Clinicopathological findings in horses with a bi- or tripartite navicular bone.
Authors: van der Zaag, Weerts, van den Belt, Back
Journal: BMC veterinary research
Summary
Navicular bone partitioning—where the navicular bone fails to fuse completely during development—is frequently misdiagnosed as a parasagittal fracture during lameness investigations, yet remains poorly characterised in the equine literature. Van der Zaag and colleagues examined three cases (a 10-year-old Belgian Warmblood, 7-year-old Quarter Horse, and 5-year-old Dutch Warmblood) presenting with chronic Grade 3/5 forelimb or hindlimb lameness persisting over months to years, using radiography, nerve blocks, and pathological examination to establish diagnosis and underlying pathology. All three horses displayed bipartite or tripartite navicular configurations on radiographs; pathological specimens revealed chronic degenerative changes including cartilage loss, subchondral cystic lesions, and cartilage indentations at partition sites, suggesting foetal vascular disturbance during endochondral ossification created structurally weak zones predisposed to degeneration. The authors propose that whilst navicular partitioning itself is congenital, the clinical lameness emerges through repeated biomechanical stress at these ossification fault lines in the adult horse, leading to progressive cartilage deterioration and poor long-term prognosis. Clinicians evaluating chronic distal forelimb or hindlimb lameness should consider navicular partitioning in their differential diagnosis, particularly when pain localises to the navicular region; distinguishing this condition from true fractures is essential for prognostic counselling and managing owner expectations regarding athletic potential.
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Practical Takeaways
- •When evaluating chronic forelimb or hindlimb lameness that localizes to the distal foot, consider navicular bone partition as a differential diagnosis alongside parasagittal fracture—careful radiographic assessment is essential to distinguish these conditions
- •Horses with confirmed navicular bone partition have a poor prognosis for soundness due to progressive degenerative changes at partition sites; early recognition is critical for informed client communication regarding management options
- •Bilateral partitions may occur; if partition is identified unilaterally, radiographic examination of contralateral limbs is warranted to assess for subclinical involvement that may predispose to future lameness
Key Findings
- •Three cases of navicular bone partition (bi- or tripartite) presented with Grade 3/5 chronic recurrent lameness persisting 4 months to 2 years
- •Navicular bone partition is hypothesized to have congenital vascular origin resulting from aberrant endochondral ossification during fetal development
- •Pathological examination revealed chronic degenerative changes with marked subchondral cystic formation at partition sites in affected horses
- •Navicular bone partition is often misinterpreted as parasagittal fracture on radiographic examination, requiring clearer recognition for accurate diagnosis