Distal border synovial invaginations of the equine distal sesamoid bone communicate with the distal interphalangeal joint.

Objectives: Macroscopic studies have suggested a link between distal border synovial invaginations of the navicular bone and the distal interphalangeal joint. However, many practitioners consider that these invaginations are directly and solely related to navicular disease. The objective was to investigate the communication pattern of these synovial invaginations with the synovial compartments of the distal interphalangeal joint and the navicular bursa, using minimally invasive imaging techniques.
Methods: In a prospective observational study, 10 cadaveric limbs with radiographically evident distal border synovial invaginations were randomly assigned to computed tomography arthrography or bursography groups, using iopamidol.
Results: In 5/5 limbs, contrast medium filled the invaginations following distal interphalangeal arthrography. In the other five limbs, no contrast medium filled the invaginations following bursography.
Clinical Significance: Contrary to existing beliefs, these invaginations are more likely associated with distal interphalangeal joint synovitis and may not be directly linked to primary navicular bone pathology, but might reflect distal interphalangeal arthropathy. Therefore, the rationale for assessment of these invaginations in stallion selection or pre-purchase examinations as a predictive sign for navicular disease is questionable. Nonetheless, comorbidities are frequent in the equine distal limb. Enlarged synovial invaginations may also be seen in limbs with concomitant primary navicular disease. Further studies are needed to elucidate possible inter-related pathological processes.