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Advanced ultrasound screening for temporomandibular joint (TMJ) internal derangement
WHY WAS THE STUDY PERFORMED?
The temporomandibular joint (TMJ) exists between the mandibular condyle and the concave mandibular fossa (or glenoid fossa) of the temporal bone, and the convex articular eminence of the temporal bone (Figure 1). This joint is unique in that all the articular surfaces are covered by fibrocartilage instead of articular cartilage1. The TMJ contains a flexible fibrocartilage disc which is reported to be 2mm thick anteriorly and 3 mm thick posteriorly2. This hinge joint allows both forward and backward translation of the mandibular condyle and articular disc2. Internal derangement of the TMJ is defined as a mechanical fault of the joint that interferes with smooth joint function which is attributed to abnormal interaction between the articular disc, condyle and articular eminence1. Articular disc displacement is the most common cause of internal derangement of the TMJ3. Disc displacement is categorised based on the relationship of the disc to the mandibular condyle and can be described as anterior, anterolateral, anteromedial, lateral, medial and posterior1. The most common pattern of disc displacement is either anterior or anterolateral, which accounts for more than 80% of disc displacement4 .
Sonographic assessment of the TMJ may be undertaken to investigate the structural integrity of the TMJ using static and dynamic imaging and identify structural changes such as displacement or snapping of the articular disc if present and guide injections if required3,5 . Such a request can induce panic in a sonographer, particularly if they are not familiar with the relational anatomy, sonographic technique, and normal and abnormal sonographic appearances of this joint. This study was undertaken to investigate a sonographic technique that may be used for dynamic and static imaging of the TMJ and as a screening diagnostic tool for TMJ internal derangement6 .
Figure 1. Anatomy of the Temporomandibular joint (TMJ) with the mouth in the closed position. MC = mandibular condyle, AE = articular eminence of temporal bone, MF = mandibular fossa of temporal bone, EAM = external auditory meatus. Fibrocartilage lining MF, AE and MC shown in blue.
HOW WAS THE STUDY PERFORMED?
Sonographic imaging of the TMJ using a defined technique was compared with coronal and sagittal magnetic resonance (MR) imaging in bilateral TMJs in 10 asymptomatic control participants (between 20 and 30 years of age). The main structures identified include the mandibular condyle, mandibular fossa, articular eminence, and articular disc.
REVIEWED BY Michelle Fenech ASA SIG Musculoskeletal
REFERENCE Friedman SN, Grushka M, Beituni HK, Rehman M, Bressler HB, Friedman L. Advanced Ultrasound Screening for Temporomandibular Joint (TMJ) Internal Derangement. Radiol Res Pract. 2020; 2020:1809690.
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A 15-7 MHz hockey stick transducer (L15-7io, Philips iU22 Ultrasound System, Netherlands) was used to obtain sonographic imaging of the long axis of the articular disc. To do this, the transducer was placed parallel to the articular disc when the mouth was in three positions and the transducer orientation was described in terms of a clock face:
1. In closed mouth position – transducer oriented in either 5 o’clock (right TMJ) or 7 o’clock (left
TMJ) position
2. In semi-open mouth position – transducer oriented in either 3 o’clock (right TMJ) or 9 o’clock (left TMJ) position
3. In open mouth position – transducer oriented in either 1 o’clock (right TMJ) or 11 o’clock (left
TMJ) position (Figure 2).
Sonographic and MR imaging of 61 symptomatic participants was also conducted (using same sonographic technique described above) to compare imaging findings.
WHAT THE STUDY FOUND
Figure 2. Transducer positions (outlined by black rectangle) to demonstrate the long axis of the articular disc with the mouth in 3 positions: A. Closed mouth B. Semi-open mouth C. Open mouth
In the control population, the normal articular disc appeared as a bowtie or saddle shape on MR imaging. Sonographically, the disc appears as a hypoechoic c-shaped structure that straddles the hyperechoic mandibular condyle. During dynamic mouth opening, the normal articular disc maintains a constant relationship and rainbow shape between the mandibular condyle and temporal bone as the mandibular condyle moves anteriorly (Figure 3).
In the case population disc displacement was defined in this study and was classified as:
Figure 3. Shape and position of the normal articular disc which can be identified sonographically in the closed (A) and open mouth (B) positions. AE = Articular eminence of temporal bone, MF = mandibular fossa of temporal bone, MC = mandibular condyle. Articular disc = blue semicircular structure which moves in relation to the mandibular condyle.
anterior, posterior, medial and lateral displacement relative to the mandibular condyle1. Medial and lateral displacement of the articular disc was not able to be identified confidently using sonographic imaging in this study. Displacement of the articular disc may be sub-classified as anterior displacement with reduction (anteriorly displaced disc returns to normal position on mouth opening), and anterior displacement with no reduction (anteriorly displaced disc does not return to a normal position with mouth opening which can result in a locked jaw)1. This classification was used in this study. Disc displacement can be further described as either be complete or partial, however these descriptions were not used to define displacement in this study. Furthermore, deformation of the shape of the disc and/or irregularity of the bony contour of mandibular condyle may be identified sonographically but also was not noted in this study.
29 of the 61 case participants had disc pathology identified on MR imaging. Sonographic imaging demonstrated disc pathology in 23 participants (79% sensitivity, 100% specificity when compared to MR imaging). Anterior displacement was the most common type of disc displacement identified.
RELEVANCE TO CLINICAL PRACTICE
A sonographic assessment of the TMJ may be requested, and an understanding of the structures to be imaged, the sonographic technique, the normal and abnormal sonographic appearances, particularly the position of the articular disc in reference to the mandibular condyle, and an understanding of pathology encountered is required and is outlined nicely in this paper. n
REFERENCES
1. Bag AK, Gaddikeri S, Singhal A, Hardin S, Tran BD, Medina JA, et al. Imaging of the temporomandibular joint:
An update. World J Radiol. 2014;6(8):567-82.
2. Alomar XM, Medrano JM, Cabratosa JM, Clavero JAM, Lorente MM, Serra IM, et al. Anatomy of the
Temporomandibular Joint. Semin Ultrasound CT MR. 2007;28(3):170-83.
3. Tu K-H, Chuang H-J, Lai L-A, Hsiao M-Y. Ultrasound Imaging for Temporomandibular Joint Disc Anterior
Displacement. J Med Ultrasound. 2018;26(2):109-10.
4. Paesani D, Westesson PL, Hatala M, Tallents RH, Kurita K. Prevalence of temporomandibular joint internal derangement in patients with craniomandibular disorders. Am J Orthod Dentofacial Orthop. 1992;101(1):41-7.
5. Klatkiewicz T, Gawriołek K, Pobudek Radzikowska M, Czajka-Jakubowska A. Ultrasonography in the Diagnosis of Temporomandibular Disorders: A Meta-Analysis. Medical science monitor : international medical journal of experimental and clinical research. 2018;24:812-7.
6. Friedman SN, Grushka M, Beituni HK, Rehman M, Bressler HB, Friedman L. Advanced Ultrasound Screening for
Temporomandibular Joint (TMJ) Internal Derangement. Radiol Res Pract. 2020;2020:1809690.
