Rheumatology, Department of Internal Medicine and Surgery, Florence, Italy
Correspondence to: d.melchiorre{at}iol.it
We have read the letter about the difficulty in interpreting ultrasonographic (US) images of the temporomandibular joint (TMJ), which argues about the method of US examination presented in our previous paper. We wish to point out that the first description of our method of US examination was published first in 1997 [1] and again in 2003 [2]. In both papers the methodology is described extensively, and I believe that the authors can easily access these journals of the Italian and international literature.
On the basis of our experience in adults and children, we are able to assert that the distance between capsule and bone should be measured on the posterior or in the middle condylar convexity, as already reported [3]. On the other hand, in Figs 3 and 4 of this letter, the distance between capsule and bone cannot be measured if a joint effusion is present. This is because the anterior condylar convexity in children can be seen easily because of immaturity of the temporal bone while in the adult it is a source of artefacts because it covers part of the condylar head.
It should also be stressed that the technique of TMJ evaluation has been improved in the last decade. In fact, on the basis of our experience, the high-frequency probe is not needed to detect the main features of the TMJ. In the past (1993), we used to study the TMJ with a 7.5 MHz probe, but subsequently we have used a 813 MHz probe and now we use a multifrequency linear probe at 815 MHz. However, to study the TMJ, the 8 MHz frequency may detect joint effusion, condylar alteration and disc displacement, because, with a tiny window, a high frequency does not add any information.
In order to define remodelling, bone erosion and osteophytes on the TMJ, reliable techniques are needed but unfortunately they are not yet available.
The Italian colleagues forget that our US results were verified by concomitant MRI, reaching a sensitivity of 70.6% and specificity of 75.0% in the assessment of the joint effusion. These data clearly show that we are still missing 30% in the assessment of alteration of the disc. This suggests that the US technique needs to evolve continuously in order to reach better consistency in defining effusions and the limits of the bones forming the TMJ. Our recent paper reports sensitivity of 65.8% and specificity of 80.4% in the assessment of the alteration of the disc in a greater number of patients in a comparison between US and MRI [4].
In conclusion, we suggest that the TMJ may be reliably assessed with a probe of 8 MHz with high sensitivity and specificity to detect joint effusion, condylar alteration and disc displacement.
References
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