DISCUSSION
The present study investigated the accuracy of clinical findings in determining the presence or absence of internal derangement of TMJ according to the set criteria by RDC/TMD and the superior diagnostic imaging modality like magnetic resonance imaging (MRI).
For this study, 14 patients between 11 to 40 years of age were selected. The control group of 5 healthy volunteers without any sign & symptoms of TMD showed a different age distribution; they were between 20 to 30 years.
Out of a total of 14 patients, the study consisted of 9 female & 5 male patients. The ratio of female to male in this group of patients with TMDs was 1.8:1. The results of this study show that the prevalence of TMDs was higher in women than in men. Several related studies have reported comparable results10,14.
In the present study, the author has investigated the accuracy of five clinical parameters for determining the presence or absence of anterior disc displacement. The MRI findings obtained from 28 joints with TMDs were compared with their initial visits’ clinical findings. The sensitivity values of the clinical parameters were considerably low, in contrast with their high specificity. It means that false–negative diagnoses were made more frequently than false-positive diagnosis7. It was in accordance with the study carried out by Yatani et.al15. Thus results obtained from these studies indicate that it is challenging to predict disc derangement based on clinical symptoms alone. In other words, not all joints commonly present characteristic clinical signs and symptoms of disc derangement2,7,8,16.
The most common clinical sign in this study group was tenderness in the pre-auricular region (18 out of 28 joints, i.e., 64%), the cause being unclear. Okeson et al. 10 reported that disc displacement of TMJ is the crucial cause of facial and TMJ pain. Based on these observations, pain/tenderness in the preauricular region could be associated with alteration of retrodiscal tissue17.
A study carried out by Kobs G et al. 9, concluded that although clicking is a predictor of anterior disc displacement with reduction, it was not present in his entire study population. In the present study, joint noise was found in 16 out of 28 joints (57%), thus indicating that TMJ clicking might occur as a consequence of frictional incompatibility between the disc and the eminence when the posterior band of the disc moves anteriorly or posteriorly beyond the apex of the articular eminence. Other causes may be a deviation in the condylar form (remodeling), adhesion, or muscular incordination18-22.
Muscle tenderness and limited mouth opening were found in Thirty-six percent in the present study. Deflection/deviation was found in 9 joints out of 28 joints (Thirty-two percent) and was the least among all the clinical symptoms7.
In anticipation of osseous changes in the long-standing internal derangement of TMJ and to rule out other TMJ organic pathologies, the authors could have chosen the various radiographic and imaging modalities to determine the status of the disc. However, none of the modalities (conventional radiograph, specialized radiograph, and CT- axial and coronal view) could substantiate and locate the disc position23,24,25.
The predictive value of the clinical diagnosis of ADDWR was 0.65 in a study by Barclay et al. 2. The present study showed a 7 non-symptomatic joint with ADDWR on MRI. 2 joints clinically diagnosed ADDWR showed anterior disc displacement without reduction with MRI. 1 joint clinically diagnosed as anterior disc displacement without reduction did reduce on opening. 1 joint clinically diagnosed as anterior disc displacement without reduction appeared normal on MRI. Whereas 1 joint clinically diagnosed as anterior disc displacement without reduction could not be interpreted in MRI, 3 joints clinically diagnosed as MRI correctly diagnosed ADDWR, and 4 joints clinically diagnosed as NDD was confirmed by MRI2, 19, 20, 21, 22.
There was a low agreement (33% to 70%) between clinical diagnosis and MRI diagnosis in symptomatic & asymptomatic joints2, 6, 7-9. The present study showed only 36% (4/11) of the asymptomatic joints had a normal disc position, detected by MRI. The prevalence of disc displacement in asymptomatic subjects is between 16% and 33%2.
A previous study has shown that contralateral non-symptomatic joints in subjects with internal derangement in the other TMJ frequently have disc displacement10, 14; the present study findings also correlate with this study (7/11 ADDWR).
In accordance with the available literature, posterior disc displacement is exceptionally uncommon, and it was not observed in the present study12. Superior disc position is commonly used to refer to normal disc positioning in the sagittal oblique closed mouth view. The method used to judge disc position in this study was the closed mouth sagittal view assessment of the posterior band’s position relative to the top of condyle as a superior disc position. It was considered normal if the posterior band of the disc is at position17.
In the current study, the medial displacement proportion was more significant than lateral displacement (4 joints were medial; 2 joints lateral). These findings are in accordance with the existing literature18, which suggests that medial displacement occurs more frequently than lateral displacement and can be attributed to the force of muscles attached to the disc. It has been speculated that one reason for medial disc displacement is muscle spasm of the superior belly of the lateral pterygoid muscle3.
Most clinical studies on anteroposterior arthrography and sagittal & coronal MRI have shown that the displacement’s medial component is more frequent than the lateral component. The percentage of medial displacement was more significant in anterior disc displacement without reduction, and sideways displacement was also most frequent in anterior disc displacement without reduction8.
The anterior disc displacement without reduction is the most common internal displacement depicted among TMJ derangement, but the present study showed that the NDD was most common in the study population diagnosed by MRI. (13 NDD; 11ADDWR and 2 anterior disc displacement without reduction). The limited protrusive movement was the most accurate clinical sign used for diagnosing anterior disc displacement without reduction8. However, this study did not support it as only 1 patient had limited mouth opening out of 2 patients diagnosed anterior disc displacement without reduction with MRI18. It could be due to contradicting views in clinical parameters based on protrusive movements/deflection and no single specific criteria in diagnosing specific TMJ disc displacement19-25.
The overall diagnostic agreement of 88.25% (15/17) between specific RDC- diagnosis, and MRI in the current study is in accordance with various contemporary studies9,13. Several authors have investigated the reliability of the clinical diagnosis of ID using MRI as a ’gold standard’. The reported percent agreement ranged from 59% to 90%. A positive RDC examination is predictive for internal derangement but not reliable with regard to the type of disc displacement. The clinical examination is of limited value in determining the TMJ disc’s true position and its functional movement. When accurate information about the TMJ disc position is clinically essential, MRI should be performed; the clinical examination alone cannot provide sufficient information2,7,9,16, 18-20.
The combinations of TMJ radiographs are useful only in long-standing pathology, leading to visible changes in the osseous structures. However, these are still relevant in ruling out and eliminating osseous pathology for a confirmed diagnosis of soft tissue pathology of TMJ.
Based on the results of this study, the main strength is that the RDC/TMD criteria are not alone sufficient for the diagnosis of the internal derangement, and perhaps, it should be supported by the MRI to reach a confirmatory diagnosis so that a comprehensive approach can be initiated towards the management of the internal derangement of the TMJ by the clinicians. However, this study’s major drawback was a small sample size before reaching a definitive conclusion. A further study examining a group of volunteers with or without a history of TMD and using the same diagnostic criteria as set by RDC/TMD, MRI with larger sample size, multi-center trials needs to be conducted.