Arthroscopic findings in a fixed disc case of the TMJ
Hallazgos artroscópicos en un caso de disco articular adherido de la ATM

The fixed disc syndrome (anchored disc phenomenon, adhered disc, stuck disc, static disc) is a clinical entity defined by the existence of an acute close lock affecting oral aperture^1,2 (sharp reduction in oral aperture of under 25 mm without pain, or with pain that is spontaneous or just on palpation of the affected joint, with or without a previous history of pathologic joint dysfunction). The magnetic resonance images show a disc that is fixed to the articular eminence restricting the translation of the condyle, and that remains stuck to it during the rotation of the mandibular condyle. The disc may have a normal position or it may not (anterior displacement), and a normal (biconcave) morphology is usual⁴ (Fig. 1).

From its first description by Dorrit Nitzam^1,2 other studies have been published that clearly define this internal articular dysfunction^3,4 and it should be kept in mind when making the differential diagnosis of any acute closed lock of the TMJ.

In order to be able to diagnose an acute closed lock as a fixed disc syndrome, a proper magnetic resonance study is essential, as the diagnosis is by means of an imaging study, not a clinical study. The true position of the disc and its mobility can be more adequately defined if dynamic images in various phases of oral aperture and with medium-lateral planes are obtained.

In the case presented by the authors, the patient was suffering from chronic internal dysfunction of a joint, which was corroborated by the existence of an anterior disc displacement without reduction (ADDWR) of the left TMJ. This is the joint that the patient said was painful and that probably resulted in limited mouth opening. The MRI images of the right TMJ show a disc with normal morphology that is flat and that appears to be situated in front of its normal position (in the closed mouth position the mandibular condyle is in contact with the posterior band of the disc and not with the anterior band). It remains attached to the glenoid fossa during mouth opening, but the mandibular condyle stops during the translation process just when it encounters the displaced left articular disc. Perhaps the symptoms could be interpreted as an acute closed lock in the middle of an anterior displacement without reduction on the left side, leading to secondary impairment of the normal movement of the right condyle when recapturing the anteriorly displaced disc.(Fig. 2).

A detailed study with dynamic MRI shows the existence or not of intra-articular effusion and helps to carry out a radiological diagnosis that is more precise. However, the findings described in the arthroscopy confirmed, in principle, the hypothesis for the authors’ diagnosis: left ADDWR and right fixed disc. The rapid diagnosis of this pathology is very important because treatment should always be surgical (it is probably the only cause of internal disturbances at the moment for which conservative treatment is not indicated initially).

Treatment should be directed at eliminating the possible intra-articular factors leading to the pathologic symptoms: elimination of the negative pressure in the superior space of the TMJ, lavage of the substances responsible for the loss of articular lubrication, re-establishing the normal physiology of the TMJ, and ensuring normal movement of the different joint components. This is only achieved by means of arthrocentesis⁵ or arthroscopy.^4,6

Carrying out arthroscopy allows us to visualize directly what is happening within the joint and it helps us to understand the physiopathology of entities that are still not well defined such as the fixed disc. The adhesion of the disc to the fossaeminence cartilage may be due to the first stage when negative pressure is created within the superior joint space secondary to changes in the normal lubrication of the TMJ⁷. For this to happen, the production of free radicals would previously have been activated and there would therefore be intra-articular inflammation.⁸ If the pathological situation is maintained, adherences between the disc and the articular cartilage may occur, together with disc displacement and changes in the normal morphology of the disc. This is the reason why on the initial diagnosis we sometimes find fixed discs in a more forward position and with morphologic changes.⁴

The arthroscopic signs that appear on these joints correspond therefore to the physiopathologic description given: isolated synovitis in earlier cases and adherences in the cases that have been evolving for longer.⁴ The findings described in this work suggest that the existing synovitis was located precisely in the area where there was contact between the disc and fossa (vacuum effect) with the remaining synovial joint membrane being normal. There would therefore not be (at least macroscopically) any primary inflammation leading to alterations in the lubrication of the joint, and therefore we should ask ourselves why the suction effect has occurred within the joint. We have found, however, arthroscopic marks with certain frequency in patients with a history of indirect trauma on the TMJ (mandibular fractures), with it therefore being possible to interpret this as traumatic synovitis secondary to the impact of the mandibular condyle on the articular disc (in the lower space), and of this against the posterior side of the eminence in the upper space. Perhaps the existence of ADDWR in the contralateral joint may be responsible for the abnormal movements of the «healthy» joint leading to the trauma of this disc, and therefore to the localized synovitis and the adherences responsible for the stuck disc.

The presentation of new fixed disc clinical cases may help us to understand the physiopathology behind this relatively new pathological entity, which could be triggering a far from negligible amount of internal joint disturbances that could be avoided with proper diagnosis and treatment from the onset.