Gomputed tomography of the normaltemporoMaandibular joint

EDWIN h. GHRISTiANSENi, TERENCE T: CHAN^, JOSEPH R. THOMPSON^ANTON N. HASSO', DAVID B. HINSHAW JR' AND SIGVARD KOPP*

^Department of Endodontics^ School of Dentistry,, Loma Linda University, '^Department of Radiation Sciences,'Section of Neuroradiology, Lima Linda University Medical Center, Loma Linda, California, USA, 'Department of

Stomatognathic Physiology, School of Dentistry, University of Lund, Malmo, Sweden

Christiansen EL, Chan TT, Thompson JR, Hasso AN, Hinshaw DB Jr, Kopp S: Computedtomography of the normal temporomandibular joint. Scand J Dent Res 1987; 95: 499-309.

Abstract - A study was made in two parts, retrospective (I) and prospective (II), on two samplesof 36 and 17 individuals, respectively, who had temporal bone CT studies for reasons unrelatedto TMJ pain and dysfunction. Groups I and II had no radiographic signs of TMJ disease andGroup II had neither radiographic nor clinical signs of TMJ disease. Both groups were consideredto have normal joints. Joint morphometrics for the two groups (I/II) were as follows; transversecondylar dimensions were 18.5/18.1 mm. Condylar angulation averaged 24''/25° and intercondy-lar distance averaged 83/83 mm while extra condylar distance averaged 118/118 mm. Thecondyle in the sagittal plane showed a smooth and rounded form with anterior-superior jointspace averaging 1.9/1.7 mm while the central-superior joint space averaged 2.3/2.2 mm. Themedial-horizontal joint space averaged 3.9/3.7 mm. The slope of the central portion of thearticular eminence averaged GO'/eO" in the sagittal plane.

Key words: anatomy; computed tomography; mandible; temporomandibular joint.

Edwin L. Christiansen, Department of Endodontics, School of Dentistry, Loma Linda, California92350, USA.

Accepted for publication 17 February 1987.

Pain and dysfunction of the temporoman- CT appearance of the normal TMJ. Ourdibular joints (TMJ) are not uncommon review of the literature has shown that whilecoHiplaints in patients presenting at dental references have been made to the normal CTand medical clinics. Thin section computed appearance of the TMJ, no stibstantiatingtomography (CT) has provided new diag- morphometrics are presented (1, 2). Sincenostic possibilities for this large group of pa- the first paper by SOARES etal. (3), interest intients. The purpose of this retrospective TMJ CT has concentrated on scan protocolsstudy was to describe the normal TMJ as it and imaging of the meniscus {4—10). Severalis depicted with computed tomography. papers presented case reports, CT for facial

To evaluate the CT appearance of the fractures and specific research topicsabnormal TMJ it is necessary to define the (11—15). Obvious variations of TMJ

500 CHRISTIANSEN ET AL.

Table 1

Age distribution in tmmber of individuals for Groups Jand II by sex separated in three classes of approximately20y width. The mean (M) and standard deviation (SD)

of age in years are induded

Groups

WomenMen

Total

21-40

I/II

4/16/2

10/3

41-60

I/II

9/45/4

14/8

61-83

I/II

9/43/2

12/6

M

I/II

54/5547/50

SD

I/II

18/1615/15

omy and the absence of a morphometric GTdescription of the normal joint has led us toundertake this study.

Material and metiiods

Axiai plane close sequence CT studies of twogroups (I, II) of individuals that induded thetemporoman dibular joints form the basis for thisstudy. Group 1 {K = 36) represents, a retrospective

Fig. J. Direct sagittal view of right TMJ showing level at which measurements were made in axialplane.

CT OF NORMAL TMJ

study and Group II {n= 17) represents a prospec-tive study of temporal bone scans which, for bothgroups, were not made specifically for the TMJ.Additionally, while there was no history taken norany clinical examination made of Group I, GroupII was. examined as to any past or present TMJsymptomatology^ such as pain, clicking or locking.For Group II, the position of the mandible (centricocclusion with light intercuspation) was. controlledwhereas it was not controlled for Group I. Thescans were loaded on a video display terminal(VDT) where they were evaluated for technicaladequacy with respect to display of the joint ele-ments, joint space and freedom from movementartifacts.

Criteria for selection of the two groups were asfollows: 1} the scans musE be in the axiai planeparallel to Reid's baseline, 2) the subjects must be'21 yr or older, 3) no-reports in the medical recordof pain or dysfUnction of the TMJ, 4) no reportsof head trauma, 5) no radiographic signs, of TMJdisease and 6) no craniofacial neopiastic disease.The GT scan reports and the hospital records werereviewed for indications of trauma or neopiasticdisease. The distribution of age and sex of theindividuals for each group is shown in Table h

AM patients were imaged wstb the General Elec-tric 8800 CT/N scanner {General Electric Co.,Medical Systems Operations, Milwaukee, WI;USA) with supine po.sitioning and axial, imagingplanes. The scan parameters, most frequendy usedincluded the adult head calibration file, 1.2prospective soft tissue targeting, 1.6 retrospectivebone targeting, 9.6 second scan times and i.5 mmsections. When the scan data was not retrospec-tively Reviewed (General Electric Co.), tbe ex-tended scale video display function was selectedfor optimum visualization of bone.

Morphometric analysis of the right and leftjoints of each group was identical. All measure-ments and assessments in the axial plane weremade at the level of the summit of the articulareminence (Fig. 1) because this level most fre-quently corresponds, to maximum condylar di-mensions. Furthermore, at this location, \'isualiz-ation of the soft tissue and osseous joint elementsis maximized because there is no interference fromadjacent bony structures^ particulariy the articu-lar eminence. Assessments in the vertically refor-matted coronal plane were made along the trans-verse axis of the condyle. Measurements in thevertically reformatted sagittal plane were perpen-

dicular to the transverse axis of the condyle ai itsvisually estim.ated center.

The antero-superior (AS) sagittal joint spacewas measured at the center of the condyle., as theshortest distance between the bony surfaces of thecondyle and the articular eminence (Fig. 2A)..This joint space represents tHe thin central articu-lar portion of the meniscus as it is normally posi-tioned between the bony joint elements in thesagittally viewed closed mouth position (Fig. 2B).Coronal centro-superior (CS) joint space wasmeasured from the central superior portion of thecondyle' to the nearest point in the glenoid fossa(Fig. 2G). The medial-horizontal (MH) jointspace was measured from the height of contourof the bony surface of the medial condylar pole,horizontally to the adjacent wall of the glenoidfossa.

Condylar angulation was visually estimated,then measured by depositing the cursor at themedial and lateral poles of tbe magnified (4.0times) axial image and reading to the nearest I /10th degree directly from the VDT (Fig. 3A).Intercondylar and extracondylar distances weremeasured from the heights of contour of the re-spective condylar poles (Fig. 3B}. Condylar form,in the axial planCj was assessed as either ellipsoid,concavoconvex or ovoid (Fig. 4A-C). Condylarform i,n the coronal plan.e was tabulated as one offour types according to a previous study of dryskull material (16) (Fig. 5A—D). Angulation ofthe articular eminence in tbe sagittal plane wasmeasured directly from the film with a protractoralong .a visually estimated line that provide a vis-ual best-fit of tbe slope (Fig. 6).

In most individuals the slope of tbe eminencewas readily determined. In a few individuals theeminence was smoothly sigmoid over its entiretyand estimating the slope was more difficult. Inthese cases, the slope was estimated by a tangentto the curve of the eminence. The length andangulation of the inferior bundle of the lateralpterygoid muscle in the axial plane were measuredfrom the condylar center to the medial recess orantero-posterior midpoint of tbe lateral pter)'goidplate and read directly from the VDT (Figs. 7A,B), Differences between sides and sexes in thisstudy were tested for statistical significance byStudent's ,(-test for comparing the means of twosmall samples and correlation to age was testedby Pearson's product-moment correlation coef-ficient (r).

502 CHRISTIANSEN ET AL.

. sf-^' '"<$r^

POST BAND

CENTRALARTICULAR

PORTION

(LAMINAR ZONE /

CT OF NORMAL TMJ 503

Fig. 2. a, vertically reformatted sagittal image along antero-posterior condylar axis for determinationof antero-superior (AS) joint space, form and slope of articular eminence, b, drawing made from sameGT section as A illustrating relation of normal meniscus, to osseousjoint elements, c, vertically reformat-ted coronal image along transverse condylar axis illustrating central-superior (CS) and medio-horizontal(MH) joint space.

Results

The results of this study are shown in Table2 and Figs. 4 and 5. The average transversedimensions of the condyles iti men (19.6 mm)and wonien (17.7 mm) in Group I weresignificantly different (P<0.02). The extra-

condylar distance in men and vv'omen inGroup I and II was 121 mm and 115.6,respectively, and the diiference betweenthese values was also significant (/'<0.05).No significant differences between right andleft sides and no significant correlation to agewas found for any of the variables investi-

504 CHRISTIANSEN ET AL.

CT OF NORMAL TMJ 505

• ' I . *

=/. K,

i i . 5. a, axial section, bone detail images were utilized in determination of condylar angulation (AN)relative to coronal plane (XX). b, axial section demonstrating measurement of transverse condylardimension, c axial section demonstrating extracondylar (line AB) and intercondylar (line CD) measure-ments.

Discussion

There is the possibility of a radiographicallyundetected and asymptomatic meniscalproblem in Group I since no clinical examin-ation of the TMJ was made of the individ-uals in this group. However, this possibilityis greatly reduced in Group II, where theclinical examination should have disclosed

such a problem of any clinical significance.We therefore consider the joints of the indi-viduals in Group II to be normal from al!aspects. The radiographically normal jointsin the asymptomatic individuals of Group Ido not differ io morphometric pattern fromGroup II and there is no reason therefore tosuspect an asymptomatic meniscal problemof any relevance for this study.

506 CHRISTIANSEN ET AL.

oFig. 4. Axial plane condylar form. Relative fre-quency is (A) 40% elliptical, (B) 40% concavo-convex and (C) 20%. ovoid.

The average age of the individuals in thisinvestigation is higher by 15 yr in womenand 7 yr in men than what is seen on averagein the TMJ clinic at this university. Ratherthan being a liability to the study, the agedistribution of this population is presumed

^7000A B C D

Fig. 5. Coronal plane condylar form (according to YALE et al. (15) and relative frequency (%). I (A)34%, II (B) 43%, III (C) 19% and IV (D) 9%.

... '<

. : •

Fig. 6. Slope and form of articular eminence was determined from verdcally reformatred images. LineAB illustrates slope of eminence.

CT OF NORMAL TMJ 507

Fig.. 7. a, ieiigth and angulation of inferior belly of lateral pterygoid muscle measured from condylarvisual center (arrow) to lateral surface (arrow) of lateral pter^'goid plate, b, axial image, soft tissuedetail of same subject as .A demonstrating deployment (dotted line) of inferior belly of lateral pterygoidmuscle.

508 CHRISTIANSEN ET AL.

Table 2

Distribution for Groups I {n — 36) and JI (n~17) of mean (M), range (R) and standard deviation (SD) ofcondylar anguiation (degrees), transverse (TR) condylar dimension (mm), mttero-posterior (AP) condylar dimension(mm)j antero-superior (AS) sagittal plane joint space (mm)y centra-superior (CS) coronal plane joint space (mm),extracondylar distance (mm), slope of articular eminence (degrees), angle (degrees) and length (mm) of inferior

belly of lateral pterygoid muscle

GroupTR condylar angnlation.'VP condylar dimensionAS joint spaceCS joint spaceMH joint spaceIntercondylar distanceExtracondyiar distanceEminence angulationMuscle angulation

MI/II

23.9/25.418.5/18.01.9/1.72.3/2.23.9/3.6

83.0/83.0'118.5/117.559.6/60.037.8/37.9

RI/II

30.9/22.69.2/8.02.5/2.15.3/3.26.0/4.0

22.6/22.628.8/28.855.0/47.014.9/14.2

SDI/II

6.6/6.22.4/2.50.5/0.50.9/1.11.1/Ll4.6/6.26.8/8.2

12.4/11.93.1/3.7

to provide a continuum of appearance ofnormal joints.

The inferior crest of the articular emi-nence was selected as the location formeasurements primarily because this is thesite where we make many of the CT scanevaluations of TMJ patients. Determinationof the slope of the articular eminence wasthe most subjective measurement in thestudy. The average error of measurementwas estimated to be + 5° in those individualswhere the slope was easily determined and+ 10° where it was nat.

The mean value for condylar angulationis comparable to studies using conventionalradiographic techniques (17), however, thestandard deviation is less by about 3° (arelative deerease of 33%), indicative of amore homogeneous group. Condylar angu-lation was not signiftcantiy correlated to agein these studies of normal individuals buthas been found to be correlated to age inindividuals with diseased TM-joints (18).We anticipated that we would fmd greaterdifferences when we analyzed for differencesbetween left and right sides and by sex. Sur-prisingly, there were significant differencesin only two variables by sex, transverse

condylar dimension and extra condylar dis-tance.

The results of this sttidy are consistent withprevious reports of TMJ morphometrics for 'older-(19) and younger (20) adults, wherethe mean condylar transverse dimensionswere 19.8 mm and 20.5 mm, respectively.Their description of coronal and axialcondylar morphology is essentially the sameas that reported in this study.

It is understood that padents do not nor-mally have CT head scans unless a diseaseprocess is suspected. However, the patientsin these two samples are considered normalinsofar as the temporomandibular joints areconcerned and the parameters presentedshould therefore be valid as normal morpho-metric values.

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