We read with interest the article by Rajan et al. reporting five cases of transoral gap arthroplasty. We would like to address some major setbacks of this procedure that may be of interest and importance, especially for those with limited experience in this area.
One of the authors’ inclusion criteria was Sawhney grade I, II, and III temporomandibular joint (TMJ) ankylosis cases ; they excluded cases with an ankylotic mass involving the zygomatic arch, particularly when this affected the lower border. Conceptually, grade III TMJ ankylosis involves a union between the zygomatic arch and a medially displaced mandibular condyle. In the classification system used, grade II ankylosis also includes union with the zygomatic arch but over a smaller area. Therefore the inclusion of grade II and III cases in their case series contradicts their exclusion criterion.
Ankylotic bone is recognized as a reparative process similar to that found with callus formation, such as in childhood fractures or inadequately immobilized fractures. In our experience of treating TMJ ankylosis patients over several years, in most cases we have found a mixed pattern of TMJ adhesion (both bony and fibrous) despite radiological delineation between the two TMJ articular surfaces. More often after release of the ankylotic mass, we have observed immature bone instead of fibrous tissue between the articular surfaces. The reason for the sluggish mineralization of adhering tissue even after several years is not known. In juxta-articular adhesion TMJ ankylosis we usually find bony adhesions at the posterolateral TMJ surface, while posteromedial adhesions are associated with a medially dislocated condyle. In most cases we have found immature bone rather than fibrous tissue in the inter-articular space. An irregular radiolucent line can be seen on computed tomography (CT), suggesting small areas of bony adhesion. The bony tags on the condylar component can be well appreciated on three-dimensional CT reconstructions ( Fig. 1 ). The strength of adhesion of the ankylotic mass may vary, which challenge the force of detachment while excision.
In our experience, transoral excision is unpredictable because of the heterogeneous nature of the TMJ ankylosis, particularly when posterior and medial bony adhesions are present. In such cases, the ankylotic mass usually requires greater pressure with an osteotome for release. Via an intraoral approach, the direction of the osteotome is guided by the articular eminence, which directs it obliquely towards the centre of the glenoid fossa, and excessive force may damage the glenoid fossa.
The authors also mention that they were able to engage the posterior border with a channel retractor while excising the ankylotic mass. It is noteworthy that in TMJ ankylosis the space between the external auditory meatus and ankylotic mass is usually reduced to almost 0–2 mm, which makes it difficult to place any retractors posteriorly ( Fig. 2 ). The blind use of a bur or osteotome posterior to the infratemporal fossa may damage both the external auditory meatus and the skull base due to failure to appreciate the true extent of the ankylotic mass.