Posterior disc displacement in the temporomandibular joint

J Oral

Maxillofac 1273,

Surg 1998

56: 1266-

Posterior Disc Displacement in the Temporomandibular Joint Per-Lennart Tore A. Larheim,

Westesson,

MD, DDS, PbD, *

DDS, P&D, f and Hisashi

Tanaka,

MD+

The purpose of this study was to describe the imaging characteristics of posterior disc displacement of the temporomandibular joint (TMJ). Materials and Methods: The study was based on 35 joints with posterior disc displacement and a control material of bilateral TMJ images of 62 healthy volunteers. The imageswere analyzed, and criteria for posterior disc displacement were developed. 1 Results: Posterior disc displacement was characterized by the disc or a major part of the disc being located posterior to the superior prominence of the condyle. Three subcategoriesof posterior disc displacement could be identkied: a thin flat disc, a grosslyposteriorly displaceddisc, and a perforated disc with a portion of the disc displacedposteriorly. Posterior disc displacementwas not seenin any of the asymptomaticvolunteers. Conclusion: Posterior disc displacement of the TMJ is rare but hasprobably been overlooked in the past because of a lack of well-defined imaging characteristics. Purpose:

Disc displacement is the most common abnormality seen in images of the temporomandibular joint (TMJ). Most frequently the displacement is anterior, anterior lateral, or anterior medial.ld Posterior displacement has been considered exceedingly rare and has essentially been thought of asnonexistent. Casereports and descriptions in textbooks have documented the existence of the condition,4,5,7-*zbut no systematic description of the imaging characteristic and correlation to morphology have been documented in the literature. In our clinical and scientific work with TMJ imaging of patients and cadaver joints, we have collected 35 joints with posterior disc displacement. This report describes the imaging criteria and classification of posterior disc displacement of the TMJ.

*Professor

of Radiology,

Department

of Radiology,

University

of

Rochester School of Medicine and Dentistry, Rochester, NY. tProfessor and Chairman of the Department of Oral Radiology, Department of Orthodontics and Temporomandibular Disorders, Eastman Dental Center, Rochester, NY. *Assistant Professor of Radiology, Department

of Radiology,

Uni-

versity of Rochester School of Medicine and Dentistry, Rochester, NY. This study was conducted while Drs Larheim and Tanaka were Visiting Researchers at the University of Rochester, Rochester, NY. Dr Iarhehn was supported by the Medical Research Councils of Norway. The study was also supported by the National Institutes of Health, Grant #8059. Address

correspondence

and reprint

Department of Radiology, ter, NY 146423648.

601 Elmwood

Q 1998

of Oral and Maxillofacn

American

02%2391/98/561

Association l-0008$3

requests

to Dr Westesson:

Ave, PO Box 648, Roches Surgeons

00/O

1266

Materials

and

Methods

This study included images of 32 TMJs of 23 symptomatic patients, three cadaver joints, and a control material of 62 healthy volunteers with asymptomatic TMJs. The volunteers consisted of 29 females and 33 malesranging in age between 20 and 46 years. All of the volunteers were examined with unilateral arthrography and bilateral magnetic resonance imaging (MRI) after a clinical examination. Only subjects without current or prior signs or symptoms of TMJ disorders were included in the control group. Nineteen of the patients with posterior disc displacement were female, and four were male, ranging in age from 9 to 69 years. Eighteen of the patients were examined with MRI and three with arthrography. Two patients had both examinations. Over the B-year period when these cases were collected, approximately 3,200 patient were seen for MRI of the TMJ, and approximately 600 patients for arthrography. MRI consisted of oblique sagittal and oblique coronal images in the closed-mouth position and oblique sagittal images in the open-mouth position.‘” Both proton density and T2-weighted images were included in all three sequences.13The arthrographic examination was performed as lower-space arthrography under fluoroscopic guidance, with transcranial images in the closed- and open-mouth positions.l3 When the initial lower joint space injection showed normal arthrographic findings or an uncertain diagnosis, the upper joint space was alsoinjected. The cadaver specimens were obtained from fresh cadavers in association with an autopsy examination that included the brain. Information about premortem

WESTESSON,

LARHEIM,

AND

clinical symptoms was not available. The specimens (two male and one female, with a mean age of 74 years) were collected when studying approximately 500 TMJ autopsy specimens for morphology. The cadaver specimens were analyzed with a cryosectional technique.2 One of the specimens also had MRI and histologic evaluation.

FIGURE 1. Normal TMJ. A, Oblique sagittal proton density MR image (2000/20) at closed mouth showing superior position of the disc howl. 5. Obliaue sagittal image in thk oben mokh position showing a normal condyledisc (arrow] relationship.

1267

TANAKA

Results MRI of a normal joint with superior disc position and normal disc function on opening is shown in Figure 1 as a reference. In the normal joint, the posterior band of the biconcave disc is located superior to the condyle in the closed-mouth position (Fig

1268

POSTERIOR TMJ DISC DISPLACEMENT

1A). On mouth opening, the condyle rotates in the lower joint space, and the disc-condyle complex translates anteriorly inferiorly along the articular eminence. During mouth opening (Pig IB), the condyle is located inferior to the central thin zone of the disc and the disc is located with its posterior band posterior to the condyle. Posterior displacement of the disc was characterized on MR images by the disc tissue being located posterior to the condyle, between the posterior surface of the condyle and the postglenoid tubercle (Pig 2). Three distinctive groups of posterior displacement were identified in the patients. The largest group consisted of 26 joints in which the posteriorly dispiaced disc appeared as a flat band of tissue on top of the condyie extending posterior to the condyle (Pigs 2,3). The normal biconcave configuration was absent. Typically the disc tissue covered the top of the condyle and extended posteriorly between the posterior surface of the condyle and the glenoid fossa. There was generally no or minimal disc tissue seen anterior to the condyle (Pig 3). This posterior disc displacement was frequently associatedwith a medial component (Pig 3B). In the second group (three joints), the entire disc

FIGURE 3. Posterior and media disc displacement. A, Oblique proton density MR image [2000/20) of the medial portton of the jornt in the closed mouth position showing the disc [arrows) posterior to the condyle. 5, Oblique coronal MR image (2000/20) showing the disc (arrowhead) medial to the condyle.

FIGURE 2. Posterior disc displacement. Oblique proton density MR image (2000/20). The condyle and tern oral component are normal. The disc (arrows) is located posterior to t f e condyle. The thin disc-like tissue superior to the condyle is thought to be the anterior attachment of the disc that has been pulled posteriorly in the joint.

was displaced posteriorly (Pig 4). Typically there was no disc tissue covering the top of the condyle, but instead the entire disc was seen posterior to the condyle in the closed-mouth position. On mouth opening, a band of tissue was frequently seenconnecting the posteriorly displaced disc to the anterior joint capsule (Pig 4B). It is assumed that this tissue represents the anterior disc attachment that has been pulled into the joint by the posteriorly displaced disc and has developed fibrotic changes. This band was

WESTESSON,

LARHEIM,

AND

1269

TANAKA

FIGURE 4. Complete posterior disc displacement. A, Oblique proton density MR image (2000/20) in the closed mouth position showing the disc (arrows) completely posterior to the condyle. There is remodeling of the condyle, with a small osteophyte superiorly and a concavity posteriorly. 5, Oblique sagittal MR image (1.500/20) in the open mouth position showing the disc (arrowhead) posterior to the condyle. The disc-like tissue superior to the condyle is thought to be the anterior disc attachment that has been pulled posteriorly into the joint.

generally better seen in the open-mouth views than in the closed-mouth images. A similar condition is illustrated in Figure 5, which represents a cryosection of an autopsy specimen with posterior disc displacement. The chronic nature of the posterior disc displacement was documented by the frequent finding of a depression on the posterior bony surface of the condyle both in the cryosectional material and in patients (Fig 4A). The third group consisted of three joints where the disc had a central perforation and a large part of the

disc was displaced posterior to the condyle and a small portion was anterior to the condyle (Fig 6). On the arthrograms, posterior displacement was detected only when contrast material was injected into both the lower and the upper joint spaces. With contrast only in the lower joint space (Fig 7A, B), there were no specific criteria to differentiate the appearance of posterior disc displacement from a normal joint because the anterior recess appeared similarly small in both instances. On the dual-space arthrograms (Fig 7C, D), the diagnosis became more obvious, with the contrast in the enlarged posterior recess extending into the area posterior to the condyle where the upper joint space normally does not extend. Twenty-one patients had examination of both the right and left TMJs. Bilateral posterior disc displacement was found in nine and unilateral displacement in 12 patients. The contralateral joint showed normal disc position in six and anterolateral displacement in five patients. No posterior disc displacement was seen in the control material. Seventy-seven percent of the joints in the asymptomatic volunteers showed normal superior disc position, and 23% showed different forms of disc displacement. Sixty-five percent of the subjects had normal disc position, and 35% showed unilateral or bilateral disc displacement. All forms of disc displacement, with the exception of posterior displacement, were represented in the asymptomatic volunteers (partial anterior, anterior without lateral or medial component, anterolateral, anteromedial, lateral, and medial). Microscopic examination was performed on one cadaver joint, and it documented that the tissue posterior to the condyle was fibrous tissue with the fiber orientation and characteristics as seen in the disc Cl% 8).

Discussion This article has described imaging criteria for the diagnosis of posterior disc displacement of the TMJ using MRI and arthrography. Thus, on MRI, if lowsignal tissue is seen posterior to the superior prominence of the condyle on sagittal images, this should be interpreted as posterior displacement of the disc. The differential diagnosis is remodeling with fibrosis of the posterior disc attachment (retrodiscal tissue), but this condition generally occurs in cases with anterior disc displacement. The fibrosis of the posterior disc attachment is generally located superior to the condyle (Fig 9) rather than posterior to the condyle and should therefore be easily distinguished. No case with posterior disc displacement was observed in our asymptom-

1270

FIGURE indicated

POSTERIOR

5. Cryosection for orientation.

showing complete posterior disc displacement There is folding of the most posteroinferior portion

atic volunteers, although a variety of disc displacements were seen in this group. It should be noted that with the size of the control group and the low prevalence of posterior disc displacement, it would be relatively unlikely to lind a case of posterior disc displacement in this series of 62 asymptomatic volunteers. In the symptomatic patients with posterior disc displacement, three separate subcategories could be identified. Most frequently the disc tissue posterior to the condyle appeared like a band of tissue covering the condyle and extending posterior to it. The distinction from a normal disc position was the signal characteristic of the posterior disc attachment. Normally this attachment produces a high to intermediate signal on the MR images, as seen in Figure 1. In those cases with posterior disc displacement, there was clearly a portion of this attachment with low signal characteristics identical to the disc. About half of the cases had a sideways (medial) component to the posterior disc displacement. This was especially true for the first category with a thin disc covering the condyle. The observation of a medial component to the displacement suggests that coronal MRI is essential for complete diagnosis and understanding of the position of the disc. A medial component to

[arrowheads). The condyle of the disc (long arrow).

(C) and

TMJ

the

external

DISC

DISPLACEMENT

auditory

canal

[E) are

FIGURE 6. Perforated disc with a portion of the disc posteriorly displaced. Oblique proton density MR image (2000/20) shows a portion of the disc [smaii arrowhead) posterior to the condyle. There is a central perforation over the condyle and a small portion of the disc remains anterior (/urge arrowhead). There was joint effusion in both the upper ond lower joint spaces documented on T2weighted image (not shown). The condyle has a superior osteophyte and a posterior concavity.

WESTESSON,

LARHEIM,

AND

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TANAKA

FIGURE 7. Arthrogram showing posterior disc displacement A, 6, Transcranial lower joint space arthrogram and schematic drawing showing contrast medium in the lower point space. The contrast medium surrounds the condyle [c). There is no Indication of a posterior disc displacement. C, D, Dualspace arthrogram and schematlc drawing. Contrast medium has been injected into both the lower and the upper point spaces. The posterior extension of the upper joint space is abnormal and indicates posterior disc displacement. The disc is solid black in the schematic drawing (D) and is Indicated by arrowheads in D.

the posterior displacement was far more frequently found than a lateral component in this series. This is interesting because recent studies have indicated that both lateral and medial components of anterior disc displacement are found with nearly the same frequency.” There is even a tendency to seemore lateral than medial components to the displacement in an unselected series of imaged patients.5 It therefore seemsthat there is an association between posterior and medial displacement of the disc. Arthrographically, upper joint space opacification was necessary for the diagnosis of posterior disc displacement. An enlargement of the posterior recess of the superior joint space together with a large filling defect between the upper and lower joint spaces posteriorly was interpreted as evidence of posterior displacement. The lower joint space injection by itself may be incorrectly interpreted asnormal superior disc position because of the relatively small anterior recess. This again emphasizes the idea that if the arthrographic diagnosis is unclear after the injection of the lower joint space or it is normal, the upper joint space should be injected for a complete diagnosis. Bilateral posterior displacement was found in about half of the patients in this series. Therefore, bilateral imaging is recommended for complete diagnosis. There were striking similarities in the appearance of

D

the two sidesin most patients, as has been described in the past for other types of disc displacement.‘” The prevalence of posterior disc displacement is unknown. Posterior disc displacement remains an unusual entity, but it is probably more frequent than hitherto appreciated. The cases reported represent those collected (lessthan 1%) over an B-year period in clinical work with arthrography and MRI. However, it is possible that several casesof posterior disc displacement have been missed in our clinical work because we were not aware of the imaging criteria for this entity earlier. It is alsopossible that a number of cases have been missed because of the lack of upper joint space injection. Even in the autopsy material, it is possible that cases were missed because we were unaware of this entity and its morphologic criteria. The clinical symptoms of the patients in this study were not specific and were not significantly different from those patients presenting with other types of disc displacement. We also noted that at least in one patient with bilateral posterior disc displacement there was one asymptomatic joint. Other studies have described clinical symptoms such as posterior open bite or inability to close on the posterior teeth, and this seemsto be a common feature of acute posterior disc displacement.‘).‘i The treatment of posterior disc displacement has

1272

FIGURE lower

8. Photomicrograph of a posteriorly displaced disc (1) and upper(U) joint spaces are indicated for orientation

POSTERIOR TMJ DISC DISPLACEMENT

documenting

been described as manipulation of the joint under local or general anesthesia followed by short-term maxillomandibular fixation. l”,15 Successful surgical treatment by anterior repositioning and suturing of the disc has also been documented.7r9We believe that

FIGURE

9. Posterior disc attachment fibrosis. Oblique sagittal MR (2000/20) of a joint with anterior disc displacement (arrow head). The posterior disc attachment (long arrow] shows fibrotic changes. This is different from the appearance of a posteriorly displaced disc. image

the histologic

criteria

consistent

with

disc

tissue.

The condyle

(C), disc

(D),

many of these treatments are related to acute posterior disc displacement. Becauseposterior disc displacement was not suspected clinically in the casesthat are presented here, we believe that these are more chronic in nature, and other treatments may also be appropriate. The cause of posterior disc displacement is unknown. Although it has been thought to be of traumatic origin, 11,16 further study is needed for understanding of this entity. The study by Engelke’O associated posterior disc displacement with a forceful wide opening. Lack of anterior prominence of the disc has also been discussed as predisposing to posterior disc displacement. Another probable cause is a large perforation in the central part of the disc causing posterior displacement of the distal part, as was previously found in a case of chronic arthritis.12 The findings in this subgroup of posterior disc displacements were confirmed surgically in one case in our series. This patient had evident fibrous adhesions between the disc and the condyle posteriorly, and this appeared to be secondary to fragmentation and perforation of the disc.

1273

LESLIE B. HEFFEZ

References Westesson P-L: Double contrast arthrotomography of the temporomandibular joint: Introduction of an arthrographic technique for visualization of the disc in articular surfaces. J Oral Maxillcfat Surg 41:163, 1983 2. Westesson P-L, Bronstein SL, Liedberg JL: Internal derangement of the temporomandibular joint: Morphologic description with correlation to joint function. Oral Surg Oral Med Oral Path01 1.

59:323,

1985

Katzberg RW, Westesson P-L, Tallents RH, et al: Temporomandibular joints: MR assessment of rotational and sideways disk displacements. Radiology 169:741, 1988 Paesani D, Westesson P-L, Hatala MP, et al: Prevalence of internal derangement in patients with craniomandibular disorders. Am J Orthod Dentofac Orthop 101:41, 1992 Tasaki MM, Westesson P-L, Isberg AM, et al: Classification of temporomandibular joints disc displacement and prevalence in patients and asymptomatic volunteers. Am J Orthod Dentofac Orthop 109:249,1996 Katzberg RW, Westesson P-L, Tallents RH, et al: Anatomic disorders of the temporomandibular joint disc in asymptomatic subjects. J Oral Maxillofac Surg 54:147, 1996 Behan RJ: Loose cartilage in the temporomaxillary joint. Ann Surg 67:536, 1918 Steinhardt G: Zir Pathologie und Therapie des Gelenkknackens bei Kieferschliessbewegungen. Dtsch Zahnlrzte Wochenschr 37:1013, 1934

3.

4.

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7. 8.

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of the temporomandibular 9. Gallagher DM: Posterior dislocation joint meniscus: Report of three cases. J Am Dent Assoc 113:411, 1986 10. Engelke W: Posterior dislocation of the articular disc: A rare case? Deut Zeitschrift Fiir Mund- Kiefer- und Gesichts-Chirurgie 14:86, 1990 11. Pressman BD, Shellock FG, Schames J, et al: MR imaging of temporomandibular joint abnormalities associated with cervical hyperextension/hyperflexion (whiplash) injuries. JMRI 2:569, 1992 12. Larheim TA, Smith H-J, Aspestrand F: Temporomandibular joint abnormalities associated with rheumatic disease: Comparison between MR imaging and arthrotomography. Radiology 183: 221, 1992 13. Katzberg RW, Westesson PL: Diagnosis of the Temporomandibu-

IarJoint. Philadelphia, PA, Saunders, 1993 14. Isberg A, StenstrGm B, Isacsson G: Frequency of bilateral temporomandibular joint disc displacement in patients with unilateral symptoms: A five year followup of the asymptomatic joint. A clinical and arthrotomographic study. Dentomaxlllofac Radio1 20:73, 1991 of the temporo15. Blankestijn J, Boering G: Posterior dislocation mandibular disc. Int J Oral Surg 14:437, 1985 16. Ross JB: Diagnostic criteria and nomenclature for TMJ arthrography in sagittal section: Part I. Derangements. J Craniomandib Disord 1:185, 1987

Surg

1998

Discussion Posterior Disc Displacement Temporomandibular Joint

in the

Leslie B. Heffeez,DMD, MS Professor and Head, of Illinois at Chicago Mercy Hospital and

Oral and Maxillofacial Surgery, University and Director, Mercy Dental Center, Medical Center, Chicago, lllinols

This report neither confirms nor rejects the hypothesis that the entity of posterior disc displacement exists. Embryologically, the articular disc is derived from the lateral pterygoid muscle entrapped within the joint blastema. Differentiation and maturation of this tissue under function and developmental growth of the condyle and temporal bone result in the classic normal disc anatomy described posteroanteriorly as retrodiscal tissue, posterior band, intermediate zone, anterior band, and anterior attachment. Magnetic resonance imaging of normal disc tissues portrays typical signal intensities and morphology, ie, a low signal in an approximate bow-tie configuration.’ However, pathological tissues do not portray the same signal characteristics, because displaced discs show changes in proteoglycan distribution and hence absorb water differentially. As a result, a displaced disc may appear to be fragmented if one exclusively interprets the low signal intensity as the disc proper. In fact, the disc frequently will have an intermediate signal intensity in the displaced condition.2

Are the authors reporting a posteriorly displaced disc or embryologically did the articular tissues simply develop prominent fibrotic bands within the inferior portion of the retrodiscal tissue? I favor the latter hypothesis, because it is more in keeping with the histological and pathological findings, as well as the embryological development of the joint. A dense inferior lamina in the retrodiscal tissue would cause a low signal intensity, which could be interpreted as the disc. The authors interpret the low signal intensities superior and anterior to the condyle as anterior attachment. These signals could just as easily be interpreted as disc. Figures 2 and 3A do not reject the classic histological findings of fibrotic tissue on the inferior aspect of the retrodiscal tissue. Figure 3B is a midcondyle section showing anteromedial rotation of the disc. The low signal intensity on the posterior aspect of the condyle, interpreted as the disc in Figure 3A, would not have appeared within this section. The phenomenon of rotational disc displacement could explain a normal disc position on a central section and displaced disc position on a medial section. It would have been helpful to view corresponding T2weighted images to further delineate disc anatomy and rule out signal void phenomena. Noncorrected transcranial arthrography lacks the specificity to definitively diagnose posterior disc displacement. Single space arthrography is even less diagnostic. In this study, 600 cases were evaluated with arthrography. The presentation of the data is confus-