric definition. In this way, the image graphically defines the measurement and eliminates any ambiguity that might exist from textural descriptions alone. An image for each cephalometric definition was submitted and is viewable using the RELMA program. All were in a form similar to the image in Figure 1 but with only points, lines, and angles relative one measurement.

4.0 DISCUSSION

We believe that using a methodology of expanding an existing terminology standard to unify a group of existing standards in a specialized domain (an orthodontics case file system in this case) has the following benefits:

4.1 Facilitate sematic interoperability

As we move to the next phase of our project, defining the process of accepting donated cases from other practices or institutions, we now have an extremely powerful and recognized standard to refer donors to that will significantly simplify the form of the cephalometric data we will accept. If a donated case has cephalometrics defined using just one of the existing standards prior to our work with LOINC, we will help the donator map the cephalometric measurements to the LOINC standard. If a donated case has cephalometrics not defined in the current LOINC release, we intend to use the LOINC submission process to propose new terms when needed in a manner similar to what we have already done.

LOINC now contains the most comprehensive set of cephalometric measurements because we have aggregated them from among all of the existing standards. Having a machine readable representation of the cephalometrics in our case file database will facilitate creation of web-based tools that may allow users of the case file database to perform complex analyses. Coding our database with the new LOINC terms for cephalometrics will also greatly simplify the complexity of linking of our database with others that may be created or discovered in the future. Linking with another database would be simpler even if the other database is not coded with the new LOINC standard, because the LOINC terms are a stable target with more rigorous definition and documentation than any of the existing cephalometric standards.

There are a variety of commercial software packages that help orthodontic practitioners obtain and analyze cephalometric measurements from their patients to inform the creation of a treatment plan.[9, 10] Likewise, there are a variety of commercial electronic dental records systems currently in use. Incorporating vocabulary standards like LOINC into such systems would provide a uniform representation of these measurements and thus enable semantic interoperability between systems. Furthermore, using widely adopted messaging and vocabulary standards would allow dental and orthodontic records to be exchanged using the same infrastructure that is currently being used to communicate other health information such as laboratory results, radiology reports, and clinical notes.

4.2 Disambiguate conflicts and confusion between existing standards

We discovered that eight measurements with identical variable names in different standards actually were different measurements, in that one of the references defined the measurement using a constructed point rather than a physical anatomical point. Constructed points are defined by of the intersection of two lines and not defined directly by an anatomical feature. In these cases, we created new cephalometric definitions by appending the term “constructed” onto the existing, erroneous identical name for the measurements containing a constructed point. We also defined a separate LOINC term in the same manner as with the others so that this subtle but real difference would be clearly delineated. Such differences may be minute for use in the clinical domain, but could be significant in the research domain. For example, investigators might compare two measurements with the same variable name that are not the same and come to spurious conclusions. These subtle differences also could cause unintended consequences when these variables are machine read and computed such as with the development of complex cephalometric analysis tools.

4.3 Established a clear process for maintenance, corrections and expansion

By no means do the authors believe that this work is perfect or complete. All terminology standards require continuous maintenance and updating. Despite significant efforts to insure accuracy, we fully expect the LOINC terms created through this work may require corrections and hopefully additions in the future. The LOINC Committees’ revision process, tools, and support infrastructure for handling corrections and additions is one of the key reasons we choose LOINC as the unifying standard we mapped our case file collection to. If any of the existing cephalometric atlases/analyses are ever updated or yet another one is discovered or created, the well-established LOINC revision process and tools will be able to accommodate revision of the appropriate LOINC terms. By using an internationally recognized standard, we have met our project’s needs and provided a framework that will be helpful to our future work and perhaps to other projects as well.

Using LOINC part file definitions to define and standardize the anatomical points used to define the cephalometric measurements provides for greater flexibility for managing any potential future changes to the cephalometric term set in the LOINC database. For example, if a point definition changes, it will be immediately clear which other existing LOINC terms also use that point definition and can be then updated accordingly. Otherwise, if a point definition were to ever change, it would be somewhat problematic to search through all of the cephalometric definitions to determine which ones are affected by a particular point definition change.

We also hope that this work had demonstrated and begun a process that holds the potential to continue to unify other cephalometric definitions not represented in the corpus of patient records that our case files system represents. There are hundreds of other cephalometric measurements that may be represented in multiple standards that could be linked together to a unifying standard as we have done here. We hope our work has provided a concrete example of how adopting a terminology standard for a biomedical informatics project can provide multiple benefits and will inspire others to do the same.

4.4 Do not create yet another standard

When working in a specialized domain that perhaps has some particular characteristics or needs, one can easily be tempted to design a completely new terminology standardized that quickly and ideally meets the immediate needs of the project at hand. It is certainly easier and perhaps more attractive to create your own “standard” than to work with a committee where the needs for your domain compete with the needs of many others. This approach, however, is obviously not scalable to all other projects and will likely create more problems in the long term than it solves in the immediate term. Although it may require significantly more effort to adapt an existing standard to the needs of a specialized domain, the long term benefits of the virtual connection to the projects that use the existing standard will usually significantly outweigh any immediate term savings of time (and perhaps frustration.) We took the approach to adopt an existing standard (LOINC) with our orthodontics case file system. Although it certainly required extra effort, we believe the long term benefits unquestionably justify the effort. Not only did we solve the immediate needs of our project, we also have participated in moving an existing standard forward and perhaps helping other projects in the future.

Perhaps Betsy Humphreys, deputy director of the U.S. National Library of Medicine, who has been extensively involved in the development of the NLM’s Unified Medical Language System, an effort to catalog and map over 100 terminology standards, best captured this sentiment. When concluding her acceptance speech for the Morris F. Collen Award for Excellence at the 2009 American Medical Informatics Symposium, she said, “..If you are thinking of creating a new terminology standard, please don’t!”[31]

4.5 Other

In addition to the benefits described above, we unexpectedly discovered that two anatomic point definitions in our case files system (those for Gonion and Gnathion) differed slightly from the way we noticed these points were defined in our case file collection. The orthodontist who identified the points in our case file collection used constructed points while the reference atlases used specific landmarks to define these points directly. For example, Gonion is defined in the references as “the most posterior-inferior point on the outline of the mandible, lies on the contour of the chin at the point of intersection of the facial axis” while the Gonion in our case file system was defined using the intersection of two “planes” or lines, where each line is defined by two anatomic points: “Lies at the intersection of the mandibular plane (Go-Me) and the facial plane ( Na-Pg)”. The actual difference in location between points identified by the two different methods can be negligible or considerable depending on the specific case. Therefore it is important to be able to detect the difference between these two methods whether it is for treatment or for research purposes. To preserve the difference in the points’ definitions, we defined two LOINC terms where the “constructed” Gonion and Gnathion are defined in addition to two terms where the definition of Gonion and Gnathion are described using landmarks from tracings of the mandible. This is another example of the power and the benefit of using an existing standard and LOINC in particular -- that is to be able to preserve a fairly nuanced difference in data, defined by slightly different definitions of measurement techniques.

Prior to this work, we found a total of 21 “cephalometric measurements” already defined in the LOINC database. However, only seven of these were actually true cephalometrics, i.e., defined as measurements taken from two dimensional X-ray images or where in LOINC, the method of measurement was defined as “XR.measured”: “A point-nasion line to nasion-B point line”, “Frankfort horizontal plane to mandibular plane”, “Frankfort horizontal plane to nasion-pogonion line”, “Nasion-glabella line to nasion-pronasale line”, “Sella-nasion plane to Frankfort horizontal plane”, “Sella-nasion plane to nasion-A point line”, and “Sella-nasion plane to nasion-B point line”. These seven true cephalometric measurements were also represented in LOINC but where the method of measurement was defined as “CT.measured” and “Digital model.measured”. These 21 definitions were not cross referenced to the external or pre-existing standard or standards as we did with our work.

LOINC parts, such as anatomic point definitions on this case, are helpful constructs in managing LOINC term definitions. Working with the LOINC support staff, we were able to define LOINC parts for the anatomic point definitions which were then used in the LOINC cephalometric measurement definitions we constructed. In this way, if the definition of an anatomic point is ever called into question or needs revision, it is possible to easily identify all of the LOINC term definitions that use a particular anatomic point (defined as a LOINC part.) This makes it much easier for the LOINC support staff to maintain the LOINC database and helps make the cephalometric definitions more rigorous because the anatomic point definitions are consistent across all cephalometric term definitions.

5.0 CONCLUSIONS

We have unified the existing cephalometric definitions from ten existing cephalometric standards to one unifying terminology set using an existing standard (LOINC). We believe that this approach holds the potential to continue to unify other cephalometric definitions not represented in the corpus of patient records that our case files system represents. There are hundreds of other cephalometric measurements that may be represented in multiple standards that could be linked together to a unifying standard as we have done here. We hope our work has provided a concrete example of how adopting an existing terminology standard for a biomedical informatics project can provide multiple benefits and will inspire others to do the same.

• Ten existing cephalometric standards were unified to one terminology set.

• LOINC was used as the unifying standard the ten standards mapped to.

• This methodology could be used for other similar projects.