External Acoustic Meatus Approach for Ultrasonographic Evaluation of the Temporomandibular Joint: An Anatomical Validation and Proof-of-Concept Study.

Temporomandibular disorders (TMD) represent a public health problem, affecting 31% of adults and the elderly and 11% of children and adolescents. Interest is growing in using ultrasound to evaluate the temporomandibular joint (TMJ). However, researchers need to standardize a reliable method. Further studies are required to provide anatomical validation. We aim to evaluate a new ultrasound approach, with anatomical validation and proof of concept, to determine whether it is technically feasible to visualize the temporomandibular joint. This two-phase anatomical validation and proof-of-concept study included six fixed cadaveric head specimens and three healthy volunteers. Four cadaveric specimens were dissected, and two were sectioned to evaluate the potential efficacy of the new access route for ultrasound examination of the TMJ. Subsequently, a proof-of-concept study was conducted on three volunteer patients to evaluate different probes designed to obtain ultrasound images of the TMJ. The anatomical results reveal TMJ-related structures that interfere with the extraoral ultrasound approach. Cross-sectional images assess the distances and relationships between the articular bone surfaces of the TMJ and the structures of the external acoustic meatus. Ultrasound through the cartilaginous portion of the external acoustic meatus allowed visualization of the articular surfaces of the TMJ. This approach enabled measurement of the distance between the articular bone surfaces and tracking of the complete path of the condyle during mouth opening and closing. The main contribution of this study is anatomical: it identifies and validates a clinically relevant access route that can expand the anatomical basis of TMJ ultrasound. Larger studies, including reference images, reproducibility analyses, and symptomatic cohorts, are required before diagnostic applications can be established.