Purpose: The Videofluorographic SwallowingStudy (VFSS) has become the routine method forassessing swallowing dysfunction and according-ly, much research has been conducted on thisprocedure. However, due to a lack of standardiza-tion of the method of analysis of VFSS, it is oftendifficult to compare the results of such studies.Therefore, we conducted a comparative study ofVFSS’’s spatial measurement using different stan-dard planes used in the past study and Camper’’splane and examined which plane was the mostpreferable.

Method: VFSS was performed on 20 healthyyoung volunteers (26.9±3 years) and 9 healthyelderly (77.3±3 years). Each subject swallowed 4mlof thin liquid barium. We measured hyoid dis-placement and opening of the upper esophagealsphincter (UES) by using four different standardplanes.

Results: In the young group, the correlationbetween anterior hyoid displacement and UESopening was significant in all standard planes. Inthe elderly group, the correlation between anteriorhyoid displacement and UES opening was signifi-cant only in Camper’’s plane. Moreover, this plane ishard to be affected by morphological change asageing.

Conclusions: Camper’’s plane was found to be asthe most preferable plane for analyzing swallowing

function.

Key words: swallowing, standard plane, videofluo-rography, Camper’s plane, dysphagia.

Introduction

The Videofluoroscopic Swallowing Study (VFSS)has become the standard method for evaluating swal-lowing dysfunction as it allows an examination of bothoral and pharyngeal function1,2. To date, numerous clin-ical studies and researches using VFSS to examineswallowing function have been reported. These studiescan be divided into two types of analysis of the swal-lowing process: temporal3-10 and spatial10-14. Theresults of temporal analyses are readily comparable,relying as they do on the same mode of time-basedmeasurement. However, the results of the spatially-based studies are more difficult to compare becausethe ‘standard’ planes or anatomical reference pointsused differ among these studies and because some ofthe planes used are less reliable as standardizedanatomical reference points.

In spatial studies, the cervical spine is the most com-monly used reference point for the standard plane10-12.Anatomical reference points also used in these studiesinclude the occlusal plane on the upper jaw13,Frankfort’s (FH) plane14, and SN plane11 on the neuro-cranium. The majority of dysphagic patients are elder-ly17 and many of them suffer from cerebrovascularand/or other diseases. Approximately 40% of patientswho suffer from acute cerebrovascular disease havesymptoms of dysphagia15,16. However, in the elderly, dis-eases of ageing such as a round back18, osteo-

Original Article

Videofluoroscopic Kinesiologic Analysis of Swallowing: Defining a Standard Plane

Ayako Nakane, Haruka Tohara, Yukari Ouchi, Shino Goto and Hiroshi Uematsu

Gerodontology, Department of Gerodontology, Division of Gerontology and Gerodontology, GraduateSchool, Tokyo Medical and Dental University

J Med Dent Sci 2006; 53: 7–15

Corresponding Author: Ayako NakaneTokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku,Tokyo 113-8549, Japan Tel: +81-3-5803-5562 Fax: +81-3-5803-0208E-mail: fujigerd@tmd.ac.jpReceived September 16; Accepted December 2, 2005

phytes19 or loss of teeth20 mean that the cervical spineor the occlusal plane often cannot provide appropriatereference points. On the other hand, standard planeson neurocranium like FH plane and SN plane are stableanatomical markers that are relatively unchanged byaging20.

If we review the swallowing process, it would seemthat a standard plane on the upper jaw is the preferredreference point for a spatial analysis using VFSS. Thepurpose of swallowing is to send a food bolus from themouth to the esophagus safely, a process thatrequires sufficient opening of the upper esophagealsphincter (UES). The UES contracts to stop air fromentering the digestive tract during respiration andphonation and to prevent the aspiration of esophagealcontents back into the larynx. The sphincter is locatedon the inlet of the esophagus and normally—exceptduring processes such as swallowing, belching andvomiting—closes the pharyngo-esophageal segment.The cricopharyngeal muscle is attached to the cricoidcartilage and relaxes when swallowing, but does notopen automatically22. Instead, successful opening of theUES requires an anterior-superior excursion of thehyoid bone and cricoid cartilage23-25. Especially, forwardmovement of hyoid bone has been reported to havemuch relation to opening of UES13,26. And literaturereported that 3.5-36.6% of the patients with dysphagiahave UES dysfunction27-32 and training of supra-hyoidmuscle that pulled hyoid bone improved UES openingof elderly and dysphagic patients33-35. Therefore, wehave to have more profound knowledge about the rela-tionship between the displacement of hyoid bone andUES opening. In particular, the relationship betweenforward displacement of hyoid bone and UES openingis important to know because they highly correlatedwith each other26. If the standard plane of spatialmeasurement is to reflect the relationship of thesestructural movements effectively then a point of refer-ence along the upper jaw would be preferred.

It has been suggested that Camper’s plane36, a linerunning from the superior border of the tragus to theinferior border of the ala of the nose, might be apreferable standard plane for swallowing analysis. Itsanatomical reference points are relatively stable even inthe elderly. Given these potential benefits, this studysought to investigate the hypothesis that Camper’splane is valid when used as a spatial marker in VFSS.We thus designed a comparative study that usesCamper’s plane as well as several standard planesused in previous studies10-12.

Material and Methods:

SubjectsSubjects were 20 young and 9 elderly healthy volun-

teers without any history or symptoms of swallowing dif-ficulty. Young group consisted of 10 females and 10males, and the average age was 26.9±3.0 (mean±SD) with a range from 23 to 34 years. Elderly groupconsisted of 3 females and 6 males. And the averageage was 77.3±3.4 (mean±SD) with a range from 72to 81 years. This study was approved by the EthicsCommittee of the Tokyo Medical and DentalUniversity Hospital. Informed consent was obtainedfrom each subject before examination.

ProcedureSubjects were seated comfortably in a chair as if they

were eating at a table. VFSS (Medix-900DR, HitachiMedical Corp) was performed from a lateral projectionto assess the swallowing movement. A radiopaque ballmarker made of lead (12.8mm diameter) wasattached to the chin of each subject to calibrate theimage. Radiopaque disk markers (Gold-Silver-Palladium alloy, 5mm diameter, 1mm thickness) werealso attached at the base of the nose and at the inferi-or margin of the tragus as a reference point forCamper’s plane (Fig 1). A liquid barium was deliveredwith a 10ml disposable plastic syringe by a single oper-ator and each subject was instructed to hold the bolusin their mouths until given a cue to swallow. A bolus of

A. NAKANE et al. J Med Dent Sci8

Fig. 1. Example of Camper’s plane and the displacement of hyoidbone on the Camper’s plane. A: base of nose, B: inferior margin oftragus�: The reference point of hyoid bone (the most anterior-superiorpoint on hyoid bone).△: The position of hyoid bone at rest.▲: The position of hyoid bone during swallowing reflex.①: horizontal displacement. ②: vertical displacement.

4ml of thin liquid barium sulfate8,22,26 (barium/water50/50% weight/volume; Barytgen sol, FushimiPharmaceutical Co.,Ltd., Kagawa, Japan.) was swal-lowed by each subject.

Data analysisThe VFSS image was recorded on a digital video

recorder (GV-D1000, NTSC, Sony, Japan, 30frames/s). Immediately after each recording, theVFSS images were captured on a personal computeras AVI format movie files and manipulated for quanti-tative analysis (Adobe Premiere, Adobe Photoshop,and Adobe Systems. Inc., CA, USA). Spatial measure-ment was performed to analyze hyoid (Fig 1) and UESopening (Fig 2). Hyoid displacement during swallowingwas measured by using four kinds of standard planes,Camper’s plane, C2C4 plane10, C2C5 plane11, andC3C5 plane12 (Fig 3). FH plane and occlusal planewere not used in this study because these wereapproximately parallel to Camper’s plane36. And SNplane was not studied also because this plane is gen-erally not included in radiation area when looking atswallowing function35. The reference point of hyoidbone was the most anterior-superior point of hyoidbone.

Due to the lack of an obvious anatomical structure,UES opening size was measured via a lateral VFSSview aimed at the narrowest point of opening betweenC3 and C6 during the moment of maximal distention forthe passage of the liquid barium bolus26,37,38(Fig. 2).

Fig. 3 shows the four kinds of standard planes usedin this study. Fig. 3-a shows Camper’s plane. The Xaxis represents Camper’s plane (the line passingthrough the marker on the base of the nose and theinferior margin of the tragus), while the Y axis isdefined by the line perpendicular to the X axis that inter-sects it at the marker on the inferior margin of tragus.Fig. 3-b shows C2C4 plane. The Y axis is defined asthe line passing through the inferior margins of C2 andC4 and the X axis represents the line perpendicular tothe Y axis that intersects it at the marker on the inferiormargin of the tragus. Fig. 3-c shows C2C5 plane. The Yaxis here is the line passing through the inferior mar-gins of C2 and C5 while the X axis is defined by the lineperpendicular to the Y axis that intersects it at themarker on the inferior margin of the tragus. Fig. 3-dshows C3C5 plane. The Y axis represents the linepassing through the inferior margins of C3 and C5 andthe X axis is the line perpendicular to the Y axis thatintersects it at the marker on the inferior margin of thetragus.

In order to compare measurements from each stan-dard plane, we focused on the relationship betweenhyoid displacement and UES opening since hyoidexcursion is involved with the opening of the UES23-25.The correlation between the anterior-superior dis-placement of the hyoid as measured against each stan-dard plane and the UES opening size was calculated.

Pearson’s correlation coefficients were calculated byusing SPSS (SPSS 11.0J, SPSS Japan Inc., Tokyo,

9STANDARD PLANE FOR KINESIOLOGIC ANALYSIS OF SWALLOWING

Fig. 2. Example of UES opening. VF image and the illustration are shown.The narrowest point of UES opening between C3 and C6 during maximal distention of the bolus passage

Japan). Statistical significance was indicated whentwo-tailed p values were less than 0.05.

Moreover, angles between X axis on Camper’splane and Y axis on the other planes were measured tolook at the effect of aging on cervical vertebrae as ref-erence point.

Results

UES opening and hyoid displacementIn the young group, the mean UES opening size was

0.30±0.09cm when subjects swallowed (Table 1).The anterior displacement of the hyoid was 0.64±

0.26cm on the Camper’s plane, 0.65±0.31cm on theC2C4 plane, 0.65±0.32cm on the C2C5 plane, and0.63±0.32cm on the C3C5 plane. And all of the corre-lation between UES opening and anterior hyoid dis-placement were significant. The superior displace-ment of the hyoid was 0.18±0.37cm on the Camper’splane, 0.45± 0.47cm on C2C4 the plane, 0.38±0.37cm on C2C5 the plane, and 0.35±0.39cm onC3C5 the plane. UES opening and superior hyoid dis-placement correlated negatively, and significantly onlyin Camper’s plane.

In the elderly group, the mean UES opening size was0.72±0.17cm (Table 1). The anterior displacement ofthe hyoid was 0.97±0.37cm on the Camper’s plane,

A. NAKANE et al. J Med Dent Sci10

Fig. 3. Four kinds of standard planes.a. Camper’s plane: X axis was Camper’s plane (the line passing through the marker on the base of nose and inferior margin of tragus), andY axis was defined by the line perpendicular to the X axis that intersects it at the marker on the inferior margin of tragus. b. C2C4 plane: Y axis defined as the line passing through inferior margin C2 and C4 and X axis defined by the line perpendicular to the Yaxis that intersects it at the marker on the inferior margin of tragus. c. C2C5 plane: Y axis defined as the line passing through inferior margin C2 and C5 and X axis defined by the line perpendicular to the Yaxis that intersects it at the marker on the inferior margin of tragus. d. C3C5 plane: Y axis defined as the line passing through inferior margin C3 and C5, and X axis defined by the line perpendicular to theY axis that intersects it at the marker on the inferior margin of tragus.

1.06±0.51cm on the C2C4 plane, 1.10±0.52cm onthe C2C5 plane, and 1.06±0.49cm on the C3C5plane. And the correlation between UES opening andanterior hyoid displacement was significant only inCamper’s plane. The superior displacement of thehyoid was 0.03±0.66cm on the Camper’s plane,0.25±0.52cm on C2C4 the plane, 0.42±0.59cm onC2C5 the plane, and 0.06±1.00cm on C3C5 theplane. UES opening and superior hyoid displacementcorrelated negatively.

UES opening and anterior hyoid displacement in bothgroups significantly correlated only in Camper’splane. However, superior hyoid displacement didn’t rep-resent UES opening. In short, anterior hyoid displace-ment on Camper’s plane should be measured when therelationship between hyoid displacement and UESopening needs to be investigated.

None of young subject had cervical osteophytes andround back. Two elderly had cervical osteophytes at C4and C5 region, and four elderly had mild round back.

The angle between each standard planeIn the young group, the angle between X axis on

Camper’s plane and Y axis was 100.65°±8.44° onC2C4 plane, 102.40°±7.99° on C2C5 plane, and

102.05°± 10.86° on C3C5 plane.In the elderly group, the angle between X axis on

Camper’s plane and Y axis was 106.89°±9.24° onC2C4 plane, 109.67°± 11.25° on C2C5 plane,110.33°± 13.89° on C3C5 plane. In addition, theangle with round back between X axis on Camper’splane and Y axis was 113.00°±7.7° on C2C4 plane,117.75°±10.05° on C2C5 plane, 120.25°± 11.87° onC3C5 plane. The angle with cervical osteophytesbetween X axis on Camper’s plane and Y axis was94.00°± 1.41° on C2C4 plane, 95.50°± 3.54° onC2C5 plane, 91.50°± 2.12° on C3C5 plane. Theangle between X axis on Camper’s plane and Y axiswith normal elderly was 107.33°±3.21° on C2C4plane, 108.33°± 3.79° on C2C5 plane, 109.67°±2.52° on C3C5 plane (Table 2).

Discussion

Past reports using several standard planesIn this study we sought to compare the efficacy and

validity of a range of standard planes commonly usedfor spatial analysis in VFSS. The standard planesused in our study included C2C4 plane, C2C5 plane,

11STANDARD PLANE FOR KINESIOLOGIC ANALYSIS OF SWALLOWING

Table 1. The relationship between UES opening size and displacement of hyoid at swallowing on four standard planes.

C3C5plane and Camper’s plane. Our findings showedCamper’s plane was the most reasonable standardplane. However, it is hard to compare our findings topast reports directly as there is a lack of standardizationof anatomical reference points used in the spatialanalysis of VFSS. While some preference has beenshown for using the cervical spine as a standard refer-ence, studies to date have used a variety of measures.

For instance, Hattori10conducted a study examiningthe influence of wearing complete dentures on swal-lowing function using the cervical spine (C2, C4) as astandard plane. VFSS was performed on nine healthyedentulous elderly volunteers. This study showedthat, during swallowing, the hyoid and larynx movedmore in subjects without dentures than in those withdentures. Haishima et al.11 compared three types ofcoordinate planes in order to investigate the growthdirection pattern of organs related to swallowing usingcephalograms. They resulted C2C5 plane was thebest coordinate plane when looking at the growthdirection of organs related to swallowing. Furukawa12

conducted a study on the laryngeal displacement dur-ing deglutition. Forty-eight males ranging in age from30 to 70 years were analyzed by means of cineradiog-raphy. The standardized line passed through theanterosuperior margin of C3 and the anteroinferior mar-gin of C5; the laryngeal displacement was measuredboth horizontally and vertically. This study indicated thatthe superior displacement of the larynx during the slowascending phase (the voluntary stage of deglutition)increased with age.

Ishida et al.13 studied hyoid displacement during theswallowing of both chewed solid food and liquid.VFSS was performed on 12 healthy volunteers rangingin age from 20 to 28 years. The standard plane used inthis study was the occlusal plane, that is, an antero-posterior (X) axis which passed through the metalmarkers on the upper canine and posterior molarteeth. The vertical axis was defined by a line perpen-dicular to the X axis that intersected at the marker onthe upper canine. This study found that a superior dis-placement of the hyoid bone when swallowing was

related primarily to events in the oral cavity and secon-darily to motions of the jaw and tongue. Yet anterior dis-placement of the hyoid was also related to pharyngealprocesses, especially the opening of the upperesophageal sphincter.

Finally, Mays et al.14 investigated the relationshipbetween the Frankfort Mandibular Plane Angle (FMA)and hyoid bone displacement in swallowing. The FMAis the angle between Frankfort’s plane and themandibular plane. VFSS was performed on 12healthy subjects in order to examine forward andupward displacement of the hyoid bone. Their resultsindicated that the greater the FMA, the smaller the hor-izontal displacement of the hyoid.

To date research using VFSS has tended to adopt avariety of different standard planes when adopting aspatial approach to the analysis of swallowing. This lackof consistency means that it is hard to compare theresults of these studies. Furthermore, the majority ofsubjects involved in these studies are healthy adults.Accordingly, an area that remains unexamined inVFSS studies is whether the standard planes com-monly adopted are useful for measuring swallowingfunction in elderly patients.

Hyoid displacement and UES openingThere have been several reports about the relation-

ship between hyoid displacement and UES opening.And they looked into the anterior hyoid displacement,but not into superior hyoid displacement13,26,39. In ourstudy, anterior hyoid displacement had relation toUES opening, however, superior hyoid displacementdidn’t contribute to UES opening. This is because of thedirection and the order of the displacement of eachstructure when swallowing. During swallowing reflex, atfirst hyoid bone moves superiorly, and immediately afterthat, larynx moves superiorly. And then, hyoid bonemoves anteriorly, and immediately after that, UESopens13,24. Therefore, anterior hyoid displacement hadrelation to UES opening, and superior hyoid displace-ment had relation to laryngeal movement3. In brief,anterior component of hyoid displacement on valid

A. NAKANE et al. J Med Dent Sci12

Table 2. The angle between X axis on Camper’s plane and Y axis on the other planes.

standard plane should be looked at when the relation-ship between hyoid displacement and UES openingneeds to be studied.

A possible standard plane for the elderlyFor instance, cervical osteophytes and other hyper-

trophic changes of the cervical spine are found inapproximately 20-30% of the elderly population19.Furthermore, a number of studies have found thatpatients with swallowing difficulties are more likely tohave cervical osteophytes. Granville et al.40 studied theprevalence of cervical osteophytes and the relationshipbetween osteophytes and swallowing function.Results showed that cervical osteophytes were preva-lent in about 11% of dysphagic patients over 60years-of-age with the most common region for osteo-phytes being the C5-C6 (40%), C4-C5 (23%), and C2-C3 (14%) sections of the spine.

Koyama et al.41 reported the influence of osteo-phytes on swallowing and found that large osteo-phytes interfered with the downward tilt of the epiglottisand the opening of the cricopharyngeal sphincter. Incontrast to Granville’s study, the area most commonlyaffected by osteophytes in the Japanese subjects inKoyama’s study was C3-C4-C5 and C4-C5. These find-ings reflect racial differences in the range of neck move-ment. In Asian adults the range of neck movement islarger at the C4-C5 region than in Westerners, there-fore, in Asian subjects, this region is more prone todeveloping osteophytes42. Strasser et al.43 reported therelationship between the size of cervical osteophytesand the frequency of aspiration. This study showed thatcervical osteophytes larger than 10mm can be acause of aspiration. Another report44 found that dys-phagic patients who had cervical osteophytes largerthan 19mm were more likely to be aspirators. In ourstudy, two elderly out of 9 had cervical osteophytes atC4 and C5. Their osteophytes were not too large tointerfere the epiglottis downward movement duringswallowing, but rotated the coordinates that had refer-ence point on cervical spine toward dorsum (Table 2).Therefore, anterior hyoid displacement and UESopening might not be correlated well in the elderlygroup when using cervical spine as reference point.Anterior hyoid displacement might be underestimated inthe subject with cervical osteophytes because of therotation of the coordinates.

Another disease of ageing which may interfere withthe validity of commonly used standard planes such asthe cervical plane is increasing curvature of the thoracicspine, or what is commonly referred to as ‘round

back’18. Tsuritani et al.45, for instance, have reportedthat round back is associated with fractures of the cer-vical spine caused by osteoporosis. In this study, 4elderly out of 9 had mild round back. Standard plane ofthe subject with round back was bent forward (Table 2).This might be another reason of poor correlationbetween anterior hyoid displacement and UES openingin elderly group when using cervical spine as referencepoint. This forward-bend coordinates might underesti-mate anterior hyoid displacement.

On the other hand, when using Camper’s plane as astandard, anterior hyoid displacement and UES open-ing correlated well in both of young group and elderlygroup (Table 1). Hyoid bone is hanging down from neu-rocranium and mandible. Furthermore, jaw closeswhen swallowing46. According to them, coordinates did-n’t rotate for hyoid bone when using Camper’s plane asa standard. This is the advantage when looking at thehyoid bone displacement of elderly. Moreover, losingteeth is very common in eldely20.

In summary, the fact that many of the standardanatomical reference points used in swallowing studiesmay be affected by disease in elderly patients.Therefore, the need for a standard plane which is rela-tively unaffected by ageing processes is strongly sug-gested.

The usefulness of Camper’’s plane This study used Camper’s plane, a line that runs

along the upper jaw approximating the occlusal planeand passing through the inferior margin of the tragusand the base of the nose, as one of the anatomicalmarkers for spatial analysis. This plane is alwaysused as a reference plane when making upper full den-ture clinically, but we were motivated to use it as stan-dard plane because Sakaguchi et al.47 reported thatCamper’s plane coordinates as the organic standardplane to enable easy evaluation of the movements ofperioral soft tissue. Because the component of move-ments that is specific to perioral soft tissue during mas-tication is equal repetition spatially and stable move-ment temporally and useful for evaluation of thesmoothness of masticatory movement.

We have noted a number of reasons why Camper’splane is preferable to other standard planes.

Firstly and most importantly, the results of our studysuggest that Camper’s plane is a highly reliable refer-ence point for measuring swallowing function comparedwith the other standard planes used in our study.Indeed, anterior displacement of the hyoid bone andUES opening correlated significantly in both of the

13STANDARD PLANE FOR KINESIOLOGIC ANALYSIS OF SWALLOWING

young and the elderly group when using Camper’splane as a standard (Table1).

Secondly, Camper’s plane is a reliable standardplane in both of the young and the elderly as all its ref-erence points lie on the upper jaw, and are thereforeunaffected by the shape of the cervical spine, cervicalosteophytes or loss of teeth.

Lastly, we like to add another advantage. Camper’splane enables clinicians and researchers to minimizeunnecessary radiation exposure during VFSS. WhileFH plane and SN plane also have reference points onthe upper jaw, these planes require wider radiationexposure than Camper’s plane because their referencepoints include Po (Porion) and Or (Orbitale), and S(Sella turcia) and N (Nasion) respectively48.

In light of this, we surmised that Camper’s plane isthe preferable standard plane for swallowing studies,not only in the elderly but in the patient population moregenerally. Standardization of the standard planewould allow comparison among studies and enableresearchers to examine the impact of factors such asage and cervical deformation on swallowing.Furthermore, regulation and standardization of theirradiation area would not only lessen exposure butwould also contribute to a greater ability to make gen-eralizations across studies.

Conclusion

This study sought to compare the validity of severalstandard planes in assessing the spatial measurementof swallowing using VFSS. The results indicate thatCamper’s plane is preferable as an anatomical refer-ence point as the correlation between UES openingand anterior hyoid displacement was strongest whenusing this plane as a standard. Furthermore, unlikeother standard planes, Camper’s plane is largelyunaffected by specific morphological changes causedby aging, and is also safer due to its narrower irradia-tion area. As a standard, the Camper’s plane ispreferable for the videofluoroscopic kinesiologicanalysis of swallowing function.

Acknowledgements

We would like to thank Dr. S. Morita of the Division ofRehabilitation Medicine, Tokyo Medical and DentalUniversity for his invaluable guidance and R. T. K. Niwaof the Radiological Center, Faculty of Medicine, Tokyo

Medical and Dental University Hospital.This research was supported in part by the

Research Grant for Longevity Sciences (H16-1) fromthe Ministry of Health, Labour and Welfare, Japan.

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15STANDARD PLANE FOR KINESIOLOGIC ANALYSIS OF SWALLOWING