Deep erosions of the palmar aspect of the navicular bone diagnosed by standing magnetic resonance imaging.
Authors: Sherlock, Mair, Blunden
Journal: Equine veterinary journal
Summary
# Editorial Summary: Deep Palmar Navicular Erosions on Standing MRI Palmar (flexor) surface erosions of the navicular bone have historically proved challenging to visualise on conventional radiography, yet they represent a significant cause of persistent lameness in mature horses. Sherlock, Mair and Blunden's 2009 investigation examined 16 horses diagnosed with deep palmar navicular erosions using standing low-field MR imaging, correlating MR findings with clinical presentation, conventional imaging and, where available, post-mortem pathology. The condition presented as sudden-onset lameness in 63% of cases, with radiographs preceding MR imaging showing only equivocal changes in seven horses; MR imaging revealed characteristic focal areas of altered signal intensity across the deep digital flexor tendon, palmar fibrocartilage, subchondral bone and medulla, with histopathology confirming localised fibrocartilage degeneration, focal osteonecrosis and fibroplasia. The prognosis proved poor—only one of 16 horses returned to previous performance levels, whilst seven were subsequently euthanased—highlighting the destructive nature of deep lesions once established. The authors' suggestion that earlier detection of shallow erosive lesions via MR imaging might permit timely intervention to arrest progression merits serious clinical consideration, particularly given that conventional radiography frequently fails to identify these lesions in their potentially more tractable phases.
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Practical Takeaways
- •Standing MR imaging should be used for suspected palmar navicular erosions as radiography often appears normal or equivocal and delays diagnosis
- •Deep palmar navicular erosions carry a poor prognosis—44% of cases resulted in euthanasia and only one horse returned to work, supporting early diagnosis of shallow lesions to allow therapeutic intervention
- •Sudden onset lameness with positive MR findings on the palmar navicular aspect warrants careful prognosis discussion with owners regarding likelihood of return to performance
Key Findings
- •Standing low-field MR imaging diagnosed deep palmar navicular erosions more effectively than conventional radiography, which showed equivocal changes in 7/16 horses
- •Sudden onset lameness occurred in 63% of cases, with 6/16 horses presenting with bilateral lameness
- •Histologically, lesions showed fibrocartilage degeneration with underlying focal osteonecrosis and fibroplasia in the navicular bone
- •Poor prognosis for return to performance: 44% euthanased and only 1/16 horse returned to previous work level