The distal sesamoidean impar ligament: comparison between its appearance on magnetic resonance imaging and histology of the axial third of the ligament.

This research focused on understanding the correlation between abnormalities in the distal sesamoidean impar ligament (DSIL) in horses as indicated by Magnetic Resonance Imaging (MRI), and the actual physical condition of the ligament as revealed by histopathology. Notably, it was found that certain MRI indications, such as the presence of a cystic structure in the distal third of the navicular bone, suggest significant alterations in the infrastructure of the DSIL.

Research Objectives

The study aimed to establish if there was:

• A correlation between the histopathology (the study of changes in tissues caused by disease) and MRI findings of the DSIL
• A relationship between MRI detected abnormalities at the origin of the DSIL, its insertion, and the body of the ligament

Methods

The researchers used fifty limbs from twenty-eight horses for the study. They used high-field MRI to detect and grade abnormalities in the DSIL, its origin on the navicular bone, and its insertion on the distal phalanx. They also examined histologically sections of the axial third of the DSIL and graded them based on fibre orientation, integrity of fibroblasts, collagen architecture, and vascularity. They applied statistical tests – Spearman rank correlation and Chi-squared tests – to establish associations between the MRI and histology findings.

Results

The researchers found significant correlations between:

• A cystic structure in the distal third of the navicular bone or a distal border fragment and the histological grade of the DSIL’s body.
• A cystic structure in the distal third of the navicular bone and the presence of a distal border fragment or entheseous new bone at the insertion of the DSIL, swelling of the DSIL, and increased signal intensity in fat suppressed images of the DSIL.
• Distal elongation of the flexor border of the navicular bone and the presence of one or more distal border fragments.
• Swelling of the DSIL’s body, irregularity of its palmar border and increased signal intensity in fat suppressed images of the DSIL.

Conclusion

The presence of a cystic structure in the distal third of the navicular bone detected through MRI, a distal border fragment, or increased signal intensity at the insertion of the DSIL, may suggest substantial alterations in the infrastructure of the DSIL. The findings of this study contribute to a better understanding of the probable histopathological conditions reflected by specific MRI observed abnormalities in the DSIL.