The aim of this study was to assess the radiographic changes in untreated adults with bilateral anterior disc displacement without reduction. A cohort study was designed to compare the bone changes, effusion, disc configuration, and pseudo-disc changes on two magnetic resonance images obtained at least 24 months apart. Twenty-eight patients (22 female, six male) with a mean age of 33.1 years (range 20–57 years) were included. The mean interval between the initial visit and the follow-up visit was 36.2 months. At the initial visit, the frequencies of bone changes, effusion, disc deformation, and pseudo-disc changes were 51.79%, 35.71%, 100%, and 0%, respectively. At follow-up, the frequency of effusion had decreased significantly. The frequency of bone changes had increased significantly to 75%, but newly formed cortical bone was present in five condyles. All discs remained deformed. Pseudo-disc changes were detected in five joints. Over a long period of observation, there was a significant decrease in effusion and a significant increase in bone changes. However, some adaptive changes occurred.
Anterior disc displacement (ADD) is the major form of internal derangement of the temporomandibular joint (TMJ) and includes disc displacement with reduction (ADDWR) and disc displacement without reduction (ADDWoR). ADD occurs in people of all ages and both sexes, although female adults are more susceptible. Clinically, ADD may lead to pain, noise, mandible dysfunction, etc. At present, the outcome of ADD during its natural course is rather controversial. Some researchers consider ADD to be a ‘self-limited’ disease or ‘normal variant’, while others consider that ADD might be progressive, as seen on imaging, and believe that degenerative joint disease is significantly related to ADD, especially to ADDWoR, even if the symptoms and signs of the TMJ disorder have been relieved or have vanished.
Magnetic resonance imaging (MRI) has a perfect performance in the diagnosis of ADD and is used as the gold standard test. Not only are the shape and position of the disc easily discerned on MRI, but the changes in the bones and the posterior attachment of the disc can also be identified clearly. Pseudo-disc changes may occur in the posterior attachment of the disc. Normally, the disc is between the condyle and the fossa. When the disc is anteriorly displaced, the posterior attachment is between the condyle and the fossa. Over time, a process in which there is a decrease in vascularity and a proliferation of fibrosis may occur in the posterior attachment. On MRI, the posterior attachment presents like the disc, while the real disc is anteriorly displaced. The particular histological changes in the posterior attachment have been called pseudo-disc changes. However, pseudo-disc changes have seldom been reviewed in previous studies.
Hall speculated that bony changes related to ADD might be different in different age groups. ADD in adults could result in degenerative changes, but it might lead to a limitation of mandibular growth in adolescents. The present authors have conducted a series of research studies on disease progression without treatment in patients with ADDWoR using serial MRI. In these previous studies, with a mean follow-up of 13.6 months, it was found that the bone changes of the condyle could worsen in adolescents with unilateral ADDWoR, and that the condylar height could even be shortened.
The purpose of this study was to evaluate the natural course of bilateral TMJ ADDWoR in adults using MRI as the investigative tool. The null hypothesis was that the condyle undergoes progressive bony changes during the natural course of TMJ ADDWoR.
Patients and methods
A cohort study was designed and implemented to address the research purpose. A brief description of the diagnosis and treatment program at the study clinic is given in order to provide the reader with a better understanding of the patient cohort. On first presentation to the clinic, an MRI scan was recommended for those patients with symptoms suggestive of ADD in order to confirm the diagnosis. Treatment options for ADD include no treatment, physical therapy, drugs, the use of a splint, or surgery. If the patients chose to undergo no treatment, regular return visits were then suggested. A second MRI was recommended to reassess the imaging changes in ADD during its natural course, whether the patient remained symptomatic or not. This study was approved by the institutional review board.
The following inclusion criteria were applied: (1) age >20 years, both sexes; (2) two MRI records obtained more than 24 months apart; (3) MRI done in the study clinic between January 2007 and June 2014; (4) bilateral ADDWoR confirmed by MRI; (5) no treatment given either before the first visit or during follow-up.
Patients for whom the MRI was of poor quality due, for example, to movement artefacts, were excluded.
A 1.5-T MRI scanner (Signa; General Electric, Milwaukee, WI, USA) with bilateral 3-inch TMJ surface coil receivers was the machine exclusively used to take all the MRIs. On MRI, the normal condyle has a good round contour with continuous and clear cortical bone. The normal disc is biconcave in configuration, with a signal intensity lower than that for the bone cortex, but higher than that for the muscle tissue.
All assessments of the MRI scans were done twice with an interval of 1 week by the first author. Inconsistencies were discussed and resolved by all of the authors.
Bone changes of the condyle were noted when erosion, sclerosis, flattening, or osteophyte formation were detected. The loss of the biconcave disc shape and/or unusual signal properties was defined as a deformed disc configuration. Effusion was noted when increased intensity was seen in T2-weighted images. Pseudo-disc changes of the posterior attachment were noted when the signal intensity increased and was similar to that of the disc.
Intra-rater variability was assessed with Cohen’s kappa value for the two assessments. The Mantel–Haenszel χ 2 test was performed to analyze the differences in frequency of bony changes, joint effusion, and disc deformation between the initial visit and the second visit. SAS software version 9.13 for Windows (SAS Institute Inc., Cary, NC, USA) was used for all data processing, and the level of statistical significance was set at 0.05 for all tests.
A total of 56 joints in 28 patients were included based on the eligibility criteria. The age of the patients at the initial visit ranged from 20 to 57 years, with a mean of 33.1 years. The interval between the initial visit and the follow-up visit ranged from 24 to 51 months, with a mean interval of 36.2 months. All patients reported that the symptoms of ADD had improved a lot and were satisfied with the outcome during the natural course of the condition without any treatment. Twenty-two patients were female (78.6%) and six were male (21.4%) ( Table 1 ).
Cohen’s kappa values for intra-rater reliability were all above 0.75 for the detection of bone changes, effusion, disc deformation, and pseudo-disc changes, indicating that the assessment was reliable.
At the initial visit, the frequencies of effusion, disc deformation, and bone changes of the condyles were 35.7%, 100%, and 51.8%, respectively. No pseudo-disc changes were detected. At follow-up, the frequency of effusion had decreased to 17.9% ( P < 0.05). All the displaced discs remained deformed. The frequency of bone changes of the condyle had increased to 75% ( P < 0.05). Pseudo-disc changes in the posterior attachment were found in five joints (8.9%) ( Table 2 ).
|Initial visit, n (%)||Follow-up, n (%)|
|Effusion||20 (35.7%)||10 (17.9%)|
|Deformation||56 (100%)||56 (100%)|
|Bone changes||29 (51.8%)||42 (75%)|
|Pseudo-disc changes||0 (0%)||5 (8.9%)|
Most of the affected condyles presented more than one type of bone change ( Table 3 ). Erosion companied by osteophyte formation was the most common presentation at both the initial visit and the follow-up visit. At the follow-up visit, flattening without osteophyte formation or erosion was present in five condyles, indicating stable remodelling of the cortical bone of the condyle; the authors consider this type of bone change as adaptive ( Table 4 ). The MRI scans of two patients are presented in Figs 1 and 2 . The first patient showed flattening of the condyle on follow-up, whereas the second patient presented pseudo-disc changes.
|Bone changes||Initial visit, n (%)||Follow-up, n (%)|
|Erosion||2 (6.9%)||2 (4.8%)|
|Osteophyte||1 (3.4%)||2 (4.8%)|
|Sclerosis||3 (10.3%)||4 (9.5%)|
|Flattening||0 (0%)||5 (11.9%)|
|Erosion + osteophyte||10 (34.5%)||11 (26.2%)|
|Sclerosis + osteophyte||7 (24.1%)||10 (23.8%)|
|Flattening + osteophyte||2 (6.9%)||1 (2.4%)|
|Flattening + erosion||2 (6.9%)||3 (7.1%)|
|Sclerosis + erosion||1 (3.4%)||1 (2.4%)|
|Sclerosis + erosion + osteophyte||1 (3.4%)||1 (2.4%)|
|Flattening + erosion + osteophyte||0 (0%)||2 (4.8%)|
|Total||29 (100%)||42 (100%)|