Association between temporomandibular joint disc position evaluated by magnetic resonance imaging and mandibular condyle inclination evaluated by computed tomography

Temporomandibular joint disc displacement is common in the world's population and could be associated with bone and functional characteristics of the temporomandibular joint. The aim of these study was to analyse the association between temporomandibular joint disc position evaluated by magnetic resonance imaging (MRI) and the inclination of the mandibular condyle evaluated by computed tomography (CT). One hundred and seventy temporomandibular joints (TMJ) were retrospectively analysed. The temporomandibular disc position was evaluated by MRI and classified into three types: normal (N), disc displacement with reduction (DDWR) and disc displacement without reduction (DDWoR). The mandibular condyle measurements evaluated by CT included horizontal, sagittal and coronal inclination. ANOVA followed by post hoc Tukey's test was used to evaluate the interaction between condylar inclination and disc position. There was an association between disc position and the horizontal and sagittal condylar inclination (P < .05). There are statistically significant differences in the mean of horizontal and sagittal inclination of the mandibular condyle between the DDWoR and the other disc positions (P = .002 and P = .004). Disc position was not statistical associated with coronal inclination of condyle (P > .05). These results indicate that the inclination of the mandibular condyle may be different in TMJ with various disc position. A more medial horizontal inclination and a more posterior sagittal inclination of the mandibular condyle are associated with DDWoR.     

MRI evaluation of the classification,frequency, and disc morphology of temporomandibular joint disc displacements: a multicenter retrospective study in a Turkish population

Objectives  Magnetic resonance imaging (MRI) of the temporomandibular joint (TMJ) and temporomandibular disorders (TMDs) have been discussed in detail for various populations. As no such study has examined the Turkish population, we determined the frequency of TMDs in the Turkish population through a multicentric investigation using MRI. Methods  This retrospective study examined 504 TMJs of 252 symptomatic patients who had undergone bilateral MRI investigation in four different dental schools. The image analysis included the assessment of disc position and morphology, and recaptured the coronal and sagittal planes in the closed and open mouth positions. The TMJ disorders were classified using the Clinical Diagnostic Criteria for Temporomandibular Disorders (CDC/TMD). The correlations among the groups of TMJs and disc morphologies were analyzed statistically using the chi-square test (P ≤ 0.05). Results  Disc displacement and abnormal disc morphology were detected in 69.5% of the symptomatic TMJ patients. Of the joints examined using MRI, 154 were normal, 135 had anterior disc displacement with reduction (ADDwR), 145 had anterior disc displacement without reduction (ADDwoR), 30 had partial anterior disc displacement, and 18 had sideways disc displacements. Regarding disc morphology, enlargement in the posterior band was the most commonly encountered type and was observed in 152 TMJs. Overall, the average time for referral for treatment, which was defined as the time from symptom onset until the time of referral, was 1.5 years. Conclusions  The most common type of disc displacement found in the Turkish population studied was ADDwoR. In addition, patients did not perceive the symptoms of TMDs as a disease and did not seek help until the TMJ derangement caused a major complaint.     

Magnetic resonance imaging findings of internal derangement in temporomandibular joints without a clinical diagnosis of temporomandibular disorder

The purpose of this study was to assess the prevalences of magnetic resonance (MR) imaging findings of internal derangement (ID) in temporomandibular joints (TMJs) without a specific clinical diagnosis of temporomandibular disorder (TMD), and to investigate whether in this TMJ group the variable of pain may be linked to MR imaging findings of ID. The study comprised 109 patients, who were assigned a clinical uni- or bilateral TMJ-related diagnosis of 'absence of TMD'. Bilateral sagittal and coronal MR images were obtained subsequently to establish the prevalence of TMJ ID. An MR imaging diagnosis of ID was found in 99 (55.9%) of the 177 TMJs investigated. About 30.3% of the closed mouth-related TMJ positions characterized by disc displacement presented with anterior disc displacement, while 27.3% had anterolateral and 25.3% anteromedial disc displacement. Analysis of the data revealed the presence of TMJ pain to be associated with significantly more MR imaging diagnoses of disc displacement without reduction than disc displacement with reduction (P < 0.05), while there was no significant difference in the prevalences of ID and those of absence of ID (P > 0.05). Using chi-square analysis, no significant relationship was found between the presence of TMJ pain and the MR imaging diagnosis of TMJ ID (P=0.93). Use of the kappa statistical test indicated poor diagnostic agreement between the presence of TMJ pain and the MR imaging diagnosis of ID (kappa=0.01). The results suggest TMJs with a clinical diagnosis of 'absence of TMD' to be associated with a high rate of IDs, while in these instances the clinical variable of TMJ pain may have no effect on prevalences of MR imaging diagnoses TMJ ID. The data confirm the aspect of clinical diagnostic criteria as an unreliable instrument in predicting MR imaging diagnoses of TMJ ID.     

The effects of changing position and angle of the proximal segment after intraoral vertical ramus osteotomy

The authors evaluated changes in position and angle of the proximal segment, including the condyle, after intraoral vertical ramus osteotomy (IVRO) with and without a Le Fort I osteotomy to verify whether displacement of the proximal segment could induce postoperative complications. Changes in condylar angle, ramus angle, and displacement of proximal segment were measured pre- and postoperatively. The position of the temporomandibular joint (TMJ) disc was examined pre- and postoperatively. Trigeminal nerve hypoesthesia in the lower lip was assessed bilaterally. The postoperative horizontal condylar angle was significantly smaller than the preoperative one on the deviated and non-deviated sides (P<0.0001). The postoperative coronal condylar angle was significantly larger than the preoperative one on the deviated side (P=0.0483). The postoperative sagittal ramus angle was larger than the preoperative one on the deviated (P<0.0001) and non-deviated (P=0.00005) side. Most joints with an anteriorly-displaced disc with and without reduction improved on the non-deviated side; 5 of 16 joints improved on the deviated side. Results suggest the position and angle of the proximal segment, including the condyle, could change after IVRO. This could be associated with symptomatic improvement in TMJ, and extreme medial displacement of the proximal segment could delay recovery from lower lip hypoesthesia.     

ADAMTS‐4 and ADAMTS‐5 expression in human temporomandibular joint discs with internal derangement,correlates with degeneration

Temporomandibular joint (TMJ) internal derangement (ID) is one of the most common form of temporomandibular disorders. There is evidence showing the increased expression of matrix metalloproteinases (MMPs) in the cells from degenerated TMJ disc. ADAMTS are a large family of metalloproteases which are responsible for proteoglycans degradation. The present study aimed to evaluate ADAMTS‐4 and ADAMTS‐5 immunohistochemical expression in human TMJ discs from patients affected by ID, and to find out if there is any correlation with the degree of histopathological changes. Eighteen temporomandibular displaced disc specimens and sixteen TMJ disc control were used for the present study. Specimens were immunohistochemically processed and ADAMTS‐4 and ADAMTS‐5 expression were obtained respectively for the anterior (AB), intermediate (IB) and posterior (PB) bands and compared to the histopathological degeneration score (HDS). Immunoreactivity for ADAMTS‐4 and ‐5, was observed in both not degenerated and degenerated human TMJ discs. Both the percentage of ADAMTS‐4 and ‐5 immunostained cells (ES) and the intensity of staining (IS) were significantly greater in affected specimens compared with those in control discs. The ADAMTS‐5 ES and IS of the 3 bands of the disc correlated to the TMJ disc HDS (0.001 < P < 0.05), on the other hand only AB and IB, ADAMTS‐4 immunostaining scores correlated to HDS. According to these findings it can be assumed in that the more histopathological changes in the disc are detected, the higher levels of ADAMTS are produced. This in turn can lead to ECM breakdown and in turn to a more advanced disc displacement.     

Transformation of temporomandibular joint disc configuration in internal derangement patients using magnetic resonance imaging

PurposeThe normal disc configuration is biconcave; however, the deformed disc can be found in internal derangement (ID) of the temporomandibular joint (TMJ). The purpose of this study was to evaluate the relationship between the transformation patterns of TMJ disc configuration during mouth opening and disc displacement status, disc reduction ability and TMJ clinical symptoms.MethodsTMJ MR images from volunteers and ID patients were analyzed for closed and open mouth positions. MR images of ID patients were classified into 4 groups: symptomatic joint with anterior disc displacement with or without reduction (ADW or ADWo) and asymptomatic joint with ADW or ADWo. The disc configurations in both positions were categorized as biconcave, biplanar, convex or folded; then the patterns of transformation were observed.ResultsFor the ADW group, the most common disc configuration for closed and open mouth positions were biplanar (66.7%) and biconcave (86.3%). The transformation pattern was significantly related to disc reduction ability (p < 0.05).ConclusionsThe transformation patterns of disc configuration during opening were related to anterior disc displacement and disc reduction ability.     

Apoptosis in displaced temporomandibular joint disc with and without reduction: an immunohistochemical study

J Oral Pathol Med (2011) 40 : 103–110 Internal derangement (ID) of the temporomandibular joint (TMJ) is due to an abnormal relationship of the articular disc to the mandibular condyle, glenoid fossa and articular eminence. The two most common types of internal derangement are anterior disc displacement with (ADDwR) and without reduction (ADDwoR). Disc displacement is associated with degenerative tissue changes. The histological features of discs from patients with TMJ ID reflect a general remodelling caused by abnormal loading. A correlation has been demonstrated between TMJ ID and apoptosis. Few investigations have addressed the role of apoptosis or caspase activity in TMJ ID. The apoptosis activation process was studied in different areas of discs from 18 patients with ID (both ADDwR and ADDwoR) and four cadavers (controls), with emphasis on the expression of caspase 3, whose activation makes the death process irreversible. The results showed a greater proportion of caspase 3‐positive cells in ADDwR and ADDwoR than in control discs. Immunopositivity also varied between disc areas; in particular, in ADDwoR sections labelled cells were significantly more numerous (P < 0.01) in the posterior disc attachment than in the anterior and intermediate bands. In addition, a significantly greater proportion of labelled cells was seen in the anterior (+) and intermediate (++) band of ADDwR compared with ADDwoR discs both bands (P < 0.05). These data suggest the importance of programmed cell death in the progression of TMJ ID.     

The evaluation of temporomandibular joint disc position in TMJ disorders using MRI

The purpose of this study was to correlate disc position and the type of disc displacement, intra-capsular effusion and degenerative changes of the condyle as demonstrated in MRI studies. In this study, 126 temporomandibular joints (TMJs) of 63 patients with TMJ disorders were investigated using clinical examination and MRI. One hundred and twelve TMJs were found to have internal derangement as disc displacement. The angle between the posterior margin of the disc and the vertical line drawn through the centre of the condyle was measured on MRI for each TMJ. The positions of the discs were normal, 0 degrees-10 degrees, in 11.11%; slightly displaced, 11 degrees-30 degrees, in 37.30%; mildly displaced 31 degrees-50 degrees, in 15.08%; moderately displaced, 51 degrees-80 degrees, in 7.14% of the TMJs with anterior displacement with reduction (ADDR). The disc position was severely displaced anteriorly, as over 80 degrees, in all TMJs with anterior disc displacement without reduction (ADD), constituting 27.78% of all cases. We found that the smaller the degree of disc displacement the milder the internal derangement and that the intra-capsular effusion was more frequently associated with TMJ with ADDR. The degenerative condylar changes were more severe with an increased degree of anterior disc displacement.     

3T磁共振成像显示颞下颌关节盘的技术研究

目的探索3T磁共振成像（MRI）显示颞下颌关节盘的序列、参数及电影成像方式的技术特点,并为临床研究颞下颌关节盘病变提供形态与功能影像学参照。方法选择15例正常志愿者和7例颞下颌关节损伤患者为研究对象,采用GE Signa HD 3T MRI和颞下颌关节专用表面线圈对颞下颌关节进行扫描,获得斜矢状、斜冠状闭口位FSE-XL/T1WI、FLAIR/T1WI、FSE-XL/PDWI、FSE/PDWI+FS、FRFSE-XL/T2WI、FRFSE/T2WI+FS扫描及斜矢状张口位FSE-XL/T1WI、FSE-XL/PDWI图像。由口腔颌面外科医师和MRI医师共同对各序列进行打分,分析各序列不同加权像对颞下颌关节盘的显示效果。结果PDWI对关节盘的显示效果得分最高,能清楚显示关节盘的解剖结构与形态。T2WI对关节盘损伤、撕裂、穿孔和关节囊积液显示良好,对关节盘移位情况则以PDWI序列显示效果为好。结论3T MRI可以清楚地显示关节盘在关节运动中的动态改变与病变受累情况,对颞下颌关节软组织损伤的诊治有重要价值。T1WI、PDWI及T2WI应作为常规的扫描方法。     

The use of pseudo-dynamic magnetic resonance imaging for evaluating the relationship between temporomandibular joint anterior disc displacement and joint pain

The relationship between temporomandibular joint (TMJ) pain and the magnetic resonance imaging (MRI) finding of articular disc displacement is debated. The purpose of this study is to investigate the correlation between TMJ pain and anterior disc displacement (ADD) using pseudo-dynamic MRI. A retrospective review of MRI studies was carried out on 130 TMJs in 65 patients presenting unilateral TMJ pain. The contralateral asymptomatic joints served as the control group. Bilateral oblique sagittal and coronal MRIs as well as pseudo-dynamic studies in the oblique sagittal plane were obtained. The disc–condyle relationship was divided into three subtypes (normal disc position, ADD with reduction, and ADD without reduction), based on the pseudo-dynamic MRI findings. Fisher's exact test was used to determine whether the TMJ pain was linked to ADD. The results showed that TMJ pain was significantly related to ADD (with and without reduction) compared to the group with a normal disc position (P = .0001). A significant correlation was found between TMJ pain and the ADD subtype without reduction, as compared to the ADD subtype with reduction (P = .0156). These data suggest that a displaced disc, particularly in the subtype without reduction, is an important source of pain.     

CT双对比颞下颌关节造影术的临床应用

目的介绍CT双对比领下颌关节造影技术，并评价其在颞下颌关节功能紊乱综合征中的诊断价值。方法对14例常规关节造影诊断困难的病例，进行CT双对比颞下颌关节造影检查。结果14例患者经CT双对比造影检查为正常考1例，可复性盘前移位者1例，不可复性盘前移位老2例，关节盘穿孔2例，关节盘粘连8例。结论CT双对比颞下颌关节造影术是常规关节造影的重要补充，对关节盘粘连有特殊的诊断价值。     

Risk factors for temporomandibular joint pain in patients with disc displacement without reduction - a magnetic resonance imaging study

The purpose of this study was to evaluate whether the magnetic resonance (MR) imaging variables of temporomandibular joint (TMJ) internal derangement, osteoarthrosis and/or effusion may predict the presence of pain in patients with a clinical disorder of an internal derangement type (ID)-III. The relationship between TMJ ID-III pain and TMJ internal derangement, osteoarthrosis and effusion was analysed in MR images of 84 TMJs in 42 patients with a clinical unilateral diagnosis of TMJ ID-III pain. Criteria for including a TMJ ID-III pain patient were report of orofacial pain referred to the TMJ, with the presence of unilateral TMJ pain during palpation, function and/or unassisted or assisted mandibular opening. Bilateral sagittal and coronal MR images were obtained to establish the presence or absence of TMJ internal derangement, osteoarthrosis and effusion. Using chi-square analysis for pair-wise comparison, the data showed a significant relationship between the MR imaging findings of TMJ ID-III pain and those of internal derangement (P=0.01) and effusion (P=0.00). Of the MR imaging variables considered simultaneously in the multiple logistic regression analysis, osteoarthrosis (P=0.82) and effusion (P=0.08) dropped out as non-significant in the diagnostic TMJ pain group when compared with the TMJ non-pain group. The odds ratio that a TMJ with an internal derangement type of disk displacement without reduction might belong to the pain group was strong (2.7:1) and highly significant (P=0.00). Significant increases in risk of TMJ pain occurred with 'disk displacement without reduction in combination with osteoarthrosis' (5.2:1) (P=0.00) and/or 'disk displacement without reduction in combination with osteoarthrosis and effusion' (6.6:1) (P=0.00). The results suggest that TMJ pain is related to internal derangement, osteoarthrosis and effusion. However, the data re-emphasize the aspect that these MR imaging variables may not be regarded as the unique and dominant factors in defining TMJ pain instances.     

Changes in the temporomandibular joint position depending on the sagittal osteotomy technique and extent of mandibular movement

The bilateral sagittal split osteotomy (BSSO) and high oblique sagittal split osteotomy (HSSO) are common techniques for mandibular movement in orthognathic surgery. The aim of this study was to evaluate the influence of both techniques, as well as movement distances and directions, on the position of the temporomandibular joint (TMJ). A total of 80 mandibular movements were performed on 20 fresh human cadaver heads, four on each head. Pre- and postoperative cone beam computed tomography was used to plan the surgical procedure and analyse the TMJ. Reference measurements included the anterior, superior, and posterior joint spaces, intercondylar distances and angles in the axial and coronal planes, and the sagittal, coronal, and axial angulations of the proximal segment. Only minor differences were found between the BSSO and HSSO techniques, particularly in terms of the intercondylar angle in the axial plane (P < 0.03) and the condylar angle of the proximal segment in the sagittal plane (P < 0.011). Observed changes in the TMJ were mostly opposite when moving the mandible forwards and backwards and increased with increasing movement distance. BSSO and HSSO result in similar changes in TMJ position. The extent of the movement distance influences the position of the condyle more than the osteotomy technique.     

颞下颌关节增强磁共振成像研究

目的：探讨磁共振对比增强剂Gd—DTPA对颞下额关节紊乱病的临床诊断意义。方法：对12名临床诊断为颞下颌关节紊乱病患进行磁共振增强前后扫描，观察影像增强效果。结果：Gd—DTPA对关节盘位置正常的关节闭口斜矢状位前伸部及张口位双板区具有显的增强效果；对可复性及不可复性关节盘前移位张闭口位前伸部及双板区均有明显的增强效果；对冠状位也有明显增强效果。结论：磁共振对比增强剂的增强效果明确，为提高临床诊断准确性及作为磁共振常规扫描的辅助手段提供理论依据。     

颞下颌关节侧向咬合位与对刃位薄层塑化断面对照研究

目的:对比分析下颌对刃位、侧向咬合位颞下颌关节的运动解剖形态,为颞下颌关节病变提供解剖依据。方法:将8例新鲜尸头摆置成对刃位5例、下颌侧向咬合位3例,以颞下颌关节为中心,切割成8cm×8cm×10cm的标本块,利用生物塑化技术,制成斜矢状位、斜冠状位、轴位塑化断层标本共16套。下颌侧向咬合位工作侧、非工作侧关节形态改变与对刃位相对照。结果:下颌侧向咬合位工作侧,髁突在关节窝内向后、向上、向外移位,关节盘位置无变化,关节盘双板及后带受压;非工作侧,髁突向下、向前、向内侧移位,关节盘后带位置向下移位,无前移位,关节盘中带外侧位居上下关节面之间,明显受压变薄。结论:关节盘并非随髁突作同步同向运动。关节盘在髁突作滑动运动时发生移位;当转动运动、滑动运动复合出现时,关节盘发生移位;而在关节窝内发生的转动运动,关节盘不发生移位。     

Temporomandibular joint internal derangement: detection with 12.5 MHz ultrasonography

The purpose of this study was to determine whether 12.5 MHz ultrasonography (US) could be used to assess the presence or absence of temporomandibular joint (TMJ) internal derangement (ID). In 48 consecutive patients with TMJ disorders 192 TMJ positions were investigated by US to analyse the functional disc-condyle relationship (DCR). In order to compare the respective findings with those of a diagnostic method offering a high accuracy, coronal and sagittal magnetic resonance imaging was carried out immediately afterwards. With US showing a sensitivity of 0.58 and 0.75, and a specificity of 0.92 and 0.84 for disc displacement with and without reduction, the data revealed US to be marginal in detecting the presence, but sensitive in detecting the absence of the respective types of a TMJ ID. In addition, with a positive predictive value of 0.83 and 0.71, and a negative predictive value of 0.81 and 0.87 for disc displacement with and without reduction, the results indicate that US may be insufficient in establishing a correct diagnosis for the presence or absence of the respective types of TMJ ID. Regarding the diagnosis of absence or presence of TMJ ID, the results demonstrate high-resolution (HR)-US to be sensitive in detecting the absence, and reliable in predicting the presence of TMJ ID. In view of the fact that the 12.5 MHz US technique proved to be a reliable diagnostic aid for the detection of normal, and the prediction of abnormal DCR, the results of this study should be of further interest and encourage research in its potential uses and diagnostic capabilities.     

Modified arthroscopic anterior myotomy for internal derangement of the temporomandibular joint: clinical and radiological results

The aim of this study was to present the results of a modification of the arthroscopic anterior myotomy for the treatment of internal derangement (ID) of the temporomandibular joint (TMJ): the minimally invasive arthroscopic anterior myotomy (MIAAM). Fifteen joints with Wilkes stages III–IV ID treated with this technique were studied. Clinical data evaluated were pain (visual analogue scale, VAS) and articular movements (preoperatively and at 1, 3, 6, 9, and 12 months postoperative). The position of the disc at 1 year after surgery was compared with the pre-surgical position, using magnetic resonance imaging (MRI). The mean pain level according to the VAS decreased from of 67.8 pre-surgery to 29.0 at the 12-month follow-up (P < 0.001). Functionally, mouth opening increased from a mean 27.8 mm to 36.0 mm (P < 0.001). Evaluation of the MRI images showed statistically significant improvements in disc position in both the closed (P = 0.00002) and open-mouth (P = 0.00001) position. The incidence of re-arthroscopy was 13.3% (2/15). This procedure is an effective method for the improvement of joint function and reduction of pain in patients with ID of the TMJ. However, MIAAM is moderately effective in regards to repositioning of the disc.     

张口位MRI动态研究在诊断颞下颌关节盘前移位中的应用

目的：探讨颞下颌关节张口位磁共振动态成像在颞下颌关节盘前移位中的诊断价值。方法：对30例有颞下颌关节疼痛或弹响MRI患者60侧颞下颌关节行常规MRI静态扫描,并用快速自旋回波扫描获得开口度为0．5cm的图像,依次进行到患者达到最大开口位。然后采用模拟动态观察。分别由两名专科医师对动态扫描和常规静态扫描时关节盘移位进行诊断,并比较诊断结果。结果：静态MRI检查中关节盘可复性前移位21侧,关节盘不可复性前移位18侧,关节盘侧向移位2例,位置正常19例。动态MRI检查中关节盘可复性前移位23侧,关节盘不可复性前移位19侧,位置正常18例。结论：张口位动态MRI联合静态MRI观察对髁突、关节盘运动功能的评价非常重要,对区别可复性与不可复性关节盘前移位具有重要作用。     

Validation of the clinical diagnostic criteria for temporomandibular disorders for the diagnostic subgroup - disc derangement with reduction

Research is needed to assess the validity of the clinical diagnostic criteria for temporomandibular disorders (CDC/TMD). The purpose of this study was to test the reliability of the clinical diagnosis of temporomandibular joint (TMJ) internal derangement type (ID)-I as compared with the magnetic resonance imaging (MRI) 'gold standard'. The study comprised 168 TMJs in 84 patients, who were assigned a clinical TMJ-related diagnosis of ID-I (disc displacement with reduction) in at least one TMJ. Bilateral sagittal and coronal MR images were obtained subsequently to establish the corresponding diagnosis of the disc-condyle relationship. For the CDC/TMD interpretations, the positive predictive value (PPV) of ID-I for disc displacement with reduction (DDR) was 44%, and for the presence of an ID 69%. The overall diagnostic agreement for ID-I was 47.6% with a corresponding K-value of 0.05. Most of the disagreement was the result of the false-positive interpretations of ID-I, and false-negative interpretations of an 'absence of ID'. The results suggest CDC/TMD for ID-I to be insufficient reliable for determination of ID and/or DDR. Patients assigned a clinical TMJ-related diagnosis of ID-I may need to be supplemented by evidence from MRI to determine the functional 'disc-condyle relationship'.     

Hyperintensity signal in the joint space of the temporomandibular joint on fat-saturated T2-weighted magnetic resonance imaging

Our aim was to investigate the incidence of a hyperintense signal in the joint space of the temporomandibular joint (TMJ) on fat-saturated T2-weighted magnetic resonance images (MRIs). We studied 112 patients (224 joints) with disorders of the TMJ who were examined by T2-weighted MRI, and recorded the association between displacement of the disc and the hyperintense signal using the κ coefficient. A hyperintense signal was found in 4 of 91 joints (4%) when the disc was in the normal position, in all 19 joints with anterior disc displacement with reduction, and in 108 of the 114 joints (95%) with anterior disc displacement without reduction. There was a significant correlation between displacement of the disc and the hyperintense signal (p < 0.001). The κ coefficient was 0.91. Such a signal in the joint space of the TMJ on fat-saturated T2-weighted MRI may indicate the presence of synovial fluid in the joint space with displacement of the disc.