Comparison of magnetic resonance imaging findings in 880 temporomandibular disorder patients of different age groups: a retrospective study

Temporomandibular disorder (TMD) is a general term for a series of diseases including masticatory muscle, temporomandibular joint (TMJ) and surrounding structures that affect up to about 40% of the population [1]. Pain, joint noises and limited mouth opening are the main reasons for patients seeking medical attention. According to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) in 2014 [2], TMD comprises two main groups of disorders, namely painful disease (myalgia, arthralgia and headache attributed to TMD) and TMJ disease (disc displacement disorders, degenerative joint disease, and subluxation). TMJ internal derangement (TMJ ID) is a disorder involving disc and condyle, and up to 80% of TMD patients are accompanied by TMJ ID symptoms [3].

The diagnosis of TMD requires both clinical examination and imaging evaluation around the TMJ area. Magnetic resonance imaging (MRI), computed tomography (CT), cone beam CT, TMJ arthrography, panoramic radiography, plain radiography, transcranial radiography can be used to image the TMJ [4]. Among them, MRI is considered to be the most reliable non-invasive way to evaluate TMD ID due to its advantages in soft tissue imaging [5]. T1 weighted images(T1WI), T2 weighted images (T2WI) and proton-density images (PDWI) are required and the most frequent used section thickness is 3 mm. Disc shape and position, synovial membrane, lateral pterygoid muscle can be clearly displayed by MRI, as well as the early signs of TMJ dysfunction, like thickening of anterior or posterior band, rupture of retrodiscal tissue, changes in disc shape, joint effusion [6]. MRI can also reflect the changes of condylar bone to some extent, although it is not as good as CBCT.

Previous studies focused mainly on the correlation of clinical examination with MRI in TMD. Boboc et al. [7] found that adolescents with GJH have a greater risk of developing TMJ disc displacement, especially disc displacement without reduction. Emshoff et al. [8] analyzed the correlation between TMJ pain and MRI findings, and reported that the MRI findings of osteoarthritis, joint effusion, and bone marrow edema were correlated with TMJ pain. And, Hosgor et al. [9] reported joint effusion increased in direct proportion to the severity of pain and disc displacement. In terms of gender, Luo et al. [10] investigated the size and morphology of articular disc and condyle in young asymptomatic adults and found the thickness of the anterior band of the disc and the media-lateral dimensions of the condylar head were gender-related. On the contrary, Demir et al. [11] compared TMD patients' complaints, clinician's examination findings, and MRI findings by considering gender and found no significant difference. MRI findings of different ages are still unclear.

Unlike other joints (the disease worsens with age), TMD is a common disease with a peak incidence at childbearing age [12]. The MRI images based on oblique sagittal adiposity-suppressed T2W1 in TMD patients in different age groups were retrospectively analyzed and compared, including disc morphology, disc position, joint effusion, condyle movement and condyle morphology. The objective of this study is to provide reference for clinical diagnosis and treatment.

MRI findings of TMJ in TMD patients of different ages are still unclear. This study aimed to retrospectively analyze and compare the characteristics of MRI features of TMJs in different age groups. A total of 1760 TMJs from 880 patients were included in the study and divided into three groups: ≤ 18Y, 19-30Y and > 30Y. The results showed that except condylar morphology, there were significant differences in the distribution of disc morphology, disc position, joint effusion and joint motion among different age groups. And, there were significant differences in the distribution of the degree of anterior disc displacement, condyle morphology and joint effusion in different disc morphology among different age groups (except for the distribution of joint effusion in > 30Y), among which the first two types were correlated with the disc morphology, but not with the joint effusion.

MRI is considered as the gold standard for the diagnosis of TMD because it accurately reflects the state of soft tissue. DC/TMD combined with MRI can improve diagnosis specificity and sensitivity [18]. Clinically, MRI is often used to evaluate intra-articular soft tissue, like the shape and position of the articular disc, joint effusion. Dynamic MRI sequences are beneficial for the evaluation of morphology and function, especially in TMD patients [19]. In this study, in order to obtain the trend of MRI imaging features of the total sample size, TMJs on the left and right sides was compared, and no statistical difference was found. In terms of the shape of disc, biconcave ranked first followed by contracture, irregular and lengthened. And in terms of the position of disc, m-ADD ranked first followed by NA, s-ADD and PDD.

There are few studies on the morphology of articular disc at different ages, and the classifications various. Vervaeke et al. [5] divided it into crumpled, rounded, flat, and disc perforations. Vogl et al. [19] divided it into biconcave, biplane/flattened, degenerated. Fan et al. [20] divided it into oval shape, flat shape and beak-like shape. We divide the disc into biconcave, contracture, irregular and lengthened disc. The overall distribution trend of the shape of disc in 1760 TMJs is: biconcave ranked first followed by contracture, irregular and lengthened. There were significant differences in the distribution of articular disc morphology in different age groups. In ≤ 18Y group, the proportion of TMD patients with contracture discs ranked the first (37.2%), while in 19-30Y and > 30Y group, biconcave ranked first (33.7% and 36.4% respectively). The proportion of lengthened disc ranked the last in all the three age groups with about 14.4%.

Combined with clinical practice, we believe that morphology of articular disc may be related to the symptoms of TMD. Therefore, the correlation between articular disc morphology and articular disc position, joint effusion and condylar bone morphology at different ages was evaluated in this study.

The importance of articular disc position in TMD has been extensively studied [21, 22]. Among the 1760 TMJs, only 26% of discs with the posterior edge located in the normal 12 o'clock position with respect to the condyle, which smaller than luo et al. (33%) [23]. There were significant differences in the distribution of articular disc position in different age groups and the different articular disc morphology. The distribution of m-ADD ranked the first, accounting for about 61.8%. It should be noted that the proportion of PDD decreased significantly with the increase of age, and the proportion was greater than s-ADD in patients ≤ 18Y. We think it may be because the condyle is not fully developed in patients younger than 18 years of age [24]. Generally, the order of articular disc position in different articular disc morphology is as follows. 1) biconcave: normal ranked the first (60.7%), followed by s-ADD, m-ADD, PDD; 2) contracture: m-ADD ranked the first (96.4%), followed by normal, s-ADD, PDD; 3) lengthened: normal ranked the first, followed by m-ADD, s-ADD, PDD; 4) irregular: m-ADD ranked the first (97.0%), followed by normal, PDD and s-ADD (0.0%). However, in ≤ 18Y group, 72.4% of the positions of the biconcave disc were normal, followed by m-ADD, and m-ADD ranked first of lengthened disc. There was a correlation between the degree of anterior disc displacement and the disc shape in all age groups.

It has been reported that joint effusion primarily occur in joints with disc displacement and are strongly associated with joint pain [25, 26]. We found that there were statistically significant differences in the distribution of joint effusion among the three age groups. Of the 1760 TMJs, 83.3% were free of joint effusion and 91.2% were slight. The incidence of joint effusion of contracture disc was significantly higher than that of other types. However, There was no correlation between articular effusion and articular disc morphology.

We know that joint motion is related to disc displacement. Limited mouth opening may restricted by disc displacement, such as ADDWoR and ADDWR with intermittent locking [27‐29]. Hypermobility may related with morphology of the musculoskeletal system[30]. There were significant differences in the distribution of joint motion among different age groups. The proportion of limited in ≤ 18Y group (54.4%) was significantly higher than that in 19-30Y group (29.5%) and > 30Y group (43.3%). It can be seen that most patients in the ≤ 18Y and > 30Y groups were accompanied by restricted mouth opening when visited the doctor.

Liu et al.[31] reported that MRI can detect condylar bone abnormalities, but could not efficiently detect the severity. There was no statistical difference in the distribution of condyle morphology in different age groups, but there was statistical difference and a correlation in the distribution of condyle morphology in different articular disc morphology. The condyle morphology was normal in 51.5% of 1760 TMJs. The morphology of articular disc that are easy to cause abnormal condylar bone are irregular, contracture, lengthened and biconcave in order. In > 30Y group, the proportion of condyle bone abnormality in contracture disc was 66.3%, which was significantly higher than that in other age groups.

There were significant differences in MRI images of disc shape, disc position, joint effusion, joint motion and condyle morphology among different age groups. The morphology and position of the articular disc changed significantly with age, but the proportion of abnormal condylar bone remained about 50%. The greater the degree of disc folding, the more prone to bone abnormalities.