Functional anatomy of the equine temporomandibular joint: Collagen fiber texture of the articular surfaces.

This research article explores the structure of the collagen fiber apparatus in the temporomandibular joint (TMJ) of horses, aiming to understand typical features that indicate biomechanical adaptations.

Overview of Study

• This study was carried out to understand the architecture of the collagen fiber apparatus in the TMJ of horses. This specific area was chosen because there was limited ultrastructural and histological data on it and hence no basis for biomechanical and histopathological considerations.
• The main method employed in this research was the split-line technique, which helped visualize the collagen fiber alignment. The study was conducted on 16 adult warmblood horses with no history of TMJ disorders.

Findings and Observations

• In the central two-thirds of the articular surfaces of the articular tubercle, the articular disc and the mandibular head, split-lines, which are lines indicating the preferred orientation of fibers, ran in a correspondent rostrocaudal direction, i.e., from the front to the back of the horse.
• However, the lateral and medial aspects of these articular surfaces displayed different split-line patterns. The articular disc showed curved arrangements, while the bony components exhibited punctual split-lines.
• Mediolateral (from side to side of the horse’s body) oriented split-lines were observed in the rostral and caudal border of the articular disc and in the mandibular fossa (a depression in the mandible where the TMJ fits).

Interpretations and Conclusions

• The complex movements during the equine chewing cycle are likely assigned to different areas of the TMJ. It was inferred from the study that different portions of the joint adapt to different functions based on their collagen fiber alignment.
• The split-line pattern of the equine TMJ suggests that a relative movement of the joint components occurs in a preferred rostrocaudal direction. This movement is mainly observed in the central aspects of the TMJ.
• The lateral and medial aspects of the articular surfaces, on the other hand, show split-line patterns that indicate movements primarily around a dorsoventral axis. This suggests that different parts of the joint allow varied types of movements making the TMJ a complex joint enabling varied motions.