What do synovial invaginations in equine MRI really mean?

Alterations to the synovial invaginations of the navicular bone are associated with pathology of both the navicular apparatus and distal interphalangeal joint when evaluated using high field MRI

Thomas J. McParland, Caitlyn R. Horne, James B. Robertson, Lauren V. Schnabel, Nathan C. Nelson

Objective: to measure specific characteristics of the synovial invaginations of the navicular bone in horses to determine whether any single characteristic was associated with abnormalities in the DIPJ or navicular apparatus (NA) using high field MRI and a sample of 200 horses’ feet.

Results: A significant relationship was found between the number of invaginations and global DIPJ score, with higher invagination numbers associated with higher DIPJ scores. For invagination depth and CSA, a significant relationship was noted with global scores of both the DIPJ and NA.

Conclusions: These findings suggest that primary DIPJ disease and NA pathology should be considered when noticing alterations to navicular synovial invaginations on MRI.

This study challenges conventional thinking that synovial invagination changes are solely indicative of pathology within the navicular apparatus. The study showed an association between more severe imaging findings of the distal interphalangeal joint of the horse with more severe imaging findings of the synovial invaginations of the navicular bone. These results suggest that changes to the synovial invaginations should prompt the clinician to more broadly consider underlying causes and clinical implications.