The diagnostic value of ultrasonography to determine the temporomandibular joint disk position

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1 Vol. 84 No. 6 December 1997 ORAL AND MAXILLOFACIAL RADIOLOGY Editor: Sharon L. Brooks The diagnostic value of ultrasonography to determine the temporomandibular joint disk position Rtidiger Emshoff, MD, DMD, a Stefan Bertram, MD, DMD, b Ansgar Rudisch, MD, c and Robert Gagner, MD, DMD, a Innsbruck, Austria UNIVERSITY OF 1NNSBRUCK Objective. Temporomandibular joint (TMJ) arthrography and magnetic resonance imaging are the imaging techniques of choice in patients presenting with signs and symptoms of TMJ disorders suggesting soft tissue pathosis. With the disadvantage of arthrography as an invasive procedure and magnetic resonance imaging posing a problem in clinical availability and cost, the purpose of this study was to determine whether ultrasonography could be used to assess the presence or absence of disk displacement in patients with TMJ disorders. Study design. In 17 patients, 100 TMJ positions were investigated by static and dynamic ultrasonography to analyze the diskcondyle relationship. To compare the respective findings with those of a diagnostic method offering high accuracy, coronal and sagittal magnetic resonance imaging was carried out immediately afterwards. Results. With static ultrasonography showing a sensitivity of 0.41 and a specificity of 0.70 and dynamic ultrasonography a sensitivity of 0.31 and a specificity of 0.95, the data revealed that static and dynamic ultrasonography are marginal in detecting the presence of disk displacement, but dynamic ultrasonography is sensitive in detecting the absence of disk displacement. However, with a positive predictive value of 0.61 and a negative predictive value of 0.51 for static ultrasonography, and a positive predictive value of 0.88 and a negative predictive value of 0.55 for the dynamic technique, the results indicate that both modalities are insufficient in establishing a correct diagnosis for the presence or absence of disk displacement. Conclusion. In view of the fact that dynamic ultrasonography proved to be a reliable diagnostic aid for the detection of normal disk position, the results of this study should be of further interest and encourage research in its potential uses and diagnostic capabilities. (Oral Surg Oral Meal Oral Pathol Oral Radiol Endod 1997;84:688-96) Patients with temporomandibular joint (TMJ) disorders (TMD) may present with a cluster of joint and muscle disorders characterized primarily by pain, joint sounds, and irregular or deviating jaw function. 1,2 With the rapid progress in TMJ imaging techniques, disk displacement has increasingly been thought to be involved in the development of pain and dysfunction. 3-5 However, the question of whether disk displacement is the result, cause, or accompanying factor remains a point of controversy. 6,7 Arthrography and magnetic resonance imaging (MRI) are common diagnostic methods for the evaluation of disk displacement. Arthrography as a dynamic aresident, Department of Oral and Maxillo-Facial Surgery. bconsultant, Department of Oral and Maxillo-Facial Surgery. CResident, Department of Magnetic Resonance Imaging. Received for publication Mar. 24, 1997; returned for revision May 28, 1997; accepted for publication July 15, Copyright 1997 by Mosby-Year Book, Inc /97/$ /16/84979 investigation technique for the disk-condyle relationship has been shown to provide a diagnostic accuracy of 83% when used with video fluoroscopy, 8 while MRI has a diagnostic accuracy of 95% when coronal and sagittal imaging techniques are combined. 9 However, arthrography is invasive and may be complicated by pain, disk perforation, and allergic reactions1 ; MRI poses a problem in terms of clinical availability and cost. Recent studies have suggested ultrasonography as a noninvasive and dynamic imaging technique to provide insight into the dynamics of the TMJ. Gateno and coworkers ll noted a sensitivity and specificity of 95% for identifying the position of the condyle. They investigated 20 patients during mandibular ramus osteotomy procedures and succeeded in visualizing varying degrees of condylar movement in relation to the glenoid fossa. Stefanoff and associates 12 evaluated the incidence of internal derangements in asymptomatic volun- 688

2 ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 84, Number 6 Emshoff et al. 689 Fig. 1. Ultrasonographic investigation of the TMJ region with the transducer positioned against the patient's face in a horizontal direction overlying the zygomatic arch and TMJ. teers. They determined the position of the TMJ disk in 23 subjects and described an incidence of 2.1% for disk derangement. In view of the fact that previous studies failed to compare the respective results with those of a diagnostic method offering a high degree of accuracy, the purpose of this study was to assess the value of ultrasonography as a diagnostic aid in patients with TMDs. MATERIAL AND METHODS This study included 17 patients presenting with signs and symptoms of TMD. There were 14 females and 3 males, between the ages of 16 and 60 years, with a mean age of 33.8 years. Subjects were informed about the 'study procedure, and informed consent was received. Clinical TMD diagnosis was made according to the research diagnostic criteria published by Dworkin and LeResche 13 in To determine the diagnostic value of static and dynamic ultrasonography in detecting the presence or absence of disk displacement at various mouth opening positions, subjects underwent clinical, ultrasonographic, and MRI investigation. Each subject received an individual nonferromagnetic intermaxillary device to obtain the different mouth opening positions, and evel2~ time the patient underwent clinical investigation, ultrasonic and MRI was performed immediately afterwards. As this was a single-blind study, the clinician for the clinical investigation, the operator for the ultrasonography, and the radiologist with the MRIs independently established the presence or absence of the respective diagnosis of disk displacement. The clinical records and images were interpreted by the respective investigators without knowledge of the results of the other investigations. The ultrasonogra- Fig. 2. Longitudinal to transverse scan of the TMJ region showing absence of disk displacement at closed-mouth position. The glenoid fossa (curved arrow), the disk (arrow), and the condyle (small arrow) are visualized. Fig. 3. Longitudinal to transverse scan of the TMJ region showing absence of disk displacement at maximum-mouth opening position. The glenoid fossa (curved arrow), the disk (arrow), and the condyle (small arrow) are visualized. phy operator and the radiologist were not allowed to ask the subject any questions or evaluate clinical data. Ultrasonographic investigation using longitudinal to transverse scans was performed with a linear (B-scan) 7.5 Mhz small-part transducer. The transducer was connected to a Picker (Picker International GmbH, Vienna, Austria) echocamera (CS 9300), with the diagnosis made directly from the screen. The sonograms were performed by a single oral and maxillofacial surgeon experienced in ultrasonography of the head and neck. All trials were conducted in a darkened room with the patient sitting in an upright position. The transducer

3 690 Emshoffet al. ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY December 1997 Table I. Summary of results regarding evaluation of TMD diagnosis, VAS pain level, MRI diagnosis of disk position, ROM, and type of internal derangement TMD diagnosis, TMD diagnosis, VAS MRI diagnosis of DP ROM Patient no. patient-related TMJ side TMJ-related pain levef MOP MOP D diagnosis 1 IDT1. C/S R - 0 AMDD - MDD - NDD AMDDR L IDT 1". C/S * 75 AMDD - MDD - NDD AMDDR* 2 IDT1. C/S R IDTI*. C/S* 66 ADD - MDD - PMDD ADDNR* L IDT 1 0 ADD - PDD - PDD ADDNR 3 IDT1 R IDT1 0 MDD - NDD - NDD MDDR L IDTI* 42 AMDD - NDD - DDD AMDDR* 4 IDT1 R IDTI* 15 MDD - NDD - NDD MDDR* L 1DT1 0 NDD - NDD - NDD NDD 5 IDT2 R - 0 AMDD -AMDD - AMDD AMDDNR L IDT2* 90 AMDD - AMDD ~ AMDD AMDDNR* 6 IDT1 R IDT1 0 AMDD - MDD - MDD AMDDNR L 1DTI* 31 MDD - NDD - NDD MDDR* 7 IDT1. C/S R IDT1 0 ADD - NDD - NDD ADDR L IDTI*. C/S* 81 ADD - NDD - NDD ADDR* 8 IDT3-A. C/S R - 0 ADD - ADD 0-20 ADDNR** L IDT3-A*. C/S* 28 ADD - ADD ADDNR*.** 9 IDT1 R - - NDD - NDD - NDD NID L IDTI* 23 NDD - NDD - NDD NID* 10 IDT1. IDT2. C/S. R IDTI*. IDT2*. C/S* 10 ADD - ADD - ADD ADDNR* L - 0 ADD - ADD - ADD ADDNR 11 IDT1. S/S-TR R IDT1 0 NDD - NDD - NDD NID L IDTI*. S/S-TR* 90 AMDD - NDD - NDD AMDDR* 12 1DT1 R IDTI* 45 AMDD - AMDD - NDD AMDDR* L - 0 AMDD - MDD - MDD AMDDNR 13 C/S R - 0 NDD - NDD - NDD N1D L C/S* 60 ADD - ADD - ADD ADDNR* 14 MT1. IDT1. C/S R IDTI*. C/S* 79 AMDD - NDD - NDD AMDDR* L IDT1 0 AMDD - NDD - NDD AMDDR 15 IDT3-B R - 0 AMDD - AMDD - AMDD AMDDNR** L IDT3-B* 53 ADD - ADD - ADD ADDNR*** 16 IDT1. C/S R IDTI*. C/S* 63 AMDD - NDD - NDD AMDDR* L IDT1 - ADD - NDD - NDD ADDR 17 MT2. MPD R - - NDD - NDD - NDD NID** L - - NDD - NDD - NDD NID** VAS, Visual analog scale (100-millimeter scale); DP, disc position; MOP O, closed-mouth position; MOP 1, half-mouth opening position; MOP 2, maximum-mouth opening position; ROM, passive range of mandibular motion (interincisal distance in millimeters); MT1, myalgia type I; MT2, myaigia type II; MPD, myaigia pain dysfunction; IDT1, internal derangement type I; IDT2, internal derangement type II; IDT3-A, acute internal derangement type Ill; IDT3-B, chronic internal derangement type m (duration > 6 months); C/S, eapsulitis/synovitis; S/S-TR, sprain/strain-tranma related; R, right; L, left; NDD, absence of disk displacement; ADD, anterior disk displacement; AMDD; anteromedial disk displacement; MDD, medial disk displacement; PDD, posterior disk displacement; PMDD, posteromedial disk displacement; N1D, absence of internal derangement; ADDR, anterior disk displacement with reduction; ADDNR, anterior disk displacement without reduction; AMDDR, anteromediai disk displacement with reduction; AMDDNR, anteromedial disk displacement without reduction; MDDR, medial disk displacement with reduction; MDDNR, medial disk displacement without reduction. ttmj pain during function. *TMJ-related TMD diagnosis and ID diagnosis associated with TMJ pain during function. **Diagnosis of ID in patients with reduction in ROM. was positioned against the patient's face in a horizontal direction overlying the zygomatic arch and the TMJ. With the short lateral pole of the transducer placed adjacent to the tragus, the transducer was tilted until optimal visualization was obtained (Fig. 1). Sequential bilateral images were made at closedmouth, half-mouth, and maximum-mouth opening positions; and the respective ultrasonographic findings were classified with regard to the diagnosis of normal disk position and disk displacement. Figures 2 and 3 show typical ultrasonographs. At the various mouth opening positions, a diagnosis of normal disk position was considered when the boundary between the disk and bilaminar zone was located at or distal to the posterosuperior aspect of the mandibular condyle. Following static ultrasonographic evaluation at various mouth opening positions, dynamic imaging for the full range of mandibular opening was used to evaluate the presence or absence of disk displacement at the respective mouth-opening positions.

4 ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 84, Number 6 Emshoff et al. 691 Table II. Comparison of results regarding evaluation of TMJ-related TMD diagnosis and MRI diagnosis of disk position IDTI * IDT1 IDT2 * IDT1 * IDT3-A * MOP t DP NIDT IDT1 S-DP 1DTI* C/S* C/S* S/S-TR* IDT2* C/S* IDT3-B* C/S* S-DP* 0 ADD AMDD MDD PDD PMDD S-DD NDD ADD AMDD MDD PDD PMDD S-DD NDD ADD AMDD MDD PDD PMDD S-DD NDD S-DD S-NDD MOP O, Closed-mouth position; MOP 1, half-rrtouth opening position; MOP 2, maximum-mouth openmg position; S-DP, sum of MRI diagnoses of disk position; DP, MRI diagnosis of disk position S-DD, sum of diagnoses with disk displacement; S-NDD, sum of diagnoses without disk displacement. tmop 0, 1, and 2 in patients with TMJ-related TMD dignosis (n = 16); MOP 2 in patients without reduction in ROM (n = 14). *TMJ-related TMD diagnosis associated with TMJ pain during function. MRI was carried out with a 1.5T MR-scanner (Vision, Siemens AG, Erlangen, Germany) and a dedicated circular-polarized transmit-and-receive TMJ coil. Data were collected on a 252 x 256 matrix with a field of view of 145 mm, giving a pixel size of 0.60 x 0.57 ram. With the patient in a supine position, 15 coronal slices and 8 parasagittal slices were obtained of each TMJ using a TSE-PD sequence (TR 2800 ms, TE 15 ms) with thin slices of 3 ram. Imaging was performed at the same location and with the same mouth opening positions as for the preceding ultrasonic investigation. Those images were selected for analysis that depicted the disk, condyle, articular eminence, and glenoid fossa. Normal disk position was defined by location of the posterior band of the disk at the superior or 12 o'clock position relative to the condyle, whereas anterior, anteromedial, anterolateral, medial, lateral, posterior, and posteromedial and posterolateral disk displacements were defined by the location of the posterior band relative to the superior part of the condyle. 14 RESULTS Table I presents the results of clinical evaluation and MRI diagnosis of disk position and type of internal derangement (ID). Assigning the respective diagnoses for which the patient met criteria resulted in 15 patients being classified as ID and one patient each as myalgia type II and capsulitis/synovitis. Application of diagnostic criteria to the TMJ-related clinical data showed most joints to be associated with a diagnosis of ID type I, whereas the most common type of multiple diagnosis was ID type I in combination with capsulitis/synovitis. Comparing the distribution of TMJ-related TMD diagnoses and the presence of TMJ-related pain with the respective MRI diagnosis of disk position (Table II), no significant difference was found in the prevalence numbers of disk displacement between the pain and the contralateral non-pain side at the closed-mouth (93.75% vs 75%), half-mouth (50% vs 50%), and maximum-mouth opening position (25% vs 35.71%). An analysis of the distribution of the respective MRI diagnoses of type of ID (Table III) revealed the pain-related TMJ side to be more often associated with the presence of ID with reduction than the non-pain side (64.29% vs 35.72%), whereas diagnosis of ID without reduction was more frequently observed on the non-pain side (42.86% vs 28.57%). Sixteen subjects showed a mouth opening of at least

5 692 Emshoffet al. ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY December 1997 "fable III. Comparison of results regarding evaluation of TMJ-related TMD diagnosis and MRI diagnosis of type of internal derangement IDTI * IDT1 IDT2* IDT1 * IDT3-A * 1D~ NIDT IDT1 S-ID IDTI* C/S* C/S* S/S-TR* IDT2* C/S* IDT3-B* C/S* S-ID* ADDNR AMDDNR MDDNR ADDR AMDDR MDDR NID S-IDNR S-IDR NIDT, Absence of TMJ-related TMD; IDTI, internal derangement type I; IDT2, internal derangement type II; IDT3-A, acute internal derangement type 111; IDT3-B, chronic internal derangement type III; S/S-TR, sprain/strain-trauma related; C/S, capsulitis/synovitis; S-ID, sum of MRI diagnoses of type of internal derangement; ADDNR, anterior disk displacement without reduction; AMDDNR, anteromedial disk displacement without reduction; MDDNR, medial disk displacement without reduction; ADDR, anterior disk displacement with reduction; AMDDR, anteromediai disk displacement with reduction; MDDR, medial disk displacement with reduction; NID, absence of ID; S-IDNR, sum of diagnoses of type of internal derangement without reduction; S-IDR, sum of diagnoses of internal derangements with reduction. rid in patients without reduction in mandibular range of motion (n = 14). *TMJ-related TMD diagnosis associated with TMJ pain during function. Table IV. Evaluation of static ultrasonography compared with MRI findings Ultrasonographic diagnosis MOP MOP 0 MOP 1 MOP 2 (n = 92) (n = 33) (n = 32) (n = 27) MRI Diagnosis NDD DD NDD DD NDD DD NDD DD NDD ADD AMDD MDD PDD PMDD MOP O, Closed-mouth position; MOP 1, half-mouth opening position; MOP 2, maximum-mouth opening position; NDD, absence of disk displacement; ADD, anterior disk displacement; AMDD; anteromedial disk displacement; MDD, medial disk displcement; PDD, posterior disk displacement; PMDD, posteromedial disk displacement. 35 mm interincisal distance, thereby offering three mouth opening and six TMJ positions each, whereas in one patient presenting with a mouth opening of 20 mm, only four TMJ positions were available. Diagnostic evaluation of the presence or absence of disk displacement was obtainable in 92 (92%) of 100 TMJ positions using static and dynamic ultrasound imaging techniques. There was no failure of imaging and diagnostic interpretation in the MRI series. Regarding the diagnostic data from MRI, and static and dynamic ultrasonography (Tables IV and V), results demonstrate that 43 of the 92 mouth opening positions (46.7%) had a normal disk-condyle relationship, whereas 49 (53.3%) showed an abnormal relationship. A total of 40.8% of the TMJ positions characterized by disk displacement presented with anterior disk displacement, whereas 32.7% had anteromedial and 20.4% medial disk displacement. One patient was diagnosed as having anterior disk displacement in both joints at closed-mouth position, medial disk displacement in the right and posterior disk displacement in the left joint at half-mouth opening position, and posteromedial disk displacement in the right and posterior disk displacement in the left joint at maximum-mouth opening position. At closed-mouth position 78.8% of the 33 TMJ positions showed disk displacement, whereas at halfmouth and maximum-mouth opening positions, an incidence of 46.9% and 29.6% was found (Fig. 4). Diagnosis of anterior disk displacement was made at closed-mouth position in 42.3%, at half-mouth opening in 40%, and at maximum-mouth opening position in 37.5% of the TMJ positions associated with disk displacement (Fig. 5). A comparison of positive and negative test results 15,16

6 ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 84, Number 6 Emshoff et al. 693 MOP 0 MOP 1 MOP % 53.1% 70.4 % 9.1% 15.6 % 33.3 % 9.4 % 3.1% 3.7 % 3.7 % 3.7% INtPMDD INIPDD E]MDD INIAMDD ~ADD EZ]NDD Fig. 4. Distribution of disk positions diagnosed by MRI at closed-mouth (MOP 0), half-mouth opening (MOP 1), and maximum-mouth opening position (MOP 2). Frequencies described as percentage of disk positions related to the total number of TMJ positions investigated. NDD, Absence of disk displacement; ADD, anterior disk displacement; AMDD, anteromedial disk displacement; MDD, medial disk displacement; PDD, posterior disk displacement; PMDD, posteromedial disk displacement. Table V. Evaluation of dynamic ultrasonography compared with MRI findings Ultrasonographic diagnosis MOP MOP 0 MOP 1 MOP 2 (n = 92) (n = 33) (n = 32) (n = 27) MRI Diagnosis NDD DD NDD DD NDD DD NDD DD NDD ADD AMDD MDD PDD PMDD MOP O, Closed-mouth position; MOP 1, half-mouth opening position; MOP 2, maximum-mouth opening position; NDD, absence of disk displacement; ADD, anterior disk displacement; AMDD; anteromedial disk displacement; MDD, medial disk displacement; PDD, posterior disk displacement; PMDD, posteromedial disk displacement. (Tables VI and VII) revealed that static ultrasonography more accurately identified the presence of disk displacement at closed- and half-mouth opening positions, whereas dynamic ultrasonography more accurately identified the absence of disk displacement at all mouth opening positions. However, both modalities clearly underestimated the actual incidence of disk displacement, although with the dynamic technique there was a significant decrease in the false-positive test results at all mouth opening positions, thereby resulting in higher diagnostic accuracies at the half (62.5% vs 53.2%) and maximum-mouth opening positions (70.4% vs 55.6%). Evaluation of sensitivity and specificity revealed that static ultrasonography identified a higher proportion of disk displacements at the closed (0.50 vs 0.39) and halfmouth opening positions (0.40 vs 0.27), whereas a higher proportion of absence of disk displacements were identified with the dynamic technique at the closed- (1.00 vs 0.71), half- (0.94 vs 0.65), and maximum-mouth opening positions (0.95 vs 0.74). Using dynamic ultrasonography, the proportion of correct positive diagnoses was significantly higher at the closed- (1.00 vs 0.87), half- (0.80 vs 0.50), and maximum-mouth opening positions (0.50 vs 0.17), whereas there was only a slight increase in the respective proportion of correct negative diagnoses.

7 694 Emshoffetal. ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY December 1997 MOP 0 MOP 1 MOP % 40.0 % 37.5 % 11.5 % 12.5 % 33.3 % 25.0 % 6.7 % 12.5 % tnipmdd ~IPDD E;;]MDD INIAMDD ~ADD Fig. 5. Distribution of types of disk displacements diagnosed by MRI at closed-mouth (MOP 0), half-mouth opening (MOP I) and maximum-mouth opening position (MOP 2). Frequencies described as percentage of disk displacements related to the total number of disk displacements. ADD, anterior disk displacement; AMDD, anteromedial disk displacement; MDD, medial disk displacement; PDD, posterior disk displacement; PMDD, posteromedial disk displacement. lable VI. Summary of positive and negative test results: sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of static ultrasonography Ultrasonographic diagnosis MOP MR[ Diagnosis Positive Negative SE SP PPV NPV DA 0 DD present % DD absent DD present % DD absent DD present % DD absent 5 14 MOP O, Closed-mouth position; MOP 1, half-mouth opening position; MOP 2, maximum-mouth opening position; DD, disk displacement; SE, sensitivity; SP, specificity; PPV, positive predictive value; NPV, negative predictive value; DA, diagnostic accuracy. DISCUSSION This study showed no significant difference in the prevalence of disk displacement at the various mouth opening positions between the pain and the contralateral non-pain side. This finding is consistent with the results of previous studies, which suggest that disk displacement in one TMJ may be related to disk displacement on the contralateral side. 14,17 However, further investigations with a significantly large sample size of TMD and non-tmd subjects are warranted to evaluate whether a side-specific prevalence of disk displacement may be related to type of disk displacement and/or TMJ-related diagnosis of TMD. In addition, the suggestion of a side-specific prevalence of ID with and without reduction emphasizes the need for data corn- paring clinical signs and symptoms with imaging findings of MRI. Satisfactory interpretation of the ultrasonographic images was not achieved in 8% of the investigated TMJ positions. In view of the broad range of variations in fossa and condyle morphology 18 plus the fact that ultrasound is reflected at soft tissue-bone interfaces, results indicate that undisturbed imaging of the disk-condyle relationship may be difficult in many instances. Results of MRI in the present study showed closedmouth position to be associated with a high rate of disk displacements (78.8%). With regard to the distribution of the various types of disk displacement within the group of disk displacements at closed-mouth position, the percentage was 42.3% for anterior disk displace-

8 ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 84, Number 6 Emshoff et al. 695 Table VII. Summary of positive and negative test results: sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of dynamic ultrasonography Ultrasonographic diagnosis MOP MRI Diagnosis Positive Negative SE SP PPV NPV DA 0 DD present % DD absent DD present % DD absent DD present % DD absent 1 18 MOP O, Closed-mouth position; MOP 1, half-mouth opening position; MOP 2, maximum-mouth opening position; DD, disk dispiacement; SE, sensitivity; SP, specificity; PPV, positive predictive value; NPV, negative predictive value; DA, diagnostic accuracy. Table VIII. Positive and negative predictive values of dynamic ultrasonography and random selection with regard to the prevalence numbers evaluated by MRI studies MR1 Diagnosis US Diagnosis * Random Selection ** DD Prevalence 16 DD Prevalence 17 PPV NPV PPV NPV Classification MOP O MOP2 MOP O MOP2 MOP O MOP2 MOP O MOP2 MOP O MOP2 MOP O MOP2 Asymptomatic Symptomatic t Asymptomatic Symptomatic (No data) DD, Disk displacement; MOP O, closed-mouth position; MOP 1, half-mouth opening position; MOP 2, maximum-mouth opening position; PPV, positive predictive value; NPV, negative predictive value; US, ultrasonography; nva, no value available. *MOP 0 sensitivity, 0.39; MOP 0 specificity, MOP 2 sensitivity, 0.13; MOP 2 specificity, **Random selection given by tossing a coin: sensitivity, 0.50, specificity, ments, whereas anteromedial and medial disk displacements accounted for 46.2% and 11.5%, respectively. This finding contrasts with reports of other authors who described anterior and anterolateral disk displacement as the most frequently encountered. 14,17 With regard to the frequencies between rotational and sideways locations, declining medially or laterally, the results of the current investigation (47.7% anteromedial and medial disk displacements vs no instances of anterolateral or lateral disk displacements) are consistent with those of some authors who showed a higher frequency of the medial component to the disk displacement, 19,2 but is inconsistent with those who reported either the lateral component to the disk displacement to be more prevalent 17 or the frequencies of the medial and lateral components to be relatively equal. 14 A moderate correlation was found between the results of static ultrasonographic investigation and the respective MRI diagnosis of disk position, whereas the use of dynamic ultrasonography significantly reduced the percentage of false-positive results from 14.1% to 2.2% as evidenced by an increase in diagnostic specificity from 0.70 to The advantage of dynamic ultrasonography in investigating the disk-condyle relationship under repeated motion at the respective mouth opening positions probably made the structures involved (i.e., condyle, disk, and retrodiskal tissues) more clearly distinguishable, thereby correcting the high percentage of false-positive diagnoses with an assumed anteromedial, anterolateral, medial, or lateral disk displacement. The significance of ultrasonography as a noninvasive diagnostic technique may lie in its potential as an aid for detection and documentation of TMJ internal derangements at significantly lower costs than MRI. The high specificity values at the closed-mouth (1.00), halfmouth (0.94), and maximum-mouth opening positions (0.95) indicate that ultrasonography proved reliable both to detect a normal disk position at the various mouth opening positions and to make a correct diagnosis of disk displacement at the closed-mouth position. To determine whether in specific populations dynamic ultrasonography may be reliable in establishing the presence of disk displacement, the diagnostic values of positive and negative test results have to be calculated using the determined values of sensitivity and specificity and the respective current valid prevalence rates of disk displacement found at the various mouth opening positions. 15,16 Table VIII shows some estimations made

9 696 Emshoffet al. ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY December 1997 from recently published data, thereby comparing the respective values with those of a random diagnostic process. With a prevalence of 3% for disk displacement, 14 dynamic ultrasonography may not be used as a screening procedure in asymptomatic individuals, as 93 % of the positive test results (vs 97% by chance) have to be regarded as false positive. Further studies may provide valid prevalence rates in reliable classified TMD subgroups, thereby establishing quantified risk groups for disk displacement, in which the use of ultrasonography may gain appropriately tested diagnostic significance. However, given the low sensitivity values found in this study, more reliable diagnosis and imaging are necessary if ultrasonography is to become generally accepted as a diagnostic tool in the management of TMJ patients, especially when surgery is under consideration. In several articles in the literature, the classification, diagnosis, and treatment of TMJ pain and dysfunction are based on an appropriate diagnosis of the position and shape of the TMJ disk However, controversy remains regarding the clinical significance of disk displacement, and further studies are proposed to reconsider the relationship of disk position to pain, mandibular dysfunction, and osteoarthritis. 6,7 With additional interest and research in the potential uses and diagnostic capabilities of dynamic ultrasonography, i t may gain importance as a diagnostic aid in patients with TMJ disorders. CONCLUSION Dynamic ultrasonography is an inexpensive and noninvasive diagnostic technique with relatively high specificity that could be used to supplement clinical evaluation in patients with TMJ disorders. It may help in the identification of normal disk position in subjects presenting with signs and symptoms of TMJ internal derangements. REFERENCES 1. American Dental Association. 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