J Oral Maxillofac Surg 53:234-241, 1995

TMJ Articular Disc Position and Configuration 30 Years After Initial Diagnosis of Internal Derangement

RENY DE LEEUW, DDS, PHD,* GEERT BOERING, DDS, PHD,1- BOUDEWIJN STEGENGA, DDS, PHD,:I:

AND LAMBERT G.M. DE BONT, DDS, PHD§

Purpose: This study evaluates disc position and configuration on magnetic resonance imaging (MRI) in temporomandibular joints (TMJs) with a long history of internal derangement.

Patients and Methods: Sagittal Tl-weighted MRIs of 55 TMJs that were diagnosed with internal derangement approximately 30 years ago were made with the mouth closed and open, and the position and configuration of the articular disc were determined. For comparison, a control group consisting of 15 asymptomatic TMJs without clinical signs of internal derangement or of other TMJ disorders were studied in the same way.

Results: Anterior disc position was found in 90% of the TMJs with a history of internal derangement. Reducing disc displacement was found in one third of these TMJs, whereas permanent displacement was found in two thirds. In four joints, no disc was discernible. In one of the joints of the control group, a permanent disc displacement was found; normal disc position was found in all other joints of the control group. A biconcave disc configuration, which was considered normal, was found only in TMJs with normal disc position or with reducing discs.

Conclusion: It was concluded that, after 30 years of displacement, the TMJ disc can be clearly identified on MRI in most cases. If the disc becomes permanently displaced, its configuration deviates from the normal biconcave configuration, and its anteroposterior length decreases. Convex and folded appearances of the disc are common in this situation. However, the disc usually maintains its bicon- cave configuration as long as it resumes its position on top of the condyle during mouth opening, even if this condition lasts for several decades.

The term internal derangement (ID) is used to denote any disturbance in a joint that interferes with smooth function. 1'2 In the temporomandibular joint (TMJ), ID generally denotes articular disc displacement. 3 In the

Received from the Department of Oral and Maxillofacial Surgery, University Hospital, Groningen, The Netherlands.

* Research fellow, TMJ Research Group. t Professor and Chairman. +~ Research associate, TMJ Research Group. § Associate Professor. Address correspondence and reprint requests to Dr de Leeuw: TMJ

Research Group, Department of Oral and Maxillofacial Surgery, University Hospital, PO Box 30.001, 9700 RB Groningen, The Neth- erlands.

© 1995 American Association of Oral and Maxillofacial Surgeons

0278-2391/95/5303-000253.00/0

TMJ, the disc is normally situated in an anterosuperior position relative to the condyle. 47 In a TMJ with ID, the disc is generally displaced anteriorly or anteromed- ially relative to the condyle in the closed mouth posi- tion. Depending on the stage of derangement, the disc either regains its normal position on top of the condyle when the mouth is opened, or remains anterior to it, thus interfering with condylar translation. 4'8-11

To visualize the disc and its position relative to the condyle, several imaging techniques have been devel- oped. The most recent imaging technique, magnetic resonance imaging (MRI), provides a good definition of the soft tissues, is noninvasive, and has no associated radiologic risk. 12-1s Recent investigations have shown that MRI is a reliable technique for determining TMJ

234

DE LEEUW ET AL 235

disc posit ion. 16'17 M R I is also superior to computed tomography in diagnosing TMJ internal derangements and has a considerable number of advantages over arthrography and arthrotomography. 16 Therefore, MR/ seems the technique of first choice to identify the posi- tion of the disc and to judge its configuration.

Many studies have shown that on MRI the normal disc is depicted as a biconcave or "bow-t ie" configu- ration when viewed in the sagittal plane. 6'7'18-27 Several morphologic changes of the anteriorly displaced disc have been described, including atrophy of the anterior band, thickening of the posterior band, and shortening of the entire anteroposterior length. 14'2628 In advanced cases of ID, the disc may show a biconvex configura- tion with a tendency to fold onto itself. 14'26'27 It is un- known what happens to the configuration of the disc when it is displaced permanently for several decades, nor is it clear whether the configuration changes when a reducing disc displacement exists for several de- cades. The aim of this study was to evaluate disc posi- tion and configuration in TMJs with a long history of ID using MR/.

Materials and Methods

Forty-six former patients (mean age, 59 ___ 5.3 years), treated nonsurgically for 1D of the TMJ about 30 years ago, participated in this study. Ten volunteers (mean age, 61 _+ 6.4 years) served as control subjects. The records of the former patients were rediagnosed by two observers according to predefined criteria, based on the current knowledge on TMJ disorders. 29 When both observers agreed on the presence of ID in one or both TMJs, the case was included in the study. A detailed description of the selection criteria for both former patients and control subjects has been reported previously. 3°'3~ These included (with regard to the for- mer patients) the presence of signs indicative of a re- duced disc displacement, eg, reproducible reciprocal clicking on opening and protrusion; mandibular shift or deviation to the clicking side before the moment of clicking; no or only very slight radiographically visible degenerative changes, or the presence of signs indica- tive of a permanent disk displacement, eg, history of clicking; history of sudden onset of restricted mouth opening with cessation of clicking; mandibular shift or deviation to the affected side on opening; restricted protrusion; restricted lateral movement to the af- fected side; and radiographically visible degenerative changes. Inclusion criteria for the control group were absence of previous and present complaints of the mas- ticatory system; no TMJ noises; no restricted mouth opening; no deviation of the mandible on opening or protrusion. Participants should not be older than 70 or younger than 50 years of age.

Sagittal T 1-weighted MR images of all TMJs in both

the closed and open mouth positions were made. The participants were imaged using a dual-surface coil in a Philips Gyroscan (1.5 Tesla). The degree of mouth opening was fixed with bite blocks, which were avail- able in variable sizes. In case of a clicking TMJ, the patient was instructed to open the mouth beyond the click.

The position of the articular disc relative to the con- dyle with the mouth open or closed was determined on the MR images, and disc configuration was judged. Disc position was considered normal when it was situ- ated anterosuperior to the condyle in both the open- and closed-mouth images. When the disc was situated anterior to the condyle when the mouth was closed and regained its position anterosuperior to the condyle during mouth opening, the condition was considered a reducing disc displacement. When the disc was situ- ated anterior to the condyle in both the open and closed mouth images, it was considered a permanent disc dis- placement.

Disc configuration was judged in both the open- and closed-mouth positions and was categorized as being a bow-tie configuration (biconcave), biplanar, biconvex, folded, or amorphous. 14'26'27'32'33 The disc was consid- ered misshapen if it deviated in any way from the biconcave configuration. Additionally, whether the disc became compressed with mouth opening, and whether the anteroposterior length of the disc was shortened, were also noted.

Results

Rediagnosis of the records showed that 37 of the former patients had unilateral and nine had bilateral ID 30 years ago. Twenty-six TMJs were diagnosed with reducing disc displacement and 29 with perma- nent disc displacement. Of the control subjects, 15 TMJs were asymptomatic and clinically free from TMJ noises, deviation on protrusion, and restriction of movement.

TMJ ARTICULAR DISC POSITION

Disc position could be determined in the closed- as well as in the open-mouth images in 58 TMJs. Normal disc position was found in four TMJs, reducing disc displacement in 13 TMJs, and permanent disc displace- ment in 26 TMJs of the former patients. In the control subjects, normal disc position was found in 14 TMJs and permanent disc displacement in one TMJ.

In 12 TMJs of former patients, it was not possible to interpret disc position in either the closed- or open- mouth images (NI group). In four cases of the NI group, no disc could be discerned. In five cases, the disc could be seen in an anterior position in the closed- mouth images, but could not be discerned in the open-

2 3 6 TMJ ARTICULAR DISC: 30 YEARS AFTER INTERNAL DERANGEMENT

Table 1. Relat ionship Be tween Conf igurat ion and Posit ion of the TMJ Ar t icu lar Disc on MRI (n = 70)

Normal RDD PDD NI

OM CM OM CM OM CM OM CM

Biconcave Biplanar Biconvex Folded Convex Spectacle-shaped Amorphous No disc material discernible Blurred image

18 16 13 8 1 2 3 2

2 16 1 2 8 1

12 8

3 3 1 4

9 5 2

Abbreviations: TMJ, temporomandibular joint; RDD, reducing disc displacement; PDD, permanent disc displacement; NI, not inter- pretable; OM, open mouth; CM, closed mouth.

mouth images. In one case, the disc could be seen in an anterior position in the open-mouth image but could not be discerned in the closed-mouth image. In two cases in which the disc was located in an anterior position in the closed mouth image, the open-mouth image could not be judged because of poor image quality.

T M J ARTICULAR DISC CONFIGURATION

In all TMJs with normal disc position, and in those with a reducing disc displacement, a biconcave disc configuration was found in the open-mouth images (Table 1). The disc had the classic "bow- t ie" shape in 84% of the cases. In the closed-mouth images, the disc had the classic "bow- t i e" shape in 78% of the cases (Fig 1). In two TMJs with normal disc position and in five with reducing disc displacement, the con- figuration was judged misshapen in the closed-mouth images. With mouth opening, these discs regained a biconcave configuration (Fig 2). In three of these joints (with reducing disc displacement), the anteroposterior length of the disc was decreased.

The disc was misshapen in all TMJs with permanent disc displacement. In the open-mouth images, bicon- vex and folded configurations frequently were seen. In the closed-mouth images, the configuration of most of the discs did not fit the predefined categories. In 12 cases, the upper contour of the anteriorly displaced disc adapted to the slope of the articular eminence, thus showing a more or less concave surface, while the lower contour of the disc was more or less convex. Thus, a category referred to as convex was added (Fig 3). In eight cases, the upper contour of the disc was concave, but the lower contour had an irregular appear-

ance, with impressions of the remnants of the posterior and anterior band. This configuration was referred to as spectacle-shaped (Fig 4).

The anteroposterior length of the disc was decreased in all but one of the TMJs with permanent disc dis- placement (Fig 5). On inquiry of the patient in whom this condition was found, it appeared that TMJ clicking had ceased only recently. The disc was voluminous and had a folded configuration in the open-as well as in the closed-mouth images.

The configuration of the discs in the NI group could be judged in the closed-mouth images in seven cases and in the open-mouth image in one case. Except for one, all discs were misshapen; the anteroposterior length of the disc was shortened in five cases.

In 21 of 27 TMJs with a permanently displaced disc, the disc was compressed anterior to the condyle on mouth opening (Figs 3 and 4). In TMJs with normal disc position, or in TMJs with reducing discs, compres- sion was not observed. In the NI group, this item could not be evaluated, because information about the disc in the open-mouth position was only available in one c a s e .

D i s c u s s i o n

ID was confirmed on MR images in 92% of the TMJs of former patients. By contrast, normal disc posi- tion was seen in 93% of the TMJs of the control sub- jects. The high percentage of ID in TMJs of former patients indicates that the methods used to select the TMJs with ID were highly accurate. The low preva- lence of ID in a control group of approximately the same age indicates that the high percentage of ID in the TMJs of former patients was not simply attributable to aging.

Normal disc position was found in four TMJs of former patients. Notwithstanding the strong clinical in- dications for the presence of ID deduced from the re- cords, some other disorder producing signs closely re- sembling those of disc derangement must have misled the original observers in these four cases. Another pos- sibility is that in a small percentage of patients with ID the disc resumes its "normal" anatomic position. Surgical repositioning of the disc could not be an alter- native explanation, because this type of treatment was not used in these patients.

The finding of only one TMJ with ID in the 15 asymptomatic and clinically normal TMJs (7%) was lower than in the previous study of Westesson et al, 34 who found ID evidenced with arthrography in 6 of 40 TMJs of volunteers (15%), and of Kircos et al, 22 who found ID on MRI in 13 of 42 TMJs of volunteers (31%). Just as in our study, these volunteers were asymptomatic and free from TMJ noises or deviation on protrusion or opening, and had no restriction of

D~ LEEUW ET AL 237

FIGURE 1. Tl-weighted MRI images of the right TMJ of a 60-year-old female control subject showing a classic "bow-tie" configuration in the closed (A) as well as the open (B) mouth position.

movement . Although our sample size was somewhat

smaller than that of both aforementioned studies, this

does not seem an acceptable explanation for the con- flicting results, because obvious differences in preva-

lence even exist between the studies of Westesson and Kircos. Because the mean age of our sample (_+60

years) was considerably higher than that of both the

samples of Westesson et al (_+27 years) and Kircos et

al (+30 years), the low prevalence of ID in our control subjects is even more remarkable. A satisfactory expla-

nation for the conflicting results cannot be provided. A biconcave configuration was found in all TMJs

with normal disc position and in all TMJs with reduc- ing discs. These biconcave discs did not all have a

FIGURE 2. Tl-weighted MR images of the left TMJ of a 60-year-old male former patient. The disc has a biplanar configuration and is slightly displaced anterior in the closed mouth image (A). With mouth opening (B), the disc not only regains its position on top of the condyle but also the classic "bow-tie" configuration. (The contralateral TMJ of this patient is depicted in Fig 5).

2 3 8 TMJ ARTICULAR DISC: 30 YEARS AFTER INTERNAL DERANGEMENT

FIGURE 3. Tl-weighted MR images of the left TMJ of a 62-year-old female former patient. The disc is displaced anterior in the closed mouth image (A), and its anteroposterior length is shortened. The upper contour of the disc adapts well to the surface of the articular eminence. The lower contour shows remnants of the anterior and posterior band, resulting in a spectacle-shaped configuration. With mouth opening (B), the disc becomes folded and compressed in an anterior position relative to the condyle. Note that condylar translation is not restricted.

c lass ica l " b o w - t i e " conf igura t ion , wi th the pos ter ior b a n d be ing s o m e w h a t th icker than the anter ior band .

In our op in ion , the def in i t ion of Hasso et al, =6 who

stated that disc m o r p h o l o g y shou ld be cons ide red ab-

n o r m a l i f it devia tes in any way f rom the n o r m a l a sym-

met r ic bow- t i e shape, is a l i t t le too r igorous. Based on

the resul ts o f our study, we prefer the def in i t ion of Ka tzberg and Wes tes son , ~4 who cons ide r the disc nor-

ma l if it has a b i concave shape w h e n v i e w e d in the sagit tal plane. ~4

In a few T M J s wi th n o r m a l disc posi t ion, or wi th

r educ ing disc d i sp lacement , the disc devia ted f rom the

FIGURE 4. Tl-weighted MR images of the left TMJ of a 56-year-old female former patient. The disc is displaced anterior in the closed- mouth image (A). It has a convex configuration, and its anteroposterior length is shortened. With mouth opening (B), the disc becomes compressed in an anterior position relative to the condyle. Note that condylar translation is not restricted.

DE LEEUW ET AL 239

biconcave configuration on the MRI when the mouth was closed, but was found to be biconcave on the MRI when the mouth was open. Therefore, the presence of altered disc configuration can best be judged in the open-mouth position.

I f we consider the biconcave configuration of the disc as normal, our results confirm the statement of Katzberg and Westesson ~4 that in the early stages of internal derangement the configuration of the disc re- mains normal. Moreover, as long as the disc reduces on opening, even if this situation lasts for more than three decades, there are, at least on MRI, no signs of deformation of the disc. One patient who was diag- nosed with bilateral reducing disc derangement 30 years ago appeared to be perfectly illustrative of this statement. Clicking had recently ceased in one of his TMJs. The MRI of this joint showed a permanently displaced disc that was misshapen, yet voluminous and not shortened in the anteroposterior direction (Fig 5). The contralateral TMJ of this patient was still clicking. The MRI of this joint showed a slightly anteriorly displaced disc with a biplanar configuration in the closed-mouth image. With mouth opening, the disc regained its normal position on top of the condyle. In the open-mouth image, this reducing disc had the classical bow-tie configuration (Fig 2).

In conformity with the histologic findings of several autopsy studies, we found that all discs that were per- manently displaced had lost their original biconcave configuration. 5'28'32"35 Deviating disc configurations have been defined as biplanar and biconvex. 32'33 We

were not able to classify the discs according to these definitions, because they imply that both the upper and lower contours of the deformed disc have the same appearance. However, like Akerman et al 5 in their au- topsy study, we found the upper and lower contour of the disc to differ in joints with permanent disc displace- ment. As described in previous studies, disc configura- tion adapts to the surrounding tissues. 5'36'37 Indeed, we found the upper contour of the disc to adapt well to the slope of the articular eminence. With regard to the lower contour of the disc, however, the relationship with the surrounding tissues was not obvious. Heffez and Jordan 38 devised a fine classification of five basic disc shapes based on corrected lateral cephalometric arthrotomograms and histologic sections. Unfortu- nately, the disc configurations of our material did not fit their classification entirely. One explanation may be the long existence of permanent disc displacement in our study. Differences in visualizing disc configuration may be an alternative explanation.

To be able to appropriately classify the configuration of discs with a long-existing permanent displacement, it was necessary to add, apart from the folded configu- ration already described in previous MRI studies, a convex and a spectacle-shaped configuration. 14'26'2v

If there is a need to further classify disc configura- tion, differences in upper and lower contour of the disc must be acknowledged. In addition, it should be kept in mind that a considerable difference exists between disc configuration in the open- and closed-mouth posi- tions. Furthermore, a considerable difference may exist

FIGURE 5. Tl-weighted MR images of the right TMJ of a 60-year-old male former patient. Recently the disc became permanently displaced after a 30-year period of clicking. The disc has a folded configuration in the closed mouth image (A), which is accentuated in the open-mouth image (B). The disc is voluminous, and its anteroposterior length is not shortened. Condylar translation is slightly restricted. (The contralateral TMJ of this patient is depicted in Fig 2).

240 TMJ ARTICULAR DISC: 30 YEARS AFTER INTERNAL DERANGEMENT

between disc configuration with a recent ID and with a long-existing, permanent disc displacement.

Shortening of the anteroposterior length of the disc

was found in all TMJs with long-exist ing permanent

disc displacement. Compression of the displaced disc may have led to substantial remodeling and resorp- tion. 38'39 However, the displaced disc is not only sub-

jected to morphologic changes but also to histologic and biochemical changes. Hyalinization, dystrophic

calcification, and dehydration may cause lowering of the normal moderately low signal intensity of the disc. 7'26'27'39 Because of stretching of the retrodiscal tis-

sue and remodeling of the displaced disc, the demarca-

tion between the posterior band and the retrodiscal tissue becomes obscured. 26'39 Consequently, the low

signal intensity anterior to the condyle represents the

disc, but not its entire length. Even after about 30 years of displacement, the disc

was clearly discernible in most cases. In only four TMJs of former patients was no disc material dis-

cerned. Rupture of the disc or its posterior attachments

may be a possible explanation for the presumably se-

vere degeneration of the disc in these cases. We conclude that the degree of disc deformation

relates to the degree of anterior displacement. As long as the disc achieves an anterosuperior position on top

of the condyle with mouth opening it will have a nor-

mal biconcave appearance, However, the configuration of the disc will deviate as soon as it becomes perma-

nently displaced. Convex configurations, with the disc

folding on itself on mouth opening, are common. Fur- thermore, in TMJs with permanent ly displaced discs, the anteroposterior length of the disc shortens and its

volume decreases over time.

A c k n o w l e d g m e n t s .

The authors wish to express their gratitude to Dr E.L. Mooyaart (Department of Radiology, University Hospital Groningen) and Dr B van der Kuijl (Department of Oral and Maxillofacial Surgery, University Hospital Groningen) for their collaboration and diagnos- tic support.

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PER-LENNART WESTESSON 241

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J Oral Maxillofac Surg 53:241-242, 1995

Discussion

TMJ Articular Disc Position and Configuration 30 Years After Initial Diagnosis of Internal Derangement

Per-Lennar t Westesson, DDS, PhD University of Rochester School of Medicine and Dentistry, Rochester, NY

This article is interesting from many aspects. First, it shows that it is possible to identify patients with different degrees of disc displacement from old records with a rela- tively high degree of sensitivity. However, we do not know how many of the patients that were excluded from this study actually had disc displacement. Therefore, the specificity as well as the accuracy of the identification process is unknown, and the statement in the beginning of the discussion that "the methods used to select the TMJs with internal derange- ment were highly accurate" is not substantiated.

The article brings up the issue of the homogeneity of TMJ patient populations. The 46 patients who were examined represent a subset of patients with TMJ disease that is proba- bly very different from those usually seen in the practice of oral and maxillofacial surgery. I say this because these pa- tients were treated with conservative, nonsurgical methods such as reassurance, dietary advice, exercise therapy, appli- cation of superficial heat, and pain medication, la and all responded so well that none of them requested retreatment during the 30-year follow-up period. This is different from the patients referred for surgical treatment, usually after mul- tiple failed attempts with nonsurgical treatment. This illus- trates that patients with TMJ internal derangement are not a homogeneous group even if the morphology on the images appears similar. At least four subgroups can be identified: 1) asymptomatic individuals with disc displacement, 2) symptomatic patients with disc displacement who respond to conservative, nonsurgical treatment, 3) symptomatic patients with disc displacement who do not respond to nonsurgical treatment but who improve significantly with primary surgi- cal treatment, and finally, 4) those symptomatic patients with joint displacement who do not get better regardless of non- surgical or surgical treatment. The distinction between these

four groups is important, and I think the patients described in this study belong to the second group: those with minimal symptoms who respond to nonsurgical treatment. We are not able to prospectively separate patients with disc displace- ment into these four groups either on imaging or clinical grounds. It should be the goal of future studies to identify characteristics of patients with disc displacement so that eventually it becomes possible to prospectively understand to which category the individual patients belongs.

The authors' MR imaging technique included sagittal TI- weighted images. It would have been desirable to have coro- nal images, because studies have shown that there is a medial or lateral component to the disc displacement in up to about one third of cases. 3'4 Using coronal views increases the accu- racy of MR imaging over using only sagittal images. The value of coronal MR images has relatively recently become obvious and was probably not clear at the time these patients were examined.

In separating the different categories of disc displacement and internal derangement, T2-weighted images that depict the inflammatory components secondary to the disc displace- ment have been shown to be valuable. 5 Thus, a strong corre- lation between joint pain and joint effusion has been shown, and this is probably an important part of assessing patients who present with symptomatic TMJ disorders. The article would have been strengthened if T2-weighted images had been included. Again, the value of such images has become better understood only recently and was probably not ap- preciated at the time these patients were examined.

Previous studies have shown that disc displacement with reduction frequently involves only a partial dis- placement, with only a part of the disc being anteriorly displacement, while the rest is in a relatively normal position. This article also would have been strengthened if disc position had been studied in separate mediolateral sections of the joint and observations correlated to disc function. It has been my experience that disc displace- ment without reduction is associated with a total dis- placement, whereas disc displacement with reduction usually is associated with partial anterior displacement. It would be interesting to know if partial disc displacement could be present for as long as 30 years.